Symposium Organizers
Richard B. Jackman University College London
Christoph E. Nebel Diamond Research Center
Philippe Bergonzo Commissariat Energie Atomique (CEA/Saclay)
Roy Gat Sekitechnotron USA
J9: Poster Session
Session Chairs
Brage Golding
Geoffrey Scarsbrook
Daisuke Takeuchi
Wednesday AM, November 29, 2006
Exhibition Hall D (Hynes)
9:00 PM - J9.1
Influence of Discharge Voltages on the Structure and Properties of Nanocomposite Carbon Films Prepared using RF and D.C Sputtering.
Boqian Yang 1 , Peter Xianping Feng 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractNanocomposite carbon films are deposited by using RF and D.C sputtering techniques with argon, hydrogen, nitrogen, or mixture gas as source gases and pure graphite as a target. Structural evolutions of nanocomposite carbon films are investigated by Raman, UV-visible spectra, XPS spectra and SEM. The increase of the discharge voltage for sputtering deposition yields different patterns of the nanoscale particles. The typical diamond peak, G and D bands in the Raman spectra of the films are identified. Intensities and profiles of the diamond peak, G and D bands directly depend on the discharge voltage. The results demonstrate that the discharge voltage controls the distribution of radicals' energy and concentration in the discharging district, which affects greatly the bonding configuration of the films. The incorporation of nitrogen leads to a significant distortion of the aromatic ring symmetry, and modifies the sp3/sp2 bond ratios and bonding configurations of the films.
9:00 PM - J9.10
Low Threshold Field Emission from Amorphous Carbon Films Grown by Electrochemical Deposition.
Hideo Kiyota 1 , Mikiteru Higashi 2 , Tateki Kurosu 2 , Masamori Iida 3
1 , Kyushu Tokai University, Kumamoto Japan, 2 , Tokai University, Kanagawa Japan, 3 , Tokai University Junior College, Tokyo Japan
Show AbstractElectron field emission from diamond-related materials has attracted particular interest since the discovery that diamond possesses negative electron affinity, chemical inertness and radiation hardness. Besides the diamond, amorphous carbon (a-C) is promising material for field emitter applications because physical and chemical properties of a-C film that contains high tetrahedral sp3-phase are similar to those of diamond. While growth of a-C film has been accomplished using conventional vapor deposition techniques, some effort has been devoted to development of alternative deposition techniques such as electrochemical deposition using organic liquid. From both scientific and technological viewpoints, those attempts have encouraged innovation of deposition techniques for the diamond-related materials. In this work, we have studied field emission properties of a-C films grown by our electrochemical deposition technique. The apparatus used for deposition consists of a glass vessel, two electrodes, a DC power source, and a thermometer. Deposition of a-C films was achieved by applying a DC potential to the substrates immersed in methanol. The substrate was mounted on the negative electrode, whereas carbon plate was mounted on the counter electrode. To clarify effects of the back contact on emission properties, we attempted deposition of a-C films onto various kinds of substrates such as Si, Al and Ti. From scanning electron microscopy and Raman results, it is found that smooth and homogeneous a-C films are grown on specific substrates such as Ti and Si, suggesting that both films are suitable for field emitter applications. Raman spectra of the films show two broad peaks around 1560 cm-1 and 1350 cm-1, which are respectively referred to as G peak and D peak. From the intensity ratio of the D peak to the G peak, the respective sizes of sp2-carbon clusters embedded in a-C films were estimated to be 1.5 nm or less. Field emission measurements show excellent emission properties such as threshold fields as low as 5 V/µm. To explain the mechanism of low threshold emission, the enhancement factors were estimated to be 1300–1500 by assuming the barrier height as 4 eV. Such large enhancement factors, which are comparable to those of CNT, are attributed to the local field enhancement around sp2 clusters that result from the difference of the conductive and dielectric properties between sp2 and sp3 regions. Emission properties of a-C/Si indicate saturation of emission current under the higher field. The current saturation is explained by the potential barrier at the interface between the substrate and the a-C film. Since the interface barrier is reduced through formation of the Ti interfacial layer, it is suggested that the formation of TiC decreases the contact resistance between the substrate and a-C film. This approach, which utilizes carbide formation at the interface, is verified as useful to improve the emission properties of a-C film.
9:00 PM - J9.11
Influence of Oxygen on the Synthesis of Diamond Film at Low Surface Temperatures.
Dibakar Das 1 , Raj Singh 1
1 Chemical and Materials Engineering, University of Cincinnati, Cincinnati, Ohio, United States
Show Abstract9:00 PM - J9.12
Multiple Methods of Analyzing the Annealing Effects on the Residual Stress State of the Near-frictionless Carbon Thin Films
Bo Zhou 1 , Bart Prorok 1 , Ali Erdemir 2 , O. Eryilmaz 2
1 Materials Engineering, Auburn University, Auburn, Alabama, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractABSTRACT —The residual stress caused by deposition, thermal expansion mismatch, and other fabrication process has a large effect on the thin film mechanical properties. Accurately measuring the residual stress is one of the most important and urgent tasks for thin film technology. In this study, four methods have been applied to measure the residual stress of the near-frictionless carbon films developed at Argonne National Laboratory. These films possess excellent tribological and mechanical properties, which are promising candidates for MEMS coatings. NFC films with 1 µm thickness were grown on Si (100) substrates and annealed at 100 °C, 150 °C, 200 °C, 400 °C, and 600 °C in vacuum, respectively. The residual stress state change due to the annealing effects was determined with laser curvature measurements, Raman spectroscopy, nanoindentation, and membrane deflection experiments (MDE). During laser measurements, the substrate curvature was measured from reflecting a scanning laser beam from the sample surface and focusing it on a position-sensing detector. The stress was calculated with Stoney’s equation. Raman spectra were also used to determine the residual stress state. A freestanding NFC film obtained from opening windows on the substrate was used as a stress-free reference. As the Raman peaks shifted with the elevated temperature, the residual stress could be determined from the shift degree. The stress change was also measured from the nanoindentation tests. In this case, the residual stress was related to the indentation depth change from the stress-free curve. Finally, the stress was determined from the membrane deflection technique developed by H. Espinosa and co-workers. During a typical MDE test, a freestanding fixed dog bone shape membrane was loaded at its center with a nanoindenter wedge tip. At the same time, strain information was recorded by an interferometer focused on the bottom side of membrane as well as by the nanoindenter displacement sensor. Through this method, the mechanical properties such as Young’s modulus, fracture strength, and residual stress could be determined accurately. The results from these four methods will be compared and contrasted for residual stress measurement.
9:00 PM - J9.13
CVD Diamond Detectors in Radiotherapy Dosimetry
Caroline Descamps 1 , Dominique Tromson 1 , Christine Mer 1 , Milos Nesladek 1 , Philippe Bergonzo 1
1 , CEA Saclay France, Gif-sur-Yvette France
Show AbstractDiamond crystallographic structure makes it chemically inert and radiation hard, its atomic number (carbon Z=6) close to the equivalent effective atomic number of human soft tissues (Z=7,4) and of water (reference material in radiotherapy) enables a direct evaluation of the deposited dose without requiring corrections for material nature or energy and thanks to its bio-compatibility, it can be sterilised and is non-toxic. For all its remarkable properties, diamond is well known as an interesting material for radiation detection and more particularly for medical uses.Natural diamond use for detection application is limited because of its high cost and the severe gem selection needed to fabricate reproducible and reliable devices. The recent progress of the chemical vapour deposition (CVD) technique offers new possibilities in the fabrication of ionisation chamber as well as thermoluminescent dosimeters for the particular field of radiotherapy. This paper presents the use of CVD diamond for these two applications. For ionisation chamber fabrication, detrimental effects caused by defects in the material demonstrate the need for sample and device improvement to optimise dosimetric characteristics (linearity with dose, dose rate and stability with energy etc). First results obtained under medical irradiator are presented here. On the other side, for the use of diamond for TL applications, the purpose of this study was to control the trapping levels in the material with deliberate incorporation of impurities in CVD diamond film during the growth.Preliminary tests have enabled to select dopants to obtain optimum TL signals. For all dopants and/or impurities tested (Boron, Phosphorus, Nitrogen, Nickel etc), several parameters were probed as important in TL: the reproducibility of the response, together with the linearity of the signal with dose, optical fading, and thermal fading were studied. Results compared to commercial TL dosimeters as LiF are extremely encouraging and lead to interesting prospects for the use of diamond for TL dosimetry.
9:00 PM - J9.14
Effect of Thermal Annealing on the Atomic Bond Structure Analysis of ta-C Films using Molecular Dynamics Study
Kyung Soo Kim 1 2 , Seung-Cheol Lee 1 , Kwang-Ryeol Lee 1 , Pil-Ryung Cha 2
1 , Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 , School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Show Abstract9:00 PM - J9.15
Low-temperature Deposition of Nanocrystalline Diamond Film by Plasma-assisted Hot Filament CVD.
Wook-Seong Lee 1 , Heqing Li 1 , Hak-Joo Lee 1 , Jong-Keuk Park 1 , Jeung-Hyun Jeong 1 , Young-Joon Baik 1
1 Thin Film Materials Research Center, Korea Institure of Science and Technology, Seoul Korea (the Republic of)
Show Abstract9:00 PM - J9.16
Photoelectron Emission Study On Biomolecule-Attached Hydrogen Terminated Diamond Surfaces.
Daisuke Takeuchi 1 , Hideyuki Watanabe 1 , Tomoko Yamamoto 1 , Takako Nakamura 2 , Oliver Williams 3 , Christoph Nebel 1
1 DiaRC, AIST, Tsukuba Japan, 2 Center for Advanced Carbon Material, AIST, Tsukuba Japan, 3 IMO, Univ. Hasselt, Diepenbeek Belgium
Show AbstractDiamond is a very interesting electrode for bio sensing devices. Since Takahashi et al. [1] showed that the chemically inert surface of diamond can be modified by photochemical treatment a new chapter of diamond research activities have been initiated. Only about 2 years later, Yang et al. [2] introduced an other photochemical process where alkene molecules are covalently bonded to carbon and recently Yang et al. [3] introduced the electrochemical attachment of aryl-molecule. All these treatments are based on electron exchange mechanisms of diamond with the reactant solution. However, details are hardly understood up-to-now.
In this paper we investigate the electron affinity variation of hydrogen terminated single crystalline CVD diamond and nano-crystalline diamond exposed to photochemical attachment of 10-amino-dec-1-ene molecules protected with a trifluoroacetic acid group (TFAAD) molecules for different durations (2 to 24 hours). We apply photoelectron emission experiments (total photoelectron yield spectroscopy; TPYS) to characterize the electron affinity and relate these data to results of XPS and ATR-FTIR to get a quantitative result with respect to alkene molecule attachment.
The data show that the electron affinity is only weakly affected by the covalent attachment as only about 10% of carbon bonds are affected by the attachment. [4] Details of bonding densities from XPS, bonding arrangement from angle resolved XPS and ATR-FTIR will be discussed and correlated with TPYS data to establish a electronic model of photochemical modifications to undoped single crystalline and nano-crystalline CVD diamond.
[1] K. Takahashi et al., Bio Ind. (Japanese) 17 (2000) 44: K. Takahashi et al., Diamond Relat. Mater. 12 (2003) 572.
[2] W. Yang et al., Nat. Mater. 1 (2002) 253.
[3] W. Yang et al., Langmuir 20 (2004) 6778.
[4] C. E. Nebel et al., Langmuir 22 (2006) 5645.
9:00 PM - J9.17
Device Simulation and Design Optimization for Diamond Based Insulated-gate Bipolar Transistors.
Richard Jackman 1 , Haitao Ye 1 , Niall Tumilty 1 , Mose Bevilacqua 1 , David Garner 2
1 London Centre for Nanotechnology / Electronic Engineering, UCL , London, London, United Kingdom, 2 , Cambridge Semiconductor, Cambridge United Kingdom
Show Abstract9:00 PM - J9.18
Resistive and Conductive Ultra-nanocrystalline Diamond Studied by Impedance Spectroscopy.
Richard Jackman 1 , Haitao Ye 1 , Mose Bevilacqua 1 , Jennifer Gerbi 2 , John Carlisle 2 , Dieter Gruen 2 , Oliver Williams 3
1 London Centre for Nanotechnology / Electronic Engineering, UCL , London, London, United Kingdom, 2 , Argonne National Laboratory, Argonne, Illinois, United States, 3 IMO, University of Hasselt, Hasselt Belgium
Show Abstract9:00 PM - J9.19
Deep UV Detection with Diamond-based Devices.
Richard Jackman 1 , Irving Liaw 1 , Stephane Curat 1 , Ian Boyd 1
1 , UCL , London, London, United Kingdom
Show Abstract9:00 PM - J9.20
Unipolar Devices from Phosphorus-doped Diamond: Ohmic and Schottky Contacts.
Richard Jackman 1 , Haitao Ye 1 , Stephane Curat 1 , Niall Tumilty 1 , Mose Bevilacqua 1 , Milos Nesladek 2 , Philippe Bergonzo 2
1 London Centre for Nanotechnology / Electronic Engineering, UCL , London, London, United Kingdom, 2 , CEA-LIST, Saclay France
Show Abstract9:00 PM - J9.21
Neuronal-diamond Interfacing
Richard Jackman 1 , Stephane Curat 1 , Ralf Schoepfer 2 , Christian Specht 2 , Oliver Williams 3
1 London Centre for Nanotechnology / Electronic Engineering, UCL , London, London, United Kingdom, 2 Pharmacology, UCL , London, London, United Kingdom, 3 IMO, University of Hasselt, Hasselt Belgium
Show Abstract9:00 PM - J9.22
Electrical Transport and Defect Spectroscopy of Free Standing Single Crystal CVD Diamond Prepared from Methane Rich Mixtures
Andrey Bogdan 1 , Anna Bogdan 1 , Ken Haenen 1 4 , Katrien De Corte 2 , Milos Nesladek 1 3
1 Institute for Materials Research IMO, Hasselt University, 3159 Diepenbeek Belgium, 4 , Division IMOMEC, IMEC vzw., 3159 Diepenbeek Belgium, 2 , HRD Reserach, B 2500 Lier Belgium, 3 DRT, DETECS, CEA Saclay, 91191 Gif Sur Yvette France
Show Abstract9:00 PM - J9.24
Schottky Diodes on Diamond: High Temperature Performance as a Function of Morphology.
Nirmal Govindaraju 1 , Dibakar Das 1 , Peter Kosel 2 , Raj Singh 1
1 Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, Ohio, United States, 2 Department of Electrical, Computer Engineering and Computer Science, University of Cincinnati, Cincinnati, Ohio, United States
Show Abstract9:00 PM - J9.25
Diamond-like Carbon Film Deposition on an Artificial Heart Blood Pump Using a Free-shape Type Electrode with r.f. Plasma CVD Processing.
Kazuya Kanasugi 1 , Yasuharu Ohgoe 1 , Keisuke Sato 1 , Kenji Hirakuri 1 , Osamu Miyashita 1 , Akio Funakubo 1 , Yasuhiro Fukui 1
1 Department of Electronic and Computer Engineering, Tokyo Denki University, Saitama Japan
Show Abstract9:00 PM - J9.26
Surface Bio-functionalisation of Micro- and Nano-Crystalline Boron Doped Diamond Surfaces for Bio-sensing Applications.
Mathias Bonnauron 1 , Charles Agnès 2 3 , Jacques De Sanoit 1 , Christine Mer 1 , Philippe Bergonzo 1 , Milos Nesladek 2 , Pascal Mailley 3 , Franck Omnès 2 , Omar Elmazria 4
1 LIST (CEA-Recherche Technologique) DETECS/SSTM/LTD-CEA/Saclay, CEA, Gif-Sur-Yvette France, 2 LEPES - UPR11 CNRS, CNRS, Grenoble France, 3 Départment de Recherche sur la Matière Condensée, UMR 5819, CNRS-CEA-Université J. Fourier, Grenoble France, 4 LPMIA UMR-CNRS, CNRS - Université Henri Poincaré, Nancy France
Show Abstract9:00 PM - J9.27
Growth and Characterization of P-doped Polycrystalline n-type CVD Diamond.
Ken Haenen 1 2 , Andrada Lazea 2 1 , Vincent Mortet 1 2 , Milos Nesládek 3 1 2
1 Institute for Materials Research (IMO), Hasselt University, Diepenbeek Belgium, 2 Division IMOMEC, IMEC vzw, Diepenbeek Belgium, 3 LIST (CEA-Recherche Technologique)/DETECS/SSTM/LTD, CEA/Saclay, Gif-sur-Yvette France
Show Abstract9:00 PM - J9.28
Fabrication and Properties of Large CVD Diamond Single Crystals.
Szczesny Krasnicki 1 , Chih-Shiue Yan 1 , Shih-shian Ho 1 , Joseph Lai 1 , Hai-Yuan Shu 1 , Thomas Yu 1 , Ho-kwang Mao 1 , Russell Hemley 1
1 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States
Show Abstract9:00 PM - J9.29
A Sensitive TSC Technique for the Study of Defects in Synthetic Diamond Films.
Stefania Miglio 1 , Riccardo Mori 1 , Mara Bruzzi 1 , Franco Bogani 1 , Antonio De Sio 2 , Emanuele Pace 2
1 Department of Energetics, University of Florence, Florence Italy, 2 Department of Astronomy and Space Science, University of Florence, Florence Italy
Show Abstract9:00 PM - J9.3
Modelling the Location and Configuration of Impurities in Diamond Nanoparticles.
Amanda Barnard 1 , Michael Sternberg 2
1 Department of Materials, University of Oxford, Oxford United Kingdom, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWhile it has been known for some time that diamond nanoparticles contain unintentional impurities resulting from synthesis, the deliberate (controlled) doping of diamond nanoparticles is expected to be important for the development of nanodevices in the near future. The success and reliability of such devices will be largely dependent upon the positions of the dopants within the particles, and the nature of the bonding of the dopant atoms to the surrounding carbon atoms. Therefore, it is highly desirable to know whether imputities (such as nitrogen or boron) will be preferentially located within the core or at the surface of diamond nanoparticles; or possibly at edges or corners. The issue is further complicated by the existence of bucky-diamond particles, which offer alternative substitution sites with naturally reduced coordination in the outer shells. Presented here are results of density functional tight binding (DFTB) simulations examining the configuration and potential energy surface (PES) of substitutional N in isolated nanodiamond and bucky-diamond particles. The morphology of the nanoparticles have been selected so as to offer combinations of {100}, {110} and {111} surfaces, {100}/{110}, {100}/{111}, {110}/{110} and {111}/{111} edges, and {100}/{110}/{110} and {100}/{111}/{111} corners. The PES for N substitution along paths from the nanoparticle centre to each terminus predict that N is unlikely to be positioned in the core these nanoparticles. Further results on smaller nanoparticles, and hydrogenated versions of each structure indicated that the particular (energetically preferred) position will be sensitive to the specific size, shape and degree of surface passivation.
9:00 PM - J9.30
Growth of High-quality Doped Homoepitaxial Single Crystalline Diamond (111) by Microwave-plasma Chemical-vapor Deposition.
Richard Jackman 1 , Haitao Ye 1 , Milos Nesladek 2 , Philippe Bergonzo 2
1 London Centre for Nanotechnology / Electronic Engineering, UCL , London, London, United Kingdom, 2 , CEA-LIST, Saclay France
Show Abstract9:00 PM - J9.31
Attempts to p-Dope Ultrananocrystalline Diamond Films in a Hot Filament Reactor.
Paul May 1
1 School of Chemistry, University of Bristol, Bristol United Kingdom
Show AbstractWe have used a hot filament reactor to deposit ultrananocrystalline diamond (UNCD) films using Ar/H2/CH4 gas mixtures. Attempts have been made to dope the film p-type by additions of diborane to the gas mixture. Results will be presented on the effects of adding varying amounts of B2H6 to the gas mixture, both in terms of changes in the film electrical conductivity, composition and crystallite morphology.
9:00 PM - J9.32
Synthesis and Characterization of Nanocrystalline Diamond Fibers.
Zhenqing Xu 1 2 , Sathyaharish Jeedigunta 3 2 , Manoj Singh 1 2 , Ashok Kumar 1 2
1 Department of Mechanical Engineering, University of South Florida, Tampa, Florida, United States, 2 Nanomaterials and Nanomanufacturing Research Center, University of South Florida, Tampa, Florida, United States, 3 Department of Electrical Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractIn the family of carbon nanostructures, nanocrystalline diamond exhibits exceptional hardness, chemical inertness, and high thermal and electrical conductivity. In our study, we have reported the synthesis of one-dimensional nanocrystalline diamond fibers by a novel two-step template method. Si nanowires (SiNW) were first obtained by the thermal chemical vapor deposition (CVD) method and then nanocrystalline diamond crystals were coated on these nanowires to form fibrous like structures. These nanocrystalline diamond fibers were characterized by scanning electron microscopy (SEM), visible micro-Raman spectroscopy and high-resolution transmission electron microscopy (HR-TEM). The surface morphology of as prepared samples showed that the fibers were 0.3 - 2 μm in diameter and lengths in the order of 20 – 100 microns respectively. The Raman peaks at 1140 and 1333 cm-1 were attributed to the nanocrystalline diamond nature of the fibers. The high-resolution transmission electron microscopy was performed in order to study the nanostructures of the diamond fibers. The nanocrystalline diamond fibers have prospective applications such as high-temperature and high power electronic devices. It can also find applications as biosensors such as the electrochemical detection of neurotransmitters.
9:00 PM - J9.33
Effect of Hyrdrogen Passivation on RMS Roughness and Electronic Structure of Diamond-like Carbon films
Joshua Smith 1 , Robert Nemanich 1
1 Physics, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractHydrogen terminated diamond-like carbon is extremely effective at ionizing neutral particles scattered from its surface. This effect can be exploited to measure the neutral particles in interplanetary and interstellar space. There are two properties that make tetrahedral amorphous carbon films (ta-C), a subset of DLC films, attractive for this application. The first is the property of negative electron affinity (NEA) which is a condition such that the vacuum level of the surface occurs below the conduction band minimum. NEA affects the surface electronic structure to provide a higher conversion efficiency. Second, DLC films are extremely smooth over long length scales which results in favorable angular scattering properties. The purpose of this study was to measure the RMS roughness and ultraviolet photoemission spectrum before and after hydrogen passivation. Several samples were grown at different substrate temperatures in a remote plasma electron cyclotron resonance (ECR) CVD system. The samples were characterized by Raman spectroscopy to determine sp2 and sp3 content. UPS was performed on the samples to determine the band structure, and atomic force microscopy was performed to determine RMS roughness at different length scales. Both techniques were performed before and after hydrogen passivation. RMS roughness was unchanged after passivation. For a 5 μm by 5 μm area, the roughness was 0.1nm.
9:00 PM - J9.34
Diamond like Carbon films for nanoimprint lithography applications and PECVD of Carbon-Carbon composites
Seetharaman Ramachandran 1 , L. Tao 1 , W. Hu 1 , G. Lee 1 , L. Overzet 1
1 Electrical and Computer Science Engineering, University of Texas at Dallas, Richardson, Texas, United States
Show Abstract9:00 PM - J9.35
Sulfur Incorporated Diamond Films by DC Plasma Assisted Hot Filament Chemical Vapor Deposition From Ar/H2S/CH4/H2 Gas Mixture.
Kishore Uppireddi 1 , Fabrice Piazza 1 , Vladimir Makarov 2 , Oscar Resto 1 , Brad Weiner 2 , Gerardo Morell 1 3
1 Dept of Physics, University of Puerto Rico,Rio Piedras, San Juan, Puerto Rico, United States, 2 Dept of Chemistry, University of Puerto Rico,Rio Piedras, San Juan, Puerto Rico, United States, 3 Dept of Physical Science, University of Puerto Rico,Rio Piedras, San Juan, Puerto Rico, United States
Show Abstract9:00 PM - J9.36
Stability and Biocompatibility of Ice Ih on Nanostructured Diamond (111).
Alexander Wissner-Gross 1 , Efthimios Kaxiras 1 2
1 Physics, Harvard University, Cambridge, Massachusetts, United States, 2 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractRecent progress has been made toward inexpensive CVD growth of polycrystalline diamond films, which may have important soft matter and biological applications. In this work, we investigate the thermal stability of epitaxial ice Ih on a diamond (111) film. The film is partially hydrogenated and decorated with charged adatoms in order to electrically polarize the ice. The TIP4P/Ice water model is used for our molecular dynamics studies. We observe enhanced heat transfer from ice to diamond and an elevated ice melting point. We explore the consequences of this increased ice stability for solvation of biomolecules approaching the diamond film.
9:00 PM - J9.37
Diamond Film Synthesis on Glassy Substrates.
Katsunori Yagi 1 , Yoshiki Takagi 1 , Kiyoshi Kuribayashi 1 , Tsuyoshi Hayashi 1
1 Division of Enviromental and Eco-material Engineering, Teikyo University of Science & Technology, Uenohara-city, Yamanashi-pref, Japan
Show Abstract9:00 PM - J9.38
Nano Crystalline Diamond Synthesized by Hot Filament Chemical Vapor Deposition.
Takayuki Hirai 1 , Yoshinori Kanno 1 , Yoshiki Takagi 2 , Kuribayashi Kiyoshi 2 , Tsuyoshi Hayashi 2
1 , University of Yamanashi, Kofu, Yamanashi, Japan, 2 , Teikyo university of science & technology, Uenohara, Yamanashi, Japan
Show Abstract9:00 PM - J9.39
Pressure and Methane Concentration Effect on Diamond Growth with High Growth Rate.
Xianglin Li 1 , J. Perkins 2 , Robert Nemanich 2 , Zlatko Sitar 1
1 MSE, NCSU, Raleigh, North Carolina, United States, 2 Physics, NCSU, Raleigh, North Carolina, United States
Show AbstractDiamond films with preferred orientation (100) were grown at a high growth rate on (100) silicon substrates by microwave plasma chemical vapor deposition (MPCVD), following the standard Bias-Enhanced Nucleation (BEN) procedure. The growth rate and diamond quality were investigated as a function of process pressure (25-150 Torr), methane concentration in hydrogen (1-20%), and deposition temperature (800-1200°C). Up to a 20-fold increase in the growth rate of diamond films was observed within the above process parameters, however, the high methane concentrations and high temperatures yielded inferior diamond film quality, as exhibited by the appearance of the sp2 and nano-diamond peaks in the Raman spectra. There is a minimum pressure limitation allow for the good diamond quality with higher methane concentration growth. And a maximum methane concentration also exists for allow better crystal quality of diamond at high pressure. A detailed study of the crystalline quality and phase purity as a function of total pressure and methane concentration will be presented.
9:00 PM - J9.4
Comparison of Microwave Capacitors Fabricated on MEPCVD Diamond and Bulk Silicon
Venkataramanan Gurumurthy 2 3 , Sathyaharish Jeedigunta 2 3 , Samuel Baylis 2 3 , Priscila Spagnol 1 , Ashok Kumar 3 4 , John Bumgarner 1
2 Electrical Engineering, University of South Florida, Tampa, Florida, United States, 3 Nanomaterials and Nanomanufacturing Research Center, University of South Florida, Tampa, Florida, United States, 1 College of Marine Science, University of South Florida (USF), Largo, Florida, United States, 4 Mechanical Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractThe excellent properties of CVD Diamond such as low surface roughness; high thermal conductivity and negligible RF losses up to 65GHz make it an ideal candidate for applications in the microwave regime. Ba1−xSrxTiO3(BST) thin films with x = 0.5−0.6 are preferred for use in room temperature tunable microwave circuit components due to their relatively low dielectric loss and good dielectric non-linearity. The key issue in the development of these devices is maximizing the electric field induced change in the material while keeping losses to a minimum. The use of diamond on silicon can reduce the RF losses and thus improve the device performance. In this research work, the performance of Ba0.5Sr0.5TiO3based parallel plate capacitors fabricated on CVD Diamond will be compared with those fabricated on bulk silicon. Our ultimate goal is to develop varactors exhibiting high Quality Factors at microwave frequencies. BST thin films were deposited by RF Magnetron sputtering method on microwave plasma enhanced chemical vapor deposition (MPECVD) diamond and the deposited films were characterized for their crystallinity and surface morphology. XRD analysis showed a preferential orientation of the BST thin films in the (111) direction while BST thin films on ulk silicon were comparatively more crystalline. The surface morphology of the BST films analyzed by Atomic Force Microscopy (AFM) showed dependence of the BST surface roughness on the roughness of the underlying diamond layer. The roughness values obtained when BST was deposited on nanocrystalline diamond reanged from 20nm to 26nm.
9:00 PM - J9.40
Diamond for Quantum Devices.
Steven Prawer 1
1 Center for Excellence for Quantum Computer Technology, University of Melbourne, Parkville, Victoria, Australia
Show Abstract9:00 PM - J9.5
Effect of Post Deposition Treatment of the Metal Contacts on the Electrical properties of Nitrogen Doped Nanocrystalline Diamond Films.
Sathyaharish Jeedigunta 1 2 , Priscila Spagnol 3 , Zhenqing Xu 2 4 , John Bumgarner 3 , Ashok Kumar 2 4
1 Electrical Engineering, University of South Florida, Tampa, Florida, United States, 2 Nanomaterials and Nanomanufacturing Research Center, University of South Florida, Tampa, Florida, United States, 3 Center for Ocean Technology, University of South Florida, Tampa, Florida, United States, 4 Department of Mechanical Engineering, University of South Florida, Tampa, Florida, United States
Show AbstractThe nitrogen doped nanocrystalline diamond (NDD) films have been grown on mirror polished Si (100) substrates using the following deposition parameters: 1 % CH4, 10 % to 40 % N2 and the remaining was balanced with argon, microwave power 800 W, pressure 100 T and a substrate temperature of 800 to 850° C in a Cyrannus I Iplas microwave plasma enhanced chemical vapor deposition (MPECVD) system. The structural characterization of the films has been conducted by the micro-Raman, and the scanning electron microscopy (SEM). The Raman spectra showed three characteristic features in the visible region- 1140 cm-1, 1336 cm-1 and 1550 cm-1 representing the signature of nanocrystalline diamond, D-band (sp3) and G-band respectively. A bi-layer of Ti/Au was deposited and patterned (top) to form the front and back contacts of the substrate. The post deposition annealing was carried for 30 minutes in three different environments- such as argon, hydrogen and air in temperatures up to 600° C. The current-voltage (I-V) measurements were carried on the metal/diamond/Si/ metal sandwich structure before and after annealing. I-V measurements showed ohmic characteristics to the diamond films grown in 20 % nitrogen even before any treatment. The room temperature electrical conductivity measurements conducted by four point probe technique showed a highest conductivity of approximately 110 ohm-1 cm-1 for the diamond film grown in 20 % nitrogen. The post deposition treatment has shown an improved ohmic characteristics in the nitrogen doped nanocrystalline diamond films.
9:00 PM - J9.6
Electronic Differences between Highly Oriented and Azimuthally Disordered (100) Polycrystalline Diamond
Phillip John 1 , Neil Polwart 1 , John Wilson 1
1 , Heriot-Watt University, Edinburgh United Kingdom
Show Abstract9:00 PM - J9.7
Improved Diamond FET Characteristics by H2-O2 Plasma Pretreatments of HPHT Diamond Substrates
Alexandre Tallaire 1 , Makoto Kasu 1 , Kenji Ueda 1 , Yoshiharu Yamauchi 1 , Toshiki Makimoto 1
1 , NTT-Basic Research Laboratories, NTT Corporation, Morinosato, Atsugi-Shi Kanagawa , Japan
Show AbstractThe highest diamond-based RF FET characteristics were reported with ft of 45 GHz, fmax of 120 GHz and output power of 2.1 W/mm at 1 GHz [1]. However, in high drain current (IDS) regime, the current gain (gm) usually decreases, while gate leakage current is normally observed in low gate bias (IGS) region. These limitations are mainly related with the presence of surface defects such as hillocks or unepitaxial crystallites (UNC) that frequently appear during the growth of homoepitaxial CVD diamond films on HPHT diamond substrates.We recently managed to strongly reduce the density of hillocks and UNC by using an appropriate high-power hydrogen/oxygen plasma pretreatment of the HPHT diamond substrates prior to CVD diamond growth. Such pretreatment selectively etches away crystalline imperfections such as impurities or threading dislocations that are likely to be preferential sites where twinning occurs during the CVD diamond growth, leading to the formation of hillocks and UNC. FET devices with gate length ranging from 1 to 5 μm were then fabricated on the hydrogen terminated surface of thin CVD film grown on pretreated substrates and their characteristics were measured.The maximum IDS reached was increased up to a factor of 2 as compared with samples grown on unpretreated substrates. In particular, in the high IDS region (for higher VGS between -2.5 and -3.5 V), almost no saturation of the current was observed. We also confirmed suppression of gate leakage. These behaviors are attributed to an efficient suppression of the unepitaxial crystallites and hillocks formed during CVD growth. [1] K. Ueda, M. Kasu et al. Abstract of Applied Diamond Conference, May 2006, A15.1.This work was supported in part by SCOPE project of the Ministry of Internal Affairs and Communications, Japan.
9:00 PM - J9.8
The Large-sized Diamond Single Crystal Synthesis by Hot Filament CVD.
Ko Yamazaki 1 , Kazuyuki Furuichi 1 , Iori Tsumura 1 , Yoshiki Takagi 1 , Kiyoshi Kuribayashi 1 , Tsuyoshi Hayashi 1
1 Division of Environmental and Eco-material Engineering, Teikyo University of Science & Technology, Uenohara-city, Yamanashi-pref, Japan
Show Abstract9:00 PM - J9.9
DNA Bonding to CVD Diamond Probed by Scanning Electron-, Fluorescence-, and Atomic force- Microscopy.
Christoph Nebel 1 , Dongchan Shin 1 , Daisuke Takeuchi 1 , Nori Tokuda 1 , Hiroshi Uetsuka 1 , Bohuslav Rezek 2 , Takako Nakamura 3
1 SFD, Diamond Research Center, Tsukuba, Ibaraki, Japan, 2 Institute of Phyics, ASCR, Prague Czech Republic, 3 Center for Advanced Carbon Materials, AIST, Tsukuba Japan
Show AbstractBioelectronics is a rapidly progressing field at the junction of physics and biochemistry, applying different electrodes like gold, carbon, Si and recently diamond to immobilize biomolecules. These substrates show different characteristics with respect to flatness, homogeneity, availability and are also very different in chemical stability, reproducibility and biochemical manipulations. Diamond is a promising candidate for bio-electronic devices as it shows good electronic and chemical properties, is considered to be biocompatible and can be grown single-, poly- or nanocrystalline, either by homo-epitaxy or by hetero-epitaxy on a variety of substrates. To attach bio-molecules to diamond, photochemical surface modifications [1,2] can be applied where excitations of electrons from the valence-band maximum into the chemical reactant triggers the bonding mechanism [3]. While this technology is successfully applied on a variety of diamonds (nano-, poly-, single-crystalline diamond), which are very different with respect to sp2-, sp3-fractions, grain-boundaries, lattice orientation, and H-termination, no data are available about the homogeneity of photo-attached linker and bio-molecule layers on those films. In this paper we discuss the homogeneity of photochemically attached linker- (10-amino-dec-1-ene protected with trifluoroacetic acid group), cross-linker and DNA-molecules to poly- and single-crystalline diamond films. We apply scanning electron microscopy (SEM) to elucidate the variation of negative electron affinities on H-terminated smoothly polished polycrystalline (PCD) and on atomically flat single crystalline CVD diamond. Fluorescence microscopy is applied to detect the variation of color-center labeled double-stranded (ds) DNA. The homogeneity and layer thickness of ds-DNA is characterized by atomic force microscope (AFM). These experiments reveal that photochemical surface modifications gives rise to inhomogeneous DNA bonding, if the diamond films are inhomogeneous due to variations of surface electronic properties (electron affinity), grain boundaries and sp2/sp3 fractions. Fluorescence microscopy applied, show laterally varying intensities of typically 20 %, which resembles the grain structure detected by SEM on polycrystalline diamond, while on single-crystalline diamond the intensity is homogeneous. AFM shows also different DNA thicknesses on different facets of PCD. The lateral variation of DNA is attributed to local variations of photo-electron excitations during the photochemical surface-grafting of diamond. 1.Takahashi, K.; Tanga, M.; Takai, O.; Okamura, H., Sakai, Y.; Bio. Ind. 2000, 17, 44.2.Yang, W.; Auciello, O.; Butler, J.E.; Cai, W.; Carlisle, J.A.; Gerbi, J.E.; Gruen, D.M.; Knickerbocker, T.; Lasseter, T.L.; Russell Jr, J.N.; Smith, L.M.; Hamers, R.J. Nature Materials 2002, 1, 253. 3. Nebel, C.E.; Shin, D.; Takeuchi, D.; Yamamoto, T.; Watanabe, H.; Nakamura, T.; Langmuir 2006, 22, 5645.
Symposium Organizers
Richard B. Jackman University College London
Christoph E. Nebel Diamond Research Center
Philippe Bergonzo Commissariat Energie Atomique (CEA/Saclay)
Roy Gat Sekitechnotron USA
J12: Field-emission
Session Chairs
Wednesday PM, November 29, 2006
Room 306 (Hynes)
3:00 PM - **J12.1
Nanodiamond and Carbon Nanotube Field Emission Devices.
Jim Davidson 1 , Karthik Subramanian 1 , Yong Wong 1 , Weng Kang 1 , Bo Choi 1
1 , Vanderbilt University, Nashville, Tennessee, United States
Show AbstractWe are fabricating and examining nanocarbon derived electron emission devices, specifically, nanodiamond lateral field emission diodes and gated carbon nanotube triodes. These novel microstructures provide interesting means of accomplishing electronics that are unaffected by temperature and radiation.Nanodiamond lateral field emitters have promise for high-speed and high-power applications with their small inter-electrode spacing and efficient emitter geometry[1]. The characteristic properties of nanocrystalline diamond including smaller grain size (5-10 nm), smoother surface morphology, increased sp2-carbon content and higher electrical conductivity are favourable for lateral field emitters. In this work, we report the fabrication process advancement and field emission behavior of the nanodiamond comb-shaped field emitter array in diode configuration. The nanodiamond lateral device was fabricated on a silicon-on-insulator (SOI) wafer. The lateral diode design includes arrays of high aspect-ratio nanodiamond emitter fingers arranged in a comb-like structure with spacing as small as 2 μm from the nanodiamond anode (figure available). The 9000-fingered lateral field emission diode (8 μm anode-cathode spacing) exhibited a low turn-on voltage of 10 V (electric field: 1.25 V/μm) which is one of the lowest reported for lateral field emission devices, and a high emission current over 25 mA at an anode voltage of 260 V (field ~ 32 V/μm),(figure available. Also, we have recently demonstrated a FE triode amplifier, (figure available), based on aligned carbon nanotubes (CNTs) synthesized by microwave plasma chemical vapor deposition method[2]. We have verified that the gated device with convex-shaped CNT emitters is a functioning triode amplifier with low gate leakage current, large dc gain of ~352, low gate turn-on voltage of ~25 V, and useful ac gain. Compared to other emitters, CNTs possess the advantages of very high aspect ratio, small radius of curvature, lack of vacuum-arcing, chemical inertness and thermal stability. Unlike TE-based triode, the high frequency operation of a FE triode is dictated by the cutoff frequency (fT) and not the electron transit time. Preliminary FE results, (figure available), show that the improved triode amplifier array has a gate turn-on voltage of ~ 42 V and a very low gate leakage current of ~1% of the anode current.Fabrication and electrical performance of these configurations will be presented.[1] K. Subramanian et al., Diamond and Related Materials 14, 2099 (2005).[2] Y.M. Wong, W.P. Kang et al., Diamond Relat. Mater. 14 (2005) 2069–2073.
3:30 PM - J12.2
Field Penetration Effects on Field Emission and Thermionic Field Emission from Nanostructured Carbon Films.
Franz Koeck 1 , Robert Nemanich 1
1 Physics, NC State University, Raleigh, North Carolina, United States
Show Abstract3:45 PM - J12.3
The Field Emission Properties of Diamondoids.
Jason Fabbri 1 , Peter Schreiner 2 , Jeremy Dahl 3 , NIcholas Melosh 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 Chemistry, Justus-Liebig University of Giessen, Giessen Germany, 3 MolecularDiamond Technologies, Chevron Technology Ventures, Richmond, California, United States
Show AbstractThe search for a material that can provide stable electron field emission with high current densities at a low applied voltage has attracted many researchers. Such a material could have successful commercial applications in areas such as display technology as well as important applications in research as an electron source. Due to its many advantageous properties, diamond materials have garnered much interest in this field. In particular, the negative electron affinity (NEA) of hydrogen terminated diamond surfaces has been viewed as an advantageous property for a field emission material. In this respect, diamondoids hold promise as an interesting new material for high performance field emission. Thus, we have analyzed the field emission properties of diamondoidthiol monolayers and diamondoid crystals. We base our analysis on the Fowler-Nordheim theory of field emission, and compare the field emission from diamondoids to that from other candidate materials.
4:00 PM - J12: F-Emission
BREAK
Wednesday PM, November 29, 2006
Room 306 (Hynes)
4:30 PM - **J13.1
Growth, Processing, and Characterization of Tetrahedral Amorphous– Carbon Thin Films for MEMS.‡
Thomas Friedmann 1 , John Sullivan 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractTetrahedral Amorphous-Carbon (ta-C) thin films deposited by pulsed laser deposition at room temperature can be processed into microelectromechanical machines (MEMS) if one is careful to relieve the internal stresses and stress gradients built up during growth. Both the concentration of 4-fold bonded carbon and the initial compressive stress (2-8 GPa) grow as the laser fluence on the target increases. Typically, a thermal anneal is used (~650 °C for ~ 2 minutes) to relieve these stresses, but we have also shown that it is possible to use laser annealing (a lower thermal budget process) to achieve stress relief. Interestingly, we find that films grown at lower laser fluences with correspondingly lower 4-fold content (less diamond-like) do not stress relax when annealed. Thus, for MEMS applications where stress free films are required, one must carefully control the laser fluence. We have used etch back experiments to characterize the residual stress gradients found in ta-C films after both thermal and laser annealing and find that there are significant interfacial stresses at the substrate/film and film/air interfaces. These gradients arise due to the growth energetics and must be accounted for when producing MEMS devices in order to reduce curvature in released devices.Processing of ta-C thin films into MEMS devices is relatively simple. In our case, we typically use lift-off to pattern an aluminum hard mask followed by etching of the ta-C in an oxygen plasma. The etched devices are released using a wet etch of the underlying sacrificial layer. The release stiction found in our devices is dependent upon the material that the ta-C contacts. For ta-C/ta-C contacting surfaces, the adhesion energies are typically very low (~ 1µJ/m2), being comparable to those of SAMS-coated Si MEMS devices, and structures tend to spontaneously release upon drying from a deionized water soak. For ta-C/Si interfaces the adhesion strengths are greater (~1 mJ/cm2), and devices tend to be adhered after release. We have found that it is possible to release these adhered devices with near 100% efficiency using laser irradiation at low fluence.‡ Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
5:00 PM - J13.2
Characterization of Polycrystalline Diamond Thin Films Deposited by Hot Filament Chemical Vapor Deposition for MEMS Application.
Jingchun Zhang 1 4 , Jerry Zimmer 2 , Roger Howe 3 4 , Roya Maboudian 1 4
1 Chemical Engineering, University of California, Berkeley, California, United States, 4 Berkeley Sensor & Actuator Center, University of California, Berkeley, California, United States, 2 , sp3 Diamond Technologies, Santa Clara, California, United States, 3 Electrical Engineering, Stanford University, Stanford, California, United States
Show Abstract5:15 PM - J13.3
Diamond/aluminum Nitride Piezoelectric Bimorph Cantilevers for Sensor Applications.
Vincent Mortet 1 2 , Laurent Le Brizoual 3 , Jiri Potmesil 4 , Milan Vanecek 4 , Ken Haenen 1 2 , Marc D'Olieslaeger 2 1
1 Institute for Materials Research (IMO), Hasselt University, Diepenbeek Belgium, 2 Division IMOMEC, IMEC vzw, Diepenbeek Belgium, 3 LPMIA, Université Henry Poincaré, Vandoeuvre-les-Nancy France, 4 Institute of Physics, Academy of Sciences of the Czech Republic, Prague Czech Republic
Show Abstract5:30 PM - J13.4
Nanofabrication of Diamond-like Carbon Templates for Nanoimprint Lithography.
L. Tao 1 , S. Ramachandran 1 , C. Nelson 1 , T. Lee 1 , L. Overzet 1 , M. Goeckner 1 , M. Kim 1 , G. Lee 1 , W. Hu 1
1 Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas, United States
Show Abstract
Symposium Organizers
Richard B. Jackman University College London
Christoph E. Nebel Diamond Research Center
Philippe Bergonzo Commissariat Energie Atomique (CEA/Saclay)
Roy Gat Sekitechnotron USA
J14: Defects and Theory
Session Chairs
Thursday AM, November 30, 2006
Room 306 (Hynes)
10:00 AM - J14.1
Irradiation-induced Structural Modifications in Multifunctional Nanocarbons.
Sanju Gupta 1
1 Physics and Materials Science, Missouri State University, Springfield, Missouri, United States
Show AbstractSevere environmental tolerability is the prime factor in the development of novel space materials exhibiting excellent physical properties accompanied by lightweight, reusability, and multifunctional capabilities. Diamond has a reputation being radiation hard besides a range of outstanding physical properties and hence it is preferable in harsh environments. Carbon nanotubes are also of great interest because of several unsurpassable physical properties and it needs to be shown that they are physically stable and structurally unaltered when subjected to irradiation. Films of poly-/micro- and nanocrystalline diamond and carbon nanotube deposited by microwave plasma-assisted CVD technique were submitted to gamma radiation (1, 5, and 20 Mrads) and to low and medium energy electron-beam irradiation to study their effects on the microscopic structure and corresponding physical properties to establish property-structure correlation. Microstructural and physical properties assessment prior to and post-irradiation include scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy (RS), X-ray diffraction (XRD), field emission (FE), and high-resolution transmission electron microscopy (HRTEM). Dramatic improvement in the field emission properties for microcrystalline diamond and relatively small but systematic behavior for nanocrystalline diamond with increasing radiation dose is discussed in terms of the critical role of defects which tends to form clusters. The results also indicate that nanocrystalline carbon tends to reach a state of damage saturation, suggesting the possibility of development of radiation buffer/shields materials. These results are also discussed in terms of sp3C --> sp2C inter-conversion [1]. Experimental studies of electron beam irradiation on the carbon nanotubes show that multi-walled tends to be relatively more robust than those of single-walled. This is because increased exposure on an individual bundles of single-wall nanotube promoted graphitization, pinching, and cross-linking similar to polymers forming intra-molecular junction (IMJ) within the area of electron beam focus, possibly through aggregates of amorphous carbon. Formation of novel nanostructures (nano- ring and helix-like) due to irradiation is also observed. The possible radiation mechanism will be briefly discussed. It is also suggestive that knock-on collision may not be the primary cause of structural degradation, rather but a local reorganization occurs. These studies gleam on the dynamics of nano-manufacturing and a regime of possible relevance to these materials for a) short-term space missions; b) radiation hard programmable logic circuits; and c) radiation pressure sensors. The investigations mentioned above are also supported using theoretical simulations. *This work is supported in parts by ONR Grant and internal funds.
10:15 AM - J14.2
Materials Design of Ferromagnetic Diamond
Hiroshi Katayama-Yoshida 1 , Kazuhide Kenmochi 1 , Kazunori Sato 1 , Akira Yanase 1
1 , ISIR, Osaka University , Ibaraki, Osaka, Japan
Show AbstractDiamond is a wide band gap semiconductor and one of the most attractive materials for electronic applications because of its exceptional hardness, high thermal conductivity, high mobility of carriers and high breakdown voltage. Moreover, recently superconductivity has been reported in boron-doped diamond. In this paper, we explore another potentiality of diamond and we propose a materials design of ferromagnetic diamond based on first-principles electronic structure calculations [1]. For the electronic structure calculations, we use the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method to take substitutional and magnetic disorder [2]. In order to introduce magnetic centers into non-magnetic pure diamond, we suppose H impurities at the tetrahedral interstitial site (H-int). In order to estimate the stability of the ferromagnetic states, we calculate total energy difference between the ferromagnetic state and the paramagnetic state. This energy difference gives an estimation of Curie temperature within the mean field approximation [3]. First, only H-int are introduced into diamond up to 1%. In this case, we find that the H-int keeps local magnetic moment, because the H-int makes deep impurity band in the gap and effective electron correlation energy in the impurity band is larger than the band width of the impurity band. This impurity band is just half-filled, and the system is insulating and shows paramagnetism. Next, by B or P doping we introduce carriers into the diamond with H-int. By introducing substitutional B (P) impurities into the system, holes (electrons) are doped into the impurity band, and simultaneously the ferromagnetic state is stabilized due to the double exchange interaction [4]. The stability of the ferromagnetism is optimized when B (P) is doped up to 0.5%, i.e., half of the H concentration, because in this case the Fermi level locates at the center of the majority (minority) impurity band and the energy gain due to the double exchange mechanism is maximized. Further B or P doping suppress the ferromagnetism and finally the system becomes nonmagnetic when the impurity band is completely empty or occupied. Calculated Curie temperature is about 70 K within the mean field approximation for 0.5% B-doped diamond with 1% H-int. The calculated density of states shows half-metallic density of states and the spin polarization at the Fermi level is 100% in this system. In this work, we propose the material design for half-metallic and ferromagnetic diamond by controlling the occupancy of the deep impurity band. This concept can apply many other systems to realize ferromagnetism without transition metal impurities and we propose the concept as “deep impurity band engineering”. 1. K. Kenmochi et al., Jpn. J. Appl. Phys. 44, L51 (2005) 2. H. Akai and P. H. Dederichs, Phys. Rev. B 47, 8739 (1993)3. K. Sato et al., Europhysics Lett. 61, 403 (2003)4. K. Sato et al., J. Phys. Condens. Matter 16, S5491 (2004)
10:30 AM - J14.3
Energetics, Electronic Properties, and Geometries of B-Doped Diamond: A First-Principles Study.
Susumu Saito 1 , Tomohisa Maeda 1 , Takashi Miyake 2
1 Department of Physics, Tokyo Institute of Technology, Tokyo Japan, 2 Research Institute for Computational Sciences, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Show AbstractWe study B-doped diamond in the framework of the density-functional theory and in the many-body theory with the GW approximation to discuss the electronic and geometrical properties of superconducting B-doped diamond. The materials studied are both substitutionally doped and interstitially doped phases. The total-energy analysis has revealed that substitutional doping is energetically much more stable than the interstitial doping. Therefore, substitutionally doped phases, the BC7 phase and the BC15 phase, are studied in detail. From the GW study as well as from the density-functional study, it is found that the substitutional doping up to very high doping level gives rise to hole-doped valence band which should be responsible for metallic and superconducting behavior of the material. In addition to the cubic-cell geometries, we also discuss the effect of the deformation of the cell which are expected to be present in the superconducting samples produced using homoepitaxial growth technique on diamond (100) and (111) surfaces. Interestingly, a small but finite deformation from cubic cell is found to change the electronic density of states of the material near the Fermi level. Based on these interesting differences, we will address the origin of much higher superconducting transition temperature of the (111)-growth samples than the (100)-growth ones. In addition, we will discuss the effect of the non-uniform B doping into the diamond lattice also in connection with the preference of the (111) homoepitaxial growth over the (100) growth.
10:45 AM - J14: Defects
BREAK
J15: Diamond Electrochemistry
Session Chairs
Thursday PM, November 30, 2006
Room 306 (Hynes)
11:15 AM - **J15.1
Electrochemical Charge Transfer to Diamond.
John Angus 1 , Vidhya Chakrapani 1 , Alfred Anderson 2
1 Chemical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Chemistry, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractIn recent years the electrochemical properties of hydrogen-terminated, conducting diamond have received wide attention for sensor applications, for novel devices, and as a working electrode for destruction of organic wastes.1 Hydrogen-terminated diamond actively interacts with its ambient giving rise to a p-type surface conductivity.2 The direction of electron transfer between diamond and its surroundings depends on the relative positions of the Fermi level of diamond and the chemical potential of electrons in the surrounding medium.3, 4 In this paper we discuss the charge transfer between macroscopic diamond samples and aqueous solutions as a function of pH, dissolved oxygen concentration, and surface termination. Titration of aqueous solutions of known pH permits the estimation of the position of the Fermi level in diamond. Measurements of contact angle, work of adhesion, and zeta potential are reported. The observation of some of these effects in other systems, e.g., nanotubes and GaN, is also discussed.1. A. Fujishima, Y. Einaga, T.N. Rao, D.A. Tryk, Eds., “Diamond Electrochemistry,” BKC Tokyo, Elsevier, Amsterdam, 20052. M. I. Landstrass, and K. V. Ravi, Appl. Phys. Lett., 55, 975 (1989).3. F. Maier, M. Riedel, B. Mantel, J. Ristein, L. Ley, “Origin of Surface Conductivity in Diamond,” Phys. Rev. Lett. 85 (2000) 3472-3475.4. V. Chakrapani, S. C. Eaton, A. B. Anderson, M. Tabib-Azar, and J. C. Angus, “Studies of Adsorbate-induced Conductance of Diamond Surfaces,” Electrochem. and Solid State Lett.1 (2005) E4-E8.
11:45 AM - **J15.2
Surface and Electrochemical Studies of Thin Film Diamond
John Foord 1
1 Department of Chemistry, University of Oxford, Oxford United Kingdom
Show AbstractConductive diamond electrodes are now finding increasing use in electrochemistry, as a result of their stability and reproducibility, which is effectively coupled with a wide operating potential window, low background currents and a resistance to electrode fouling. Although much of the original work has tended to focus on bare, macroscopic electrodes manufactured from polycrystalline diamond, interest has begun to focus on the use of different forms of diamond, the development of ultramicroelectrodes, and the use of surface functionalisation methods. The present work focuses on some recent developments in these areas. Surface functionalisation in other thin film systems is normally either carried out using physical adsorption or chemical adsorption approaches. We explore some new varied routes in this regard, and compare the results obtained in terms of control of surface concentration, and dependency on the nature of the diamond surface used, as well as phase stability, with the photochemical functionalisation method which has tended to dominate work in this area to date. Advantages and disadvantages of the different methods are considered, and possible applications discussed. In separate work we also investigate new approaches to the fabrication of ultramicroelectrodes (UME’s) using thin film diamond materials. Again, the results are compared to existing approaches in this particular area, and the particular applications of the techniques developed are considered.
12:15 PM - J15.3
Nano Diamond Tip Array Electrodes.
Mahendra Sunkara 1 , Rupa Dumpala 1 , Boris Chermomordik 1
1 Chemical Engineering, University of Louisville, Louisville, Kentucky, United States
Show Abstract12:30 PM - J15.4
CVD Diamond Ultramicroelectrode Arrays for Chemical and Bioanalyte Sensing
K. Soh 2 , Weng Kang 1 2 , J. Davidson 1 2 , Y. Wong 1 , D. Cliffel 3 2
2 Interdisciplinary Program in Materials Science, Vanderbilt University, Nashville, Tennessee, United States, 1 EECS, Vanderbilt University, Nashville, Tennessee, United States, 3 Chemistry, Vanderbilt University, Nashville, Tennessee, United States
Show AbstractBoron-doped diamond synthesized by microwave plasma chemical vapor deposition (MPCVD) exhibits behavior desired for of an excellent voltammetric electrode such as wide working potential window, low background current, resistance to fouling and long-term response stability. In electrochemical analysis and sensing, the superior detection figures of merit for diamond electrodes, particularly the limits of detection and sensitivity, can be further improved by shrinking electrode geometries with microfabrication techniques. When the critical electrode dimensions become equivalent or smaller than the thickness of the diffusion layer, the microelectrode will exhibit greatly enhanced electrochemical behavior from that of a macroelectrode. Increased sensitivities and decreased limits of detection can be achieved due to enhanced mass transport to the interfacial reaction zone. As the electrode dimension becomes smaller than the diffusion length, the flux of reactant to the electrode becomes dominated by non-planar diffusion. The background signals are low due to decreased overall electrode area, relative to the geometric area. Both of these factors lead to enhanced signal/background ratios, increased sensitivities and decreased limits of detection. Due to its small geometry, it would have low current, a small ohmic drop, and a small time constant. Although the low ohmic drop is desirable, the small current is not. Using an array of sensing elements on a single chip can diminish this problem.This work reports on the design, fabrication and experimental evaluation of diamond ultramicroelectrode arrays for chemical analysis and bioanalyte sensing. Boron-doped diamond ultramicro arrays with different array geometries, sizes, densities and interelement spacings were fabricated using micropatterning technology and selective diamond deposition (SAD) technique to yield microelectrode arrays. Examples of diamond ultramicroelectrode arrays fabricated include square and rectangular arrays of different interelement spacings and densities, ultramicroband arrays with two different interelement spacings and densities. Experimental results have shown that the ultramicroband array displayed sigmoidal pseudo-steady-state cyclic voltammograms characteristic of microband electrodes. The ultramicroband arrays displayed higher faradaic current per unit area, than either of a square ultramicroelectrode array or the conventional planar diamond electrode from earlier reported work. Detail experimental data of the array’s geometrical parameters on the electrochemical sensing behaviour and sensing of bioanalyte will be presented.
12:45 PM - J15.5
Simple and Effective Way to Improve the Stability of Titanium Based Boron Doped Diamond Film Electrode
Liang Guo 1 , Guohua Chen 1
1 Chemical Engineering, Hong Kong University of Science and Technology, Hong Kong Hong Kong
Show AbstractBoron-doped diamond film coated titanium (Ti/BDD) becomes extremely attractive in the field of electrolysis and analysis because of the combined properties of these two unique materials. Stability of electrode has been a big concern. In the present research, a highly stable Ti/BDD anode was fabricated using staged temperatures (650oC and 750oC) Hot Filament Chemical Vapor Deposition (HFCVD) method. The service life of this electrode was found to be 804 hours under accelerated life testing conditions of current density of 1000mA/cm2 in 3M H2SO4 solution. This value is over 3 times of 244 hours, a value for the electrode prepared using a constant temperature (750oC) HFCVD under optimal conditions. The electrodes were physically characterized with micro-Raman, XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscopy) techniques. The surface SEM images showed that the diamond particles displayed cubooctahedral facet with the crystal size being 1~2μm for the staged temperature method. In contrast, clear cut faceted crystals with triangular and rectangular habits were observed for the diamonds fabricated under a constant temperature condition with the relatively larger particle diameters ranging 1~7μm. Micro-Raman spectra indicated the slightly low crystallinity for the sample prepared with staged temperatures because of its relatively small particle size. XRD analysis showed that the diamond crystals were of (111) preferential orientation. The titanium carbide (TiC) phase intensity was lower for the staged temperatures than the constant temperature one. Combined with the XRD and micro-Raman results, the cross-sectional SEM pictures indicated a multilayer structure of Ti/TiC/(Diamond + Amorphous Carbon)/Diamond for the staged temperature sample, and the structure of Ti/TiC/Diamond for the constant temperature one. CV (Cyclic Voltammetry) studies in 0.5M Na2SO4 solution showed the working potential window for the stable electrode was 3.7 (-1.42 ~ 2.27)V, only 0.1V smaller than 3.8 (-1.48 ~ 2.32)V, the value for the electrode prepared at a constant and optimal temperature. For the Fe(CN)63-/4- redox kinetics, α (electron transfer coefficient) and ko (heterogeneous electron transfer rate constant) for the stable electrode and the one prepared at an optimal constant temperature were 0.296 and 9.235×10-4cm/s, and 0.289 and 1.676×10-4cm/s, respectively. Diamond film delamination was believed to be the main reason causing electrode failure. The super stability of the electrode prepared using staged temperature HFCVD is believed to be attributed to the close contact at the interface between the diamond film and TiC. This close contact was achieved by a layer of mixed diamond and graphite that serves as a sort of cement between the TiC and the diamond film.
J16: Biosensors
Session Chairs
Thursday PM, November 30, 2006
Room 306 (Hynes)
2:30 PM - **J16.1
Detection of DNA Hybridization by Diamond Solution Gate Field Effect Transistors – A New Type of DNA Sensor Based on Charge Detection
Hiroshi Kawarada 1 , Kwangsoup Song 1 , Junghoon Yang 1
1 Electrical Engineering & Bioscience, Waseda University, Tokyo Japan
Show AbstractWhen free single strand DNAs (negatively charged biomolecules) hybridize with the complementary DNAs immobilized in the electric double layer, the charge change is detected using field effect transistors (FETs). In the case of Si based FETs, however, thick gate insulator inevitable for the ion protection degrades the sensitivity of the charge change because of low capacitance density. On diamond FET surface channels, DNAs or other biomolecules can be immobilized directly without gate insulator leading to high sensitive structure for the charge detection [1]. When target DNAs hybridize with probe DNAs immobilized on the surface channel, the surface holes can be induced and detected as the drain current increase or the positive shift of the threshold voltage in the p channel diamond FET if the hybridization takes place in the electric double layer. The current increase or the voltage shift is more clearly and reproducibly observed in the diamond FETs where the surface has been partially aminated and the probe DNAs have been immobilized directly to the channel. The difference between complementary, 1-base mismatch, 3-base mismatch, and non complementary target DNAs has been detected both by the I-V characteristics and the real time shift of the gate voltage keeping the constant drain current. As charge detection DNA sensor, diamond is superior to other semiconductors because of its high sensitivity in charge change, stability in detection, and strong bonding with biomolecules. [1] K.S.Song. H.Kawarada et al.,Jpn. J. Appl. Phys., 43,L814 (2004).
3:00 PM - J16.2
Covalent DNA Attachment on CVD Diamond for Electrochemical Hybridization Sensors
Dongchan Shin 1 , Nori Tokuda 1 , Sung-Gi Ri 1 , Christoph Nebel 1
1 Diamond Research Center, AIST, Tsukuba, Ibaraki, Japan
Show AbstractThe development of DNA-functionalized transducers for electronic recognition of specific base sequences attracts increasing attention, since such devices are expected to induce significant changes in a variety of fields, like gene therapy, drug development and environmental protection. Electrochemcial genosensors require highly sensitive and reproducible detection of interacting events in electrolyte solution which limits the use of established semiconductor materials, as most of them simply degrade in such harsh environments. Diamond is known for a long time to be chemically inert but only recently it has been shown that it can be biofunctionalized by use of photo- and electrochemical methods [1-3]. Parallel to the development of surface chemical modifications, the tuning of bulk electronic properties has been established using boron (p-type) and phosphorus (n-type) as dopants. In addition, diamond can be grown for the development of highly sensitive detectors in single crystalline structure, but also on large area poly-, nano- and ultra nano-crystalline. The later structures contain grain boundaries which are decorated with sp2 carbon and will therefore have limited electronic sensing quality. In the present work, we summarize our research on covalent surface attachment of oligonucleotides on single crystalline CVD diamonds, to establish electronic active DNA hybridization sensing. We apply electrochemical reduction of diazonium salts [2] on metallically boron-doped single crystalline diamond for electrochemical detection. Each modified surface is characterized by XPS, AFM and cyclic voltammetric experiments to detect the linker molecules, area density, and orientation. The benzene grafted surfaces are further modified by cross linker molecules and ss-DNA. DNA hybridization reaction, the distinction between complementary and non-complementary oligonucleotides, is monitored by cyclic voltammetry and differential pulse voltammetry, using redox couple [Fe(CN)6]4-/3- as a electroactive marker. The electronic variation from ss-DNA to ds-DNA is in the range of 200 microA/cm2, as detected by differential pulse voltammetry. To optimize the electronic response and the discrimination quality, the DNA density is decreased to improve washing properties and the ionic flow through the layer. The deduced properties will be discussed taking into account surface bio-molecular properties (molecule arrangement, density) and mediator diffusion limitations, to discuss possible discrimination levels and life-cycles of DNA electrochemical sensors.1. K. Takahashi et al.; Bio Industry 2000, 17, 44.2. J. Wang et al.; Langmuir 2004, 20, 11450.3. Yang, W.; et al., Nature Materials 2002, 1, 253.
3:15 PM - J16.3
Diamond Based Ion-Sensitive Field Effect Transistors for Cellular Biosensing
Richard Jackman 1 , Stephane Curat 1 , Olivier Gaudin 3 , John Foord 2
1 London Centre for Nanotechnology / Electronic Engineering, UCL , London, London, United Kingdom, 3 Physics, University of St Andrews, St Andrews United Kingdom, 2 Chemistry, University of Oxford, Oxford United Kingdom
Show AbstractDiamond is one of the few biocompatible semiconductors, making the generation of diamond based electronic devices for biosensing applications of great interest. Field effect transistors (FETs) have been fabricated from conventional materials, such as silicon, with the aim of detecting cellular activity for some years, but in addition to the toxicity of the Si, the devices lack sensitivity and are readily corroded during use. Diamond offers a potential solution to these problems, and we have been designing and fabricating diamond FETs and evaluating their performance as sensors within biological systems.Single crystal diamond surfaces can display p-type character when hydrogenated, a phenomenon known as 'surface transfer doping'. We have exploited this effect to generate MESFET structures, which perform as extremely effective devices both at room temperature and up to 300C. Ungated devices have been used in a wide range of solutions as ion sensitive FETs (ISFETs) with great success. A range of ions have been detected (H, Cl, Br, I) with high levels of sensitivity. Devices are not corroded under a wide range of conditions (eg pH 2-10). The prospects for this technology to be exploited for the detection of cellular activity will be discussed.
3:30 PM - J16.4
DNA-ISFETs from Single Crystalline Diamond.
Christoph Nebel 1 , Dongchan Shin 1 , Tomoko Yamamoto 1 , Takako Nakamura 2
1 SFD, Diamond Research Center, Tsukuba, Ibaraki, Japan, 2 Center for Advanced Carbon Material, AIST, Tsukuba, Ibaraki, Japan
Show AbstractThe possibility of label-free electrical detection of DNA-hybridization utilizing semiconductor field-effect sensors offers a new approach to fast, simple and in-expensive analysis of nucleic acid samples. The inherent miniaturization of such devices and their compatibility with advanced micro fabrication technology can make them very attractive for DNA diagnostics. DNA-FETs are obtained by immobilization of well-defined sequences of single-stranded (ss) DNA onto a transducer layer, which provides the specific recognition process between the two complementary ss-DNA strands. Most of the microelectronic-compatible materials like silicon, SiOx, and gold show, however, degradation of the interface which inhibits the development of integrated sensor. Single crystalline CVD diamond is a promising candidate for DNA-FET applications as it is bio-compatible, chemically inert, can be bio-functionalized, and shows as recently demonstrated a high sensitivity with respect to ions in electrolyte solution [1]. ss-DNA can be bonded to diamond using photochemical and electrochemical techniques. In most cases a dense surface functionalization is achieved using alkene or benzen molecules with area densities in the range (1014 -1015 )1/cm2 [2]. Double stranded (dd) DNA is, however, a large molecule (diameter ~ 2 nm) so that only about 3x1013 1/cm2 molecules can be bonded to achieve a dense layer. In addition, such dense layers are not favorable for electronic detection of DNA hybridization as the redistribution of ion concentration within the intermolecular spacing and the alteration of ion sensitivity is minimized.In this paper we present data of DNA-FETs produced from initially hydrogen terminated undoped single crystalline CVD diamond. In-plane FET structures have been realized by use of photolithography and oxygen plasma etching. The active detector area is 0.5 mm x 1 mm. Au has been used as drain and source contacts, Pt as reference electrode. The hydrogen terminated diamond surface was bio-functionalized, applying photo-attachment chemistry with linker molecule area densities varied between 1012 to 1015 1/cm2. The intermolecular spacing of DNA on diamond is therefore changed between 0 and 8 nm. The sensitivity of DNA-FETs is characterized with respect to the geometric arrangement of DNA, using AFM, XPS, fluorescence microscopy and field effect transistor characterization techniques. The ISFET gate potential shifts for around 50 mV from ss-DNA to ds-DNA with large changes in drain source current amplitudes. A critical discussion of theoretically expected and really detected threshold shifts of diamond based DNA-FETs will be given.Keywords: Biosensor, DNA-FET, Single Crystalline Diamond[1] C.E. Nebel et al. J. Appl. Phys. 2006, 99, 33711. [2] C.E. Nebel, et al., Langmuir 2006, 22, 5645.
3:45 PM - J16.5
Biomolecule Immobilization on Polycrystalline Boron Doped Diamond Electrodes
Rabah Boukherroub 1 2 , Yannick Coffinier 1 2 , Sabine Szunerits 3 , Bernadette Marcus 3 , Michel Mermoux 3 , Didier Delabouglise 3
1 Institut de Recherche Interdisciplinaire (IRI), CNRS, Villeneuve d'Ascq France, 2 Institut d'Electronique, de Microélectronique et de Nanotechnologie (IEMN), CNRS, Villeneuve d'Ascq France, 3 Laboratoire d'Electrochimie et de Physicochimie des Matériaux et des Interfaces , CNRS-INPG-UJF, Grenoble France
Show Abstract4:00 PM - J16: Biosensors
BREAK
J17: Keynote II
Session Chairs
Thursday PM, November 30, 2006
Room 306 (Hynes)
4:30 PM - **J17.1
Lift –off Process to get Free-standing High Quality Single Crystal Diamond Films and Suspended Single Crystal Diamond Devices.
Jie Yang 1 2 , Chiou-Fu Wang 3 , Evelyn Hu 3 , James Butler 1
1 Gas/Surface Dynamics section, Naval Research Laboratory, Washington DC , District of Columbia, United States, 2 , NOVA research Inc., McLean, Virginia, United States, 3 , University of California, Santa Barbara, California, United States
Show AbstractThrough ion implantation plus electrochemical etching, and a lift-off process, 3.5x3.5 mm and 7x7 mm freestanding and suspended single crystal diamond devices, microdisks and beam structures, have been fabricated on HPHT (high pressure high temperature) Ib substrates. The selective ion implanted energy created subsurface damage while maintaining an undamaged top surface; homo-epitaxial growth was subsequently carried out on the material. After annealing, the damaged layer was selectively removed by electrochemical etching. Different implant species and different implantation energies have been simulated and tested to optimize the process. The electrochemical etching process has been monitored by optical video. Both AC and DC electrical powers were used for the Electrochemical etching process. PL and Raman spectra have been used to characterize the implanted substrate and lifted-off films. AFM has been used to monitor the surface changes after mechanical polishing, ion implantation, anneal and the lift-off process. Our research has revealed that the parameters of ion implantation (implant species, dose and energy) dramatically affect the lift-off process. The etching mechanism and critical parameters will be discussed. PL showed some difference between the uppermost layers of the homo-epitaxial film and the lift-off interface. Three principal defects have been observed: growth defects from HPHT process, polishing marks and stress, and point defects. How these defects affect the electrochemical etching will also be discussed.
5:00 PM - J17.2
Influence of HPHT Diamond Defects on CVD Homoepitaxial Diamond Growth
Alexandre Tallaire 1 , Makoto Kasu 1 , Kenji Ueda 1 , Toshiki Makimoto 1
1 , NTT Basic Research Laboratories, NTT Corporation, Morinosato, Atsugi-Shi Kanagawa , Japan
Show AbstractCVD diamond films are usually epitaxially grown on (100)-oriented HPHT diamond substrates. These substrates usually contain a large amount of crystalline defects such as dislocations, polishing grooves, inclusions or impurities that may strongly influence the final quality of the CVD diamond film. Substrate pretreatments have thus already been shown to allow improvement of the quality of the CVD grown film. However the reasons for such improvement as well as the relation between the surface defects on the HPHT substrates and the appearance of unepitaxial crystallites (UNC) or hillocks on the grown film are still not well understood.In this work, we performed pretreatment of HPHT (100) substrates using a high power hydrogen plasma with addition of a low content of oxygen prior to epitaxial CVD diamond growth. After etching step, since crystalline imperfections at the substrate surface act as velocity sources where etching is locally enhanced, the substrate surface was fully covered by etch pits with four-fold symmetry, having their sides parallel to the <110> directions. However, we clearly distinguished two types of etch pits. Some were shallow with flat (100) facet at their bottom (type A). Such pits are likely originating from preferential etching at a groove or an isolated impurity. The other type of pits (type B) consisted in deep inverted pyramids with a single point at their bottom and with four (111) facets on their sides. This last type of pits probably comes from locally enhanced etching at a threading dislocation emerging at the substrate surface.The imperfections responsible for type A pits are supposed to lead to the appearance of hillocks on the CVD film. To the contrary, the defects responsible for type B pits are assumed to be the origin of most of the unepitaxial crystallites observed on the CVD diamond films since it is energetically more favorable for twinning to occur at this location. A detailed study of the first instants of CVD growth on etched diamond substrates will be provided in order to elucidate the relation between the etch pits and the growth defects.This work was supported in part by SCOPE project of the Ministry of Internal Affairs and Communications, Japan.
5:15 PM - **J17.3
Low Effective Work Function of Nitrogen Doped Diamond Films.
Franz Koeck 1 , Robert Nemanich 1
1 Physics, NC State University, Raleigh, North Carolina, United States
Show AbstractThermionic electron emission from nitrogen doped diamond thin films can be described in terms of emission from the conduction band observed as a spatially uniform electron discharge from the surface. Crucial to a reduced emission barrier is the negative electron affinity of the diamond surface which aligns the vacuum level below the conduction band minimum by about 1.3 eV. It has been established that nitrogen in a single substitutional site forms states 1.7 eV below the conduction band. These nitrogen donor states contribute to a thermionic emission current which can be described by the Richardson formalism. A fitting procedure indicates a work function as low as 1.4 eV which was verified by UV photoemission spectroscopy (UPS). Temperature dependent UPS measurements display a shift of the Fermi level towards the conduction band with increased temperature. With a nitrogen donor concentration of 1019 cm-3 this shift of the Fermi level towards the CB was calculated to be about 0.5 eV. These results indicate that at elevated temperatures of about 600 °C, the Fermi level becomes located within the near vicinity of the vacuum level by tenths of an eV.