Symposium Organizers
Robert R. Keller National Institute of Standards and Technology
W. Jud Ready Georgia Institute of Technology
Meyya Meyyappan NASA Ames Research Center
Manish Chhowalla Imperial College London
B1: Carbon Nanotube Devices - FETs and Interconnects
Session Chairs
Monday PM, November 29, 2010
Room 310 (Hynes)
9:15 AM - **B1.1
Application of Carbon Nanomaterials to Interconnects and Transistors for Low Power-consumption Large-scale Integrated Circuits.
Shintaro Sato 1 2 3
1 , Fujitsu Laboratories Ltd., Atsugi Japan, 2 , MIRAI-Selete, Atsugi Japan, 3 , AIST, Tsukuba Japan
Show AbstractAs the dimensions of large-scale integrated circuits (LSIs) decrease, it is becoming more and more difficult to improve the speed and the power consumption of LSIs just by miniaturization. We are trying to employ carbon nanomaterials including carbon nanotubes (CNTs) and graphene, which have excellent electrical properties, for interconnects and transistors of future low power-consumption LSIs. In this presentation, I will talk about CNT interconnects, which have been addressed at Fujitsu and MIRAI-Selete for years. Special emphases will be placed on the fabrication process of CNT vertical interconnects [1] and their reliability. I will also explain our recent progress on the application of graphene to transistor channels. Graphene synthesis on a 200-mm Si wafer and the fabrication of graphene transistors using newly-developed transfer-free processes [2] will be described. Furthermore, a self-organized structure consisting of graphene connected vertically to aligned CNTs [3] will be introduced. Possible applications of such a structure will also be described.
The work related to CNT interconnects was completed as part of the MIRAI Project supported by NEDO. The graphene-related work was partly supported by the Japan Society for the Promotion of Science (JSPS) through its “Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program).”
[1] S. Sato, et al., Sensors and Materails, 21, 373 (2009). [2] D. Kondo, et al., Appl. Phys. Express 3, 025102 (2010). [3] D. Kondo, et al., Appl. Phys. Express 1, 074003 (2008).
9:45 AM - B1.2
Direct Comparison of Separated Carbon Nanotube Thin-film Transistors Using 95% and 98% Semiconducting Nanotubes and Their Application in Digital Integrated Circuits.
Chuan Wang 1 , Jialu Zhang 1 , Chongwu Zhou 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractPre-separated, semiconducting enriched carbon nanotubes hold great potential for thin-film transistors and integrated circuit applications due to their high mobility, high percentage of semiconducting nanotubes, and room-temperature processing compatibility. Here in this paper, we report, for the first time, the progress on the application of separated nanotube thin-film transistors for macroelectronic integrated circuits. We have systematically and directly compared the key performance metrics such as on-current density, on/off ratio, transconductance, and mobility of devices using separated nanotubes with 95% and 98% semiconducting nanotubes and revealed the trade-off between the on-current density and on/off ratio. The devices with optimized performance have been used to demonstrate integrated digital logic blocks with symmetric input/output behaviour, which is crucial to allow the cascading of multiple stages of logic blocks and larger scale integration. Moreover, due to the highly uniform nature of the devices, integrated inverters with different voltage gains have be achieved by simply changing the device dimensions in the layout design, and the results are in accordance with conventional silicon field-effect transistor circuit design theory. Our approach can serve as the critical foundation for future nanotube-based thin-film macroelectronics.
10:00 AM - B1.3
Inverters based on Carbon-nanotube Transistors with Switching Frequencies Above 1 MHz on Glass.
Hyeyeon Ryu 1 , Daniel Kaeblein 1 , Ute Zschieschang 1 , Oliver Schmidt 2 , Hagen Klauk 1
1 Organic Electronics, Max Planck Insitute for Solid State Research, Stuttgart Germany, 2 Electrical Engineering and Information, Technology,Chemnitz University of Technology, Chemnitz Germany
Show AbstractNanoscale field-effect transistors (FETs) based on individual semiconducting carbon nanotubes are of interest for circuits with high integration densities that can be made on inexpensive, large-area substrates, such as glass or flexible plastics. While the static performance of FETs based on individual carbon nanotubes has been discussed many times [1-3], there are only a few reports on the dynamic performance of carbon-nanotube circuits [4-6]. Bachtold et al. and Javey et al. measured signal delays of 30 msec [4] and 750 µsec [5], but the switching speed of their circuits was limited by off-chip interconnects that introduced with large parasitic capacitcances. Chen et al. realized fully integrated circuits with a record delay of 1.9 nsec [6], but these complementary circuits required p-channel and n-channel carbon-nanotube FETs, the latter of which are difficult to obtain and are usually not stable in air. We have fabricated arrays of p-channel carbon-nanotube FETs on glass substrates, integrated the FETs with on-chip load resistors based on vacuum-deposited amorphous carbon films, and measured signal delays as small as 12 nsec. First, an array of probe pads was defined by electron-beam lithography, Ti/AuPd evaporation, and lift-off. Gate electrodes were then defined by e beam lithography and deposition of 30 nm thick Al. The Al gates were briefly exposed to an oxygen plasma to create a 3.6 nm thick AlOx layer, and a 2.1 nm thick phosphonic acid monolayer was then allowed to self-assemble from solution. The total thickness of the AlOx/SAM gate dielectric is 5.7 nm. Carbon nanotubes produced by arc discharge were then deposited from a suspension. Using scanning electron microscopy an individual nanotube was located on each gate, and a pair of AuPd source/drain contacts was defined by e beam lithography for each device. The channel length is ~400 nm. Some of the devices are metallic, but many show useful FET characteristics with ON/OFF ratios up to 107 and ON-state drain currents >1 µA at 1 V. To realize logic circuits we fabricated load resistors on the same substrate by evaporating a thin layer of amorphous carbon, patterned by e-beam lithography. The resistors have excellent linearity and resistances between 105 and 108 Ω, depending on the geometry and film thickness. Inverters composed of a carbon-nanotube FET and an amorphous-carbon load resistor have full output swing and small-signal gain up to 15. To estimate the dynamic performance of the FETs we extracted the time constants from the measured output-signal transitions. When the FETs switch from the OFF-state to the ON-state, the time constant is about 12 nsec, which suggests a maximum frequency of ~10 MHz. [1] Javey et al., Nano Lett. 2005, 5, 345. [2] Appenzeller et al., Phys. Rev. Lett. 2004, 93, 196805. [3] Chen et al., Appl. Phys. Lett. 2005, 86, 123108. [4] Bachtold et al., Science 2001, 294, 1317. [5] Javey et al., Nano Lett. 2002, 2, 929. [6] Chen et al., Science 2006, 311, 1735.
10:15 AM - B1.4
Stable Conversion of Separated Carbon Nanotube Thin-film Transistors from P-type to N-type by Atomic Layer Deposition of High-k Oxide and Its Application in CMOS Digital Circuits.
Jialu Zhang 1 , Chuan Wang 1 , Yue Fu 1 , Yuchi Che 1 , Chongwu Zhou 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractPre-separated, semiconducting enriched carbon nanotubes hold great potential for thin-film transistors (TFTs) and integrated circuit applications due to their extraordinary mobility, high on/off ratio and room-temperature processing compatibility. The main challenge it still facing is how to fabricate air stable N-type thin-film transistors with industry compatible techniques. Here in this paper, we report the method of converting as-made P-type separated nanotube thin film transistors (SN-TFTs) into N-type transistors by adding a high-k oxide layer on top of the device using Atomic Layer deposition (ALD) and its application in CMOS macroelectronic digital circuit. The absorption of oxygen and accumulation of fixed charge in the nanotude dielectric layer interface during the ALD process are proved to be the reasons of the carrier type conversion by designed experiments. The N-type devices exhibit comparable electrical performance as the P-type SN-TFTs in terms of on-current, on/off ratio and device mobility. A CMOS inverter with symmetric input/output behaviour and large noise margin has also been demonstrated. The excellent performance gives the feasibility of cascading multiple stages of logic blocks and larger scale integration. Our approach can serve as the critical foundation for future nanotube-based thin-film macroelectronics.
10:30 AM - B1.5
All-semiconducting Nanotube Networks: Towards High Performance Printed Nanoelectronics.
Nima Rouhi 1 , Dheeraj Jain 1 , Katayoun Zand 1 , Peter Burke 1
1 Electrical Engineering and Computer Science, University of California-Irvine, Irvine, California, United States
Show AbstractIn this work, we present progress towards devices fabrication using all semiconducting nanotubes as the starting material. DC analysis of device characterization shows a high mobility, up to 40 cm2/V-s, and good on/off ratio in the range of more than 103 and 104 in some cases. A critical issue is the ink formulation and dependence of electronic properties on the nanotube density after deposition.I.FABRICATIONDevices reported here were fabricated using a solution enriched up to 90% in semiconducting single walled carbon nanotubes (diameter range – 1.2-1.7 nm, length range 300 nm to 5 μm). These solutions were made using density gradient centrifugation process for the separation of nanotubes with different chiralities. Prior to the deposition of nanotubes, the surface of Si/SiO2 wafer was modified with APTES (a conventional method). Nanotube solution was then either spin-coated or poured vertically on these wafers.Following the nanotube deposition, the wafer was patterned for source and drain deposition using standard photolithography. We also studied the effect of gate length on mobility, and on/off ratio, for devices with different gate lengths (5~100 μm).E-beam evaporation was used to deposit source and drain electrodes (Pd/Au). The Si wafer acts as the back gate and 300 nm of SiO2 was used as the gate dielectric.II.ELECTRICAL MEASUREMENTSThe ID-VD extracted from the dc measurement shows that the current-voltage relationship is linear for small VD ranging from -1 V to 1 V (triode region), indicating good ohmic contact between nanotubes and electrodes. By applying more negative VD the devices clearly show saturation behavior. Since we are using purified all-semiconducting (90% semiconducting) tubes in the channel, we are expecting high on/off ratio, which is true in our devices. The on/off ratio is more than 1000 in almost all devices. Mobilities up to ~40 cm2/V-s are observed using conventional MOSFET equations and curve fitting the ID-VD characteristic.III.CONCLUSIONIn summary we reported thin film transistors fabricated using semiconductor-enriched carbon nanotubes. The dc electrical measurements show a great improvement in terms of mobility (up to 40 cm2/V-s), on/off ratio (10,000), and transconductance compared to previous works. Since these are some of the first spin-on, all semiconducting nanotube devices ever made, these initial results are indeed quite promising for printed RF electronics.
10:45 AM - B1.6
New Dynamic Air-brush Technique for SWCNTs Deposition: Application to Fabrication of CNTFETs for Electronics and Gas Sensing.
Paolo Bondavalli 1 , Louis Gorintin 1 , Pierre Legagneux 1
1 Physics, Thales Research and Technology, Palaiseau France
Show AbstractThis contribution deals with Carbon Nanotubes Field Effect transistors (CNTFETs) based gas sensors fabricated using a new dynamic air-brush technique (patented) for SWCNTs (and nanomaterials in general) deposition. The main novelty is that our technique is compatible with large surfaces, flexibles substrates and allows to fabricate high performances transistors exploiting the percolation effect of the SWCNTs networks achieved with extremely reproducible characteristics. Indeed we have developed a machine which allows us the dynamic deposition on heated substrates of SWCNT solutions, improving dramatically the uniformity of the SWCNTs mats. In the frame of our research the CNTFETs have been developed for gas sensing applications using a patented approach shown in previous presentations. Indeed we have fabricated arrays of CNTFETs achieved using four different metal electrodes on the same chip to exploit the change of metal/SWCNTs junction characteristics as a function of the gas detected in order to identify a sort of electronic fingerprinting. This phenomenon is related to the change of the metal work function and so of the Schottky barrier and seems to be extremely selective. Although the deposition technique has been developed to fabricate CNTFETs, this technique is extremely versatile and can be used for other kinds of applications such as fabrication of bolometers, replacements of ITO layers, in OLED, for light and cheap ultracapacitors on flexible substrates. This technique could really allow these nanomaterials to strike the market on these applications. We will presents statistics on the distribution of the CNTFETs fabricated with our technique which demonstrate its suitability for industrial applications. Moreover results of gas sensing using compact chips composed by 4 different metals electrodes will be shown (NO2, NH3, Humidity, DMMP for concentration between 100ppb et 10ppm).This work has been performed in the frame of the Projects NANOSENSOFIN (CO sensing) and CAPTEX (explosives sensing) funded by ANR.
11:00 AM - B1:CNT Devices
Break
11:15 AM - **B1.7
Energy Dissipation in Carbon Nanotube and Graphene Electronics.
Eric Pop 1
1 Electrical & Computer Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractPower consumption is a significant challenge, often limiting the performance of integrated circuits from mobile devices to massive data centers. Carbon nanoelectronics have emerged as potentially energy-efficient future devices and interconnects, with both large mobility and thermal conductivity. This talk will focus on power dissipation in carbon nanotubes and graphene, with applications to low-energy devices, interconnects and memory elements. Experiments have been used to gain new insight into the fundamental behavior of such devices, and to better inform practical device models. The results suggest much room for energy optimization in nanoelectronics through the design of geometry, interfaces, and materials.
11:45 AM - B1.8
Thermionic Field Emission in Carbon Nanotube Transistors and Proposal of Surface Inversion Channel Model.
David Perello 1 , Innam Lee 1 , Seong Chu Lim 2 , Woo Jong Yu 2 , Young Hee Lee 2 , Minhee Yun 1
1 Electrical and Computer Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Energy Science, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractCarbon nanotube transport has been studied by many researchers. However, no analytical model describing transport has been reported in the literature, nor has any explicit dependence of transport characteristics been clarified by using a single CNT. In this work, we derived and confirmed with experimental evidence a novel theoretical model that is based on innovative assumptions at specific gate voltages (this is a strict requirement). The model we derived is an analytical correlation of saturation current and differential conductance with the work function of the metal. This model fits very well to the experimental observations and clarifies the long-sought-after dependence of contact resistance (differential conductance) with the work function of the contact metal by using a single CNT contacted by over a hundred metal contacts with 5 different metal types (Hf, Cr, Ti, Au, Pd). This type of fabrication and analysis has never been performed before, giving the results unprecedented consistency within statistical errors and allowing us to confirm the first-to-date CNT transport model proposed and derived in the literature.The systematic nature of this study goes far beyond prior analysis of transport by taking a proven and historical theory and adapting it with specific conditions for CNTFETs, without the use of any unphysical correlation constants in the fitting. The simple and elegant theoretical model derived is further applicable to others materials and systems where many standard spectroscopic and electrical measurement techniques cannot be utilized due to size or material degradation involved in the testing.We secondly examined electrical measurements of CNT FETs with the same metal types as above on a single CNT over the range 30 K < T < 300 K to extract information about the energy barriers and dipoles at the contact for various metal contact types. We propose a “surface inversion channel” or SIC model to explain underlying transport mechanisms at the unpinned metal-carbon nanotube (CNT) interface. The model is extracted from interpretations of the Schottky barrier measurements of devices, and confirmed by our first-observation of field-enhanced, ‘contact’ band to band tunneling. The SIC model explains a breadth of open questions in the debate between contact and doping effects in CNT, including why long-term (unprotected) air-stable n-type CNT transistor operation is difficult, or why specific metal-contacted CNT are (weakly) ambipolar even after air exposure, while other metal-contacts with lower work function are strictly unipolar p-type. In addition to clearing up previous inconsistencies in the literature regarding CNT band alignments, both the model and core methodology are applicable in examining other low dimensional systems.
12:00 PM - B1.9
Enhanced Electron Field Emission from Carbon Nanotube Matrices.
Archana Pandey 1 , Abhishek Prasad 1 , Mark Engelhard 2 , Chongmin Wang 2 , Yoke Yap 1
1 Physics, Michigan Technological University, Houghton, Michigan, United States, 2 EMSL, Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractField emission from as-grown carbon nanotube (CNT) films often suffered from high threshold electric field, and low emission site density due to screening effects. These problems can be resolved by patterned growth of CNTs on lithographically prepared catalyst films. However, these approaches are expensive and not applicable for future emitting devices with large display areas. Here we show that as-grown CNT films can have low emission threshold field and high emission density without using any lithography processes. We have reduced screening effects and work function of as-grown CNT films and created the novel CNT matrices by addition vapor- and/or liquid- phase deposition. Furthermore, these CNT matrices can continuous emit electrons for 40 hours without significant degradation.The fabrication of our CNT matrices is described as follows. First, CNT films were grown by plasma-enhanced chemical vapor deposition. These vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs) are having typical length and diameter of xx microns and xx nm, respectively. Spacing between these CNTs is ~xx nm in average, leading to poor emission properties due to the screening effect. These as-grown samples were then subjected to the deposition of strontium titanate (SrTiO3) by pulsed-laser deposition to reduce both the work function and screening effect of CNTs. The emission properties of these coated samples can be further improved by fully filled the spaces between VA-MWCNTs by plo-methyl metha acrylate (PMMA). The coating of SrTiO3 on as-grown VA-MWCNTs was confirmed by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The field emission threshold electric field was decreased from 3.8 V/µm for as-grown VA-MWCNTs to 1.8 V/µm for SrTiO3 coated VA-MWCNTs. The addition filling with PMMA and mechanical polishing can further reduce the threshold to 0.775V/µm for the so called PMMA-STO-CNT matrices. Long term emission stability and emission site density were also enhancedBased on our theoretical simulation, a new emission model was then proposed to explain the enhanced performances of our CNT matrices. All these results will be discussed in the meeting. *E-mail address:
[email protected] (Y. K. Yap)This work was supported by the Defense Advanced Research Projects Agency (Contract number DAAD17-03-C-0115 through the U.S. Army Research Laboratory), and the U.S. Department of Army (Grant number W911NF-04-1-0029 through the City College of New York). A portion of the research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research located at Pacific Northwest National Laboratory.
12:15 PM - B1.10
Electrical Resistivity and Contact Resistance in Carbon Nanotube Vertical Interconnects.
Nicolo Chiodarelli 1 2 , Yunlong Li 1 , Kai Arstila 1 , Olivier Richard 1 , Daire Cott 1 , Marc Heyns 1 3 , Stefan De Gendt 1 4 , Guido Groeseneken 1 2 , Philippe Vereecken 1 5
1 , imec, Leuven Belgium, 2 Department of Electrical Engineering, Katholieke Universiteit Leuven, Leuven Belgium, 3 Metallurgy and Materials Engineering , Katholieke Universiteit Leuven, Leuven Belgium, 4 Chemistry Department, Katholieke Universiteit Leuven, Leuven Belgium, 5 Center for Surface Chemistry and Catalysis, Katholieke Universiteit Leuven, Leuven Belgium
Show AbstractCarbon Nanotubes (CNT) are carbon allotropes with outstanding electronic properties. Charge transport can be ballistic, current densities larger than 10^9 A/cm^2 can be sustained without degradation and a high thermal conductivity has been reported. For these reasons, CNT could be the perfect material for manufacturing vertical interconnects of improved performances, reliability and heat-transfer capability as required for the future generations of microchips. The electrical performance of current vertical CNT interconnects, though, are still far from their ballistic limit. The reasons reside in the poor control on the quality of both the CNT and their electrical contacts. Growing CNT of sufficient high quality using catalytic CVD processes, in fact, is not straightforward within the limited temperature budget for the wiring levels of advanced microchips: about 400C. Moreover, electrically testing the quality of both CNT and contacts can only be done after a complex process for integrating the material into dedicated and properly designed 3D structures. Hence, the risk of materials modification or of introducing spurious components which would corrupt the electrical characterization is increased. This work addresses the issues mentioned above by integrating and electrically characterizing vertical CNT bundles grown with a catalytic CVD method. A process flow is practically implemented on 200mm wafers to selectively grow CNT into via conduits at temperatures as low as 400C. The structure and the process were designed to closely mimic those of real contacts such that all the integration issues encountered can be directly translated and applied to real microchips.The electrical characterization is based on measurements of the CNT resistance as a function of the CNT length which is tightly controlled by tuning the polishing time during a chemical mechanical polishing step. With this technique which is quite unique for vertical CNT interconnect, the two most important parameters for quantitatively assess the electrical quality of the CNT and the contacts are extracted: the electrical resistivity and the contact resistance. These parameters are used for electrically benchmarking different CNT growth conditions and to evaluate the impact of process steps on both the contacts and the CNT. Thus, the methods proposed constitute a powerful technique for optimizing the process and develop CNT of superior electrical quality. This can be of relevant technological importance for interconnects as well as for all those applications that rely on the electrical properties of CNT grown with a catalytic CVD method at low temperature.
12:30 PM - B1.11
Towards Extremely Low Resistance in Highly Organized SWNT Interconnect Devices.
Young-Lae Kim 1 , Hyun Young Jung 2 , Swastik Kar 3 , Yung Joon Jung 2
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States, 3 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractHighly organized single-wall carbon nanotubes (SWNTs) networks and bundles are becoming the most promising candidate replacing copper-based interconnects in the future semiconducting industry. Here, we present the strategy of using highly organized SWNT network structures with extremely low contact resistance as well as enhanced electrical conductivity. Nanoscale organized SWNT network architectures were fabricated by using a template guided fluidic assembly process, developed in our laboratory. These SWNT network structures can withstand current densities up to~ 3×10^7 A/cm^2, comparable or better than copper at similar dimensions. Also, to decrease resistivity of SWNT network structures further, Pt nanoclusters sized in 1-2 nm were decorated on the surface of SWNTs. The increase in conductivity of the SWNT is caused by an increase in conduction channels close to their Fermi levels due to decorated Pt nanoclusters, with a possible conversion of the semiconducting SWNTs into metallic ones. Furthermore, we investigated the effect of cleaning processes on the contact resistance of our developed SWNT based interconnect devices. We have found that with improved cleaning processes after SWNT assembly (using warm acetone, IPA, and longer photoresist developing time), the contact resistance between SWNTs and contact electrodes of Ti/Au was decreased as low as 0.74 % of the overall resistance in the SWNT network structures, showing the significance of removing PMMA residues or other organic impurities that might exist on the surface of SWNTs. These results demonstrate a big step toward the integration of carbon nanotubes with comparatively high current density and extremely low contact resistance for future nanoscale electrical interconnect applications.
12:45 PM - B1.12
3-D Assembly of SWNTs for CMOS Interconnects.
Taehoon Kim 1 , Cihan Yimaz 1 , Sivasubramanian Somu 1 , Ahmed Busnaina 1
1 NSF Nanoscale Science and Engineering Center for High-rate Nanomanufacturing (CHN), Northeastern University, Boston, Massachusetts, United States
Show AbstractCarbon nanotubes (CNTs) have been considered as potentially useful interconnect materials for future VLSIs, due to their superior electrical properties, including their abilities to sustain a high current density and to exhibit ballistic transport along the tubes. Recently many researchers reported that bundle of CNTs could be grown selectively in via holes using chemical vapor deposition (CVD). However, CNT growth (synthesis) requires high temperatures that would damage CMOS circuits (causing metal diffusion and causing shorts). In our present work, room temperature directed assembly is utilized to assemble nanotubes in the vias instead of CNT synthesis. The electric field assisted directed assembly method assembles the SWNTs aligned perpendicular to the substrate in the vias. The process is very fast (less than a minute per wafer) and is scalable. This makes it a very promising approach for large-scale assembly of CNTs. Three dimensional assembly has been accomplished before, however, it mostly involved assembly between two electrodes where the separation between electrodes has to be with few microns and where the SWNT is connected the two electrodes. This requires having two metal layers already on the wafer for the SWNT to connect in 3-D. We developed a new 3-D assembly technique using only one electrode that’s connected to the SWNT, wherein another electrode is used that is placed far away (more than 1 cm away) from the wafer to maintain the applied potential. The assembled nanotubes are then connected to the next layer of the CMOs circuit and since all nanotubes ends are connected to each metal, contact resistance is expected to be small.
B2/Y2: Joint Session: Nanocarbon-based Electronics Integration
Session Chairs
Monday PM, November 29, 2010
Ballroom B, 3rd floor (Hynes)
2:30 PM - **B2.1/Y2.1
Carbon-based Materials as Key-enabler for ``More Than Moore".
Franz Kreupl 1
1 , SanDisk Corp., Milpitas, California, United States
Show AbstractCarbon-based materials like are heavily investigated as future CMOS-like devices and in interconnect applications. While much of the interest has been devoted to the device aspects in competition to conventional CMOS transistors, the talk here will focus on some less known applications of carbon. Proposed are interconnect applications like on-chip and DRAM capacitors, gate material or through-silicon vias (TSV), novel non-volatile memories, sensors or superior diodes. The quality and resistivity of the carbon layer depends on the deposition method, precursor and temperature, but optimum conditions can be found to achieve a benefit over competing materials in terms of temperature budget, resistivity, stress and ease of integration .The mere properties of the carbon layer is as important as their interaction with different interfacing materials like high-k materials, semiconductors and metals. Some important question which needs to be answered are, is there diffusion of carbon or from the interfacing materials? How does this impair breakdown behaviours? What are the effective work-functions for different interface materials? The answers to these questions will lead us to applications of graphene-like layers in MIM capacitor structures, DRAM capacitors and mid-gap gate-material, attractive for low power CMOS. The question on how these graphene-like layers interface with silicon will give us in the end powerful low-barrier Schottky diodes which can deal with the high temperature requirements of a front-end process. Therefore, for the first time, carbon-silicon Schottky-diodes can be incorporated in a CMOS flow. Stress, built during deposition of the many layers during a process has serious impact on the integration. Thin layers of carbon can reduce the overall stress and can ease the integration. For through-silicon vias the most economic approach of “via-first” was limited up to now to c-Si or poly-Si approach due to the high temperature requirement. Carbon layers can fill very high aspect ratio vias (up to 400) and offer a much better alternative to Si in terms of resistivity, stress and cost. If modifications of the carbon layers can be achieved at reasonable temperatures the overall resistivity can be dropped down to 10 uOhmcm which makes it already attractive for competition with W and Cu wiring. The study of maximum possible current densities in the carbon layers results in the finding of a new non-volatile memory based on the conductivity of different carbon configurations. This will not only enable cross-point memory architectures but could also be implemented in configuring FPGAs.Finally, the spin transport properties of carbon may be beneficial to solve the problems of the high current densities in spin-torque magnetic memories and for the ubiquitous GMR sensors where Neel coupling limits the sensitivity.Overall, the properties of carbon promise applications in a wide range of possible “More than Moore” scenarios for microelectronics.
3:00 PM - **B2.2/Y2.2
Optical Properties of Single and Few-layer Graphene: A Flexible New Material Set.
Tony Heinz 1
1 , Columbia University, New York, New York, United States
Show AbstractGraphene provides many distinctive mechanical properties, including very high strength and flexibility. Combined with the unique characteristics of electrons in graphene, the material offers the possibilities for a wide range new applications. In this paper, we present results of recent investigations of the optical properties of graphene. In addition to their intrinsic scientific interest, these studies help to lay the foundations for a range of photonic and optoelectronic applications from transparent electrodes to tunable infrared optical elements. The system of single-layer graphene (SLG) is known to provide unusually high carrier mobility and sheet conductivity. On the other hand, the material is highly transparent. Over a broad range of wavelengths in the near-infrared to visible, experiments by our group and others have shown that the absorption of SLG conforms closely to the theoretically predicted value of πα = 2.3%, where α denotes the fine-structure constant. Departures from this simple result have been observed at both shorter and longer wavelengths. In the infrared, electrical gating and doping can significantly modify the absorption.A richer set of optical response can be seen in few-layer graphene samples. Our measurements reveal peaks in the absorption spectrum that evolve systematically with the layer thickness of the graphene samples. These features can be understood in terms of a picture of zone-folding of the bulk 3-D graphite bands to produce the 2-D bands of FLG. In addition, external perturbations can be used to tune the band structure and optical response. For the case of graphene bilayer, measurements of the material in the presence of a perpendicular applied electric field demonstrate the possibility of induction of a tunable band-gap that can exceed 200 meV in size.A further distinctive features of graphene is the possibility of applying very high levels of strain. We discuss the development of these strains by bending graphene layers placed on a polymer substrate. In this fashion, strains of several percent can be produced. We have been able to examine the phonon structure of graphene under the influence of such strains by means of Raman spectroscopy. This provides insight into the response of the graphene phonons, as well as a methodology for the local characterization of strain.
3:30 PM - B2.3/Y2.3
Seeding Atomic Layer Deposition of High-k Dielectrics on Epitaxial Graphene with Organic Self-assembled Monolayers.
Justice Alaboson 1 2 , Qing Hua Wang 1 , Albert Lipson 1 , Jonathan Emery 1 , Michael Bedzyk 1 2 , Jeffrey Elam 2 , Michael Pellin 1 2 , Mark Hersam 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractFor graphene-based field-effect transistors and related nanoelectronic devices, chemical functionalization schemes are needed to integrate graphene with high-k dielectrics. Here, we report on the use of the organic molecule perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) as a seeding layer for the atomic layer deposition (ALD) of HfO2 and Al2O3 dielectrics on epitaxial graphene (EG) grown on the SiC (0001) surface. PTCDA forms a well-ordered, self-assembled monolayer on EG as observed by ultra-high vacuum scanning tunneling microscopy at room temperature. While ALD-grown dielectric films on bare graphene were discontinuous and riddled with pinholes, uniform and ultrathin ALD films were achieved on PTCDA-functionalized EG as determined by atomic force microscopy. X-ray reflectivity measurements establish that both PTCDA and graphene remain intact after ALD deposition. Capacitors were fabricated on PTCDA-EG utilizing a 10nm HfO2 and 3nm Al2O3 dielectric stack, where capacitance values of ~700 nF/cm2 and leakage currents of ~5 x 10-9A/cm2 were measured at 1 V gate bias. The high capacitance and low leakage current measured across the dielectric stack demonstrate the viability of organic self-assembled monolayers as seeding layers for high-k dielectrics in graphene-based nanoelectronics.
4:15 PM - **B2.4/Y2.4
Graphene: A Tunable Electronic Surface.
Michael Fuhrer 1
1 Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland, United States
Show AbstractGraphene is unique: a massless, gapless two-dimensional electron system contained in a single-atom thick plane of carbon. While the properties of the two-dimensional electron system have been widely studied, the fact that graphene consists of all surface atoms offers new opportunities to exploit graphene as a tunable electronic surface and interface. In this talk, I will first discuss the electronic structure of graphene, and its implications for electronic properties, and then I will discuss its tunable surface properties. A back-gate voltage can be used to tune graphene’s workfunction over a range of some 600 meV, and chemical doping, such as deposition of alkali metal in ultra-high vacuum or in an electrochemical cell, can extend this range much further, opening possibilities for graphene as a workfunction-matched interface for organic semiconductors. Graphene may be used as a sensitive detector to observe chemical reactions occurring on its surface at concentrations below 1/1000th of a monolayer, and the tunable workfunction of graphene offers the possibility of electronically tunable catalytic action. Finally, ion irradiation can be used to create atomic vacancies in graphene which have local magnetic moments. These moments couple strongly to conduction electrons in graphene via the Kondo effect, offering the possibility of tuning conduction-electron-mediated magnetism in graphene via defect engineering.
4:45 PM - **B2.5/Y2.5
Nanoelectronics and Macroelectronics Based on Carbon Nanotubes.
Chongwu Zhou 1
1 Electrical Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractCarbon nanotubes offer great promise but also face significant challenges for future electronic applications. This talk will focus on our recent work on: 1. Assembly and integration of massive aligned nanotubes for nanoelectronics, 2. Metal tube removal based on light irradiation, and 3. Thin film transistors (TFTs) based on separated nanotubes for macroelectronics. We will report our wafer-scale processing of aligned nanotube electronics. Massive aligned nanotubes were synthesized over complete 4 inch quartz and sapphire substrates, and then transferred to Si/SiO2 substrates. CMOS analogous fabrication was performed to yield submicron high performance transistors and defect-tolerant logic circuits.In addition, we will present the metal-to-semiconductor conversion of carbon nanotubes induced by light irradiation. The light irradiation process is scalable to wafer-size scales and capable of yielding improvements in the channel-current on/off ratio up to 5 orders of magnitude in nanotube-based field-effect transistors. Furthermore, we will report wafer-scale processing of TFTs based on separated nanotube, including key technology components such as assembly of high-density, uniform separated nanotube networks, high-yield fabrication of devices with superior performance, and demonstration of organic light-emitting diode (OLED) control circuit. References[1] “CMOS-analogous wafer-scale nanotube-on-insulator approach for submicron devices and integrated circuits using aligned nanotubes”, Chongwu Zhou et al., Nano Letters, Vol. 9, 189, 2009. [2] “Scalable Light-Induced Metal to Semiconductor Conversion of Carbon Nanotubes”, Chongwu Zhou et al., Nano Letters, Vol. 9, 3592, 2009. [3] “Wafer-Scale Fabrication of Separated Carbon Nanotube Thin-Film Transistors for Display Applications”, Chongwu Zhou et al., Nano Letters, Vol. 9, 4285, 2009.Keywords: carbon nanotubes, nanoelectronics, macroelectronics, thin film transistors
5:15 PM - B2.6/Y2.6
Fabrication of Electronic Devices with Highly-enriched Semiconducting Single Walled Carbon Nanotubes.
George Tulevski 1 , Aaron Franklin 1 , Bhupesh Chandra 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractThe exceptional transport properties of Single-Walled Carbon Nanotubes (SWCNTs) make them promising materials for various technological applications where high mobilities and current densities are desired. Despite their promise, the implementation of SWCNTs into technologies is limited by the materials processing tools available to sort and assembly SWCNTs into sophisticated structures. This talk will focus on our recent efforts to overcome these limitations, including recent results on sorting and assembly of SWCNTs for the fabrication of electronic devices. Enrichment of semiconducting SWCNTs is achieved using a modified size-exclusion chromatography technique to yield solutions with > 97% semiconducting SWCNTs. The material and semiconducting yield is characterized both optically and electrically. The method is simple and highly scalable to large quantities. Following separation, the SWCNTs are assembled into aligned arrays to form multi-channel CNT-FETs with short channel lengths (100 – 500nm). The arrays can be selectively placed anywhere on the substrate and can extend for millimeters. The devices display high drive currents while maintaining large on/off ratios (> 106), even at channel lengths were direct transport occurs. The CNTs were also used as the active material in thin-film transistors and display similarly high performances. The results described here show a possible path forward for the integration of SWNCTs into future technologies.
5:30 PM - B2.7/Y2.7
Large-scale, Bottom-up, CMOS-compatible Integration of Chirality-sorted Carbon Nanotubes.
Aravind Vijayaraghavan 1 2 , Marc Ganzhorn 2 , Ninette Stuerzl 2 , Frank Hennrich 2 , Ralph Krupke 2
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Karlsruhe Institute of Technology, Karlsruhe Germany
Show AbstractIn order to realize the tremendous potential of single-walled carbon nanotubes (SWCNTs) in electronic, optoelectronic and electromechanical applications, it is essential to integrate SWNTs into existing microelectronic products and techniques. Specifically, SWNTs of a particular type (chirality) need to be assembled at specific locations and orientations in lithographically patterned circuits at close to 100% efficiency. We demonstrate here, how this can be accomplished. SWNTs are sorted into single-chirality fractions, for example by selective polymer wrapping. They are also enriched to high-purities in only semiconducting species, centered on a favorable diameter of 1.4 nm, using density-gradient ultracentrifugation. We have shown previously that SWNTs and graphene can be assembled at ultra-large-scale integration densities using dielectrophoresis (DEP), which in addition is self-limiting to one SWNT per device location. By adapting DEP for sorted SWNT solutions, we assemble SWNTs of specific chirality or electronic type at nearly 100% integration densities. DEP can simultaneously assemble SWNT devices in multiple orientations, and is the only CMOS compatible route available for doing so. Pre- and post-processing steps to extract high performance from such devices are also described.In addition to its importance in applications, understanding fundamental SWNT properties also critically depends on the ability to study them specifically. We show that by fabricating arrays of identical SWNTs, we can perform multiple measurements on identical SWNTs and correlate interesting features. For instance, we demonstrate a strong correlation between D-peak in Raman spectroscopy, dark-exciton peaks in photoluminescence spectroscopy and low conductance and mobility in electron transport measurements. References: Vijayaraghavan, A., et al, Toward Single-Chirality Carbon Nanotube Device Arrays, ACS Nano, 2010, 4(5), 2748-2754.Ganzhorn, M.; et al; Large-scale, CMOS-compatible integration of high-performance semiconducting single-wall carbon nanotube devices. SubmittedVijayaraghavan, A.; et al, Dielectrophoretic Assembly of High-density Arrays of Graphene Devices for Rapid Screening. ACS Nano 2009, 3(7), 1729–1734.Vijayaraghavan, A.; et al, Ultra-Large Scale Directed Assembly of Single-Walled Carbon Nanotube Devices. Nano Letters 2007, 7, 1556-1560.
5:45 PM - B2.8/Y2.8
Selective Integration of Individual Metallic Single-walled Carbon Nanotubes for Parallel Sensor Assembly.
Brian Burg 1 , Julian Schneider 1 , Vincenzo Bianco 2 , Niklas Schirmer 1 , Dimos Poulikakos 1
1 Department of Mechanical and Process Engineering, ETH Zurich, Zurich Switzerland, 2 Dipartimento di Ingegneria Aerospaziale e Meccanica, Seconda Università degli Studi di Napoli, Napoli Italy
Show AbstractThe dielectrophoretic separation of individual metallic single-walled carbon nanotubes (SWNTs) from heterogeneous solutions and their simultaneous deposition between electrodes is achieved and confirmed by direct electric transport measurements. Out-of-solution guided parallel assembly of individual SWNTs was investigated for electric field frequencies between 1 and 200 MHz. At 200 MHz, 19 of the 22 deposited SWNTs (86%) displayed metallic behavior, whereas at lower frequencies the expected random growth distribution of 1/3 metallic SWNTs prevailed. A threshold separation frequency of 188 MHz is extracted from a surface-conductivity model, and a conductivity weighting factor is introduced to elucidate the separation frequency dependence. Low-frequency experiments and numerical simulations show that long-range nanotube transport is governed by hydrodynamic effects whereas local trapping is dominated by dielectrophoretic forces. The electrokinetic framework of dielectrophoresis in low-concentration solutions is thus provided and allows a deeper understanding of the underlying mechanisms in dielectrophoretic deposition processes for long and large-diameter SWNT-based low-resistance device integration, such as piezoresistive SWNT based pressure sensors.Reference: Burg, B. R.; Schneider, J.; Bianco, V.; Schirmer, N. C.; Poulikakos, D. Langmuir 2010, DOI: 10.1021/la1013158.
Symposium Organizers
Robert R. Keller National Institute of Standards and Technology
W. Jud Ready Georgia Institute of Technology
Meyya Meyyappan NASA Ames Research Center
Manish Chhowalla Imperial College London
B5: Poster Session: Carbon-Based Electronic Devices
Session Chairs
Manish Chhowalla
Robert Keller
Meyya Meyyappan
Jud Ready
Tuesday PM, November 30, 2010
Exhibition Hall D (Hynes)
B3: Graphene Devices - FETs
Session Chairs
Tuesday PM, November 30, 2010
Room 310 (Hynes)
9:30 AM - **B3.1
Graphene Electronics and Optoelectronics.
Phaedon Avouris 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractThe excellent carrier transport properties in graphene and the modest tuning of the current by a gate field make graphene ideal for high-frequency analog device applications. I will discuss the device physics, fabrication and operation of RF graphene transistors on a wafer scale with cut-off frequencies up to 100GHz using epitaxially grown graphene. Despite the gapless nature of graphene, built-in electric fields at graphene-metal contacts can be used to construct ultrafast photoconductors. Such devices will be demonstrated and utilized for the reliable detection of 10GBit/s optical data streams. I also will discuss the electrical bandgap opening in bilayer graphene and demonstrate bilayer transistors operating at room temperature.
10:00 AM - B3.2
Optimizing the Characteristics of Graphene Field-effect Transistors through Dielectric Engineering and Self-aligned Gating.
Damon Farmer 1 , Yu-Ming Lin 1 , Phaedon Avouris 1
1 , IBM TJ Watson Research Center, Yorktown Heights, New York, United States
Show AbstractMuch of the interest surrounding graphene is due to the high field-effect carrier mobility that is exhibited by graphene-based field-effect transistors (FETs). This makes graphene a material of great promise as the active element in electronic devices, particularly those based on high-frequency operation. However, many key issues still need to be addressed in order to fully exploit graphene for technological applications. For instance, the two-dimensional nature of the graphene lattice causes it to be very sensitive to its material environment. As a result, many of the challenges in the field of graphene electronics are fundamental material engineering issues. This includes preservation of the carrier mobility after gate dielectric deposition and the elimination of parasitics in graphene devices. Here, we present a device fabrication process that addresses both of these issues by employing mobility-preserving gate dielectrics in conjunction with a self-aligned gating technique that minimizes the parasitic capacitances and resistances in the device. The self-alignment process utilizes the inherent nucleation inhibition of atomic-layer-deposited films with the graphene surface to achieve electrical isolation of the gate electrode while simultaneously maintaining electrical access to the graphene channel. This process produces electrode separation lengths of only 15 - 20 nm, which allows for improved device stability and performance. Due to the aforementioned sensitivity of graphene to its environment, the material compatibility issues that must be overcome in order to realize such devices will be given particular emphasis.
10:15 AM - B3.3
Comparative Study of the Effective and Hall Mobility of Graphene.
Archana Venugopal 1 , Xuesong Li 3 , Carl Magnuson 3 , Boyang Han 3 , Wiley Kirk 2 , Luigi Colombo 4 , Rodney Ruoff 3 , Eric Vogel 1 2
1 Electrical Engineering, University of Texas at Dallas, Richardson, Texas, United States, 3 Mechanical Engineering and Texas Materials Institute, University of Texas at Austin, Austin, Texas, United States, 2 Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States, 4 , Texas Instruments Incorporated, Dallas, Texas, United States
Show AbstractABSTRACT:Graphene has been the subject of extensive electrical characterization since 2004.[1, 2] As in semiconductor based FETs, the effective mobility (µeff) is typically used as the parameter to gauge and compare the device performance, and µeff is extracted from Id – Vg characteristics. The extraction of µeff values in graphene FETs are either based on a model proposed by Kim et al.[3], which assumes a charge carrier concentration (n) independent mobility or the Drude model[1] that assumes a carrier concentration specific mobility. Hall mobility studies[4] report a carrier concentration dependence different from either of these assumed behaviours. The relationship between Hall and µeff extracted from field effect transistors in graphene is not well understood. A comparative study of the mobility in exfoliated graphene has been performed using split C-V and Hall effect measurements between 5 K and 295 K, the results of which will be presented. The electronic transport characteristics of CVD graphene grown on Cu[5] as measured by the Hall effect and extracted from split C-Vs as a function of domain size[6] and temperature, will also be presented.REFERENCES:1.Novoselov, K.S., et al., Electric Field Effect in Atomically Thin Carbon Films. Science, 2004. 306(5696): p. 666-669.2.Berger, C., et al., Ultrathin Epitaxial Graphite: 2D Electron Gas Properties and a Route toward Graphene-based Nanoelectronics. The Journal of Physical Chemistry B, 2004. 108(52): p. 19912-19916.3.Kim, S., et al., Realization of a high mobility dual-gated graphene field-effect transistor with Al[sub 2]O[sub 3] dielectric. Applied Physics Letters, 2009. 94(6): p. 062107-3.4.Zhu, W., et al., Carrier scattering, mobilities, and electrostatic potential in monolayer, bilayer, and trilayer graphene. Physical Review B, 2009. 80(23): p. 235402.5.Li, X., et al., Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils. Science, 2009. 324(5932): p. 1312-1314.6.Li, X., et al., Evolution of Graphene Growth on Ni and Cu by Carbon Isotope Labeling. Nano Letters, 2009. 9(12): p. 4268-4272.
10:30 AM - B3.4
Graphene-based Nanogenerators with Fully Rollable and Transparent Characteristics.
Dukhyun Choi 1 , Sang-Woo Kim 2 , Won Mook Choi 3 , Hyeon-Jin Shin 3 , Jae-Young Choi 3 , Young Hee Lee 4
1 Mechanical Engineering, Kyung Hee University, Yongin, Gyeonggi, Korea (the Republic of), 2 School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon Korea (the Republic of), 3 , Samsung Advanced Institute of Technology, Yongin Korea (the Republic of), 4 Department of Physics, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractChemical vapor deposition-grown large-scale graphene sheets are employed as transparent electrodes to realize fully rollable transparent (RT) energy harvesting nanodevices using piezoelectric zinc oxide (ZnO) nanorods (called nanogenerators). Based on in-situ two probe resistance experiments and a computed simulation, we demonstrate the electrical and structural stability of graphene-based nanogenerators under external mechanical loads such as those experienced with bending or rolling. For the integrated nanogenerator, a heterogeneous three-dimensional (3D) nanostructure consisting of 1D ZnO nanorods on a 2D graphene electrode is successfully fabricated. It is investigated that our graphene electrode, with its extremely high carrier mobility at room temperature and a Schottky contact to the ZnO nanorods, results in RT-nanogenerators with excellent charge scavenging performance. The graphene-based device is expected to lead to new types of multifunctional, reliable nanosystem applications such as multiplex touch sensors and artificial skins equipped with tactile sensors.
10:45 AM - B3.5
Experimental Evaluation of AlN as a Dielectric for Graphene-based Devices.
Mark Fanton 1 , Joshua Robinson 1 2 , David Rearick 1 , Michael LaBella 1 , Kathleen Trumbull 1 , Randal Cavalero 1 , Matthew Hollander 1 2 , Zachary Hughes 1 2 , David Snyder 1
1 Electro-Optics Center, Penn State University, Freeport, Pennsylvania, United States, 2 Materials Research Institute, Penn State University, University Park, Pennsylvania, United States
Show AbstractTraditional semiconductor field effect structures rely on the use of thin oxide films to isolate the gate electrode from the channel. The use of oxides on carbon-based structures presents some unique challenges considering the high thermodynamic driving force for reaction between carbon and oxygen. In this work AlN was successfully used as a dielectric for fabricating field effect structures on epitaxial graphene on semi-insulating SiC. A process was developed for deposition of 10-20nm thick AlN films on graphene by molecular beam epitaxy. Films were grown by RF-plasma-assisted MBE at deposition temperatures between 100°C and 350°C. Growth was initiated using metal rich process conditions to prevent damage to the graphene film by the nitrogen plasma source and to encourage full coverage by the dielectric. Growth was initiated using metal rich process conditions to prevent damage to the graphene film by the nitrogen plasma source and to encourage full coverage by the dielectric. Characterization of the graphene film by Raman spectroscopy before and after AlN deposition indicated no significant degradation in structural properties. Prior to deposition of AlN the graphene films exhibited a mobility of 800cm2/V-s, and a sheet carrier density of 8x1012cm-2, as measured by Hall effect. After deposition of the dielectric the mobility decreased to as low as 350cm2/V-s and the carrier concentration increased to as much as 1.5x1013cm-2. Changes in mobility and carrier concentration will be discussed in terms of structural changes observed by Raman spectroscopy and transmission electron microscopy and changes in chemistry as monitored by x-ray photoelectron spectroscopy.
12:00 PM - B3.7
Solution-gated Graphene FET Arrays for Chemical and Biological Sensing.
Benjamin Mailly Giacchetti 2 1 3 , Allen Hsu 1 3 , Han Wang 1 3 , Ki Kang Kim 1 3 , Jing Kong 1 3 , Tomas Palacios 1 3
2 Materials Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 1 Electrical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Microsystems Technology Laboratories, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractGraphene holds great potential for bioelectronic applications and, more specifically, for fast high-sensitivity pH measurements and biosensing. Its monolayer structure (just one carbon atom thick) in combination with its very high carrier mobility enable high transconductance and low noise which are key parameters for chemical sensors with electronic readout. In fact, single molecule detection has already been demonstrated in graphene gas sensors. In this paper we report on the fabrication and preliminary characterization of the first solution-gated graphene field-effect transistor (SGFET) arrays that can operate in various liquid environments. These devices are optimized for the detection of changes of pH or of a biomolecule concentration in liquid electrolytes. These molecules induce changes in the transport properties of graphene that can easily be detected electronically.The active channel of our devices is mostly single-layer graphene films grown by low pressure chemical vapor deposition on copper foils and transferred onto a silicon substrate. After patterning the graphene film by O2 plasma etching, we deposit Ti/Pd/Au (2.5nm/45nm/15nm) drain and source contacts in order to fabricate graphene transistors. A SU8 polymer layer is then added to protect the contacts. Next, we wire-bond the graphene device to a chip carrier. In addition, a PDMS-based encapsulation technology has been developed to insulate the wires, from the electrolyte. The performance of the SGFET sensors can then be characterized by using a silver chloride reference electrode immersed in the solution as the top gate voltage.In summary, our study aims at demonstrating that graphene with its scalable technology, very high sensivity and low noise has the potential to surmount the challenges of existing silicon technologies for accurate pH and biosensing applications. Our on-going work focuses on functionalizing the graphene surface to make it selective to specific analytes. In addition, we have demonstrated that HEK 293 cells can grow and survive on our graphene films with good adhesion, which paves the way for cellular recording with graphene devices.
12:15 PM - B3.8
High Frequency Top-gated Graphene RF Ambipolar FETs Using Large-area CVD Graphene and Advanced Dielectrics.
Osama Nayfeh 1 , Madan Dubey 1
1 Sensors and Electron Devices Directorate, United States Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractAmbipolar top-gated field effect transistors (FETs) based on large area Cu catalyzed CVD-grown monolayer graphene interfaced to advanced dielectrics have been constructed and examined both for their material and electrical qualities. Interfacing of the graphene with novel insulators/substrates could be tailored for the particular application and provide for enhanced device functionality. In contrast to graphene FETs using SiO2-based top-gate dielectric, which show asymmetric electron/hole mobility (with larger hole mobility), and Dirac point shifted to positive levels, FETs constructed using advanced piezoelectric AlN show Dirac point almost near neutral levels and near symmetric electron/hole mobility. The DP is shifted likely due to compensation of the intrinsic p-type doping by n-type doping introduced by the AlN deposition and potentially via a contribution of polarization-induced carrier density. We have developed a simple drift-diffusion model to simulate the devices in the scattering-limited regime wherein key parameters are extracted from inverse modeling. Finally, we demonstrate a top-gated graphene FET with the first observation of RF operation with GHz cut-off frequency based on large area CVD graphene.
12:30 PM - B3.9
Temperature Dependant Spin Precession Measured in Exfoliated Graphene Utilizing Non-local Detection.
Joseph Abel 1 , Akitomo Matsubayashi 1 , John Garramone 1 , Vincent LaBella 1
1 , University at Albany, Albany, New York, United States
Show AbstractThe use of the electron spin has gained considerable attention lately as a possible substitute for charge-based electronics [1,2]. This talk will focus on the measurement of spin precession of a non-local spin device fabricated utilizing graphene as a transport channel. The device is fabricated similar to other non-local spin devices reported in the literature [3]. The device is prepared with exfoliated graphene on SiO2. The injection and readout contacts were fabricated with and without aluminum oxide as a tunnel barrier which was deposited using thermal evaporation of Al in ultra high vacuum (UHV) and then subsequent oxidation in O2. Then Co/Au was deposited under high vacuum and 100-200-nm-wide contacts were patterned using e-beam lithography followed by a standard liftoff technique. Scanning electron microscopy and optical images will be presented of the fabrication process and the device. The results from temperature dependant non-local Hanle measurements will be presented showing the spin precession in the graphene channel.
[1] Behin-Aein, B., Datta, D., Salahuddin, S., Datta, S. Nat Nano 5:266-270 (2010)
[2] Dery, H. Dalal, P., Cywinski, L. & Sham, L.J. Nature 447, 573-576 (2007)
[3] Tombros, N., Jozsa, C., Popinciuc, M., Jonkman, H.T., Van Wees, B.J. Nature, 448 (7153), pp. 571-574 (2007)
B4: Defects and Reliability in Nanocarbon
Session Chairs
Tuesday PM, November 30, 2010
Room 310 (Hynes)
2:30 PM - B4.1
Reliability of Carbon Nanotube-based Interconnects, Vias, and Electrical Networks.
Mark Strus 1 , Ann Chiaramonti 1 , Young Lae Kim 2 , Yung Joon Jung 3 , Robert Keller 1
1 Materials Reliability, National Institute of Standards and Technology, Boulder, Colorado, United States, 2 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 3 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractBecause of their high current carrying capability and appreciable thermal conductivity, single and bundled carbon nanotubes (CNTs) have emerged as a potential replacement for copper in future integrated circuit interconnects and vias, where minimum feature sizes will be smaller than 45 nanometers. In additional to their notable thermal and electrical properties, CNTs possess extraordinary mechanical strength and flexibility making them ideal candidates for thin-film electrical networks with applications in organic light-emitting displays and photovoltaics. While previous researchers have either investigated the physical properties of individual CNTs or concentrated on the fabrication required to incorporate them into final device form, the long-term performance and reliability of the entire CNT-based electrical devices remains largely unstudied. In the current work, we investigate the failure mechanisms of fluidically self-assembled single-walled CNT networks and dielectrophoretically fabricated individual multiwalled CNTs [1] when subjected to various conditions of electrical and thermal stress. Using the method of isothermal resistance change [2], where CNTs connected to metallic electrodes are subjected to direct currents at controlled temperatures for long periods of times, we calculate the activation energy of electromigration-based failure mechanisms. CNT interconnects are also stressed with either direct or alternating currents to determine the conditions where CNT devices are most vulnerable to either thermal-induced or electromigratory failure. In situ scanning electron microscope voltage-contrast methods and transmission electron microscope images of failed interconnect cross-sections are used to identify the location, origin, and propagation of failure. This new understanding of the potential lifetimes, performance issues, and failure mechanisms of CNT-based devices will be integral to the future improvement of CNT interconnect/network design and manufacture.[1] Kim et al., ACS Nano 3 (2009) 2818-2826[2] Park et al, Appl. Phys. 59 Lett. (1991) 175-177
2:45 PM - B4.2
Characterization of Electrically Stressed Carbon Nanotube Interconnect Assemblies by In-situ Transmission Electron Microscopy.
Ann Chiaramonti 1 , Mark Strus 1 , Young Lae Kim 2 , Yung Joon Jung 3 , Robert Keller 1
1 Materials Reliability Division, The National Institute of Standards and Technology, Boulder, Colorado, United States, 2 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 3 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractTransmission electron microscopy (TEM) is an indispensible tool for the study of materials at the nanometer scale and beyond. Ever since the first clear high-resolution electron microscopy (HREM) images of the individual walls in a multiwall carbon nanotube (CNT) were published by S. Iijima in 1991 [1], TEM has enabled groundbreaking research in this field and continues to be the tool of choice for imaging carbon-based structures at the highest spatial resolutions. Not only can TEM imaging provide real-space structural information at length scales corresponding to individual atoms, but transmission electron diffraction can be used to determine the chirality of individual single walled CNTs, thus indirectly characterizing their electronic structure. While CNTs have been proposed as a possible replacement for copper in microelectronic circuit interconnects, their behavior in such highly integrated systems is poorly understood and there are considerable manufacturing challenges to overcome before they are fully compatible with CMOS processing. One key to the eventual use of CNTs in interconnect architectures is a knowledge of their reliability in fully integrated, device-level structures, which means not only the CNT assembly itself but also its interface with metal electrodes and the dielectric material which encases it. This paper investigates the structural evolution of the carbon-metal and carbon-dielectric interfaces in CNT-based interconnect structures under conditions of AC and DC electrical stress. We will present in-situ TEM results, where simplified model CNT interconnect structures are tested inside of the microscope column, in order to observe in real-time how they respond to electrical stressing and Joule heating at the nanometer scale. I-V characteristics will be presented and correlated with TEM images of the CNT interconnect before and after failure. The reliability of CNT assemblies will be assessed via lifetime (to open circuit failure) measurements, and real-time post-mortem structural characterization of damage in the CNT bundle itself, CNT/metal, and CNT/dielectric interfaces will be shown. [1] S. Iijima, Nature 354 (1991) 56.
3:00 PM - B4.3
Voltage-contrast Scanning Electron Microscopy as a New Technique for Statistical Analysis of Metallic and Semiconducting SWNT Devices and Location and Characterization of Defects.
Aravind Vijayaraghavan 1 2 , Simone Dehm 2 , Frank Hennrich 2 , Ralph Krupke 2
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Karlsruhe Institute of Technology, Karlsruhe Germany
Show AbstractSingle-wall carbon nanotubes (SWNTs) are edging closer to electronic applications, with successful techniques now available for sorting and large-scale integration. When SWNTs are integrated into arrays or circuits at high densities, it is required to characterize the number and location of metallic and semiconducting devices among them. This is true even when such arrays are assembled using high-purity semiconducting SWNT solutions since it becomes critical to locate stray metallic devices that would significantly affect overall performance.Here, we describe voltage-contrast scanning electron microscopy (VC-SEM), as a fast, user-friendly and non-invasive technique for the simultaneous electronic characterization of arrays of SWNTs devices. We demonstrate how metallic and semiconducting SWNTs can be distinguished in an SEM under the influence of a substrate bias, and describe the underlying mechanism. In addition, devices containing SWNTs with defects can also be identified. On closer inspection, we can reveal the location and nature of such defects with nano-scale resolution. Anomalies such as charge-injection into the substrate which leads to hysteresis, as well as in-situ characterization of the creation and annealing of defects (defect engineering) will also be demonstrated using VC-SEM.References:Vijayaraghavan, A., et al, Imaging defects and junctions in single-walled carbon nanotubes by voltage-contrast scanning electron microscopy, Carbon 2010, 48(2), 494–500. (Featured on cover of Carbon 48(4))Vijayaraghavan, A.; et al, R. Imaging electronic structure of carbon nanotubes by voltage-contrast scanning electron microscopy. Nano Research 2008, 1, 321-332. Vijayaraghavan, A.; et al, Ultra-Large Scale Directed Assembly of Single-Walled Carbon Nanotube Devices. Nano Letters 2007, 7, 1556-1560.
3:15 PM - B4.4
Nanomechanical Imaging and Manipulation of Graphene via Ultrasonic Force Microscopy - ``nano-dome" Corrugations and Graphene ``nano-ironing".
Oleg Kolosov 1 , Franco Dinelli 2 , Andrew Hoyle 1 , Vladimir Falko 1
1 Physics Department, Lancaster University, Lancaster United Kingdom, 2 , CNR - IPCF, Pisa Italy
Show AbstractWhereas graphene unique properties are attracting ever increasing attention since its discovery [1], theoretical and experimental studies focus on graphene electronic properties – carrier mobility, bandgap, conductivity etc. with its mechanical properties being often overlooked. At the same time, it is these nanomechanical properties including elastic moduli, adhesion to substrate, thermal expansion and their nanoscale variability that determine graphene-substrate interface that in turn affects graphene electrical properties and its structural stability in a device. Nano and quantum electromechanical systems (NEMS and QEMS) based on graphene will also directly exploit its nanomechanical properties.This paper introduces novel experimental approaches for imaging and mapping of mechanical properties of graphene with nanoscale resolution. Scanning probe microscopy (SPM) clearly would be the first choice for such nanomechanical mapping, but, unfortunately, SPM sensitivity to mechanical properties is limited to low elastic moduli materials, e.g. polymers.We report here application of ultrasonic force microscopy (UFM) approach [2] for mapping of nanoscale mechanical properties of single and few layers exfoliated graphene on a Si/SiOx substrate. UFM uses a ultrasonic vibration of several MHz frequency applied to the sample, forcing it to elastically ”indent” itself against of dynamically stiffened SPM tip positioned at the end of force sensitive cantilever [3]. This vibration is detected by cantilever via intrinsic force nonlinearity of the tip-surface contact. UFM allows mapping of local elastic moduli and, as a useful by-product, provides ultrasound induced frictionless imaging, thereby avoiding damage to the sample and the probe.In UFM mode we observed characteristic nanoscale corrugations of graphene - bulging ”nano-domes” of ~1-2 nm height and lateral dimensions of ~50-100 nm that were interpreted as delaminations of graphene from the substrate. ”Nano-domes” had crystallographic orientation corresponding to axes of graphene and UFM indicated that they were of lower elastic compliance than surrounding areas, enabling direct differentiation of areas of tight and broken graphene-surface contact. Using ultrasound eliminated friction, it was possible to iron out the “nano-domes” with the normal force of approximately 200 nN without damage to graphene sheet, restoring mechanical contact between the graphene and substrate. Looking forward, via UFM and quantitative mechanical model of a dome, one can evaluate in-plane and out-of plane mechanical moduli of graphene as well as mechanical interaction between graphene and underlying substrate.REFERENCES[1] Novoselov, K.S. et al. Electric Field Effect in Atomically Thin Carbon Films. Science 306, 666 (2004),[2] Kolosov, O. and K. Yamanaka, Japan J. of Appl. Phys. Part 2-Letters 32(8A): L1095-L1098, (1993),[3] A. Briggs and O. Kolosov, Acoustic Microscopy,2nd edition, Oxford University Press, 2010
3:30 PM - B4.5
Irradiating Carbon Nanotubes, Their Hybrids with Dispersed Nanodiamond and Hierarchical Defects Evolution – What Does One Learn?
Sanju Gupta 1 , J. Farmer 2
1 Chemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 MURR and Physics, University of Missouri, Columbia, Missouri, United States
Show AbstractIn the family of advanced nanocarbons offering multifunctionality, carbon nanotubes as well as nanodiamond are of great interest attributed to several unique physical (mechanical, electrical, thermal, chemical and biological) properties. The effects of particle (electrons) and electromagnetic (gamma) irradiation on carbon nanotubes (SW/MWCNT) and their hybrids with dispersed nanodiamond (UDD) forming truly trigonal-tetragonal nanocomposite ensemble are studied using resonance Raman spectroscopy and electrical properties. The effect of irradiation creating lattice or structural modification allows an understanding of localized and delocalized defect states. To assess structural modifications, they were analyzed prior to and post-irradiation in terms of morphology, microscopic structure and physical properties using electron microscopy, X-ray diffraction, resonance Raman spectroscopy and electrical I-V measurements. Experiments show that irradiation generates microscopic point defects (the most likely vacancies) in a hierarchical manner much below amorphization threshold (≥ 103 kGy) and that nanocomposites tend to be radiation resilient, elucidated through the intensity, bandwidth and position variation of prominent Raman spectroscopy signatures. In the interpretation of findings the possibilities for these complex system are: 1) defect-mediated double-resonance mechanism may not explain intensity variation; 2) softening or violation of the q = 0 selection rule; 3) difference in electronegativity of sp2 C (SW/MWCNT) and sp3 C (UDD) can result in charge transfer and bond misalignment at the interface; and 4) the nanotubes are stabilized by nanodiamond particles. Furthermore, an attempt was made to identify the nature of defects (charged versus residual) through in-plane correlation length or sp2 C cluster size (La). The decreasing trend of La for both SWCNT and nanocomposites with gamma irradiation implies charging defects described in terms of dangling bonds in contrast to passivating residual or neutral defects. Moreover, the electrical properties were relatively more labile to irradiation than structural and vibrational properties [1,2].[1] Gupta et al. JAP (2010); [2] ibid. (submitted, 2010).
4:15 PM - **B4.6
Carbon-Based Green Electronics.
Kaustav Banerjee 1
1 Electrical and Computer Engineering, University of California at Santa Barbara, Santa Barbara, California, United States
Show AbstractEnergy-efficient electronic and photonic devices, circuits and systems can play an important role in reducing energy consumption and greenhouse gases. They hold tremendous promise not just for the electronics industry but also for alleviating the global scale energy crisis. As is well known, global-scale information technology (IT) depends heavily on large scale computing, which is a rapidly growing energy problem. According to the 2009 U.S. Greenhouse Gas (GHG) inventory report, with improved efficiency of IT usage, around 30% reduction per year in GHG is achievable, which is equivalent to gross energy and fuel savings of 315 billion U.S. dollars. A significant fraction of the energy consumption in the IT industry results from the computing components’ (servers etc) energy need, which in turn, depends on the power consumption of the various integrated circuits (ICs) in these components. Hence, designing “low-power” and “energy-efficient” electronics or “green” electronics (since they contribute towards maintaining a cleaner and greener environment by reducing GHG) constitutes a key area for sustaining the irreversible growth of the global IT industry. Achieving energy-efficiency is also crucial for all electronic circuits used in mobile applications (such as cell phones, PDAs and other portable devices) for increasing the battery life. Moreover, efficient harvesting of solar energy through novel photovoltaic devices is critical for global scale reduction of GHG. Low-dimensional allotropes of carbon (including carbon nanotubes (CNTs), graphene and graphene nano-ribbons (GNRs), known as carbon nanomaterials, have extraordinary physical properties that can be exploited for their exciting prospects for a variety of applications. This talk will highlight and discuss the prospects of carbon based nanomaterials for designing next generation low-power, low-loss and ultra energy-efficient active devices (such as NEMS and Tunnel-FETs), passive structures (such as interconnects, inductors, capacitors, and through-Si vias in 3-D ICs), as well as solar-energy harvesting devices targeted for designing next-generation “green” electronics.
4:45 PM - B4.7
Synthesis and Processing of Graphene for Electronic Applications: A Comparative Study of Morphology and Defects of CVD Grown Graphene.
Nikos Peltekis 1 , Shishir Kumar 1 , Niall McEvoy 1 , Georg Duesberg 1
1 School of Chemistry, CRANN, Trinity College Dublin, Dublin Ireland
Show AbstractThe unique electronic properties of graphene present potential for future electronic device applications. To this end, the quality of graphene layers is crucial, as contamination, impurities, morphology and defects can substantially affect the electronic properties and device performance. Following numerous studies on hand grafted mechanical exfoliated graphene, in addition to graphene produced by decomposition of SiC, liquid processing and CVD growth, macroscale samples of varying quality are produced. Typically, Raman spectroscopy is used to determine the quality and thickness of graphene layers. In our work we present a comprehensive study on large scale CVD grown graphene films by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and a variety of microscopy techniques. We study the effects of growth parameters, transfer techniques and annealing procedures on the electronic properties of the synthesised graphene. In addition, a new cleaning and restructuring process for graphene is presented based on a plasma cleaning and annealing process. Furthermore, extensive analysis based on high resolution Carbon 1s XPS data reveals that XPS is a very powerful technique for characterising graphene layers. This atypical approach clearly identifies the metallicity, defect density and contamination of synthesised graphene layers and presents a complementary characterisation technique to Raman spectroscopy.
5:00 PM - B4.8
Effects of Mismatch Strain and Substrate Surface Roughness on Morphology of Supported Monolayer Graphene.
Zachary Aitken 1 , Rui Huang 1
1 , University of Texas at Austin, Austin, Texas, United States
Show AbstractGraphene monolayers supported on oxide substrates have been demonstrated with superior charge mobility and thermal transport for potential device applications. Morphologicalcorrugation can strongly influence the transport properties of the supported graphene. In this paper, we theoretically analyze the morphological stability of a graphene monolayer on an oxide substrate, subject to van der Waals interactions and in-plane mismatch strains. First, we define the equilibrium separation and the interfacial adhesion energy as the two key parameters that characterize the van der Waals interaction between a flat monolayer and a flat substrate surface. By a perturbation analysis, a critical compressive mismatch strain is predicted, beyond which the graphene monolayer undergoes strain-induced instability, forming corrugations with increasing amplitude and decreasing wavelength on a perfectly flat surface. When the substrate surface is not perfectly flat, the morphology of graphene depends on both the amplitude and the wavelength of the surface corrugation. A transition from conformal (corrugated) to non-conformal (flat) morphology is predicted. The effects of substrate surface corrugation on the equilibrium mean thickness of the supported graphene and the interfacial adhesion energy are analyzed. Furthermore, by considering both the substrate surfacecorrugation and the mismatch strain, it is found that, while a tensile mismatch strain reduces the corrugation amplitude of graphene, a corrugated substrate surface promotes strain-induced instability under a compressive strain. These theoretical results suggest possible meansto control the morphology of graphene monolayer on oxide substrates by surface patterning and strain engineering.
5:15 PM - B4.9
Robust Carbon Nanotube-Based NEMS: Understanding and Eliminating Prevalent Failure Modes Using Alternative Electrode Materials.
Horacio Espinosa 1 , Owen Loh 1 , Xiaoding Wei 1
1 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractThe International Technology Roadmap for Semiconductors (ITRS, [1]) identifies emerging technologies with the potential to sustain Moore’s Law. A necessary succession from planar CMOS to non-planar/dual-gate CMOS, and ultimately to novel architectures such as carbon nanotube- (CNT)-based nanoelectromechanical systems (NEMS) is envisioned. The ITRS also identifies critical roadblocks currently precluding advances beyond CMOS. Primary among the roadblocks to NEMS are manufacturing challenges and poor reliability. Here we investigate the prevalent failure modes of CNT-based NEMS that hamper reliability. We first identify their point of onset within the design space, highlighting the extremely limited region in which failure is avoided. We use dynamic multiphysics models to elucidate the underlying causes of failure, then show that the usable design space expands dramatically when employing novel electrode materials such as diamond-like carbon (DLC). Finally, we demonstrate the efficacy of this solution through numerous successive actuation cycles without failure and applications to volatile memory operations.
In this work, an electrostatically-actuated switch consisting of a CNT cantilevered over an electrode [2-4] serves as a platform to study prevalent failure modes in CNT-based NEMS. This architecture is chosen because it shares operating principles (and thus failure modes) with many reported devices.
First, devices of incrementally-varying geometry are characterized in situ the SEM to identify prevalent failure modes and their point of onset within the design space. Two distinct failure modes are identified. For relatively long CNT cantilevers and smaller CNT-electrode gaps, irreversible stiction between the CNT and electrode is common. For relatively short CNTs and larger CNT-electrode gaps, incremental shortening of the CNT cantilever was observed with successive actuation cycles. A dynamic multiphysics model of the device reveals that the incremental loss occurs due to Joule heating from transient current spikes during device actuation rather than purely mechanical fracture of the CNT. Together, these two failure modes drastically confine the useful region of the geometric design space.
We then show that the failure-free region of the design space is dramatically expanded by using DLC electrodes in place of conventional metal thin films. We see not only reduced stiction, but complete elimination of failure by Joule heating. This enables an unprecedented number of actuation cycles and reliable function as volatile memory, providing motivation for further implementation of alternative materials in improving the performance and reliability of CNT-based NEMS.
1. International Roadmap Committee. 2009.
2. Ke, C.H. and H.D. Espinosa, J. Appl. Mech., 2005. 72: p. 721-725.
3. Ke, C.H. and H.D. Espinosa, Small, 2006. 2(12): p. 1484-1489.
4. Ke, C.H., et al., J. Appl. Mech., 2005. 72(5): p. 726-731.
5:30 PM - B4.10
A Route to Highly-conductive Graphene Oxide by CVD Repair.
Ravi Shankar Sundaram 1 , Vicente Lopez 4 , Cristina Gomez Navarro 1 3 , Marko Burghard 1 , Julio Gomez Herrero 3 , Felix Zamora 4 , Klaus Kern 1 2
1 Nanoscale Science, Max Planck Institute for Solid State Research, Stuttgart Germany, 4 Departamento de Química Inorgánica , Universidad Autónoma de Madrid , Madrid Spain, 3 Departamento de Física de la Materia Condensada , Universidad Autónoma de Madrid , Madrid Spain, 2 Institut de Physique de la Matière Condenseé, Ecole Polytechnique Fédérale de Lausanne, Lausanne Switzerland
Show AbstractThe synthesis of graphene from its oxide precursor has evolved over the past couple of years to be a very promising high yield technique for the fabrication of graphene devices. However, unlike mechanically exfoliated graphene, there exist a considerable amount of defects in the form of vacancies, holes, amorphous regions and remnant oxygen functionalities. This imparts several differences in the electrical transport in devices fabricated from this material when compared to its structurally flawless counterpart. Here, we present a novel technique for the repair of defects in graphene oxide with an aim to restore partially its hexagonal lattice. The employed chemical vapor deposition uses an ethylene gas flow over graphene oxide sheets at elevated temperatures. The cracking of ethylene induces the carbon incorporation in to the defective lattice of graphene oxide. As a result we have observed an increase of 3 orders of magnitude in conductivity and factor of ten improvement in charge carrier mobilities1. Due to its easy up-scalability, this two-step process could establish chemically derived graphene as the major component of a wide range of flexible, low cost electronic devices. 1López, V.; Sundaram, R. S.; Gómez-Navarro, C.; Olea, D.; Burghard, M.; Gómez-Herrero, J.; Zamora, F.; Kern, K. Advanced Materials 2009, 21, (46), 4683-4686.
B5: Poster Session: Carbon-Based Electronic Devices
Session Chairs
Manish Chhowalla
Robert Keller
Meyya Meyyappan
Jud Ready
Wednesday AM, December 01, 2010
Exhibition Hall D (Hynes)
9:00 PM - B5.1
Dry Contact Transfer Printing of Large-scale, Complex Patterns of Perfectly Aligned Self-assembled Single-walled Carbon Nanotubes Based on a Gecko-inspired Mechanism.
Cary Pint 1 2 , Ya-Qiong Xu 5 , Junichiro Kono 3 1 , Matteo Pasquali 4 2 , Robert Hauge 2
1 Physics, Rice University, Houston, Texas, United States, 2 Chemistry, Rice University, Houston, Texas, United States, 5 Electrical Engineering and Physics, Vanderbilt University, Nashville, Tennessee, United States, 3 Electrical Engineering, Rice University, Houston, Texas, United States, 4 Chemical and Biomolecular Engineering, Rice University, Houston, Texas, United States
Show AbstractA facile approach is demonstrated in which as-grown patterns of vertically aligned single-walled carbon nanotubes (VA-SWNT) made via a modified supergrowth technique can be transferred to nearly any arbitrary host surface. Here, the growth substrate is utilized as the stamp, and a growth cycle "inks" the stamp for contact transfer based on the gecko effect. Multiple transfers of patterned, VA-SWNTs allows large-scale complex micro-patterns of horizontally aligned SWNTs, such as grids, to be formed on the host substrate. This technique allows complex patterning of metal-free, ultra-long, highly aligned, and pristine as-grown carbon nanotubes, that is a critical step for next-generation electronics and photonics applications from carbon nanotubes. Using this bottom-up transfer approach, we are able to understand new fundamental science of anisotropic electronic transport and optical properties of ultra-long SWNT, and demonstrate new optical applications including highly efficient terahertz polarizers.
9:00 PM - B5.12
Field Emission of Coherent Electrons from Atomically Thin Graphene Edges.
Hisato Yamaguchi 1 , Katsuhisa Murakami 2 , Goki Eda 3 , Steve Miller 1 , Fujio Wakaya 2 , Mikio Takai 2 , Manish Chhowalla 1 3
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States, 2 Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Toyonaka, Osaka, Japan, 3 Materials, Imperial College London, London United Kingdom
Show AbstractPoint sources such as carbon nanotubes have shown the best electron emission properties due to local field enhancement at the tip. Cold cathode field emission from atomically sharp edges has not been widely explored. Here we report ultra-low threshold field emission of multiple coherent electron beams from the atomically thin edge of a single graphene flake. We have observed atomically spaced emission sites along the graphene edge using field emission (FEM) and field ion (FIM) microscopy techniques. The emitted electron beams interfere to form patterns that are analogous to Young’s optical interference for coherent waves. Closely spaced coherent electron beams from atomically thin edge of graphene offer tremendous prospects for development of novel applications as well as understanding the physics of linear electron sources.
9:00 PM - B5.13
Direct Observation of Rotational Grain Boundaries in Graphene.
Eric Cockayne 1 , Gregory Rutter 1 , Joseph Stroscio 1
1 , NIST, Gaithersburg, Maryland, United States
Show AbstractUsing scanning tunneling microscopy and spectroscopy, we have extensively characterized a common defect on the surface of epitaxial graphene on SiC. The defect yields a 6-fold scattering pattern in atomic-resolution topographic imaging, as well as a distinct electronic state in the differential conductance. First principle calculations offer insight into the structural composition of the defect, suggesting that the defect is a rotational grain boundary made up of 5- and 7-membered carbon rings. The defect observed is the smallest member of a family of rotational grain boundary defects that can exist in the graphene lattice. Simulated topographs of the defect yield excellent agreement with experiment.
9:00 PM - B5.14
Charge Transfer Doping of Graphene by Organic Molecules.
Xiaomu Wang 1 , Jun Du 1 , Weiguang Xie 1 , Jianbin Xu 1
1 Electronic Engineering, The Chinese University of Hong Kong, Hong Kong Hong Kong
Show AbstractIt is of great technological importance to adjust carrier density or conductivity to achieve complete graphene-based electronic circuits. In this presentation, both n-type and p-type doped exfoliated graphene are presented by virtue of adsorbing organic molecules. Through this technique, flat organic thin films can be uniformly grown on graphene sheets. Besides, the high mobility attribute of graphene is simultaneously preserved, as the adsorption on graphene surface does not significantly modify the π-bonding networks of graphene. By employing scanning electrical force microscopy, we show that the 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) molecules obtain electrons from graphene, whereas vanadyl-phthalocyanine (VoPc) molecules donate electrons to it. It is estimated that the charge transfer of F4-TCNQ and VoPc is about 0.4 and 0.1 electron/molecule repectively. Doped graphene based field-effect transistors (FETs) are also fabricated to verify the doping effectiveness as well as the mobility robustness. Our theoretical and experimental results demonstrate that doping of graphene by organic charge transfer has great potential for large scale applications.
9:00 PM - B5.16
Toward Practical Gas Sensors Using Highly Reduced Graphene Oxide.
Ganhua Lu 1 , Sungjin Park 2 , Kehan Yu 1 , Rodney Ruoff 2 , Leonidas Ocola 3 , Daniel Rosenmann 3 , Junhong Chen 1
1 Department of Mechanical Engineering, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, United States, 2 Department of Mechanical Engineering and the Texas Materials Institute, University of Texas at Austin, Austin, Texas, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractGraphene holds exciting potential to advance chemical- and bio-sensing technologies and has stimulated considerable research interest. Here, we report the fabrication and characterization of gas sensors using a back-gated field effect transistor platform with highly reduced graphene oxide (HRG) as the conducting channel. Transport measurements indicated p-dominated semiconducting behavior for HRG stored in ambient conditions. The fabricated HRG sensors were tested under nearly practical conditions (room temperature, atmospheric pressure, and dry air background) and were responsive to low-concentration NO2 and NH3 gases diluted in air. The sensing response could be attributed mainly to the charge transfer between HRG and adsorbed gaseous molecules (NO2/NH3). The performance of HRG sensors could be modulated by varying the back gate potential, which could facilitate the development of HRG sensor arrays. In particular, to address the challenge of long recovery period required for HRG sensors after analyte exposure, we have developed a calibration procedure that could be used to circumvent the run-to-run variation caused by incomplete recovery and potentially shorten recovery time needed. Preliminary analysis and experimental data both suggests that the calibration method could also be employed to deal with the variation in sensing performance among HRG devices. This calibration method may be useful for other nanomaterials gas sensors that suffer from time-consuming recovery. The sensor calibration method reported here, together with the inherent simplicity of device fabrication and the gate-tunability of sensing performance, represents a major step toward the real-world utilization of graphene-based chemical sensors.
9:00 PM - B5.17
Silicon-coated Carbon Nanotube Anodes for Lithium-ion Batteries.
Michelle Gaines 1 , Samuel Karpowicz 2 , Deborah Williams 3
1 Electro Optical Systems Laboratory, Georgia Tech Research Institute, Atlanta, Georgia, United States, 2 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 , School for Technology, Engineering, Math and Science at Therrell, Atlanta, Georgia, United States
Show AbstractCurrent rechargeable lithium-ion batteries contain anodes made of graphite. They are most often used for powering small devices such as cell phones and laptop computers, because they are cost-effective, have a sufficient theoretical reversible storage capacity (~372 mAh/g), and exhibit a long battery life. Although graphite anodes are adequate for powering these small devices, they don’t possess enough theoretical storage capacity to power larger devices, such as hybrid electrical cars, the power grid, or components found in space craft. Silicon has a much higher theoretical reversible capacity (~4,200 mAh/g), which would provide rechargeable batteries the potential to store much more energy during charging. Silicon has been reported to store up to 22 lithium ions for every five silicon atoms, compared to graphite, which can store only one lithium ion for every six carbon atoms. The only challenge with using silicon based anodes lies in their resulting pulverized structure after repeated cycles of Li-ion charging and discharging, due to the extreme volume changes from the lithiated state during charging and the delithiated state after discharging. In this work, multi-walled carbon nanotubes were used as mechanical reinforcements for amorphous silicon, which supplied an effective method for creating functional, high storage capacity, rechargeable Li-ion batteries. The carbon nanotubes were grown via thermal chemical vapor deposition on an electropolished [101] copper foil. A 10 wt% solution of iron(III) p-toluenesulfunate in ethanol was spin casted on the copper substrates, serving as the catalyst. Finally, amorphous silicon was deposited on top of the carbon nanotubes using plasma enhanced chemical vapor deposition. The anodes were paired with a cathode and electrolyte, forming a full coin cell, and electrical impedance, current density, and galvanostatic cycling measurements were collected.
9:00 PM - B5.18
Effect of Lithium: Aluminum Cathode Which Gradually Changing Work Function for Organic Solar Cells.
Park O Ok 1 , Jeon Jihye 1 , Lee Hang Ken 1 , Wang Dong Hwan 1
1 Chemical and Biomolecular Engineering, KAIST, Deajeon Korea (the Republic of)
Show AbstractEven though the fossil energy sources are much limited, the energy consumption is increasing rapidly every year. Therefore, new approaches for renewable energy of solar energy systems are urgent issues. Many of the different solar cells are under consideration by a lot of research groups all over the world such as Silicon, compound semiconductor and organic solar cells.Especially, polymer based solar cell is a quite attractive one for its flexibility, low-cost possibility, light-weight, and semi-transparency. Here we focused on how to improve the efficiency and low cost processability will be considered. It can be demonstrated by introducing a Li:Al alloy cathode. It is attributed to an improved electron collection and active layer protection. The effectiveness of this unique feature makes it possible to fabricate more efficient organic solar cells. Li:Al alloy single source in place of Al to cathode is one-step process which make buffer layer before cathode deposition. Li:Al alloy source makes gradient cathode because of Li evaporate earlier than Al and effects good electron transport from cathode. It is important that makes gradually changing workfunction cathode at interface which lowered work function at the interface that reducing the collection barrier. Moreover, Li:Al cathode can protected the active layer at the interface. Li ion can evaporate earlier than Aluminum ion because Li and Al have different thermal properties. Li:Al cathode can block up permeating carbon which hinder efficient electron transport between active and metal cathode.The Li:Al cathode of bulk heterojunction solar cells increases the short circuit current(Jsc) and power conversion efficiency(PCE) by effectively electron collection with the working of Lithium on the cathode interface. Finally, Li:Al alloy cathode with a work function gradient has been successfully fabricated via one-step evaporation process for the first time. The work function and carbon and Lithium ion concentration variation has been confirmed by the UPS and SIMS spectroscopy. The novel device showed an enhanced photocurrent density and power conversion efficiency compared to those of the BHJ PV prepared under the same fabrication condition.
9:00 PM - B5.21
UV-Vis-NIR Spectral Rayleigh Imaging of Individual Carbon Nanotubes.
Robin Havener 1 , Daniel Joh 1 , Lihong Herman 1 , Michael Segal 2 , Jiwoong Park 2
1 Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 2 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractRayleigh scattering spectroscopy has developed as a powerful technique for studying the elastic scattering of single-walled carbon nanotubes (SWNTs) on solid substrates. Previous work has shown that this technique, when combined with atomic force microscopy (AFM), can be used to identify sub-band transitions and assign chiral vectors (n, m) of individual SWNTs with diffraction-limited optical resolution. Here, we focus on the use of combined UV-Vis-NIR Rayleigh spectroscopy, using a single modified darkfield microscope, as a means of high-throughput, high signal-to-noise ratio characterization of many individual SWNTs in parallel.
9:00 PM - B5.22
Electronic Transport in Graphene Nanoribbons on Boron Nitride.
Leonardo Campos 1 , Javier Sanchez 1 , Pablo Jarillo-Herrero 1
1 Physics, MIT, Cambridge, Massachusetts, United States
Show AbstractCarbon derived structures like graphene and graphene nanoribbons are the 2D and quasi 1D materials which may allow the fabrication of room temperature ballistic electronic devices. This tantalizing possibility is a direct consequence of the high charge mobilities theoretically predicted for graphene. Although hypothetically the mean free path of graphene samples are of the order of micrometer size, its ballistic behavior has not been observed, excepted for suspended samples because of the influence of charge scatters and corrugations induced by the substrate. A possible solution to enable the observation of higher mobilities on substrate is use a nonpolar, flat substrate like boron nitride. In this work we will present a study of electronic properties of graphene nanoribbon on a boron nitride substrate showing the main differences of behavior from nanoribbons on BN to polar surfaces like SiO2. We will discuss the changes of the mobilities and the effects of the quantum confinement on the electronic band structure of the nanoribbons on its electronic transport.
9:00 PM - B5.23
Thermo Electric Power of Carbon Naotube Arrays.
Laishram Singh 1 , Karuna Kar Nanda 1
1 Materials Research Centre, Indian Institute of Science, Bangalore India
Show AbstractThermo electric power (TEP) is an extremely sensitive and incisive transport coefficient. For a semiconductor, the TEP probes the sign of the dominant carriers as well as the energy gap magnitude. We have investigated the thermo-emf of suspended buckled Carbon Nanotube (CNT) bundles or arrays. One end of the CNT bundle is kept at room temperature or at liquid nitrogen temperature and other end at higher temperature to measure the emf. Both the thermo emf and TEP are found to increase non-linearly with temperature and are negative. This suggests that the contribution is electronlike. From Current-Voltage characteristics, it is found that the CNT bundles have semiconducting nature. It is observed that emf is larger for high resistive bundles. Interestingly, the thermo electric figure of merit is found to be approaching 2. The sample used is made by pyrolysis of benzene and THF and ferrocene is used as a catalyst source. The detail results will be presented.
9:00 PM - B5.24
Optically Pumping GaN HEMTs and Trap Detection.
David Cheney 1 , Chih-Yang Chang 3 , E. Douglas 2 , B. Gila 2 , F. Ren 3 , S. Pearton 2
1 Electrical & Computing Engineering, University of Florida, Gainesville, Florida, United States, 3 Chemical Engineering, University of Florida, Gainesville, Florida, United States, 2 Materials Science & Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractWhen light energy from a mercury arc lamp is applied to a GaN HEMT at above band-gap levels, electrons in traps and the valence band are excited into the conduction band. With the traps cleared, more current flows through the channel, allowing the effects of drain current on device reliability to be better understood without having to increase the drain-source field or gate voltages.As part of our in-house 16 channel reliability test system, the addition of the optical pumping technique provides a non-destructive measurement of the trap density in a device. A significant change in the drain current suggests there are many traps in the device. We propose that by applying different frequencies of light energy at below band gap energy levels, different trap types can be determined, since different traps have been identified at specific energy levels.If a device shows little change in drain current when above band gap energies are applied, this may indicate fewer traps. From this information, we establish a baseline before putting the device under electrical or mechanical stress conditions. After the stress tests, any new traps that were created can be identified by pumping different light frequencies that are below band gap energy levels.This paper compares devices before and after stress testing using optical pumping techniques to detect the creation of new traps and of what type and energy level.
9:00 PM - B5.25
In-situ Atomic Force Microscopy of In-plane Actuating Single Wall Nanotube Electromechanical Switches.
Peter Ryan 1 2 , Yu-Chaio Wu 1 , George Adams 1 , Ahmed Busnaina 1 , Nicol McGruer 2
1 Mechanical Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Electrical Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractElectromechanical switches, consisting of small bundles of single wall nanotubes suspended between actuation electrodes have been fabricated and tested. An atomic force microscope has been outfitted with micropositioner probes to provide electrical feed-through to the device under test. A technique of imaging the switches at different stages of actuation has been developed. We present the resulting AFM scans with the electrical measurements of the switches.
9:00 PM - B5.26
Graphene Morphology Regulated by Nanowires Patterned on a Substrate Surface.
Zhao Zhang 1 , Teng Li 1 2
1 Department of Mechanical Engineering, University of Maryland, College Park, Maryland, United States, 2 Maryland NanoCenter, University of Maryland, College Park, Maryland, United States
Show AbstractThe graphene morphology regulated by nanowires patterned in parallel on a substrate surface is quantitatively determined using energy minimization. The regulated graphene morphology is shown to be governed by the nanowire diameter, the nanowire spacing and the interfacial bonding energies between the graphene and the underlying nanowires and substrate. Emerging from the simulation results are two distinct states of the regulated graphene morphology: (1) graphene wrapping around the envelope of the patterned nanowires on the substrate; and (2) graphene remaining nearly flat on the patterned nanowires. For a given nanowire diameter, the graphene morphology snaps between these two distinct states at certain critical nanowire spacing or certain critical interfacial bonding energies. Interestingly, we identify a rule-of-thumb formula that correlates the critical nanowire spacing, the critical interfacial bonding energies and the nanowire diameter in quite well agreement with the full-scale simulation results. As the graphene’s electronic properties are closely tied to its morphology, the results from the present study shed light on a feasible strategy to achieve fine control over the graphene electronic properties through morphology regulation with a resolution approaching the atomic feature size of graphene.
9:00 PM - B5.27
Nanoribbon-based Sensors for Detection of Gas Molecules.
Kirti Kant Paulla 1 , Amir Farajian 1
1 Mechanical and Materials Engineering, Wright State University, Dayton, Ohio, United States
Show AbstractGraphene nanoribbons, whose edges are hydrogen-terminated, with a width of about 1nm can be used as nono-sensors for detecting gas molecules, based on the changes in their current-voltage characteristics. We consider three different types of gas molecules, namely, carbon dioxide, carbon monoxide and nitrogen dioxide. These moleculesare relaxed on graphene nanoribbons, using ab-initio hybriddensity functional methods. The current-voltage characteristics are calculated, using Landauer's approach based on ab initio electronic structures, for different concentrations of these gas molecules. We determine that neither of these gas molecules is chemically absorbed.Our electronic transport results show that nanometer size sensors can be made from graphene nanoribbons that are capable of detecting physisorbed gas molecules. The adsorbed molecules change the local carrier concentration in the nanoribbons, and lead to modulation of current-voltage characteristics. We discuss the underlying mechanisms and some possible applications of these nanosensors for detecting and distinguishing different gas molecules.This work is supported by the National Science Foundation grant ECCS-0925939
9:00 PM - B5.28
DNA-decorated Graphene Chemical Sensors.
Ye Lu 1 , Brett Goldsmith 1 , Nicholas Kybert 1 , A.T. Charlie Johnson 1
1 Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractGraphene is a true two dimensional material with exceptional electronic properties and enormous potential for practical applications. Graphene’s promise as a chemical sensor material has been noted but there has been relatively little work on practical chemical sensing using graphene, and in particular how chemical functionalization may be used to sensitize graphene to chemical vapors. Here we show one route towards improving the ability of graphene to work as a chemical sensor by using single stranded DNA as a sensitizing agent. The resulting broad response devices show fast response times, complete and rapid recovery to baseline at room temperature, and discrimination between several similar vapor analytes.
9:00 PM - B5.30
Nucleation and Adsorption of Metal Clusters on Metal-Supported Graphene: An Experimental and Theoretical Investigation.
Lymarie Semidey-Flecha 1 , Zihao Zhou 2 , Feng Gao 2 , Dieh Teng 3 , Ye Xu 1 , David Sholl 3 , D. Wayne Goodman 2
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Chemistry, Texas A&M University, College Station, Texas, United States, 3 School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractSingle-crystal metal surfaces have been used successfully as templates to grow graphene, which develops large moiré patterns due to its interaction with the metal substrates. By depositing metal atoms on such moirés, super-lattices of small metal clusters (SMCs) with narrow size distribution have been obtained recently, notable examples including Irx/graphene/Ir(111) and Ptx/graphene/Ru(0001).1-3 Large arrays of uniform metal clusters have a number of potential applications, including catalysis, sensors, and quantum dots, so effective synthesis methods are of great interest.To explore the possibility of developing SMCs from different metals, we have deposited several metals, including Co, Rh, Pd, Pt, and Au, on graphene/Ru(0001), and characterized the resulting materials using STM.4 At room temperature, super-lattices of small clusters are obtained with Rh and Pt, whereas Co, Pd, and Au failed to be confined by the moiré and coalesced into large islands. To understand the nucleation of SMC super-lattices on graphene/Ru(0001), density functional theory (DFT) calculations are performed on the adsorption and diffusion of the monomers, dimers, and trimers of several metals. Preliminary results suggest that nucleation likely begins with dimer or trimer species, whereas single metal atoms diffuse easily on the graphene moiré. Furthermore, we investigate the bonding interaction between the SMCs, graphene, and the substrate metals as well as the chemical stability and reactivity of the clusters using CO as the probe molecule. These results represent a first step toward developing clusters/graphene/metal as a novel nanomaterial platform.References1. A.T. N’Diaye, S. Bleikamp, P.J. Feibelman, T. Michely, Phys. Rev. Lett. 97, 2006, 215501.2. A.T. N'Diaye, T. Gerber, C. Busse, J. Myslivecek, J. Coraux, T. Michely, New J. Phys. 11 406, 2009, 103045.3. Y. Pan, M. Gao, L. Huang, F. Liu, H.-J. Gao, Appl. Phys. Lett. 95, 2009, 093106.4. Z. Zhou, F. Gao, D. W. Goodman, Surf. Sci., 604, 2010, L31.
9:00 PM - B5.31
Size and Shape-dependent Electronic Structure of Nano-graphenes.
Jaewu Choi 1
1 , Kyung Hee University, Seoul Korea (the Republic of)
Show AbstractNano-graphenes on graphite were studied at room temperature by using a scanning tunneling mucroscope. In this presentation, the size, shape and edge dependent electronic structures investiagted by scanning tunneling spectroscopy will discussed.
9:00 PM - B5.32
Fabrication of Transparent Graphene/Nanoparticle Eletrode.
XiaoLiang Li 1 , YongWu He 1 , Sung Yang 1
1 , Kyung Hee University, Yongin Korea (the Republic of)
Show AbstractThere have been great interests in flexible electronics due to their potential applications in many areas including touch screens, flexible displays, printable electronics, OLED, OTFT, photovoltaics. Extensive efforts have been devoted to develop highly conductive transparent materials for application in flexible device. In particular, Graphene is promising due to its high carrier concentration, mobility, and mechanical strength. We have prepared transparent conducting films via spin coating method using water soluble sulfonated S-Graphene. We have introduced Ag nanoparticles onto S-Graphene film to enhance the conductivity. We have characterized the deposited Graphene/AgNP film using UV/Vis, AFM, sheet resistance measurement. The resulting Graphene/AgNP film showed higher electrical conductivity along with reasonable transparency. The results reveal the potential of Graphene/AgNP film as a key material for transparent electrode in flexible devices.
9:00 PM - B5.33
Synthesis of Highly Soluble Graphene.
YongWu He 1 , XiaoLIang Li 1 , Sung Yang 1
1 , Kyung Hee University, Yongin Korea (the Republic of)
Show AbstractThe synthesis of Graphene-a single layer of graphite- has attracted much attention for their possible applications in transparent electrode. Compared to transparent ITO electrode, graphene has a high mechanical strength, flexibility which makes it ideal candidate for next generation flexible transparent electrode. Graphene can be prepared by mechanica cleavage, chemical vapor deposition, and chemical reduction of exfoliated graphite oxide layer. We have prepared soluble grapheme by oxidation of graphite, exfoliation, followed by two step reduction using sodium borohydride and amination with diazonium salt. We have characterized chemically prepared graphene using UV/VIS, FT-IR, AFM, TEM, and electrical conductivity in solution and solid film. The charged units prevent the graphene sheets from aggregating in solution. We compared the synthetic yield and solubility with previously reported methods. The solubility of resulting graphene in water is much improved in acidic and neutral condition.
9:00 PM - B5.34
Scalable Approach for Radio Frequency Graphene Transistors Fabrication and Integration.
Alexander Badmaev 1 , Lewis Gomez 1 , Yi Zhang 1 , Chuan Wang 1 , Chongwu Zhou 1
1 EE, University of Southern California, Los Angeles, California, United States
Show AbstractGraphene field-effect transistors(FET) were shown to have great potential for high frequency electronics. In this report, we utilize large area graphene films grown by chemical vapor deposition(CVD) on nickel and copper substrates for highly scalable fabrication of radio frequency graphene transistors. Such CVD growth produces continuous, predominantly single-layer graphene films that are well suited for both nanoscale and macroscale graphene devices. We obtained scalable high yield fabrication of large number of graphene FETs. We analyzed graphene films and devices DC and high frequency performances and discuss practical performance limitations. Carrier mobility of ~2000 cm2/V/s, and FETs intrinsic cutoff frequencies of 10 GHz were measured. These results illustrate first steps toward implementation and integration of graphene devices for radio frequency electronics.
9:00 PM - B5.35
Species Enrichment of Carbon Nanotubes by Aromatic Polymers.
Mary Chan-Park 1 , Wang Weizhi 1 , Pan Xiaoyong 1
1 School of Chemical and Biomedical Engineering, Nanyang Technilogical University, Singapore Singapore
Show AbstractSingle-walled carbon nanotubes (SWNTs) have attractive electronics properties. For example, they have ballistic transport and excellent field effect transistor behaviour. However, all known synthesis methods produce mixtures of metallic and semiconducting SWNTs. In recent years, SWNT network rather than individual nanotubes have been proposed as the semiconducting materials. This places even greater requirements on the efficiency of the separation. Post-solution separation methods have been investigated for the separation. Various methods such as density gradient ultracentrifugation, gel electrophoresis, electrochemical etching, laser irradiation and chemical-based selections have been investigated. Chemical-based selections offer the advantages of simplicity, easy scalability and easy tuning of interactions through chemical structure tuning. We have investigated various polymers as dispersants and enrichment agents of nanotubes. We showed that that a new class of aromatic polymethacrylate polymers that show fluorescence spectrum that overlaps with absorbance of specific nanotube species can select those specific nanotubes. These class of polymers also generally select the smaller diameter nanotubes and the selectivity can be tuned by the solvent choice. Further, we also designed polymers that are degradable so that the polymers can be removed after the selection process to reduce intertube or tube-electrode resistance.
9:00 PM - B5.5
Quantitative Characterization of the Nano-topology of CNT Turfs and Mats.
David Field 1 , Hina Malik 1 , David Bahr 1
1 , Washington State Univ, Pullman, Washington, United States
Show AbstractThe mechanical response of carbon nanotube turfs and mats is dictated by the details of their topological features. In the present study, we have investigated the correlation between the mechanical behavior of multi-walled carbon nanotube turfs and the elastic stiffness as determined by nanoindentation experiments. It was anticipated that density, connectivity and tortuosity would be the parameters most closely related to performance of the CNT turfs. For the materials investigated with a rather low density of CNTs (on the order of 100 per square micron), the turf density had surprisingly little effect on the elastic stiffness. More vertically aligned structures show a tendency of lower stiffness, whereas twisted and irregular CNT turfs appear to possess a higher elastic modulus.
9:00 PM - B5.7
The MWNT/PEDOT:PSS Composite with High Conductivity, Catalytic Activity and Work Function and Application of it as Electrodes of Organic Thin Film Transistor and Dye Sensitized Solar Cell.
Dong-Jin Yun 1 , Hye-min Ra 1 , Ki-Pyo Hong 1 , Woo-Sung Kwon 1 , Shi-Woo Rhee 1
1 , POSTECH, Pohang Korea (the Republic of)
Show AbstractRecently, it has been reported that the MWNT/PEDOT:PSS composite film has a potential to be employed as buffer layer of OLED or catalysis counter electrode of DSSC. But the combination condition of MWNT/PEDOT:PSS composite was not well established and the researches for improving the electrode-performance of them were rarely known. Therefore, the various MWNT/PEDOT:PSS composite solution were formed using bare MWNT, oxidized MWNT and solvent dopant (glycerol, DMSO and ethylene glycol), and the properties of MWNT/PEDOT:PSS film spin-coated using those solutions were investigated and compared. Especially, the conductive film of high work function (5.0 eV) and low sheet resistance (~150Ω/squre) could be prepared using MWNT/PEDOT:PSS composite with UV oxidized MWNT and glycerol dopant, and moreover the performance of that as a source/drain of pentacene TFT and counter electrode of DSSC were also excellent. The bottom-contact pentacene TFT with MWNT/PEDOT:PSS S/D electrode shows high mobility of ~ 0.35 cm2/Vs and on/off ratio of ~5×105 (pentacene TFT with Au S/D electrode: ~ 0.24 cm2/Vs and ~ 105) the Dye-sensitized solar cell (DSSC) with MWNT/PEDOT:PSS/FTO counter electrode and free-FTO MWNT/PEDOT:PSS counter electrode show high efficiency of 5.9 % and 4.9 %(DSSC with Pt counter electrode: 7.0%) and fill factor of 60.2 % and 54 % (DSSC with Pt counter electrode: 65 %), respectively. On the other hands, the film properties including atomic composition, work function, transparency and resistivity of MWNT/PEDOT:PSS compositie were characterized using XPS, UPS, 4-point probe, UV-vis-spectroscopy.
9:00 PM - B5.8
Fabrication of Unipolar p-type SWCNT Thin Film Transistors on Flexible Substrates without the Electrical Breakdown Process.
Jaehyun Park 1 , Jangyeol Yoon 1 , Jeong Sook Ha 1
1 Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractSynthesized single wall carbon nanotubes (SWCNTs) have a mixture of metallic and semiconducting tubes so that their separation has been a tremendous obstacle to the practical application in electronic devices. Electrical breakdown process to selectively burn out the metallic tubes has been quite successful though it needs additional process in the fabrication of device structures. However, this process is hard to adapt on flexible substrates because it is a thermal oxidation step including high-field (~10^6 V/cm) impact ionization. In this paper, we report on the facile method to fabricate purely p-type SWCNT thin film transistors (TFTs) on flexible polyimide substrates without selective removal of metallic SWCNTs from the as-grown CNT films. The control of the concentration of ferritin catalyst was used to control the density of SWCNTs in chemical vapor deposition technique, resulting in the control of the metallic percolation pathways in the SWCNT TFTs. About 60% of the pristine SWCNT TFTs showed a perfect unipolar p-type behaviors with on/off current ratios, Ion/Ioff , higher than 10^5 and on-current (Ion) greater than 10^-7 A. We will also discuss the application of such formed p-type SWCNT TFTs as UV/visible photo-detectors.
Symposium Organizers
Robert R. Keller National Institute of Standards and Technology
W. Jud Ready Georgia Institute of Technology
Meyya Meyyappan NASA Ames Research Center
Manish Chhowalla Imperial College London
B8: Poster Session: Carbon-Based Electronic Devices
Session Chairs
Manish Chhowalla
Robert Keller
Meyya Meyyappan
Jud Ready
Wednesday PM, December 01, 2010
Exhibition Hall D (Hynes)
B6: Nanocarbon Devices - Optoelectronics, Solar Cells, and Photovoltaics
Session Chairs
Wednesday PM, December 01, 2010
Room 310 (Hynes)
9:30 AM - **B6.1
Photovoltaic and Optoelectronic Applications of Large-area Graphene-based Electronics.
Chun-Wei Chen 1 , Shao-Sian Li 1 , Kun-Hua Tu 1 , Chih-Cheng Lin 1 , Chih-Tao Chien 1 , Manish Chhowalla 2
1 Department of Materials Science and Engineering, National Taiwan University, Taipei Taiwan, 2 Department of Materials, Imperial College , London United Kingdom
Show AbstractIn this talk, we would like to present the applications of graphene-based materials on large-area photovoltaic and optoelectronic devices. Chemically derived graphene-oxide (GO) from solution processes or epitaxial graphene obtained from chemical vapor deposition (CVD) have been demonstrated to replace the ITO electrode. In addition to its high transparency and mobility of graphene, functionalized graphene electrodes can act as an “active layer” in the enhancement of light harvesting of photovoltaic devices. GO could be also a simple solution processable alternative to PEDOT:PSS as the effective hole transport and electron blocking layer in polymer photovoltaics, suggesting that future polymer solar-cell devices could be "all-carbon". In addition, photoluminescence of GO and reduced-GO will be demonstrated. The tunablity of PL emission from red to blue colors offers a potential to use graphene-based materials on solution-processable optoelectronic devices for full-color display and lighting applications.
10:00 AM - B6.2
Optical Properties of Vertically Aligned Carbon Nanofiber-arrays.
Robert Rehammar 1 , Roger Magnusson 4 , Antonio Fernandez-Dominguez 3 , Hans Arwin 4 , Jari Kinaret 1 , Eleanor E. Campbell 2 , Stefan Maier 3
1 Applied Physics, Chalmers University of Technology, Göteborg Sweden, 4 Department of Physics, Chemistry and Biology, Linköping University, Linköping Sweden, 3 Department of Physics, Imperial College London, London United Kingdom, 2 School of Chemistry, Edinburgh University, Edinburgh United Kingdom
Show AbstractThe optical properties of arrays of vertically aligned carbon nanofibers are investigated. The arrays function as two-dimensional carbon nanofiber photonic crystal slabs (CNFPC). It has been suggested [1] that CNFPC can be used to fabricate electrostatically tunable optical nanocomponents such as tunable optical filters.The CNFPCs have been investigated using generalized ellipsometry [2]. Using this technique, we have mapped out parts of the photonic band structure of the structures, and we find that their optical properties agree well with the theoretical predictions for a nanofiber array. Our study also demonstrates that ellipsometry is a convenient tool to study nano-optical components.We have also examined diffraction by the nanofiber arrays [3], and find that diffraction in different optical orders can be described by the standard theory. The intensity of the diffracted beam is seen to vary with inclination angle resulting in a radiation pattern similar to those seen for antennas but in this case at optical wavelengths. We show that the observed radiation pattern arises as interference between different scattering processes.1. R. Rehammar, J. M. Kinaret, Nanowire-based tunable photonic crystals, Optics Express, 16, 2008.2. R. Rehammar, et al., submitted.3. R. Rehammar, et al., in preparation.
10:15 AM - B6.3
Schottky Solar Cells Based on Graphene and Silicon.
Xinming Li 1 , Hongwei Zhu 1 , Kunlin Wang 1 , Jinquan Wei 1 , Dehai Wu 1
1 Key Laboratory for Advanced Manufacturing by Material Processing Technology and Department of Mechanical Engineering, Tsinghua University, Beijing China
Show AbstractGraphene has been widely used for composites, nanoelectronics and transparent electrodes owing to its unique 2D nanostructure and conductibility. For example, solution-processed graphene dispersed into polymers such as P3OT or P3HT was used as the acceptor material. Graphene films were used as conductive and transparent electrodes to replace ITO in organic and dye-sensitized solar cells. Here we directly deposited highly conductive, semi-transparent graphene films on n-type silicon (n-Si) wafer to form Schottky junction solar cells. Our results show that graphene as energy conversion materials not only contribute to charge separation and transport, but also function as transparent electrode. The power conversion efficiencies of the graphene/n-Si solar cells are up to 1.6% at AM 1.5 [1], which can be further optimized to 2.5%. Chemical doping of thionyl chloride enhances the conductivity of graphene films significantly, delivering a maximum power conversion efficiency of ~3.9%, which is about 2~3.7 times larger than that for the cells without chemical doping [2]. Though these efficiencies are still lower than those for the cells based on pure silicon, this photovoltaic model provides a new trend to develop a new type solar cell which has the relatively low cost and easy fabrication.References:[1] Li XM, Zhu HW, Wang KL, et al. Graphene–on–silicon Schottky junction solar cells. Advanced Materials DOI: 101002/adma 200904383 (2010) [2] Li XM, Zhu HW, Wang KL, et al. In preparation.
10:30 AM - B6.4
Fabrication and Photovoltaic Characteristics of Dye Sensitized Solar Cells Using Conductive Diamond Thin Film Counter Electrodes.
Alok Vats 1 , Vinod Venkatesan 1 , Andrew Seiser 1 , Geun Lee 1 , Jaurette Dozier 1 , Jeremy Feldman 1 , Lance Robinson 1 , R. Vispute 1
1 , Blue Wave Semiconductors, Baltimore, Maryland, United States
Show AbstractDye-sensitized solar cell (DSSC) technology has attracted significant attention due to the remarkable advancement in light conversion efficiencies reaching up to 11 % in prototypes. The present best DSC comprises of a Ru based sensitizer, I/I3- liquid electrolyte and a Pt coated counter electrode. In order to achieve lower cost/Watt from the dye cell modules, use of Pt as a catalyst (reduction of tri-iodide at counter electrode, I3-+2e- 3I-) poses a great economical limitation towards commercializing this DSC technology. As a result, research efforts are aimed at developing alternative materials, which can replace Pt which have chemical inertness toward I2 and comparable or superior catalytic activity. Carbon based nanomaterials or composite electrodes are anticipated to replace Pt on a long run. Various carbon materials such as carbon nanotubes (CNT), activated carbon (AC) and carbon nanofibers have been investigated as counter electrodes for DSSC applications. The conversion efficiency of the DSCs comprising of CNT and activated carbon is dependent on their high specific surface area (SSA) and superior electronic conductivity. However, achieving suitable combination of SSA and electronic conductivity leads to additional processing steps, thus they add to the cost. In this work, we investigate the PV characteristics of DSSCs comprising of boron doped diamond thin films. These conductive diamond thin films were grown using a hot wire chemical vapor deposition (HWCVD) process on a seeded substrate. The electrical conductivity in diamond thin films used in our experiments was tuned by controlling dopant concentration in the thin film and thin film thickness. The DSC were fabricated using 10-15nm nanocrystalline TiO2 paste (P25 Degussa) with average particle size of 25nm as an active layer. This active layer was doctor bladed on a ITO substrate followed by calcination at 400oC for 30 min. The liquid electrolyte comprised of a LiI/I2 based electrolyte in acetonitrile (CH3CN), a Ru based metal complex dye [cis-diisothiocyanato-bis(2,2’-bipyridyl-4,4’-dicarboxylato) ruthenium(II) bis(tetrabutylammonium)] or N719 was used as sensitizer. The counter electrode comprised of a conductive diamond thin film. For our experiments, we used conductive diamond thin films of three different thicknesses. The photovoltaic performance of these DSCs was determined using J-V characteristics and EQE under standard illumination conditions and was compared to a reference DSSC with Pt counter electrode. Results will be discussed in the light of solar cell performance as a function of quality of diamond films grown by HFCVD technique.
10:45 AM - B6.5
Fully Tuneable Single-walled Carbon Nanotube Diode.
Chang-Hua Liu 1 , Chung-Chiang Wu 1 , Zhaohui Zhong 1
1 Electrical Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractP-n diode is the most important and fundamental building block for optoelectronics. Conventionally, diode’s characteristics, such as turn-on voltage and reverse leakage current, are determined by the bandgap and the doping concentration, and active tuning of diode properties is challenging. To this end, we present single-walled carbon nanotube (SWNT) diodes with fully tuneable characteristics. These 1D diodes are fabricated on fully suspended pristine SWNTs, and the formation of p–n junction is achieved by electrostatic doping using a pair of split bottom gates. Interestingly, by controlling gate voltages, the turn-on voltage of the nanotube diodes can be widely tuned, with values exceeding the bandgap energy of nanotube. Furthermore, the diode’s reverse leakage current can also be tuned by controlling the band-to-band tunnelling current. Our measurements reveal that the strongly enhanced band-to-band tunnelling under reverse bias leads to excellent backward diode characteristics with curvature coefficient exceeding the ideal diode limit. Our work demonstrates the capability of fully tuneable SWNT diodes, and the results should open up new avenues for 1D nanoelectronics and nanophotonics.
11:30 AM - **B6.6
Graphene Photonics: Ultrafast Lasers and Photoluminescence.
Andrea Ferrari 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractThe richness of optical and electronic properties of graphene attracts enormous interest. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential to be in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, the absence of a bandgap can be beneficial, and the linear dispersion of the Dirac electrons enables ultra-wide-band tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light emitting devices, to touch screens, photodetectors and ultrafast lasers. Despite being a single atom thick, graphene can be optically visualized [1]. Its transmittance can be expressed in terms of the fine structure constant [2]. The linear dispersion of the Dirac electrons enables broadband applications. Saturable absorption is observed as a consequence of Pauli blocking [3,4]. Chemical and physical treatments enable luminescence [5]. Graphene-polymer composites prepared using wet chemistry [3-5] can be integrated in a fiber laser cavity, to generate ultrafast pulses, down to 200fs, and enable broadband tunability [3,4]. 1. C. Casiraghi et al. Nano Lett. 7, 2711 (2007).2. R. R. Nair et al. Science 320, 1308 (2008).3. T. Hasan, et al. Adv. Mat. 21,3874 (2009)4. Z. Sun et al. ACS Nano 4, 803 (2010); arxiv 1002.0653v1 (2010)5. T. Gokus et al. ACS nano 3, 3963 (2009)
12:00 PM - B6.7
Application of Graphene Electrodes in GaN Light-emitting Diodes and Organic Solar Cells.
Gunho Jo 1 , Minhyeok Choe 1 , Sangchul Lee 1 , Woojin Park 1 , Chu-Young Cho 1 , Jin Ho Kim 2 , Seok-In Na 3 , Seung-Hwan Oh 4 , Seong-Ju Park 1 , Byung Hee Hong 2 , Dong-Yu Kim 1 , Yung Ho Kahng 1 , Takhee Lee 1
1 , GIST, Gwangju Korea (the Republic of), 2 , Sungkyunkwan University, Suwon Korea (the Republic of), 3 , Korea Institute of Science and Technology, Jeonju Korea (the Republic of), 4 , Research Institute for Solar and Sustainable Energies, Gwangju Korea (the Republic of)
Show AbstractGunho Jo,1 Minhyeok Choe,1 Sangchul Lee,1 Woojin Park,1Chu-Young Cho,1 Jin Ho Kim,2 Seok-In Na,3 Seung-Hwan Oh,4 Seong-Ju Park,1 Byung Hee Hong,2 Dong-Yu Kim,1 Yung Ho Kahng1 and Takhee Lee1*1 Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju, Korea2 Department of Chemistry and SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon, Korea3Korea Institute of Science and Technology, Jeonju, Korea 4Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju, Korea.*E-mail:
[email protected], graphene has gained much attention both for fundamental science and for potential applications in optoelectronic devices, because it is highly anticipated to play a crucial role in future flexible and transparent electrode application due to its low sheet resistance, optical transparency, and excellent mechanical properties [1-3]. Here, we report on the two application examples of graphene films as transparent and conducting electrodes in optoelectronic devices. The first example is the application of graphene films as a transparent electrode of GaN light-emitting diodes (LEDs) [4]. The graphene films synthesized by chemical vapor deposition (CVD) showed a sheet resistance of ∼620 ohm/sq with a transparency of more than 85% in the 400–800 nm wavelength range. The results of the electroluminescence (EL) spectra and light output performance showed that the graphene electrode on the GaN LED device successfully operated as a transparent current spreading layer. In the second example, we demonstrate the application of graphene films as cathodes of inverted-structure organic solar cells (OSCs). The used graphene films were work-function-engineered with an interfacial dipole layer to increase the built-in potential and to enhance the charge extraction, and consequently to enhance the overall device performance. To improve the power conversion efficiency (PCE) of graphene electrode-based OSCs, several exertions including improvement of graphene quality, development of advanced-structure OSC, and interface control between the active layer and graphene electrode are required. Here, we report on the work-function-engineered graphene films by interfacial dipole layer in order to greatly enhance the performance in inverted-structure OSCs, which provide better stability and design flexibility to enhance the technology of polymer-based solar cells. References [1]G. Eda et al., Nat Nanotechnol. 3, 270 (2008).[2]H. A. Becerril et al., ACS Nano 2, 463 (2008).[3]K. S. Kim et al., Nature 457, 706 (2009).[4]G. Jo et al., Nanotechnology 21, 175201 (2010). Acknowledgement: the National Research Laboratory Program of the Korean Ministry of Education, Science and Technology and the Program for Integrated Molecular System at GIST.
12:15 PM - B6.8
Carbon Nanotubes as Charge Injection Layer in Printed Organic Diodes.
Sampo Tuukkanen 1 , Kaisa Lilja 1 , Timo Joutsenoja 1
1 Department of Electronics, Tampere University of Technology, Tampere Finland
Show AbstractHigh frequency rectification of gravure printed organic diodes has been recently demonstrated [1]. It has been previously shown that the performance of organic light emitting diodes (OLEDs) can be enhanced by using carbon nanotubes as hole-injecting electrode material [2, 3]. Nowadays, water-based carbon nanotube based inks are commercially available. Here, we have used solution processed film of single-walled carbon nanotube (SWNT) to enhance the charge injection in the anode and semiconductor interface of the gravure printed organic diodes.References[1] K. E. Lilja, T. G. Bäcklund, D. Lupo, T. Hassinen, and T. Joutsenoja, Organic Electronics 10 (2009) 1011.[2] Malti Bansal, Ritu Srivastava, C. Lal, M. N. Kamalasanan, and L. S. Tanwar, Nanoscale 1 (2009) 317.[3] Eric C-W. Ou, Liangbing Hu, Gan Ching Ruey Raymond, Ong Kian Soo, Jisheng Pan, Zhang Zheng, Youngbae Park, David Hecht, Glen Irvin, Paul Drzaic, George Gruner, ACS Nano 3(8) (2009) 2258.
12:30 PM - B6.9
Light-emitting Organic Memory.
R. Shallcross 1 , Peter Koerner 1 , Philipp Zacharias 1 , Eduard Maibach 1 , Vincent Aubert 1 , Klaus Meerholz 1
1 Physical Chemistry, University of Cologne, Cologne Germany
Show AbstractThe majority of current non-volatile memory technologies for electronic storage media utilize inorganic semiconductors as the active components, which typically require high temperature and costly processing conditions. Consequently, organic-based memory technologies have garnered great interest in order to compensate for some of the drawbacks of their inorganic counterparts. Organic electronic devices may be easily and inexpensively processed over large areas with the added benefit of utilizing flexible substrates. Ideally, device active layers would be processed from solution precursors rather than vacuum sublimation methods, which would be advantageous for utilizing high throughput, low temperature and inexpensive printing techniques for device processing.Here, we report on light-emitting organic memory (LE-OMEM) devices composed of multiple solution-processed layers, which are only possible due to the ability to crosslink each individual layer prior to subsequent layer deposition. The active layer of our LE-OMEM devices is comprised of crosslinkable, thermally stable and fatigue resistant dithienylethene (DTE) photochromes that can be optically switched between two energetically and spectroscopically distinct isomers. We demonstrate that the ON/OFF ratio (OOR) of these devices is exponentially dependent on the difference in the largest charge injection barrier between the ON and OFF state of the device, which is a function of the change in the frontier orbital energies upon isomerization. Optimized devices display impressive fatigue resistance and afforded OORs for both current and electroluminescence of greater than 1000. We focus on a variety of crosslinkable DTE molecules of varying structure and functionality with an emphasis on OOR, device stability over multiple read/write/erase cycles (fatigue resistance), and switching rates. We also investigate the number of statistically discernable grey levels between completely OFF and ON, which would allow higher order numeral systems for increased data storage density. These fundamental studies are a first step in further elucidating the operating principles and efficacy of utilizing DTE molecules in thin film LE-OMEM devices.
12:45 PM - B6.10
The Synthesis and Characterization of Semiconducting Boron-doped Amorphous Carbon Materials Using an Organic Boron Compound as a Precursor.
Yasunori Inoue 1 , Masaaki Kitano 1 , Kiyotaka Nakajima 1 , Michikazu Hara 1 2
1 , Materials and Structures Laboratory, Tokyo Institute fo Technology, Yokohama Japan, 2 , Kanagawa Academy of Science and Technology, Kawasaki Japan
Show AbstractSolar cell is attractive device which can directly convert solar energy into electric power.Most solar cells are made of silicon because this material is abundant and has good electrical properties. However, silicon solar cells have several drawbacks, such as large energy consumption for the production and low absorption coefficient. Numerous attempts have therefore been made to develop genuine environmentally benign solar cells. Amorphous carbon(a-C) materials would be promising low-cost materials for the fabrication of solar cells. In this study, boron-doped a-C materials were synthesized by carbonizing naphthalene with organic boron compound, and their characteristics and electrical properties were investigated. Boron-doped naphthalene pitch was synthesized by heating a mixture of naphthalene and triphenylborane in the presence of AlCl3 at 673 K for 50 h under nitrogen gas flow. The ratio of boron to carbon (B/C) was adjusted to 0.5, 1.0 atom% by controlling the amount of triphenylborane. The boron-doped carbon materials were heated by spark plasma sintering (SPS) (50 MPa, 873–973 K, 10 min) in argon. XRD, Raman spectroscopy and XPS were used to characterize the structure of boron-doped a-C materials. Seebeck coefficient and electric conductivity were measured to clarify the electric properties of the samples. In the Raman spectra of all samples, several broad peaks were observed at around 1600 cm-1 and 1220–1440 cm-1, assignable to graphite and polycyclic aromatic C–C bond,respectively. The XRD patterns for samples exhibited two broad diffraction peaks at 2θ angles of 10 –30° and 40–50° that mean amorphous carbon composed of aromatic carbon sheets oriented in a considerably random fashion. B1s photoelectron spectra of boron-doped a-C materials showed some peaks in range of 185–193 eV. Some of these are attributed to mixed B–C and B–O bond species (e.g. BCO2 and BC2O), indicating that boron atoms are incorporated into the a-C materials in the form of BCO2, BC2O, and that these species present in the edge of graphite sheets.The Seebeckvoltage decreases with increasing temperature difference, suggested that boron-doped a-C materials treated by SPS showed n-type semiconductivity. On the other hand, non-doped a-C showed positive Seebeck coefficient: non-doped a-C functions as a p-type semiconductor.
B7: Nanocarbon Interfaces and Contacts
Session Chairs
Wednesday PM, December 01, 2010
Room 310 (Hynes)
2:30 PM - **B7.1
Engineering at the Junctions of Carbon Nanomaterials.
Wonbong Choi 1 2
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States, 2 Nanomaterials and Device Laboratory, Florida International University, Miami, Florida, United States
Show AbstractThis talk will focus on engineering junctions of carbon nanomaterials, carbon nanotubes (CNTs) and graphene, for various applications in future technologies. Particularly, the junctions of CNT-CNT, CNT-substrate, and graphene-CNT will be used to highlight the challenges towards applications. Our recent results of electrical functionality in carbon nannomaterials’ junctions will be presented. Some of these results offer excellent opportunity to have high efficiency devices and systems; high efficiency Li-ion battery based on interfacial junction controlled CNTs, bandgap engineered serpentine CNTs, flexible field emission device based on large graphene structure. Our efforts on the strategies of manipulation of carbon nanomaterials’ junction will be reviewed and critical issues will be discussed.
3:00 PM - B7.2
W-deposited Contacts for Carbon Nanofiber Using Focused Ion and Electron Beams.
Shusaku Maeda 1 , Toshishige Yamada 1 , Hisashi Yabutani 2 , Tsutomu Saito 2 , Cary Yang 1
1 Center for Nanostructure, Santa Clara University, Santa Clara, California, United States, 2 , Hitachi High-Technologies Corporation, Hitachinaka Japan
Show AbstractCarbon nanofiber (CNF) is a promising material for interconnect applications in next-generation integrated circuits. Understanding the temperature dependence of material properties such as conductivity and contact resistance is essential as they influence circuit performance. However, in practice, it is extremely difficult to control the temperature of the test device and maintain the thermal equilibrium environment because of its extremely small thermal capacity. Therefore, we examine the increase in temperature due to Joule heat generated by a stressing current. The temperature is then obtained using a heat transport model [1]. Thus the measured conductivity can then be obtained as a function of temperature. A test device is prepared by placing a single CNF between a pair of patterned gold (Au) electrodes on a SiO2 substrate. Contacts are formed by tungsten (W) deposition using focused ion beam (FIB), with the resulting total resistance smaller than that for the pre-W-deposited device by a factor of 100-1000 [2]. A stressing current is applied to the test device, and the average total resistance during each stress cycle is measured. We have found that the resistance decreases with temperature [3]. Since FIB deposition may potentially damage the test device because of its high energy, we develop an alternative technique for metal deposition using a well-controlled electron beam in a variable-pressure scanning electron microscope (VP-SEM). In this configuration, the source gas is delivered via a specially designed gas-injection system (GIS) and guided by the focused electron beam to yield deposition on a selected target at low energy [4]. The technique is more cost-effective as the GIS can be one of the modules in an existing SEM, which allows for in situ imaging and elemental analysis before, during, and after deposition. In this study, we compare the resistances of CNF test devices formed with W-deposition using FIB and e-beam deposition techniques. The study leads to improvements in our e-beam deposition system and better control of contact properties for interconnect test devices. Our results indicate that W deposition by e-beam is successful and creates contacts comparable to that obtained using FIB. [1]T. Yamada, T. Saito, D. Fabris, and C. Y. Yang, IEEE Elec. Dev. Lett. 30, 469 (2009).[2]T. Saito, T. Yamada, D. Fabris, H. Kitsuki, P. Wilhite, M. Suzuki, and C. Y. Yang, Appl. Phys. Lett., 93, 102108 (2008).[3]T. Yamada, H. Yabutani, T. Saito, and C. Y. Yang, Nanotechnology 21, 265707 (2010). [4]D. C. Joy and P. D. Rack, Microscopy and Microanalysis, NY, 11, 816 (2005).
3:15 PM - B7.3
Interface Engineering for Graphene Transistor by Tunable Self-assembled Monolayers: Toward Improved Device Performance and Reliability.
Zihong Liu 1 , Ageeth Bol 1 , Wilfried Haensch 1 , Zhihong Chen 1
1 , IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
Show AbstractGraphene has emerged as a highly promising candidate for high-speed electronic devices due to its extraordinary electronic properties. Although the intrinsic mobility of graphene is reported over 200,000 cm2/Vs, the extrinsic field-effect mobility of such graphene transistors is orders of magnitude lower. One of the dominant sources limiting the device performance and reliability is the dielectric-graphene interface where a variety of scattering and trapping effects are present. Here we report the dielectric-graphene interface engineering for the CVD graphene transistor by applying specific tunable organosilane self-assembled monolayers (SAM) onto the oxide dielectric surface. Experimental results show the SAM-based interface engineering consistently and significantly improves the CVD graphene device mobility, hysteresis and bias stress stability. The physical mechanisms involved in the interface-limited device performance and reliability will also be discussed.
3:30 PM - B7.4
Formation of Schottky Barrier at the Graphite-graphene and Semiconductor Interfaces and Tuning the Barrier Height by Doping.
Sefaattin Tongay 1 2 , Arthur Hebard 2 , Bill Appleton 1 , Xiaochang Miao 2 , Todd Schumann 2
1 Nanoscale Institute of MEdical and Engineering Technology, University of Florida, Gainesville, Florida, United States, 2 Department of Physics, University of Florida, Gainesville, Florida, United States
Show AbstractWe demonstrate the formation of Schottky barriers on various semiconductors such as Si, SiC, GaAs and GaN using graphite/graphene as a metal. Diodes display strong rectification, and forward bias diode characteristics are well described by the thermionic emission theory (TE) in 250K – 330K temperature range. Extracted barrier heights (SBH) are also confirmed by capacitance techniques and roughly obey to Schottky-Mott relation, i.e, SBH is the difference between the work function of metal and electron affinity of the semiconductor. Since the barrier height depend on the work function of the graphite/graphene, we report tuning SBH by bromine intercalating graphite at the interface. After the intercalation, diodes display higher SBH, lower forward/reverse current density, higher depletion capacitance. We attribute these effects to charge transfer in between carbon and bromine and associated increase in graphite work function determined with X-ray photoelectron spectroscopy (XPS). Increase in the graphite work function results in higher SBH as confirmed from J-V and C-V measurements. Presented results have important implications for HEMTs, MESFET devices, sensing, high power applications on semiconductors as well as carbon-graphene electronics.
4:15 PM - **B7.5
Boron Nitride Dielectrics for High-Performance Carbon Electronics
James Hone 1
1 , Columbia University, New York, New York, United States
Show AbstractMost studies of the electrical properties of carbon nanotubes and graphene have used silicon dioxide as a dielectric substrate. However, recent work by many groups has shown that device performance is strongly impacted by the oxide. We and others have shown that freely suspended devices show improved properties, but the suspended configuration is incompatible with most device applications. As an alternative, we have studied the use of crystalline hexagonal boron nitride (h-BN) as a dielectric for graphene and nanotubes. To construct devices, we sequentially transfer these materials to substrates by a 'manual atomic layer deposition' technique. Devices on h-BN show significantly improved performance by a number of measures.
4:45 PM - B7.6
Contact Geometry Effects on Graphene Transistor Performance.
Aaron Franklin 1 , Ageeth Bol 1 , Teresita Graham 1 , Zhihong Chen 1
1 T. J. Watson Research Center, IBM Research, Yorktown Heights, New York, United States
Show AbstractGraphene is an excellent 2D material for a range of electronic applications, owing to its high mobility and ultra-thin body. Challenges with realizing high performance graphene transistors are nearly all related to establishing interfaces with the graphene to form contacts and field-modulated channels. Contact resistance is one of the obstacles that limit the achievable mobility, especially when the channel length is scaled to reduce the contribution of scattering. To date, contacts have been formed by depositing metal onto lithographically patterned graphene, resulting in top contacts (TC), which may not be ideal for minimizing contact resistance. For instance, in multi-layer graphene devices, tunneling between layers could play a significant role in contact resistance since the contacts only interface with the topmost layer. In this work, we have explored two new contact geometries, including bottom and double contacts (BC and DC), to further understand the transport mechanisms at the contacts and deduce which geometry is best suited for single- and multi-layer graphene devices. By etching shallow trenches in a 90 nm SiO2 substrate followed by the deposition of Pd contact metal to the thickness of the trench depth, bottom contacts are formed. The surface of these BC are within 1-2 nm of the SiO2, creating a nominally planar surface. Graphene is deposited onto these BC using both mechanical exfoliation and transfer of chemical vapor deposition (CVD) grown graphene. After characterizing the BC graphene devices, Pd contacts are formed directly on top of the BC, to form double contacts. Two and four-probe measurements are made to compare the three contact geometries. Results indicate which contact geometry works best for devices from multi-layer graphene as well as from single-layer graphene obtained by exfoliation and CVD growth. Overall, this study adds important insight toward realizing more optimized graphene device geometries for maximizing the achievable performance.
5:00 PM - B7.7
Graphene/Carbon Nanotube Junctions.
Melina Blees 1 , Xiaodong Xu 1 , Arend van der Zande 1 , Zhaohui Zhong 3 , Paul McEuen 1 2
1 Laboratory of Atomic and Solid State Physics (LASSP), Cornell University, Ithaca, New York, United States, 3 College of Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York, United States
Show AbstractGraphene is of great interest as a possible foundation for transparent, flexible electrodes, and recent studies have suggested that it may make unusually good contact to carbon nanotubes [1]. However, despite extensive research into the properties and applications of both materials over the last decade, fabrication challenges have prevented studies of the electronic interactions between them. Here we draw on recent advances in the creation of both large-area, single-layer graphene grown by chemical vapor deposition (CVD) and aligned arrays of parallel carbon nanotubes to explore the electrical properties of the junction between the two materials for the first time.Our fabrication begins with the growth of single-layer graphene on a copper film [2]. We transfer the film onto an Si/SiO2 chip, lithography pattern it into strips, and apply metal electrodes. In parallel, we grow aligned arrays of carbon nanotubes on y-cut, single-crystalline quartz wafers by CVD [3] and cover the nanotubes with a layer of evaporated gold and water-soluble tape as a transfer medium. We then peel the film up by hand and place it in the desired orientation and location on the graphene-bearing chip. The result is a device consisting of a graphene strip crossed by aligned carbon nanotubes with separate electrical contacts to both components.We measure the resistance of the graphene/nanotube junction using a four-point-probe technique that eliminates external series resistances from the reading. We analyze the contact with a distributed resistance model and find a minimum length for good contact, lc, on the order of 1 μm. For a sufficiently large contact of length greater than lc, the two-point resistance Rc of the junction will be on the order of the nanotubes’ intrinsic resistance over lc. Together, these two properties set a minimum size and a minimum total contact resistance on any device that uses graphene to contact carbon nanotubes.In conclusion, we have created devices that allow us to study the electrical properties of the junction between graphene and carbon nanotubes. These results demonstrate the feasibility of using graphene as the electrodes and gate and carbon nanotubes as the active element in a flexible, transparent, all-carbon transistor.[1] A. Kane, P. Collins, et al., Nano Letters, 9, 3586 (2009)[2] X. Li, R. Ruoff, et al., Science, 324, 5932 (2009)[3] S. Kang, J. Rogers, et al., Nature Nanotechnology, 2, 230 (2007)
5:15 PM - B7.8
Current Crowding, Joule Heating, and Peltier Cooling at Graphene Device Contacts.
Kyle Grosse 1 , Myung Bae 2 , F. Lian 2 , Eric Pop 2 , William King 1
1 Mechanical Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois, United States, 2 Electrical and Computer Engineering, University of Illinois, Urbana, Illinois, United States
Show AbstractSingle layer graphene is an attractive material for nanoelectronic devices, however the implementation and ultimate scaling of such devices depends on its electrical contacts to metal electrodes. We present the first study of nanometer-scale temperature mapping near graphene-palladium contacts. Thermometry is achieved by Scanning Joule Expansion Microscopy (SJEM), which measures temperature with an unprecedented sub-10 nm spa-tial resolution and 10 mK temperature resolution in such samples. Graphene devices with channel widths of 4, 6, and 8 μm were prepared on SiO2/Si substrates and contacted with Cr/Pd (0.5/40 nm) electrodes. Fabrication was completed by covering the devices with 70 nm of PMMA, whose thermal expansion acts to amplify the thermomechanical expansion signal in the SJEM measurements [1]. Temperature profiles of the graphene contacts were made using SJEM at various forward, reverse and back-gate biases. A self-consistent electrical-thermal-thermoelectric model is used to understand the temperatures measured [2]. The observed temperature fields show heating due to Joule effects in the graphene sheet, and due to current crowding into the Pd contacts. The SJEM measurements offer direct insight into the current transfer length from graphene to Pd contacts, which is of the order ~0.5 μm and of significance for future graphene electronics. The temperature profile at the contacts is asymmetric with respect to current flow between the graphene and Pd, and also changes sign between hole and electron doping. The Peltier effect can be as high as 20% of the Joule effect at graphene contacts under moderate bias conditions. The data can be understood by self-consistent modeling with only one fitting parameter, the graphene/Pd contact resistance (~500 Ω-μm2). This combined measure-ment-modeling study represents the first direct observation of thermoelectric effects at graphene contacts.
5:30 PM - B7.9
Realization of Stable Carbon Nanotube-metal Contacts with Thermal Annealing and Selective Metallization.
Chenfu Guo 1 , Xinghui Li 1 , Selvapraba Selvarasah 1 , Mehmet Dokmeci 1
1 Electrical and Computer Engineering Department, Northeastern University, Boston, Massachusetts, United States
Show AbstractIn this paper, we present a simple methodology to improve the contact resistance between single-walled carbon nanotube (SWNT) and metal by a combination of thermal annealing and deposition of Au pads on to contact areas between the carbon nanotubes (CNTs) and Au microelectrodes. CNTs have numerous advantages such as large surface area-to-volume ratio, miniature sizes and fast response. CNTs are rapidly emerging as a candidate for potential building blocks for future integrated nanoelectronics. The realization of reliable and ohmic CNT-metal contacts with a low resistance is very critical for all applications of CNTs in nanoelectronics and nanodevices, since the large noise generated by poor CNTs-metal contacts would severely degrade the performance of these devices. After creating microelectrode pairs (Au) on a silicon wafer, we next assemble CNTs by dielectrophoretic (DEP) assembly process, where the CNTs were attached to the Au microelectrodes by weak Van der Waals forces, hence the variations of two-terminal resistances between Au microelectrodes were large due to the poor CNT-metal contacts. To remedy the contact resistance problem, the devices were first treated by a thermal anneal at 300 °C for 10 minutes after the DEP process. After this annealing process, 5 µm by 5 µm squares of Au pads (thickness of Au = 50 nm) were deposited and patterned using lift off on top of the regions where the CNTs contact the microelectrodes using electron beam deposition to improve the CNT-metal contact resistance. The thermal annealing and the deposition of Au pads improved the two-terminal resistances, which ranged from 21.9 KΩ to 7.9 KΩ (before treatment), to a range of 15.5 KΩ to 4.9 KΩ (after treatment). More importantly, the stability of the two-terminal resistance was significantly improved by the localized deposition of Au pads. After the DEP process, for a sample prototype device, the two-terminal resistance was 10.903 KΩ with a standard deviation of 0.102 KΩ, where the standard deviation of all measured samples was 0.94% on the average. After annealing and Au pad deposition process, the average two-terminal resistance of this device was reduced to 5.065 KΩ with a standard deviation of 0.017 KΩ, where the standard deviation of all measured samples was 0.34% on the average. With the drastic improvement in the stability of the two-terminal resistance of the devices, a reliable and reproducible performance from CNT based nanoelectronics and nanosensors, such as CNT based FETs, gas, bio and pH sensors could be achieved.
B8: Poster Session: Carbon-Based Electronic Devices
Session Chairs
Manish Chhowalla
Robert Keller
Meyya Meyyappan
Jud Ready
Thursday AM, December 02, 2010
Exhibition Hall D (Hynes)
9:00 PM - B8.1
Bandgap Opening and High On/Off Ratio in Thermally-reduced Graphene Oxide Thin-film Transistors.
Toshiyuki Kobayashi 1 , Nozomi Kimura 1 , Daisuke Hobara 1
1 Advanced Materials Laboratories, Sony Corporation, Atsugi, Kanagawa, Japan
Show Abstract
Since as-synthesized graphene oxide (GO) is an insulator and extensively-reduced GO is a semimetal, it has been expected that moderately reducing GO enables to control the bandgap of GO [1]. While reducing GO by hydrazine vapor can control the transition from insulator to semiconductor [2], thermal reduction leads to an abrupt transition from insulator to semimetal [3]. The difference may arise from different reduction mechanisms and resulting structures of reduced GO, hence understanding the mechanism of tuning its electronic property is needed for optimizing the GO characteristics for variety of applications.
We demonstrate a technique of opening a transport bandgap of GO by simply annealing GO on SiO2/Si substrate whose surface is functionalized by 3-aminopropyltrimethoxysilane (APTMS). Annealing the GO in contact with amino group at 250 ○C for 1 h moderately reduces the GO without extensively reducing it to semimetal. Since a uniform few-layer GO thin film can be readily prepared on an APTMS-terminated substrate [4], we obtain the semiconducting GO thin film in wafer scale. We demonstrate the on/off ratio of semiconducting GO thin-film transistors exceeds 200 at room temperature, which is the highest among previously reported GO FETs. We also find that the GO on top of other GO flakes, i.e. GO which is not in contact with amino group, becomes a semimetal even on the same substrate and the same annealing condition. Therefore, it is also possible to pattern the semiconducting and semimetalic regions by locally functionalizing the substrate surface. These results open a way to understand the elements for the controlled reduction of GO and also a novel synthesis of semiconducting GO suitable for many applications including field-effect transistors, chemical sensors, and biosensors.
[1] J-A Yan et al., Phys. Rev. Lett. 103, 086802 (2009)
[2] G. Eda et al., J. Phys. Chem C 113, 15768 (2009)
[3] I. Jung et al., Nano Lett. 8, 4283 (2008)
[4] T. Kobayashi et al., small 6, 1210 (2010)
9:00 PM - B8.10
Graphene/MnSn(OH)6 Nano-composites as Advanced Electrodes for Electrochemical Super-capacitor Applications.
Gongkai Wang 1 2 , Xiang Sun 2 , Huiyang Gou 2 , Changsheng Liu 1 , Qingkai Yu 3 , Jie Lian 2
1 Key Laboratory for Anisotropy and Texture of Materials of Ministry of Education, Northeastern University, Shenyang, Liaoning, China, 2 Department of Mechanical, Aerospace & Nuclear Engineering , Rensselaer Polytechnic Institute , Troy, New York, United States, 3 Center for Advanced Materials, Electrical and Computer Engineering, University of Houston, Houston, Texas, United States
Show AbstractA composite consisting of few functional graphene sheets and MnSn(OH)6 nanocrystals (G-MnSn(OH)6 nanocomposite) was prepared by in situ soft chemical reduction and co-precipitation methods. Various approaches were employed for materials characterization including transmission electron microscopy, scanning electron microscopy and Raman spectroscopy. Most MnSn(OH)6 nanocrystals were found to deposit on the surfaces of graphene sheets by the co-precipitation method during the in situ reduction process. The electrochemical properties of as-prepared nanocomposites were investigated by cyclic voltammograms (CVs), Galvanostatic charge/discharge, and electrical impedance spectroscopy (EIS). The incorporated MnSn(OH)6 nanocrystals enhanced the capacitive performance of the nanocomposite as compared with the pure graphene electrode. Furthermore, G-MnSn(OH)6 nanocomposites exhibit higher specific capacitance than that of the simple physical mixture of pre-synthesized MnSn(OH)6 nanocrystals and graphene sheets. Therefore, the G-MnSn(OH)6 nanocomposites may be potentially applied as electrodes for high performance energy storage devices, such as supercapacitors.
9:00 PM - B8.11
Synthesis and Chemical Modifications of Single-layer and Few-layer Graphene.
Hongxin Zhang 1 2 , Peter Feng 1 2 , Gerardo Morell 1 2
1 Physics Department, University of Puerto Rico, Rio Piedras Campus, San Juan, Puerto Rico, United States, 2 , Institution for functional nanomaterials, San Juan, Puerto Rico, United States
Show AbstractTransparent single-layer and few-layer graphene with the average width up to 250nm, and length more than 3μm were produced on transition-metal templates by using super-short-pulse laser produced plasma deposition techniques. Scanning electron microscopy, transmission electron microscopy (TEM), and micro-Raman spectroscopy were used to explore the properties of the graphene. The chemical modification of graphene was conducted with different hydrogenated percentages and a series of samples exposed to atomic hydrogen for very low dose 5s, 15 s, 30 s and 50 s, respectively were obtained. As a reference, graphene exposed to pure Ar plasma under the same conditions were also obtained.To investigate the electronic properties of the hydrogenated graphene, we fabricated graphene-based field effect transistor for carring out electrical transport studies. Our results suggest that the percentage of hydrogenation can effectively control the band gap of graphene and plays a crucial role of engineering the electronic properties of graphene.
9:00 PM - B8.12
Nano-micro Hybrid Fluidic Filter Based on Coaxially Coated Carbon Nanotube Three-dimensional (3D) Networks.
Jeong Eun Seo 1 , Haegu Yeo 1 , Bio Park 2 , Suhwan Kim 1 , Simon Song 2 , Myeongmo Sung 1 , Haiwon Lee 1
1 Chemistry, Hanyang University, Seoul Korea (the Republic of), 2 Mechanical Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractMicrofluidic systems are paid attention due to their superior capabilities in chemical and biological applications. For example, using micro total analysis systems (μTAS) or lab-on-a-chip systems for clinical applications, it is possible to detect signs of cancer in blood with nascent sample consumptions. Also, a nano-micro hybrid filter on a microfluidic chip could be utilized to directly separate DNA from blood without using centrifuge. Here we report a nano-micro hybrid filter using suspended carbon nanotube (CNT) three-dimensional (3-D) networks on Si pillar substrate. These CNT networks filter was fabricated by synthesizing CNTs on the 3-D structures of Si substrates. The Si templates of pillar structures were prepared by conventional deep etching processes, respectively. By forming catalyst nanoparticles on the above Si templates using a dipping method, the CNTs were uniformly synthesized with desired density on those 3-D structures of Si substrates including high pillars. But as-grown CNT networks collapsed under the fluid pressure when the solution flows down into the channel. As the suspended CNTs were adhered to Si pillars with weak physical force, the CNTs 3-D networks were coaxially coated with Al2O3 layer using atomic layer deposition (ALD) techniques for enhancing the adhesion force to withstand normal pressure. Coaxially coated CNTs filter successfully separated nanoparticles(~500nm) in solution which contains different-sized particles. We will report the detailed characterization of nano-micro hybrid CNT 3-D networks filter. Furthermore, and application aspects of these new functional structures also will be discussed.
9:00 PM - B8.14
Graphene Interconnection of Nano-scale Electronics Based on Electroplated Copper.
Yoojin Song 1 4 , Jinsup Lee 2 , Seokwoo Jeon 2 , Youn-Seoung Lee 3 , Seong Jun Kang 4
1 Division of Industrial Metrology, Korea Research Institute of Standards and Science, Daejeon Korea (the Republic of), 4 Department of Advanced Materials Engineering for Information and Electronics, Kyung Hee University, Yongin-si Korea (the Republic of), 2 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 3 Department of Information Communication Engineering, Hanbat National University, Daejeon Korea (the Republic of)
Show AbstractWe have developed a method to integrate graphene to nano-scale electronic devices as an interconnect. The graphene is formed by chemical vapor deposition (CVD) process on an electroplated copper film. The electroplating of copper is a key process to fabricate both the copper-interconnections of integrated circuits (IC) and three-dimensional, surrounding gate devices. In our experiments, electroplating technology is adopted to form a copper catalyst layer for the growth of graphene that can be used for interconnection lines. The approach involves the deposition of copper catalyst layer as the shape of interconnection through electroplating, followed by the CVD growth of graphene. Raman spectra were collected to investigate the thickness and uniformity of the graphene layer and some preliminary conduction data were collected. The results prove this technique to be useful for the interconnection of high performance IC.
9:00 PM - B8.15
3-D Non-planar Monolayer Graphene Transistor.
Bhaskar Nagabhirava 1 , Benjamin Briggs 1 , Haiyuan Gao 2 , Yang Xu 2 , Bin Yu 1
1 College of Nanoscale Science & Engineering, State University of New York, Albany, New York, United States, 2 Department of Information Science & Electronic Engineering, Zhejiang University, Hangzhou China
Show AbstractGraphene is a 2-D carbon nanostructure exhibiting very unique mechanical and electrical properties such as large in-plane Youngs modulus (E~2TPa) and higher carrier mobility than any known semiconductor (~200,000 cm2/V-s). These attractive properties make graphene a prime candidate for a spectrum of emerging applications. While majority of the reported research to-date focusing on the behavior of the planar (2-D) structure, key properties of graphene under extreme physical deformation (e.g. bending), unavoidable in certain applications, is not fully explored. In this work, we report the electrical transport behavior and mechanical resilience of non-planar (or 3-D) graphene in one of the significantly strained conditions - uniaxial bending. Fabrication of deformed-graphene-channel field-effect transistor is carried out in a specially designed structure. Structural and mechanical analysis of the deformed monolayer graphene field-effect transistor is conducted, followed by characterization and analysis of electrical transport properties with comparison to that of the planar (2-D) device structure. We discover that, in a graphene monolayer with significant mechanical deformation, excellent electrical properties are largely preserved. The research findings point to the potential in employing non-planar graphene in emerging applications such as flexible electronics and innovative nanoelectronic devices.
9:00 PM - B8.16
Vertical Array of 1D Pillar-superlattice and 2D Graphene Hybrid Architectures for Novel Light Emitting Diode Application.
Jung Min Lee 1 , Jaeseok Yi 1 , Hae Yong Jeong 1 , Dong Hyun Lee 1 , Won Il Park 1
1 material Science and Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractOne-dimensional (1D) semiconductor nanopillar arrays have attracted much attention due to their promise for application in advanced optoelectronics and photovoltaics. In particular, vertically-aligned 1D pillar structures have small interfacial areas at the junctions, and thus they can effectively relieve strain and may accommodate large lattice mismatches at the hetero-interfaces. In addition, the active elements in 1D pillars are less affected by flexural (bending) deformation of the substrates. These mechanical characteristics of the pillar structures can lead to the fabrication of highly versatile optoelectronic devices. Here we present the fabrication of novel LEDs, composed mainly of a vertical array of 1D pillar-superlattice (PSL) structures and 2D graphene sheets. Graphene sheets coated with very thin metal layers exhibited good mechanical and electrical properties inherited from graphene, and they could be successfully mounted on the PSL arrays as top window electrodes. Optical characterizations demonstrated that the intrinsic properties of graphene including excellent optical transparency and thermal/electrical conductance were maintained even after deposition of the thin metal films. In addition, thermal annealing caused the contact resistance to decrease, which provided enhanced carrier injection to the PSLs. The resulting PSL-Gr hybrid LEDs exhibited bright light emission from a large area where the graphene sheet was connected to the PSLs. The general applicability of this approach can readily enable implementation of graphene-based systems into many complicated 3D optoelectronic and photovoltaic devices.
9:00 PM - B8.17
Spinning Millimeter Scale MWNTs for Strong Spun Fibers.
Junichi Muramatsu 1 , Akihiro Ishida 1 , Yoku Inoue 1 , Adrian Ghemes 2 , Morihiro Okada 2 , Hidenori Mimura 2
1 Department of Electrical and Electronic Engineering, Shizuoka University, Hamamatsu Japan, 2 Research Institute of Electronics, Shizuoka University, Hamamatsu Japan
Show AbstractCarbon nanotubes(CNTs) have good mechanical property. Reported tensile strength of a multi walled CNT (MWNT) is 150 GPa [1]. CNTs are expected as the light weight and high strength material. Recently, we established growth method of ultra-long MWNT array using iron chloride [2]. Good things of the method are that millimeter scale long arrays are grown in short time and it has high drawability of MWNT web. In the present work, we fabricated MWNT spun fibers using the ultra-long MWNTs. Research purpose is to achieve the strong MWNT fibers. Since the as-spun fiber breaks by sliding of short MWNTs, to improve tensile strength, it is of crucial importance to increase friction forces between MWNTs. In this study, we investigated effects of aspect ratio of MWNTs and tension in MWNT web on tensile strength.Very spinnable MWNT arrays were grown by low pressure chemical vapor deposition using FeCl2 powder as a precursor for Fe catalyst. The MWNT arrays were grown at 830 °C. The high spinnable array of 2 mm in height was grown in 16 min. Since our MWNT arrays are highly spinnable, it is very easy to draw a long-lasting MWNT web, which is a two dimensional MWNTs network. MWNT fibers were spun from the webs. To form spun fibers, no binder material was used. To investigate the relation between tension in the MWNT webs and tensile strength, spindle speed was changed from 10000 rpm to 50000 rpm. With increasing the spindle speed, tensile strength improved monotonically from 130 MPa to 300 MPa. This result indicates that high rotation speed increases internal stress of spun fibers, resulting in higher tensile strength. On the other hand, to study the relation of tensile strength to aspect ratio of short fibers, length of MWNTs, used for spinning, was changed from 1.4 mm to 2.0 mm. The fiber diameter was kept constant of 40 μm. With increasing the MWNT length, tensile strength increased monotonically, although structures of MWNTs, diameter, aspect ratio and crystallinity, were much different with those of conventional materials. The spinning theories, in which short fibers are locked with friction force between them and high aspect materials increase the friction force, seem to be applicable on nano-sized MWNT fibers.[1] B. G. Demczyk et al. Mater. Sci. Eng. A334, 173 (2002). [2]Y. Inoue et al., Appl. Phys Lett. 92, 213113 (2008).
9:00 PM - B8.18
Improvement of Tensile Strength of MWNT Fiber by Multiply Twisting.
Yoshitaka Minami 1 , Akihiro Ishida 1 , Yoku Inoue 1 , Adrian Ghemes 2 , Morihiro Okada 2 , Hidenori Mimura 2
1 Department of Electrical and Electronic Engineering, Shizuoka University, Hamamatsu Japan, 2 Resarch Institute of Electronics, Shizuoka University, Hamamatsu Japan
Show AbstractThe good mechanical properties of carbon nanotubes (CNTs) have been attracting much attention for realizing advanced applications. To utilize the high tensile strength of CNTs, we have been working on strong spun multi walled CNTs (MWNTs) fibers. Since the spun fiber breaks by sliding of short CNTs, it is important to increase friction force between CNTs. In this work, strength of multiply twisting MWNT spun fibers was studied.By our growth method, very spinnable ultra-long MWNT arrays are consistently obtained in every trial. MWNT arrays were grown by conventional low-pressure chemical vapor deposition using FeCl2 as a precursor for Fe catalyst. The height of spinnable MWNT array is higher than 2 mm as high as ever reported. From the arrays, MWNTs were first drawn into a web, which is two dimensional MWNTs network, and then the web is spun into a fiber. No chemical binder material was used to fabricate the MWNT fibers. Diameter of the fibers was raging from 20 to 40 μm. To improve internal stress of as-spun CNT fibers, we performed multiply twisting of spun fibers. In our twisting system, spun fibers were set vertically. Two or more spun fibers were twisted with applying loads to increase tension in the fibers. With increasing the load, tensile strength of CNT twisted fibers increased. Tensile strength of as-spun fiber, 327 MPa, was improved to 689 MPa by twisting with the load of 10 g. Maximum strain and Young modulus of the twisted fiber were 10 % and 13 GPa, respectively. After twisting process, each diameter of fibers decreased. These results show that, by twisting fibers with applying loads, internal stress of fibers was increased resulting in improvement of tensile strength. This work is also indicative that spinning CNT webs can not achieve fully packing of CNTs. Therefore, additional process to decrease empty spaces inside the as-spun fiber is necessary to improve tensile strength.
9:00 PM - B8.19
Position Selective and Chirality Controlled Single-walled Carbon Nanotubes Grown on the Surface Treated Substrate Using Free Electron Laser Irradiation.
Nobuyuki Iwata 1 , Keijirou Sakai 1 , Satoshi Doi 1 , Hiroki Takeshita 1 , Yuuki Tanaka 1 , Kunihide Kaneki 2 , Hiroki Kobayashi 2 , Hirofumi Yajima 2 , Hiroshi Yamamoto 1
1 Electronics & Computer Science, CST, Nihon Univ., Chiba Japan, 2 Applied Chemistry, Faculty of Science, Tokyo University of Science, Tokyo Japan
Show AbstractFor field effect transistor using single-walled carbon nanotubes (SWNTs) with extremely dense packed electronic devices, the diameter, the alignment, and the chirality of the SWNTs should be controlled. The diameter might be determined by the size of the catalyst and the in-plane alignment was also reported in growth on sapphire and quartz. Recently the research concerning about the separation of metallic and semiconducting SWNTs is extremely developed. Kataura group reported that the metallic and semiconducting SWNTs are separated with the purity of 90 and 95%, respectively, within only 11 min using SWNTs/sodium dodecyl sulfate (SDS) and sodium deoxycholate solution through the agarose gel beads column. However the position selective and chirality controlled growth have not been achieved during SWNTs growth. We propose a novel technique to grow the SWNTs with specific chirality at the desired position using free electron laser (FEL) irradiation during growth and surface treatment. The features of the variable wavelength(0.3-6μm) and the very sharp pulse width approximately 500 ps of FEL are able to enhance the SWNTs growth with specific chirality, because absorption wavelength depends on the individual chirality. As well known the SWNTs grew from the catalysts. The position of deposited catalysts can be controlled by the surface treatment of the substrate surface changing the wettability between the catalyst solution and the substrate surface. The Co/Mo catalyst was dispersed on quartz substrates by dipping technique with the speed of 600 μm/s. The SWNTs were grown by cold-wall alcohol catalytic chemical vapor deposition (CW-ACCVD) method at 1273K. The irradiated wavelength of FEL was from 532 to 1400 nm during growth. From the Raman spectra using excitation laser of 441, 532, 632 and 785nm, the G, D, and the radial breathing mode (RBM) were observed in all specimens. Without the FEL irradiation, possible chirality was 30 with the mixture of metallic and semiconducting SWNTs estimated from the RBM peak position, chiral map and Kataura plot. The most efficient wavelength of the FEL was 800 nm to control the chirality. The number of 30 kinds of chirality was much reduced to 5 of (9,7), (10,6), (14,0), (11,4) (10,5), all of which was semiconductor. It was noticeable that the FEL irradiation during growth was quite effective to control the chirality. The influence of the position selective growth will be also discussed.
9:00 PM - B8.2
De-wetted Transition Metal Co- and Ni- Films as Catalysts for Carbon Nanotubes Arrays: Structure, Morphology and Magnetic Properties.
Sanju Gupta 1 , P. Tiberto 2 , S. Bianco 3 , P. Martino 3 , F. Celegato 2 , A. Chioleri 3 , A. Tagliaferro 3 , P. Allia 3
1 Chemistry & Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 , INRIM, Turin Italy, 3 Physics, Politecnico di Torino, Turin Italy
Show AbstractInterest in the growth of carbon nanotubes by variants of chemical vapor deposition techniques using transition 3d metals (Co, Fe and Ni) as catalyst support is still a subject of intense research in view of their promising intrinsic electrical, electronic, optical, chemical and magnetic properties allowing their use for a multitude of applications include field emission displays, gas-sensors and gas-storage media, nanoprobes, electromagnetic shielding coatings and magnetic storage recording media attributed to their high aspect ratio. In this paper, we report on the morphological, structural and magnetic properties of two of the important and comparable catalysts i.e. Co and Ni films with varying thickness prior to and post de-wetting that enabled the formation of island-like structures on Si surface. Interestingly, we find different magnetic (superparamagnetic versus high coercivity ferromagnetic) states as a function of Co and Ni thickness and subsequent grain size. X-ray diffraction spectra revealed typical polycrystalline or multicomponent (fcc, hcp and oxide forms) structure directly affecting the magnetic properties. Moreover, the island-like Co and Ni films morphology facilitated the subsequent development by thermal chemical vapor deposition of carbon nanotube arrays that may enclose or embed the metal catalyst nanoparticles useful for various technologies. While we do not observe a strong magnetic anisotropy behavior from grown carbon nanotube arrays, we found an enhancement in magnetic coercivity by almost two orders of magnitude with respect to their bulk counterpart for both the metal catalysts, which is promising for low dimensional, high-density magnetic recording media applications. Carbon nanotube arrays with Ni nanoparticles exhibit a weaker magnetic moment with a non-negligible diamagnetic signal from carbon nanotubes. Ni and Fe nanoparticles in carbon nanotubes can be described by a modified Stoner-Wohlfarth model. We would like to thank Mr. P. Pandolfi for technical assistance in preparing some of the Co films and the author (S.G.) acknowledges fellowship during her visit from Politecnico di Torino, Italy. [Allia, Tiberto, Gupta et al. J. Nanoparticle Res. (in press, 2010).]
9:00 PM - B8.20
Low Temperature Growth of CNT by Triode Type RF Plasma CVD Method.
S. Ishikawa 1 , R. Kuwabara 1 , K. Yoshida 1 , Yoshiyuki Show 1
1 Dept. of Electrical and Electronic Engineering, Tokai University, Hiratsuka, Kanagawa Japan
Show AbstractCarbon nanotube (CNT) is one of the candidate materials for the interconnection in an ultralarge-scale integrated (ULSI) circuit with 32nm technology node. In this study, the vertically aligned CNT was deposited by triode type RF plasma CVD method which employs the grid electrode in addition to the anode and the cathode electrodes at low temperature below 500 oC. Moreover, influence of the process parameter on the CNT growth was discussed.The Fe and Co catalyst film was deposited on the Si and the glass substrate. The triode type RF plasma CVD equipment was used for the CNT growth on this substrate. The acetylene gas was used as source gas. The growth temperature and the RF power were varied up to 600oC and 100W. The vertically aligned CNT was formed by this CVD equipment on the substrate. The diameter of the CNT was 20nm. The growth rate of the CNT increased in an increase in the growth temperature. The RF power in the range between 50 and 100W did not affect the growth rate. These results indicate that the growth rate of the CNT is governed by the catalytic reaction between the catalyst and the hydrocarbon radical.The vertically aligned CNT was successfully formed below growth temperature of 500 oC by using Co catalyst and the grid electrode. The Co catalyst was suitable for low temperature growth comparing with the Fe catalyst. Moreover, the grid electrode prevents supplying the hydrocarbon ions, which form amorphous carbon on the catalyst. Therefore, without using the grid electrode, amorphous carbon was deposited on Co catalyst.
9:00 PM - B8.21
Electrical Double Layer Capacitor Formed with Carbon Nanotube.
R. Kuwabara 1 , Yoshiyuki Show 1
1 Dept. of Electrical and Electronic Engineering, Tokai University, Hiratsuka, Kanagawa Japan
Show AbstractThe electric double layer capacitor (EDLC) has advantage that it enables to charge and discharge in short time comparing to other energy strange devices. Acetylene black is generally added to the polarizable electrode, which is made of the activated carbon, to decrease the series resistance of the EDLC.In this study, carbon nanotube (CNT) was added in to the polarizable electrode of EDLC instead of the acetylene black as conducting material. The CNT-added polarizable electrode was applied to the coin type EDLCs.Activated carbon with a specific surface area of 2000m2/g was used as the base material for the polarizable electrode. The CNT was added into the polarizable electrode at various concentrations from 0 to 20%. The EDLC added with the acetylene black was also fabricated as a reference. All EDLCs showed a capacitance of approximately 20F/g. The capacitance was not decreased by a CNT addition of below 20%. No specific capacitance dependence relative to the CNT and acetylene black concentrations were observed up to 20%. The series resistance of the EDLCs fabricated without any conducting materials, such as CNTs, showed a high value of 40 Ohm. When the CNTs were added to the polarizable electrodes to act as a conducting material, the series resistance of the EDLC decreased with an increase in CNT concentration. An EDLC fabricated with a CNT concentration of 20% has a series resistance as low as 2 Ohm. This series resistance was lower than that of an EDLC fabricated with the same concentration of acetylene black by quarter. These results indicate that the CNT is suitable conducting material for the EDLC.
9:00 PM - B8.22
Experimental Study of Electron and Hole Mobilities in a Bilayer Graphene as a Function of Temperature and Oxygen Exposure.
Ive Silvestre 1 , Evandro Morais 1 , Alem-Mar Goncalves 1 , Leonardo Campos 1 , Rodrigo Lacerda 1
1 Physics, Universidade Federal de Minas Gerais, Belo Horizonte Brazil
Show AbstractGraphene is known as an all-surface 2D material, very sensitive to its supporting substrate and environment around it [1]. Due to this latter property, it has been used as an efficient gas sensor device [2]. In spite of these amazing characteristics, many studies has shown problems in electronic properties of graphene (and few layer graphene) when it is deposited on Si/SiO2 substrates. These problems can be explained by the spatial charge inhomogeneity in graphene, leading to formation of p-n junctions (hole-electron puddles) in this material [3]. These junctions are responsible by scattering processes in electronic transport, affecting the charge mobilities. In this work we study a bilayer graphene FET supported on a Si/SiO2 substrate, in a back-gate configuration. Cr-Au were used as source-drain contacts and produced by a typical optical lithography process. The sample was contacted in a chip holder, and inserted in a characterization furnace chamber, where the electrical properties could be evaluated with different temperatures and atmospheres. The initial value found for the resistance of the device was 2 Kohms, in accordance with the typical values in the literature. Our initial measures (Isd x Vgate) were performed at room temperature, under laboratory environment. In these initial conditions, the devices presented p-type behavior with Vg >> 0. Posterior electrical measurements were made in argon atmosphere (atmospheric pressure) as a function of the temperature. Our results show that with the increase of the temperature (300 to 500 K), the bilayer graphene exhibits a change towards an n-type character. This behavior could be explained by the fact that, in contact with the bilayer graphene, the SiO2 substrate is able to transfer electrons to it. The effect of the temperature would be to degas the bilayer, undoping it and revealing its intrinsically n-type character in contact with the substrate. These characteristics were also showed by H. E. Romero et. al [4], for a monolayer graphene. Another interesting result of our work was the significant decrease in hole mobility at high temperatures, which can be explained again by the charge inhomogeneity in bilayer graphene. The addition of different concentrations of oxygen in the chamber reversed this situation. With this last result we are able to understand the basic physics behind all these phenomena and to use our device as a promise application as a gas sensor. References: [1] M. Lafkioti et al.Nano Letters, 2010, 10, 1149-1153. [2] Y. Dan et al.Nano Letters, 2009, 9, 1472–1475. [3] J. Martin et al.Nature Physics, 2008, 4, 144-148. [4] H. E. Romero et al.ACS NANO, 2008, 2, 2037-2044.
9:00 PM - B8.23
Single Layer Graphene on Flexible Substrate Using Thermally-treated Exfoliation Technique.
Sung-Jin Kim 1 , Kyungsun Ryu 2 , John Renshaw 3
1 College of Electrical and Computer Engineering, Chungbuk National University, Cheongju Korea (the Republic of), 2 Department of Electrical Engineering, Columbia University, New York, New York, United States, 3 School of physics, Georgia Institute of Technology, New York, Georgia, United States
Show AbstractGraphene, sp2-bonded carbon atoms highly packed in a two-dimensional (2D) honeycomb lattice, has emerged a promising material because of its unique properties such as high mobility, high saturation velocity, and transparency for future electronic components.1-3 The excellent properties of single layer graphene (SLG) make it possible to fabricate various attractive devices, such as inorganic and organic field-effect transistors, gas sensors, and energy harvesting cells. In particular, the SLG has as ultrathin thickness as 0.5~1.5 nm which enables it to be applicable on a flexible substrate. In this talk, we will report single layer graphene on a flexible substrate fabricated by a thermally-treated exfoliation technique. Raman spectra analysis is used in this experiment and show that it can be applied to verify the number of graphene layers, especially on flexible substrates. This approach can be exploited to the development of next-generation graphene devices with a flexibility.This work was supported by the grant of the Korean Ministry of Education, Science and Technology(The Regional Core Research Program / Chungbuk BIT Research-Oriented University Consortium) [1] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov: Science 306 , 666 (2004). [2] C. Berger, Z. Song, X. Li, X. Wu, N. Brown, C. Naud, D. Mayou, T. Li, J. Hass, A. N. Marchenkov, E. H. Conrad, P. N. First, and W. A. de Heer: Science 312, 1191 (2006). [3] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim: Rev. Mod. Phys. 81, 109 (2009).
9:00 PM - B8.24
Surface Roughness Dependence of Graphene on Ion-beam Treated SiO2 Substrate.
Duk Hyun Lee 1 , Jin Sik Choi 1 , Ik-Su Byun 1 , Mi Jung Lee 1 , Seung-Woong Lee 1 , Bae-Ho Park 1
1 , Konkuk University, Seoul Korea (the Republic of)
Show AbstractGraphene, recently discovered two-dimensional structure of carbon, has attracted much interest due to its outstanding properties such as high mobility, current density, strength, thermal conductivity and transparency make it possible to apply logic applications, transparent electrodes and sensors, etc [1]. Since the discovery of graphene, many researches introduced their fabricating methods such as exfoliation, chemical vapor deposition (CVD) and epitaxial growth on SiC. Above all, the exfoliation method has been known as the best way to obtain the high quality graphene with simple method, in spite of their poor reproducibility and difficulty in making large area samples. It has been already reported that roughness of graphene surface has highly depends on roughness of surface roughness [2]. And it is possible that the roughness of graphene may influence the properties of graphene. In this study, we have fabricated and investigated mechanically exfoliated graphene with different surface roughness of SiO2 substrate. The graphene layer and substrate were characterized by optical microscopy, atomic force microscopy (AFM) and Raman spectroscopy. We show some results of roughness dependence of the surface of SiO2 buffer layer controlled by using ion-beam assisted reaction (IAR) treatment [3]. In order to confirm the roughness dependence of graphene, we observed surface of SiO2 substrate as well as graphene layers exfoliated on non-treated and IAR treated SiO2 substrates using AFM and Raman spectroscopy. Moreover we have made changes in chemical attraction between graphene and SiO2 substrate by changing the property of substrate from hydrophile to hydrophobic using IAR treatments. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST) (KRF-2008-314-C00111). [1] K.S. Novoselov, A.K. Geim, S.V. Morozow, D. Jiang, Y. Zhang, S.V. Dubonos, I.V. Grigorieva, and A.A. Firsov, Science 306, 666 (2004). [2] C.H. Lui, L. Liu, K.F. Mak, G.W. Flynn, and T.F. Heinz, Nature 462, 339 (2009). [3] D.Y. Byun, Y.J. Lee, S. B. Q. Tran, V.D. Nugyen, S.H. Kim, B.H. Park, S.H. Lee, N. Inamdar, and H.H. Bau, Appl. Phys. Lett. 92, 093507 (2008)
9:00 PM - B8.25
Electronic States Near Fermi Level of Chemically Derived Graphene Oxide Induced by Thermal Reduction.
Hisato Yamaguchi 1 , Hideaki Hozumi 2 , Toshiteru Kaga 2 , Goki Eda 3 , Cecilia Mattevi 3 , Shuichi Ogawa 2 , Takatoshi Yamada 4 , Yuji Takakuwa 2 , Manish Chhowalla 1 3
1 Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States, 2 Division of Materials Control, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan, 3 Materials, Imperial College London, London United Kingdom, 4 , National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Show AbstractResults from real-time ultraviolet photoelectron spectroscopy (UPS) measurements on chemically derived graphene oxide (GO) films upon thermal reduction will be presented. We observed an increase of π states at annealing temperatures of ~160 °C, consistent with an increase in the electrical conductivity. The decrease in σ states in correlation with the increase in π states suggests that the recovery of the conductivity at ~160 °C is due to the removal of oxygen. We also observed an increase in the density of states at the Fermi level at annealing temperatures above ~600 °C. Our recent study on the structural evolution of GO upon thermal reduction [1] along with theoretical studies on electronic structures of GO induced by different chemical structures [2,3] suggest that the observed increase can be due to interruption of the carbon hexagonal lattice induced by the formation of carbonyl (C=O) groups.[1] Akbar Bagri, Cecilia Mattevi, Muge Acik, Yves J. Chabal, Manish Chhowalla, and Vivek B. Shenoy "Structural evolution during the reduction of chemically derived graphene oxide" Nature Chemistry, advanced online (2010). doi:10.1038/nchem.686[2] T.O.Wehling, M.I.Katsnelson, and A.I.Lichtenstein "Impurities on graphene: Midgap state and migration barriers" Phys. Rev. B 80, 085428 (2009).[3] V.M.Pereria, F.Guinea, J.M.B.Lopes dos Santos, N.M.R.Peres, and A.H.Castro Neto "Disorder Induced Localized States in Graphene" Phys. Rev. Lett. 96, 036801 (2006).
9:00 PM - B8.26
Alternate Routes to Graphene Synthesis and Characterization.
Andrew Oyer 1 , Douglas Adamson 2 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, 2 Chemistry, University of Connecticut, Storrs, Connecticut, United States
Show AbstractGraphene, a single sheet of sp2-hybridized carbon, has quickly become a very interesting material due to its outstanding physical and conducting properties. However, an easy route to large-scale production of pristine graphene has yet to be found. Two methods of graphene production are currently being investigated including functionalized graphene, by reduction of graphene oxide, and chemical exfoliation of graphite. Functionalized graphene sheets are prepared by a two-step process of chemical oxidation and thermal reduction and exfoliation. Oxidation is achieved by a variation of the Hummers method. This process is dependant on many variables thus sheet properties vary from batch to batch, and even among sheets within a single batch. These properties, such as conductivity and band gap, arise from variations in sheet size, defects, and oxidation levels. We have found that these variations can be separated by their varying sedimentation rates. We will also present investigations utilizing various solvents as a method of producing single and few layer pristine graphene, by sonication of graphite and highly oriented pyrolytic graphite. Here we present the results of our separation of graphene oxide by various sedimentation rates as well as showing single and few sheet graphene by solvent exfoliation.
9:00 PM - B8.27
A Kinetic Monte Carlo Analysis for the Production of Singularly Tethered Nanoparticles.
Andrew Hilmer 1 , Nitish Nair 2 , Michael Strano 1
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, Massachusetts, United States, 2 Chemical and Biological Engineering, University of Colorado, Boulder, Colorado, United States
Show AbstractNanoparticles that possess a single tether to either another particle or a surface play an increasing important role in nanotechnology development, serving as a foundation for aggregation-based plasmonic sensors, self-assembled framework structures, and scanning probe tips. We explore the reaction conditions necessary to maximize singular tethering for several cases of homogeneously dispersed nanoparticles, including single-walled carbon nanotubes. In the limit of particles of monodisperse size and equal site reactivity, the number of tethers versus reaction conversion is statistically described by the well-known binomial distribution, with a variance that is minimal for the single tether case. However, solutions of nanoparticles often deviate from this ideal, and reaction events can introduce steric hindrance to neighboring sites or alter particle electronic properties, both of which can affect further reactivity. In order to study these cases we utilize the electron transfer reactions of single-walled carbon nanotubes. We find that the distribution in the number of monofunctional tubes, as a function of conversion, is largely dependent on the distribution of nanotube rate constants, and therefore tube chiralities, in the initial solution. We then look at the implications of this result on the metallic-semiconductor separation of carbon nanotubes using electron-transfer chemistries.
9:00 PM - B8.28
Periodically Modified Graphene with Holes and Nanotubes: A First-principles Study.
Susumu Saito 1 , Masahiro Sakurai 1
1 Department of Physics, Tokyo Institute of Technology, Tokyo Japan
Show AbstractWe study the electronic structure and energetics of periodically modified graphene with carbon nanotubes in the framework of the density-functional theory (DFT). It has been revealed in our previous tight-binding and density-functional study that the monolayer/bilayer graphene sheets modified periodically with carbon-nanotube arrays possess electronic properties which are also modified from their original metallic properties. Although the carbon-nanotube part used, the so-called armchair (6,6) tube, as well as graphene is metallic, these periodically modified graphene sheets have been reported to be mostly semiconducting [1]. In the present work, we further study systematically the energetics as well as the electronic properties of these graphene-based new and important semiconductor materials using the local-density approximation in the framework of DFT. Monolayer graphene modified with open-end nanotubes and bilayer graphene with connecting nanotubes are found to have mostly the direct fundamental gap, while graphene modified with closed-end nanotubes (nanotubes capped with half-fullerene) is found to be indirect-gap semiconductor. We clarify the periodicity dependence of the electronic properties of these various modified graphene systems, and also that of the energetics based on the DFT electronic structure and total energy, respectively. In addition, graphene monolayer with hydrogen-terminated carbon nanotubes is studied as well. [1] "Geometric and Electronic Structure of New Carbon-Network Materials: Nanotube Array on Graphite Sheet" T. Matusmoto and S. Saito, J. Phys. Soc. Japan Vol.71 (2002) 2765.
9:00 PM - B8.3
Large Area Graphene on Polymer Films for Transparent and Flexible Field Emission Device.
Ved Verma 1 , Santanu Das 1 , Indranil Lahiri 1 , Wonbong Choi 1
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States
Show AbstractWe present large area graphene growth and fabrication of its flexible and transparent electrode. Graphene film was grown on Cu foil by thermal chemical vapor deposition and transferred to polyethylene terephthalate (PET) by using hot press lamination and chemical etching process. The graphene/PET film shows high quality, flexible transparent conductive structure with unique electrical-mechanical properties; ~88.80 % light transmittance and ~1.1742 kΩ/sq sheet resistance. Application of graphene/PET film in fully-transparent and flexible field emission devices has been demonstrated. Field emission device was fabricated by hybrid structure of carbon nanotubes-graphene electron emitter and graphene screen. This field emission device shows a low turn on field ~2.0 V/μm and high field enhancement factor ~1023.
9:00 PM - B8.4
Transparent Reduced Graphene Electrodes for Electroactive Polymer Actuators.
Chong Min Koo 1
1 Hybrid Materials Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractTransparent and compliant graphene electrodes were fabricated in order to apply for electroactive polymer actuators. The graphene electrodes were coated on both sides of electroactive polymers by using spray coater. Graphene coating solution was consisting of graphene, polymer binder, and volatile solvent. The graphene was prepared by chemical oxidation and following chemical reduction of natural graphite. The polymer binder was UV crosslinkable. Graphene electrodes were characterized by SEM, AFM, GIWAXS, UV spectroscopy, and electrical conductivity measurements. The electrodes with the thickness of 100 nm had the transmittance of 80% and the surface resistance of 105ohm. The resulting polymer actuators with graphene electrodes had larger electromechanical performance than the actuator with conventional electrodes.
9:00 PM - B8.5
Label-free Electrochemical Biosensor Based on Graphene/Ionic Liquid Nanocomposite for the Detection of Organophosphate Pesticides.
Tae Jung Park 1 , Min Ho Yang 2 , Bong Gill Choi 2 , Nam Su Heo 1 , Seok Jae Lee 3 , Won Hi Hong 2 , Sang Yup Lee 2 1 4
1 BioProcess Engineering Research Center, KAIST, Daejeon Korea (the Republic of), 2 Department of Chemical & Biomolecuar Engineering, KAIST, Daejeon Korea (the Republic of), 3 NEMS-Bio Team, National Nanofab Center, Daejeon Korea (the Republic of), 4 Department of Bio & Brain Engineering, Department of Biological Sciences, and Bioinformatics Research Center, KAIST, Daejeon Korea (the Republic of)
Show AbstractOrganophosphorus (OP) chemicals are among the most toxic substances known and are commonly used as pesticides in agriculture and have potential use as chemical warfare agents. In order to detect OP compounds, electrochemical biosensors utilizing carbon nanotubes (CNTs) have been widely investigated due to their high accessible surface area, electronic conductivity and capacity to immobilize enzymes. Although CNTs are attractive materials for application in electrochemical devices, it is difficult to process into applications due to its tangled bundles and high cost. The recent discovery of graphene has triggered enormous interest both in academic study and applications, due to its physicochemical and electrochemical properties. Single layer of carbon atoms in graphene provides a more affordable alternative 2D lattice to CNT in applications of field-effect transistors, high sensitive sensors, microelectrical devices and nanocomposites.Here, we present the fabrication and characterization of bioelectrochemical sensor for OP chemicals based on a reduced graphene oxide (RGO)/ionic liquid (IL) composite electrode. Graphite oxide was synthesized from graphite by a modified Hummers method and then, reduced graphite oxide was obtained by chemical reduction of hydrazine solution. A total of 1 mg of RGO was added to 1 mL of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]). A volume of 5 μL of the resulting reduced graphite oxide coated with [bmim][PF6] was dropped onto the gold electrode and dried under room temperature. To immobilize the enzyme on the surface of the RGO/IL-modified electrode, the composite electrode was immersed into phosphate-buffered saline (PBS) containing 5 mg/mL of organophosphorus hydrolase (OPH) for 12 h.Transmission electron microscope was used to investigate the morphology of RGO and RGO/IL, which coated with IL, illustrating the flakelike shapes. Electrochemical workstation was used to collect electrochemical properties of RGO/IL modified gold electrodes. The peak-to-peak potential separation and formal potential of RGO/IL composite electrode was reduced relative to those of the bare gold electrode, which were attributed to the enhanced electron transfer kinetics. The quasi-reversible process of electrochemical reaction on the composite electrode was verified by the results of cyclic voltammograms following the scan rates of the OPH/RGO/IL gold electrode. After immobilizing the OPH on the RGO/IL surface, the influence of OPH resulting in resistance increased the peak-to-peak potential separation of OPH/RGO/IL. The electrocatalytic activity of OPH immobilized on the electrode surface was investigated by detecting the hydrolysis product of paraoxon in a range of 2–20 μM at chronoamperometry measurement. The corresponding calibration plots show the high sensitivity.
9:00 PM - B8.6
Facile Route to Control the Band Structure of the Nitrogen-doped Graphene via Plasma.
Hyungmo Jeong 1 , Weon Ho Shin 1 , Jeung Ku Kang 1
1 MSE, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show AbstractWe develop a method that allows control the band structure of chemical oxidized grapehen by nitrogen plasma. In Raman spectra and X-ray photoelectron spectra, nitrogen plasma give raise the nitrogen doping of the graphene. Core-level spectra of the nitrogen treated graphene show the different chemical reaction and boding configurations when each different plasma condition was applied on surface of the graphene. In addition, by using the ultraviolet photoelectron spectroscopy, we expect that the treatment of various conditions of nitrogen plasma cause a change of the band structure. The measurements revealed that nitrogen plasma treatment could control the band structure of the nitrogen doped graphene by alternation of the nitrogen binding configurations.
9:00 PM - B8.7
Highly Conductive and Transparent Single-walled Carbon Nanotube Thin Films Fabricated via Gel Coating and Their Application in Optoelectronic Devices.
Xiaoguang Mei 1 , Jianyong Ouyang 1
1 Materials Science and Engineering, National University of Singapore, Singapore Singapore
Show AbstractThin films of single-walled carbon nanotubes (SWCNTs) are promising substitutes for indium tin oxide (ITO) in the application of transparent conducting electrode due to their excellent electrical, optical and mechanical properties. Most of the traditional methods in fabricating SWCNT thin films are based on solution processing, in which SWCNTs must be firstly dispersed into aqueous solutions or organic solvents. Those methods are not applicable for large-scale fabrication due to quite limited dispersion of SWCNTs. Here, we report a gel-coating technique to fabricate transparent and conductive SWCNT thin films. SWCNTs were first dispersed into organic compounds to form a composite gel. The gels were uniformly coated the onto glass substrates and subsequently sintered at higher temperature in ambient environment to form a pure SWCNT thin film. The resulted films can be further transferred onto various flexible substrates Compared to the traditional methods, the novel gel-coating technique is more efficient and convenient. SWCNT films prepared in this method exhibited very high transmittance to sheet resistance (T/R) ratio and can be used as flexible electrodes in a wide range of applications. . The SWCNTs can be processed in a large scale in this method. Their application in optoelectronic devices like polymer photovoltaic cells will be presented as well.
9:00 PM - B8.8
Electrical and Optical Properties of Full Carbon Based Transistors.
Jinsup Lee 1 , Seong Jun Kang 3 , Seokwoo Jeon 1 2
1 Material science and Engineering, Korea Advanced Institue of Science and Technology (KAIST), Daejeon Korea (the Republic of), 3 Advanced Materials Engineering for Information and Electronics, College of Engineering, Kyung Hee University, Yongin Korea (the Republic of), 2 KAIST Institue for Nanocentury, Korea Advanced Institue of Science and Technology (KAIST), Daejeon Korea (the Republic of)
Show Abstract Thin film transistors made of carbon nanotube (CNT) have been an active field of research because of its supreme electronic mobility and flexibility on plastic substrates. However, the random, in-plane growth of CNT and the contact resistance between CNT and metal electrodes make it difficult to achieve the true mobility of CNT. In this research, we propose a new approach by combining horizontally well aligned single-walled carbon nanotubes, which is grown by surface assisted growth, as active elements and dense network of randomly oriented SWNTs as electrodes. Both of the active channel and electrode are grown at the same time by chemical vapor deposition (CVD) method with Fe catalyst deposited on ST-cut Quartz wafer. Improved device properties under flexible environment will be discussed. This device may show better electrical properties and transmittance due to its CNT-CNT contacts and metal free electrode architecture.
9:00 PM - B8.9
The Field Emission from Multiwall Carbon Nanotubes Grown on Copper Foam.
Ajay Kumar 1 , Indranil Lahiri 1 , Wonbong Choi 1
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States
Show AbstractAfter the discovery of CNTs by Iijima (1991), immense progress has been made towards many applications - especially in the field emission devices. Our group has studied field emission response of CNTs, grown on variety of substrates. In the present study, we demonstrate application of copper foam structure as the substrate for CNT growth, to get the advantage of three dimensionality and hence, larger surface area as compared to planar 2D structures. This 3D structure of Copper foam is also expected to offer better protection to the CNTs against arcing and thus, long term stability of the emitter. We have synthesized MWCNT on copper foam using thin film Ni catalyst along with a Ti diffusion barrier layer and studied the effect of the catalyst layer thickness on the CNTs morphology and the field emission response under DC and AC bias. The MWCNTs grown of copper foam shows the excellent field emission response, in terms of low turn–on-field, long time stability, and high field enhancement factor in the range of 4000 to 6000. The morphology of CNTs has been characterized with SEM and Raman spectroscopy.
Symposium Organizers
Robert R. Keller National Institute of Standards and Technology
W. Jud Ready Georgia Institute of Technology
Meyya Meyyappan NASA Ames Research Center
Manish Chhowalla Imperial College London
B9: Graphene Growth and Characterization
Session Chairs
Thursday AM, December 02, 2010
Room 310 (Hynes)
9:30 AM - **B9.1
Epitaxial Graphene: Designing a New Electronic Material.
Walt de Heer 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractSince 2001 the Georgia Tech epitaxial graphene research team and its collaborators have developed the new field of epitaxial graphene electronics. The current status of epitaxial graphene research will be presented, including the production methods and recent results from various characterization investigations. Methods have been developed to grow monolalyer and multilayer epitaxial graphene (MEG) on the C-face of hexagonal silicon carbide with of up to 100 graphene sheets and its extraordinary transport properties have been demonstrated, including the quantum Hall effect. The monolayer films have high mobilities and exhibit the half integer quantum Hall effect. The Georgia Tech Confinement Controlled Sublimation method to produce uniform epitaxial graphene layers will be explained.Surprisingly, the properties of MEG are closely related to monolayer graphene rather than graphite, as a result of an unusual rotational stacking of the graphene layers that causes the graphene sheets to electronically decouple. Consequently the electronic band structure of MEG is composed of Dirac cones. The charge carries are chiral and exhibit a non-trivial Berry 's phase. Weak anti-localization and quantum confinement has been demonstrated. Landau level spectroscopy further exhibits record-breaking room temperature mobilities and well resolved Landau levels below 1 T, indicating extremely low carrier densities and good homogeneity of the material. Efforts towards large-scale electronic device patterning will be reviewed.
10:00 AM - B9.2
Electronic Transport Properties of Top-gated Monolayer and Bilayer Graphene Devices on SiC.
Shinichi Tanabe 1 , Yoshiaki Sekine 1 , Hiroyuki Kageshima 1 , Masao Nagase 1 , Hiroki Hibino 1
1 , NTT Basic Research Laboratories, Atsugi, Kanagawa, Japan
Show AbstractEpitaxial growth of graphene on the Si face of SiC by thermal decomposition has been shown to yield large-scale monolayer graphene and bilayer graphene, which may have industrial applications. However, their electronic transport properties, especially under application of gate voltage, have not been fully investigated. Here, we report the epitaxial growth of large-area monolayer and bilayer graphene by thermal decomposition of SiC and compare their electronic transport properties in gated conditions. In monolayer graphene, carrier mobility of 11,000 cm2 V-1 s-1 was obtained by controlling the carrier density, and the half-integer quantum Hall effect under gated environment were observed. For bilayer graphene, clear signatures of band gap opening were seen. Monolayer graphene and bilayer graphene were grown on 4H-SiC(0001). The monolayer graphene was grown at a substrate temperature of around 1800 °C and Ar pressure of less than 100 Torr, while the bilayer graphene was grown at a substrate temperature of around 1270 °C in an UHV environment. The electronic transport properties were investigated in top-gated Hall bar devices. In monolayer graphene at 2 K, the carrier mobility was 3,500 cm2 V-1 s-1 at the carrier density of 8 × 1011 cm-2. It increased as we decreased the carrier density and the carrier mobility reached 11,000 cm2 V-1 s-1 at 3 × 1010 cm-2. Furthermore, we observed clear plateaus in the Hall resistance and vanishing longitudinal resistance as a function of magnetic field, which are evidences of quantum Hall states. The plateaus were quantized to values corresponding to the filling factor of half integer multiples of 4. We were also able to access different filling factors by controlling the carrier density in a fixed magnetic field. In bilayer graphene, the carrier mobility increased as we increased the carrier density and it was at most 800 cm2 V-1 s-1 at 2 K. The quantum Hall effect has not yet been observed. However, from the transistor characteristics, large on/off ratios and strong temperature dependence of the resistivity at the charge neutrality point were observed, indicating band gap opening in bilayer graphene. The monolayer and bilayer graphene devices show different electronic transport properties, which reflect the electronic structures of monolayer graphene and bilayer graphene.
10:15 AM - B9.3
Free-charge Carrier Properties of Epitaxial Graphene Grown on SiC Investigated by THz and Infrared Ellipsometry and THz Optical-hall Effect.
Tino Hofmann 1 , Alex Boosalis 1 , J. Tedesco 2 , R. Myers-Ward 2 , P. Campbell 2 , C. Eddy 2 , D. Gaskill 2 , V. Shields 3 , S. Shivaraman 3 , M. Spencer 3 , W. Schaff 3 , M. Schubert 1
1 , University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 , U.S. Naval Research Laboratory, Washington, Washington, United States, 3 , Cornell University, Ithaca, New York, United States
Show AbstractThe free-charge carrier transport in graphene has intriguing properties which may lead to seminal advances in both basic and applied research enabling terahertz frequency, Angstrom scale transistors. While contemporary CMOS technology is approaching its scaling limits, the exploitation of epitaxial graphene - if well controlled and understood - could achieve a substantial part of what is required to supplant CMOS technology. We have grown high quality graphene on Si- and C-faces of silicon carbide substrates under various conditions. We report on terahertz (THz), Far-infrared (FIR) and Infrared (IR) ellipsometry and THz-IR Optical Hall-effect (generalized ellipsometry in magnetic fields) investigations of the free-charge carrier properties in epitaxial graphene samples. Furthermore, new developments on the tunable-wavelength frequency-domain THz ellipsometry instrumentation with and without external magnetic fields that involve backward wave oscillator sources will be described.Our ellipsometric data allows the identification of multiple, parallel sheet carrier densities within the single-to-few monolayer thick graphene layers, and which crucially depend on substrate orientation and growth condition. Analysis of the multiple two-dimensional carrier sheet densities reveals their extreme yet strongly varying mobility, effective mass, and density parameters as well as the vertical carrier sheet profile. Our findings reveal striking influences of the substrate. We discuss the physical mechanisms of the substrate that influence the free charge carrier properties in epitaxial graphene such as surface polarity, dopant incorporation, surface roughness, and defects.
10:30 AM - B9.4
Graphene Production from Graphite Oxide Using Urea as Expansion Reduction Agent.
Claudia Luhrs 1 , Stephen Wakeland 1 , Ricardo Martinez 1
1 Mechanical Engineering, University of New Mexico, Albuquerque, New Mexico, United States
Show AbstractGraphene sheets were prepared from graphite oxide using a simple reduction process at moderate temperatures. The graphene generation protocol involves the use of an intimate mixture of graphite oxide (GO) with an expansion-reduction agent, such as urea, that decomposes upon heating to release reducing gases. The GO-urea mixture is then heated in an inert gas environment for a very short time to a moderate temperature (ca. 600 0C). Reaction temperature selection should be consistent with the decomposition temperature of the expansion-reduction agent. Upon cooling, graphene can readily be collected as the solid byproduct. Graphene samples were characterized by XRD, TEM, EELS, SEM, Raman Spectroscopy and the GO and urea mixtures decomposition-reduction process studied by TGA/DSC analysis. Potential uses for the products include electrode materials for supercapacitors and batteries among others.
10:45 AM - B9.5
The Influence of Growth Parameters on Properties of CVD Grown Graphene.
HoKwon Kim 1 , Cecilia Mattevi 1 , Manish Chhowalla 1 2
1 Department of Materials, Imperial College London, London United Kingdom, 2 Department of Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractThe chemical vapor deposition (CVD) growth of graphene on transition metal catalysts has been demonstrated to be one of the most promising synthesis routes toward large-scale graphene based applications [1, 2]. Using polycrystalline Cu as the catalyst is particularly appealing due to the low cost, self-limited growth of a continuous monolayer over large areas, and ability to transfer as-grown graphene onto a variety of substrates. However, mobility and conductivity values of CVD grown graphene are so far less than those of mechanically exfoliated graphene and the limiting factors to the electronic properties are not well understood. To this end, we have studied effects of growth parameters such as growth pressure, temperature, gas composition, and type of the Cu substrate on the materials and electronic quality of the graphene. By investigating the thickness, roughness, crystal structure, and stacking order through scanning electron microscopy, electron diffraction, atomic force microscopy, and high-resolution Raman mapping as a function of growth parameters, the optimal conditions for thickness controlled uniform deposition of graphene have been determined. The growth pressure, hydrocarbon concentration, and surface morphology of the Cu substrate have been shown to influence the thickness of graphene film. Furthermore, the material characteristics of graphene films produced from different growth conditions have been correlated to their electrical properties to provide insights into the factors that limit the electronic quality of CVD grown graphene. [1] K. S. Kim, Y. Zhao, H. Jang, S. Y. Lee, J. M. Kim, K. S. Kim, J. H. Ahn, P. Kim, J. Y. Choi and B. H. Hong, Nature 457, 706 (2009).[2] X. Li, W. Cai, J. An, S. Kim, J. Nah, D. Yang, R. Piner, A. Velamakanni, I. Jung, E. Tutuc, S. K. Banerjee, L. Colombo, and R. S. Ruoff, Science 324, 1312 (2009).
11:30 AM - B9.6
Low Temperature Synthesis of Highly Conductive Chemically Derived Graphene from Mild Oxidation, Intercalation, and Exfoliation of Graphite.
Goki Eda 1 , James Ball 2 , Cecilia Mattevi 1 , Luca Artiglia 3 , Gaetano Granozzi 3 , Thomas Anthopoulos 2 , Manish Chhowalla 1
1 Materials, Imperial College London, London United Kingdom, 2 Physics, Imperial College London, London United Kingdom, 3 Chemical Science, University of Padova, London Italy
Show AbstractIt is well established that structural defects arising from incomplete reduction of graphene oxide (GO) severely limit the carrier transport in the reduced material [1]. Currently, GO must be reduced at high temperatures (~ 1000 oC) to minimize residual defects in the reduced material and to optimize its electrical properties. Here, we report synthesis, deposition, and properties of partially oxidized graphene (POG) that can be reduced efficiently at low temperatures (< 300 oC) to yield highly conducting thin films. We show that mild oxidation of graphite followed by intercalation with tetrabutylammonium hydroxide (TBA) leads to a highly stable colloidal dispersion of POG. These POG sheets can be readily deposited uniformly over large areas on arbitrary substrates based on Langmuir-Blodgett assembly. We demonstrate that POG reduced at low temperatures can achieve a field effect mobility of ~ 18 cm2/Vs. We attribute the better electronic properties to the lower initial oxygen content in POG (13 % as opposed to 30 % in fully oxidized GO) and suppression of defect formation.[1] G. Eda and M. Chhowalla, Adv. Mater. 22, 2392 (2010).
11:45 AM - B9.7
Synthesis of Ethanol Soluble Few-layer Graphene Nanosheets for Flexible and Transparent Conducting Composite Films.
Nguyen Dung 1 , Chueh Yu-Lun 1 , Tai Nyan-Hwa 1
1 Materials Science & Engineering, National Tsing-Hua University, Hsinchu Taiwan
Show AbstractMore recently, few-layer graphene nanosheets (FLGs) are considered as a class of graphene materials [1], namely 2D graphitic crystals, with which the electronic property can be controlled systematically with the number of graphene layers. For the large scale production of graphene, chemical routes are the most promising approach with low cost. The aqueous phase exfoliation of graphite oxide (GO) by chemical solvents via reduction processes is the common way [2]. However, reduction of GO involves reactions with strong reducing agents like hydrazine or dimethyl hydrazine, which are highly toxic and dangerously unstable [2, 3]. Therefore, a development via exfoliation of graphite or mildly oxidized graphite (e.g. expanded graphite) into graphene sheets by environment/user-friendly available solvents is imperative. In this regard, FLGs were prepared from expanded graphite by means of refluxing in nitric acid, followed by ultra-sonicating in ammonia-ethanol solution and finally dispersing in ethanol. Raman spectroscope was used to characterize the crystal quality of FLGs. High Resolution Transmission Electron Microscope (HRTEM) and Atomic Force Microscope (AFM) studies reveal that the thickness of FLG is in the range of 2-3 nm, corresponding to the number of graphene layers around 6-9. The optical properties and bending/cycling test of FLGs as transparent conducting electrodes were characterized. The FLGs/Nafion(conductive polymer)/PET films have sheet resistances of 9.70 kΩ/sq at the transmittances of ~ 74 % (at 550 nm) while the Nafion/PET film has sheet resistance of 128 kΩ/sq at transmittance of ~90 %. For bending/cycling test, almost no change in resistance was demonstrated when the film was bent at the angle up to 145o and below 10 % deviation in resistance was found after 100 bending cycles. The results exhibit extremely mechanical flexibility for the application in flexible electronics.References:[1] A. K. Geim and K. S. Novoselov, Nature Mater. 6, 183 (2007). [2] S. Stankovich, D. A. Dikin, R. D. Piner, K. A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S. B. T. Nguyen, R. S. Ruoff , Carbon 45 (7), 1558 (2007).[3] S. Stankovich, D. A. Dikin, G. H. B. Dommett, K. M. Kohlhaas, E. J. Zimney, E. A. Stach, R. D. Piner, S. B. T. Nguyen and R. S. Ruoff, Nature 442, 282 (2006).
12:00 PM - B9.8
Large-area Synthesis of High-quality and Uniform Graphene by Chemical Vapor Deposition and Its Electrical Properties.
Kenjiro Hayashi 1 2 , Shintaro Sato 1 2 , Katsunori Yagi 1 , Daiyu Kondo 1 , Naoki Harada 1 2 , Naoki Yokoyama 1 2
1 Nanoelectronics Research Center, Fujitsu Labs Ltd., Atsugi, Kanagawa Japan, 2 Green Nanoelectronics Collaborative Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki Japan
Show AbstractWe successfully synthesized high-quality graphene on a Cu catalyst film supported on SiO2/Si wafers as large as 200 mm in diameter by chemical vapor deposition, and field effect transistors (FETs) were fabricated using the graphene as a channel. Graphene was synthesized on a Cu, Ni, or Fe film deposited on a SiO2/Si wafer using C2H4 or C2H4 diluted by Ar and H2 as the source gas. The total pressure was kept at about 1kPa. The partial pressure of the hydrocarbon gas was much lower (< 1%) than those described in previous reports [1, 2]. The growth temperatures ranged from 800 to 1000 °C. By optimizing the growth conditions, we were able to obtain single-layer or few-layer graphene all over the wafer, which was confirmed by cross-sectional transmission electron microscopy. In its Raman spectra, the G band is clearly seen and the defect-related D band is hardly distinguishable at any position on the wafer, indicating that the quality of graphene is good and uniform. In addition, we found that the intensity ratio I(D)/I(G) was sensitive to the concentration of hydrocarbon gas under our growth condition. The synthesized graphene was then patterned in the shape of a transistor channel by conventional photolithography techniques. The drain current of the fabricated transistors was successfully modulated by the gate voltage, and exhibited ambipolar behavior. Furthermore, the field effect mobility obtained was much higher than that reported in our previous study [3].This research is partially supported by the Japan Society for the Promotion of Science (JSPS) through its “Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program).”[1] Li et al., Science 324, 1312 (2009)[2] Levendorf et al., Nano Lett., 9, 4479 (2009)[3] Kondo et al., Appl. Phys. Express, 3, 025102 (2010)
12:15 PM - B9.9
Synthesis of Hybrid Two Dimensional Films of Hexagonal Boron Nitride and Graphene by Atmospheric Pressure Chemical Vapor Deposition.
Ki Kang Kim 1 , Allen Long Hsu 1 , Yumeng Shi 1 4 , Xiaoting Jia 2 , Mario Hofmann 1 , Alfonso Reina 2 , Mildred S. Dresselhaus 1 3 , Tomas Palacios 1 , Jing Kong 1
1 Department of Electrical Engineering and Computer Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 School of Material Science and Engineering, Nanyang Technological University, Singapore, 639798, Singapore, 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractWe report the synthesis of hexagonal boron nitride (h-BN) on graphene by atmospheric pressure chemical vapor deposition. After the growth of graphene on copper foil, h-BN was synthesized on graphene under boron and nitrogen source at 300 ~ 1000 oC. The films can be transferred on arbitrary substrate using poly(methyl methacrylate). The crystallinity and roughness of h-BN film were strongly dependent on the growth rate which was related to the concentration of boron and nitrogen source and the reaction temperature. The thickness of h-BN could be controlled by the reaction time and was varied in the range of 3 ~ 50 nm. Top-gated field effect transistors (FETs) have been fabricated on the h-BN/graphene hybrid film. The h-BN was used as gate dielectric due to its relatively high dielectric constant of 5, as calculated from capacitance measurements. We believed that our hybrid film allows unprecedented flexibility for new electronic devices such as flexible FET and high frequency electronics.
B10: Graphene Growth and Characterization II
Session Chairs
Thursday PM, December 02, 2010
Room 310 (Hynes)
2:30 PM - B10.1
Tuning Sub-micron Graphene Structures on Dielectric Surfaces by Controlled De-wetting of Metal Catalyst Layers.
Ariel Ismach 1 , Zhongkui Tan 1 , Yuegang Zhang 1
1 , Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractDirect deposition of graphene on various dielectric substrates is demonstrated using a single-step chemical vapor deposition process [1]. Single and few-layer graphene is formed through surface catalytic decomposition of hydrocarbon precursors on thin copper films pre-deposited on dielectric substrates. The copper films de-wet and evaporate during or immediately after graphene growth, resulting in graphene deposition directly on bare dielectric substrates. The graphene coverage can be tuned by controlling the metal de-wetting, which is dictated by the metal-surface interaction, thickness and heating time. The in-situ formation of continuous graphene layers or submicron graphene structures, such as dots and stripes, is demonstrated by controlling the above parameters. Scanning Raman imaging and spectroscopy, scanning electron microscopy, and atomic force microscopy confirm the presence of continuous graphene layers on tens of micron square metal-free areas. The electrical properties of the different graphene structures will be discussed. The revealed growth mechanism opens new opportunities for the large-scale direct deposition of graphene films and structures on dielectric materials.[1] Ismach et al. Nano Lett., 2010, 10 (5), pp 1542–1548
2:45 PM - B10.2
Electrostatic Transfer of Epitaxial Graphene to Glass.
Laura Biedermann 1 , Thomas Beechem 1 , Anthony Ross 1 , Wei Pan 1 , Taisuke Ohta 1 , Stephen Howell 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractWe report on a scalable electrostatic process to transfer epitaxial graphene to arbitrary glass substrates, including Pyrex and Zerodur. This transfer process could enable wafer-level integration of graphene with structured and electronically-active substrates such as MEMS and CMOS. We will describe the electrostatic transfer method and will compare the properties of the transferred graphene with nominally-equivalent “as-grown” epitaxial graphene on SiC. The electronic properties of the graphene will be measured using magnetoresistive, four-probe, and graphene field effect transistor geometries [1]. To begin, high-quality epitaxial graphene (mobility 14,000 cm2/Vs and domains >100 μm2) is grown on SiC in an argon-mediated environment [2,3]. The electrostatic transfer then takes place through the application of a large electric field between the donor graphene sample (anode) and the heated acceptor glass substrate (cathode). Using this electrostatic technique, both patterned few-layer graphene from SiC(000-1) and chip-scale monolayer graphene from SiC(0001) are transferred to Pyrex and Zerodur substrates. Subsequent examination of the transferred graphene by Raman spectroscopy confirms that the graphene can be transferred without inducing defects. Furthermore, the strain inherent in epitaxial graphene on SiC(0001) is found to be partially relaxed after the transfer to the glass substrates.A portion of this work was performed at CINT at Sandia National Laboratory and Los Alamos National Laboratory (Contract No. DE-AC04-94AL85000). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.[1] W. Pan et al. submitted to APL (2010).[2] K. Emtsev et al. Nature Mat. 8, 203 (2009).[3] T. Ohta et al., Phys. Rev. B 81, 121411(R) (2010).
3:00 PM - B10.3
Temperature-dependent Growth of Monolayer Graphene on Epitaxial Cu Film.
Baoshan Hu 1 , Hiroki Ago 1 2 3 , Yoshito Ito 2 , Masaharu Tsuji 1 2 , Noriaki Mizuta 2 , Seigi Mizuno 2
1 Inst. Mater. Chem. Eng., Kyushu University, Fukuoka Japan, 2 Grad. Schl. Eng. Sci., Kyushu University, Fukuoka Japan, 3 , PRESTO-JST, Kawasaki Japan
Show AbstractThe large-area monolayer graphene was synthesized on epitaxial Cu film under ambient pressure in a temperature range of 900-1000 degree centigrade and could be transferred onto insulating substrates for electric applications. Results show that the crystal quality of epitaxial Cu film was essential for growth of monolayer graphene and greatly influenced by underlying substrates, H2-annealing conditions and cooling rate. After chemical vapor deposition (CVD), some terraces were observed by AFM to occur on the surface of graphene/Cu, indicating the evolvement of Cu film by H2-annealing and CVD processes. Raman measurements confirm that the fraction of monolayer graphene was close to 100%. We also found that the thickness of graphene film was dependent on CVD time at 900 degree centigrade, but irrelevant to the CVD time at 1000 degree centigrade. In addition, LEED measurements show that graphene films grown at 900 and 1000 degree centigrade had the different crystal orientations against the underlying single-crystal Cu(111) substrate. Thus, a temperature-dependent growth mechanism of monolayer graphene on epitaxial Cu metal is proposed.
3:15 PM - B10.4
Growth of Uniform Wafer-size Graphene on Electropolished Copper.
Zhengtang Luo 1 , Ye Lu 1 , Daniel Singer 1 , Matthew Berck 1 , Luke Somers 1 , Brett Goldsmith 1 , A.T. Charlie Johnson 1
1 Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractWe demonstrate a method to grow uniform, large-size graphene on electropolished Cu foil using Chemical Vapor Deposition at atmospheric pressure and then to transfer the graphene to other substrates. Surface morphology of the catalytic Cu substrate and the concentration of carbon feedstock gas were found to be crucial factors in determining the homogeneity and electronic transport properties of the final graphene film. The use of a flat metal surface and extremely low methane concentration enables the growth of graphene samples with single layer content exceeding 95%. Field effect transistors fabricated from CVD graphene made with the optimized process have room temperature hole mobilities that are a factor of 2-5 larger than those measured for samples grown on as-purchased Cu foil with larger methane concentration. A kinetic model is proposed to explain the observed dependence of graphene growth on catalyst surface roughness and carbon source concentration.This work was supported by the Army Research Office through grant # W911NF-07-1-0399 and by the Nano/Bio Interface Center through the National Science Foundation NSEC DMR08-32802.
3:30 PM - B10.5
Defect Engineering for Graphene Tunable Doping.
Henry Medina 1 , Yung-Chang Lin 1 , Po-Wen Chiu 1
1 Department of Electrical Engineering, National Tsing Hua University, Hsinchu Taiwan
Show AbstractHere I will describe a tunable doping approach which makes use of lattice defects as anchor groups for covalent functionalization on graphene. Lattice defects that can be monitored by seeing the intensity ratio of D to G mode in Raman spectrum are generated by exposing graphene to short Ar plasma pulses, followed with gas-phase doping. Resembling the ion implantation which provides a very precise stoichiometry to introduce a specific dose or number of dopant atoms into silicon, the controllable creation of lattice defects on graphene by plasma exposure also makes the precise doping feasible. This technique provides air-stable doping functionalities on graphene and, importantly, the doping concentration can be progressively varied with the increase of doping cycles and traced by Raman technique. The lattice damage is simultaneously restored in the gas-phase doping at high temperature. It can be either N-type or P-type doping, depending on the nitrogen-containing precursors. The doping mechanisms are discussed in the framework of density functional theory.
3:45 PM - B10.6
Patterning Graphene Nanoribbons and Nanomeshes through the Self-assembled Templates.
Alexander Sinitskii 1 , James Tour 1
1 Chemistry, Rice University, Houston, Texas, United States
Show AbstractRecently, there has been considerable interest in graphene nanostructures with feature sizes less than 10 nm since they were theoretically and experimentally shown to have electronic band gaps large enough for room temperature transistor operation. Such graphene nanostructures include quantum dots, nanoribbons (GNRs) and nanomeshes (GNMs). Since patterning with sub-10-nm resolution by electron beam lithography is still quite challenging and requires state-of-the-art experimental facilities, alternative techniques for making graphene nanostructures are being developed. Here we demonstrate that colloidal particles, metal oxide nanowires and assemblies of thereof can serve as easily accessible and inexpensive masks for patterning GNRs and GNMs.In this work we have developed a new approach to making GNMs, which were recently demonstrated to be promising structures for the electronics applications. Our approach is based on patterning graphene using self-assembled monolayers of monodisperse colloidal microspheres. In addition to its simplicity and versatility, this approach permits the fabrication of GNMs with different periodicities, ranging from 100 nm to several μm, which were inaccessible via previously reported patterning techniques. Also, we demonstrate that the new approach enables independent tuning of the geometric characteristics of the GNMs, which is important for producing graphene nanostructures with variable electronic properties.In order to produce GNMs using colloidal microspheres, we developed a new technique for graphene patterning that can be defined as modified nanosphere lithography. In contrast to the conventional nanosphere lithography, where periodic arrays of close-packed colloidal particles are used as the mask for depositing separated nanoparticles, we introduced an additional reactive ion etching (RIE) step to form gaps between the close-packed colloidal spheres. In this case, if masking material is deposited on the substrate and the spheres are selectively removed, a continuous mask rather than an array of separated nanoparticles is formed on the surface, which is critical for making large-area GNMs. By changing the duration of the RIE, the size of these gaps and therefore the width of the necks in the resulting mask for etching graphene can be finely tuned over a wide range. GNMs fabricated in this work were studied by SEM, TEM, AFM, XPS and Raman spectroscopy. They exhibit promising electronic properties featuring high ON-OFF ratios and ON-state conductivities.We also employed different metal oxide nanowires, such as easily accessible CuO nanowires, for patterning GNRs, ordered arrays of GNRs and GNMs. The resulting graphene nanostructures were also characterized by microscopic and spectroscopic techniques. Properties of graphene nanostructures obtained by both ‘colloidal crystallization’ and ‘nanowire’ approaches are compared.
B11: Carbon Nanotube Growth and Characterization
Session Chairs
Thursday PM, December 02, 2010
Room 310 (Hynes)
4:30 PM - B11.1
Growth of Dense Carbon Nanotube Forests on Copper Using Iron Based Catalysts.
Gowtam Atthipalli 1 , Rigved Epur 1 , Prashant Kumta 1 2 3 , Jennifer Gray 1
1 Materials Science and Engineering, University of PIttsburgh, Pittsburgh, Pennsylvania, United States, 2 Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3 Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractWe present a detailed study of the mechanism of vertical carbon nanotube growth on copper substrates using catalyst-assisted chemical vapor deposition. The catalysts are a combination of an inconel thin film (less than 20 nm thick) sputtered onto the copper before nanotube growth and ferrocene delivered during the nanotube growth. For specific ranges of inconel film thickness and under certain growth conditions, dense vertical growth of carbon nanotubes in observed. This appears to be due to the formation of a high density of catalyst sites on the surface of the copper, which force the nanotube growth to occur in the vertical direction. The density of nucleation sites is enhanced by the presence of the vapour-based Fe catalyst, in addition to islands that form on the surface of the copper from the inconel film after heating. This technique represents a relatively simple one-step process for direct vertical growth of carbon nanotubes on copper substrates without the need for plasma-enhanced CVD techniques. Characterization of the nanotubes was done using TEM, SEM, and Raman spectroscopy. Conductivity measurements were also performed to determine their suitability as interconnects in nanoelectronic devices or as conductive electrode materials.
4:45 PM - B11.2
p-n Homo-junction Arrays of Aligned Single Walled Carbon Nanotubes Fabricated via a Type Conversion by Partial Coating with n-type Dopants.
Yoon Jangyeol 1 , Park Jaehyun 1 , Ha Jeong-Sook 1
1 Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractSingle walled carbon nanotubes (SWCNTs) have been investigated as active materials for electronic devices, because of their superior electrical performances. Synthesized semiconducting SWCNTs exhibit intrinsically p-type transfer properties in air ambient due to the electron-accepting adsorbates. So, surface treatment with electron-donating adsorbates such as β-nicotinamide adenine dinucleotide, reduced dipotassium salt (NADH) can be used to obtain n-type transfer characteristics from intrinsically p-type SWNTs. Here, we report on the fabrication and the electrical measurements of p-n homo-junction arrays composed of horizontally aligned p-type SWCNTs and n-type SWCNTs converted by coating of p-type SWCNTs with NADH. On thermally annealed ST-cut quartz substrates, well aligned SWCNTs were grown at 950°C by using e-beam evaporated Fe catalysts via chemical vapour deposition (CVD) technique. Back-gated SWCNT field effect transistor (FET) arrays were fabricated via a transfer of CVD grown SWCNTs by using thermal release tape and they showed intrinsic p-type transfer properties after the electrical break-down process. NADH coating of pristine SWCNTs FETs showed n-type transfer properties with much higher on/off current ratio than the pristine p-type SWCNT FETs, which is of particular interest in the sense that conventionally used PEI coating for the n-type doping deteriorated the performance of the transistors due to the high leakage current. Via a partial patterning of the p-type SWCNT FETs with NADH after a selective reactive ion etching, SWCNT p-n homo-junction diode arrays were fabricated. Current-voltage measurements exhibited typical rectifying characteristics with a high rectification ratio of ~103. In this paper, we showed a possible route to fabricate p-n homo-junction arrays of aligned SWCNTs, which will be widely applied in the future nano-electronics.
5:00 PM - B11.3
Chirality-selective Quenching of Single-wall Carbon Nanotube Photoluminescence by Means of Femtosecond Laser Irradiation.
Thomas Rodgers 1 , Satoru Shoji 1 , Hideaki Kobayashi 1 , Shota Kuwahara 1 , Satoshi Kawata 1 2
1 Applied Physics, Osaka University, Osaka Japan, 2 Nanophotonics Laboratory, RIKEN, Wako, Saitama Japan
Show AbstractSingle walled carbon nanotubes (SWCNTs) are produced containing a mixture of different diameters and chiral species, each of which has a unique excitonic band structure. The separation and purification of these species remains an important challenge in nanotube research. Optical resonances in the visible and near infrared spectrum allow the chiral species of SWCNT to be easily identified by spectroscopic methods. Here we report on the photoluminescence excitation spectroscopy of SWCNTs isolated in surfactant micelles and dispersed in an aqueous gel. SWCNTs were dispersed in deuterium dioxide (heavy water) with surfactant by sonication and purified by ultracentrifugation to ensure a high proportion of individual, unbundled nanotubes. These tubes were then fixed in aqueous gel to restrict the dispersion of SWCNTs under laser irradiation. We show that by focusing femtosecond pulsed laser light on the SWCNT gel, the photoluminescence of particular chiral species of SWCNTs at this area is quenched. This selective quenching of photoluminescence suggests the resonant absorption of light by a few species of nanotube with excitonic transition energies near to the wavelength of the pulsed laser. The quenching is observed to be relatively stable and permanent, comparable to the timescale of diffusion of tubes in the gel. SWCNT photoluminescence intensity has been shown to be particularly sensitive to various environmental effects, and we investigate the reasons for this quenching by pulsed laser irradiation. We observe hyper-spectral Raman imaging of the nanotube gel area exposed to the pulsed laser irradiation and compare the change in Raman spectra to the behaviour of the photoluminescence excitation spectra. The chiral selectivity of this quenching is significant, in that this may offer a pathway to separation and sorting of SWCNT chiral species by purely optical methods.
5:15 PM - B11.4
Anisotropic Multi-walled Carbon Nanotube Sheets and Fibers Fabricated from Nanotube Web.
Yoku Inoue 1 , Yoshitaka Minami 1 , Yusuke Suzuki 1 , Junichi Muramatsu 1 , Akihiro Ishida 1 , Katsunori Suzuki 3 , Adrian Ghemes 2 , Shingo Sakakibara 2 , Morihiro Okada 2 , Hidenori Mimura 2
1 Department of Electrical and Electronic Engineering, Shizuoka University, Hamamatsu Japan, 3 Graduate School of Science and Technology, Shizuoka University, Hamamatsu Japan, 2 Research Institute of Electronics, Shizuoka University, Hamamatsu Japan
Show AbstractWe invented a simple one-step growth method of ultra-long (millimeter-scale) vertically aligned multi-walled CNT (MWNT) arrays. Our method uses iron chloride as a precursor for iron catalyst. The MWNT array can easily be spun into webs, which are two-dimensional MWNT network. Using the webs, we fabricated MWNT sheets and fibers. Since MWNTs are highly aligned in the drawn direction, the MWNT products show anisotropy in electrical, mechanical and thermal properties. The anisotropic MWNT products would provide advanced features for many applications.MWNT arrays were synthesized using a conventional low pressure thermal chemical vapor deposition system. A smooth quartz substrate was placed in a horizontal quartz tube furnace with FeCl2 powder, and MWNTs were grown at 830 °C. Densely grown MWNTs are vertically aligned on a quartz substrate. The height of the array reached 2.5 mm in 20 min with the growth rate over 100 μm/min. This growth rate is remarkably high. Our MWNT array samples have a high drawable feature. The MWNT webs are easily drawn using tweezers by pulling out the edge of the array, and can be drawn over 60 m just by drawing MWNTs with no twisting. During drawing, MWTs are drawn with taking neighbors one after another with the aid of van der Waals force. Our carbon MWNT products use no chemical binder material. The tensile strength of a spun fiber, spun with 2 mm-long MWNTs, was 690 MPa. Electrical resistivity of the MWNT sheet with thickness of 0.8 μm was 0.001 ohm-cm in parallel direction, and anisotropy ratio was 7. Thermal conductivity in parallel direction was 70 W/m-K and anisotropy ratio was 8. The present MWNT products include many features, soft, flexible, strong, electrically & thermally conductive and highly anisotropic, at the same time. Our array samples are consistently spinnable for each trial. Low cost, easy to scale up CVD method promises advanced CNT products.
5:30 PM - B11.5
Highly Water Soluble Ionic Carbon Nanotubes and Their Use as Electronic Conductors in Polar Solvents.
Jan Schnorr 1 , Timothy Swager 1
1 Department of Chemistry, MIT, Cambridge, Massachusetts, United States
Show AbstractMulti-walled carbon nanotubes (MWCNTs) can be covalently functionalized while retaining their high strength and electric conductivity. With the right choice of functional groups, MWCNTs become interesting candidates for the use in structural reinforcing elements, actuators, sensors or electrical conductors. Despite recent advances in carbon nanotube chemistry, there remains a continuing challenge to obtain MWCNTs that are not only functionalized for a specific application but also possess a high solubility. Further improvements in CNT solubility could simplify their manipulation and handling and lead to new applications. One such application is the use of soluble MWCNTs as electronic conductors in an aqueous system.Utilizing a functionalization approach that was developed in our laboratory, we have synthesized MWCNTs with a high density of reactive groups which were then used to install anionic residues in a subsequent step. The obtained ionic MWCNTs are highly soluble in water (up to 30 mg per mL) as well as other polar solvent systems which greatly simplifies their handling. After confirming their high solubility, we explored the use of these ionic MWCNTs as electronic conductors in solution. As an example to investigate this, we chose the palladium/copper catalyzed Wacker oxidation, because an electron transfer from palladium to copper is an essential part of its catalytic cycle and facilitating this process should have an observable effect on the reaction rate. Using the yield of the partially completed reaction after 3 h as an indicator of the rate, we observed a negative effect when non-conductive ionic materials such as covalently modified single-walled CNTs or sodium polystyrene sulfonate were added to the reaction. This is presumably caused by sequestration of the catalysts. The addition of ionic MWCNTs, however, resulted in a pronounced increase in yield of 70 % (after 3h) compared to the CNT-free control reaction. These findings suggest that the presented soluble MWCNTs can provide a conductive connection between metal ions in solution which could be beneficial in many processes that involve an intermolecular electron transfer e. g. in organic reactions or biocatalysis.
5:45 PM - B11.6
Machining and Structural Modification of Carbon Nanotubes Using Ultrafast Laser Irradiation.
Aaron Schmidt 1 , Ryan Murphy 3 , Steven Yalisove 2 , A. John Hart 1
1 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Applied Physics Program, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractOrganized carbon nanotubes (CNTs) are potential building blocks of microelectronic interconnects, photovoltaics, and many other materials; however, practicality of these applications will depend on scalable methods to control and modify the organization of CNTs in a customized fashion. We have investigated the use of femtosecond laser irradiation as a tool to manipulate and modify vertically aligned CNT forests and patterned microstructures grown by thermal CVD. Using femtosecond pulses, laser energy is deposited into small volumes by multiphoton nonlinear optical absorption followed by avalanche ionization. This occurs at a time scale much shorter than both heat transport and electron-phonon coupling, causing the affected zone to change from solid to vapor phase and to plasma almost instantaneously, reducing collateral damages to the surroundings. We determined the damage threshold as related to the CNT density and alignment which were controlled by the CNT growth conditions and mechanical densification. Conditions for controlled machining of forests and material removal rates are identified, and the fundamental mechanisms which drive ablation and associated damage are investigated by TEM imaging of individual and bundled CNTs. At fluences near the damage threshold, the laser etches into the forest while leaving surrounding areas undisturbed; while at higher fluences the ablation process is more violent and causes a variety of effects including clustering of CNTs in the laser spot and distortion of the surrounding forest. The complex dynamics initiated by the laser pulses above the damage threshold can be used to both etch and bend CNTs in desired directions.