Remote sensing applications in harsh environments require sensor materials appropriately matched to the environment. PbZr_0.52Ti_0.48O₃ (PZT) is a candidate for remote sensing applications, where it could be used as both a sensor and power source. In this light, the evolution of the PZT-H₂SO₄ interface is explored at low pHs. A robotic microdroplet cell is developed to differentiate the electrochemical response of the cracks and pores inherent to the PZT film from that of continuous PZT. Accelerated chemical attack is observed at the pores, while the continuous PZT displays electrochemical hysteresis; the ferroelectric-solution interface can be switched between two different charge states at a given potential. As time progresses, electrochemical impedance spectroscopy reveals a change in the structure of the PZT-H₂SO₄ interface. Development of equivalent circuits to model the competing processes of pore growth, interfacial layer formation, and uniform chemical attack are guided by the evolution of film structure and chemistry as observed ex-situ with scanning electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction. The Point Defect Model for the passive state is used to explain the dissolution processes observed in the complex oxide. Application of this model to PbZr_xTi_1minus;xO₃ for x = 0.25, 0.52, and 0.95 points to the role of titanium in the creation of an ionically insulating layer that impedes further chemical attack.

Smart Sensor Systems that can operate at high temperatures are required for a range of aerospace applications [1]. For example, for future aerospace propulsion systems to meet the requirements of decreased maintenance, improved performance, and increased safety; the inclusion of intelligence into the propulsion system design and operation is necessary. These systems must incorporate technology to monitor component conditions, analyze the incoming data, and modify operating parameters to optimize system operations. Overall, the goal is to make intelligent vehicle systems by developing Smart Sensor Systems operational in harsh environments.
A Smart Sensing System as described here implies the use of sensors combined with electronic processing capability. The definition of a Smart Sensor may vary, but typically at a minimum a Smart Sensor is the combination of a sensing element with processing capabilities provided by a microprocessor [2]. A more expansive view of a Smart Sensor System is a complete self-contained sensor system that includes the capabilities for data storage, processing with a model of sensor response and other data, self-contained power, and an ability to transmit or display informative data to an outside user.
The harsh environment inherent in propulsion systems is especially challenging for Smart Sensor Systems; this paper addresses technology development for such applications. A basic sensing system for high temperature wireless pressure monitoring composed of a sensor, electronics, and wireless communication with scavenged power developed for health monitoring of aircraft engines and other high temperature applications has been demonstrated at 4750C [3]. Other efforts will be discussed including a brief overview of the status of high temperature electronics and sensors, as well as their use and applications.
References
1. G. W. Hunter and A. Behbahani, “A Brief Review of the Need for Robust Smart Wireless Sensor Systems for Future Propulsion Systems, Distributed Engine Controls, and Propulsion Health Management”, 58th International Instrumentation Symposium, San Diego, CA, June 4-78, 2012
2. G. W. Hunter, J. R. Stetter, P. J. Hesketh, and C.C. Liu 2011. “Smart Sensor Systems”, Interface Magazine, Electrochemical Society Inc., Vol. 20, no. 1, Winter, 66-69
3. G. W. Hunter, et. al, “High Temperature Wireless Smart Sensor Technology Based on Silicon Carbide Electronics”, ECS Trans. 2014 61(4): 127-138; doi:10.1149/06104.0127ecst

Lambda sensor is a solid-state electrochemical cell that provides a potential proportional to the logarithm of the oxygen concentrations at its electrodes. After Robert Bosch GmbH first introduced this sensor in the sixties, it has been extensively used for the measure of exhaust gas concentration of oxygen on internal combustion engines. An important improvement was achieved in the nineties by means of a reduction of mass and the incorporation of buried heaters. It resulted on a much rapidly starting sensor with a faster response.
The current work continues with this miniaturization approach with the aim to further expanding the availability of gas sensors to new market niches. For example, less consuming cheaper sensors could open the way to exhaustive atmosphere monitoring, by means of nets of portable wireless gas sensors (ubiquitous sensor networks). The presented fabrication route combines industrial clean room batch production processes with the use of nanometric thin films of Ytria Stabilized Zirconia (YSZ) as solid electrolyte. A drastic reduction of the power consumption is pursued by means of two convergent effects. On the one hand, the volume of the active part of the sensor allows a rapid heating with minimum power. On the other hand, the thin electrolyte provides a lower resistance, making possible to reduce the operating temperature and increase the response velocity.
A cross plane membrane potentiometric micro gas sensor has been fabricated and tested. The device is based on a thin electrolyte membrane deposited by large area pulsed laser deposition (LAPLD) on a micromachined silicon platform. 300 nm YSZ film is deposited as solid electrolyte on a sacrificial Si₃N₄ layer. A doped-silicon hexagonal supporting grid provides with the mechanical resistance to large area membranes of several square millimeters. Finally, thin porous Pt electrodes are sputtered at both sides of the electrolytic membrane.
Less than one second heating rates without damage have been observed. Oxygen partial pressure at different atmosphere has been neasured at 500 0C, showing a fast and stable response. The presented results prove the viability of potentiometric micro sensors in a nano-membrane architecture, opening the way for the fabrication of reliable, low cost, low consumption and rapid gas sensors.

Triboelectric nanogenerator (TENG) technology is an emerging new mechanical energy harvesting technology with numerous advantages. Amongst the multitude of TENG designs, the grating structure is not only the most promising for ultra-high output power but also the most complicated. In this work, the #64257;rst theoretical model of the grating structured TENG is presented with in-depth interpretation and analysis of its working principle. There are generally two different categories of grating TENGs with different output characteristics: grating TENGs with equal and unequal plate length. For each of these two categories, besides the study of the basic output profile, we performed an in-depth discussion on the influence of electrode structures, number of grating units, and thickness of the dielectric layers for the unequal plate structure in this work. As for the electrode structure, grating electrodes always lead to a better performance than plate electrodes for both of these categories. As for the most important parameters of grating TENGs—the number of grating units, our theoretical calculation clearly indicates that increasing the number of grating units to get a finer pitch will generally improve the output performance. However, when the pitch is very fine, the edge effect begins to dominate, resulting in degradation of performance when the number of units continues to increase. Thus, there exists an optimum number of grating units, and an optimum unit aspect ratio that mainly depends on the materials dielectric constant and the motion type. These are important parameters to consider for future structural design. As for the dielectric thickness in the unequal length design, the thickness of the dielectric of the longer plate should be much smaller than that of the shorter plate.
With the above theoretical understanding of the grating structured TENGs, we utilize their unique characteristics to work as self-powered motion sensors. One dimensional displacement and speed can be detected using peak/zero-crossing counting method, which is very robust against variations caused by non-uniform surface charge distribution, surface contamination or grating defects. Analysis of the OC voltage amplitude improved the displacement resolution to be 173 nm for a grating width of 100 mu;m. The real time speed can be detected by the SC current amplitude, which shows a very good linear correlation with a large dynamic speed range from 5 mu;ms^minus;1 to 0.1 ms^minus;1. This design opens a new paradigm for displacement/speed sensing by distinguishing itself from the existing technologies through a combination of self-powered, nano-resolution at a long working distance, high robustness and tolerance, non-optical simple structure as well as low cost. ^[1,2]
Reference:
1. Energy & Environmental Science 2014, DOI: 10.1039/C4EE00498A.
2. Advanced Materials 2014, 26, 1719-1724.

Individual metal oxide nanowires have been recognized as powerful gas sensor platforms with much better advantages than many of the widespread reported metal oxide based solid state resistive gas sensors. Individual MOx nanowire allows self-heating operation procedure saving up the heaters integration as part of the hot plate. Likewise, they show shorter response and recovery time solely limited by the thermal inertia of the hotplate and the chemical reaction taking place onto the sensing material surface as there is not any gas diffusion time. Moreover, they have also a total capability for being fully activated by UV illumination as all the volume of the nanowire is included in the absorption zone. It enhances the sensor response avoiding the use of heating excitation. And complementarily, their low thermal inertia allow to apply pulsed operational mode with the consequent advantage for controlling, cleaning and determining the starting point of the surface conditions.
Nevertheless, in spite of these improvements, individual nanowires, up to now, have not yet used for fabricate real sensors as there is not available suitable and feasible nanotechnologies allowing the nanomanipulation of these individual nanowires. Alternatively, serious efforts have been performed for growing them directly on micro hotplate obtaining something like a “mat” of nanowires and very different of the performance of individual nanowire acting as a quasi-perfect nanocrystal with the above described characteristics.
In this contribution, a methodology for allocate a distribution of individual nanowires between the designed interdigitated electrodes of a SOI-CMOS microhotplate is presented. It is based on a dielectrophoresis process on the previously deposited solution containing the nanowires. Electrical contacts are improved by in-situ thermal treatment using the self-heater of the hotplate. In this way, combining SOI-CMOS micro hot plate and multiples individual nanowires as sensing material distributed between the interdigitated electrodes, a high performant configuration suitable for harsh environments sensing of gases is obtained on the base of the robustness of both sensing material and microhotplate. Sensor prototypes and their characteristics will be presented taking ZnO nanowires as an example

There is a demand for thin film strain gauge materials which are capable of operating at elevated temperatures. This work investigates the performance of TiN_x thin films deposited using reactive magnetron sputtering for use as a strain gauge material. The depositions were made from a titanium target in a N₂/ Ar atmosphere without intentional heating of the substrates. Films of different composition were prepared by varying the nitrogen flow from the metallic- to the poisoned mode of reactive sputtering. The deposition pressure was kept constant by adjusting the argon flow. The atomic composition of the films was estimated using energy-dispersive X-ray spectroscopy (EDX) showing an increasing content of nitrogen with increasing nitrogen flow. No oxygen was detected in the films made in the metallic target mode while up to 10% oxygen was detected in the remaining films. The structure of the films was studied using X-ray diffraction (XRD). The XRD diffractogram of the film deposited at the lowest nitrogen flow only contained the (00.2) peak from hcp titanium. As the nitrogen flow was increased, peaks from the cubic-TiN phase were observed in the diffractograms. At intermediate flows, a (111) texture of the cubic-TiN grains was observed, while the films deposited in the poisoned mode of sputtering (high nitrogen flows) developed a (200) texture. The intrinsic stress of the films was measured using the wafer curvature method based on the Stoney equation. Films deposited in the metallic mode were in tensile stress while the films made in the poisoned mode were compressively stressed. The film resistivity was measured on films deposited on polished BK7 glass substrates using a 4-point probe. The resistivity was in the range of 0.2-0.5 m#8486;#8729;cm and was found to increase with the nitrogen flow. The stability of the resistivity was also studied at 200°C for 300 hours revealing stable behavior of films deposited in the metallic and poisoned of sputtering, however, films deposited with intermediate nitrogen flows were instable. The piezoresistive gauge factor was measured on films structured into meander-type resistors and deposited onto a thermally grown SiO₂ layer on a Si (100) wafer. The samples were strained in a 3-point bending setup in which the temperature could be controlled (TA Instruments Q800). The current-voltage (I-V) response was measured as function of load and temperature while the resistance was extracted from the slope of the I-V curves. The strain was calculated using Euler-Bernoulli beam theory. The gauge factors of the films were found to increase with increasing nitrogen flow while the temperature coefficients of resistivity changed from positive to negative.

Nanoelectromecahnical systems (NEMS) are getting more attention for their higher resonant frequency #402;_o and lower threshold voltage, thanks to their nano-scale size. However issues such as stiction, line edge roughness, nano fabrication difficulties and material fractures and fatigue limit out the material selection for NEMS device fabrication. In this work, a novel material (amorphous tungsten nitride a-WN_x) has been demonstrated to overcome most of these issues. Amorphous WN_x has high Young&’s modulus (E = 300 GPa) which makes the spring constant k_s higher. This allows the fabricated devices to overcome the stiction issue in NEMS. This together with the high conductivity (R = 0.2 mOmega;.cm) yields high resonance frequency. Slightly tensile stress ( σ = —500 MPa) makes the released free standing parts remain straight neither curving downward nor curling upward. WN_x NEMS fabricated devices has longer lifetime due to its hard surface, thanks to the high hardness (H = 3 GPa). Economic side of WN_x is as attractive as the technical side. NEMS WN_x is deposited by simple commercial PVD sputtering tool with commercial tungsten target and N₂ gas flow. All the fabrication process steps are CMOS compatible, no need for special tools, neither special condition. Laterally moving cantilever device could be fabricated using a single mask, or three masks for vertically moving device, unlike 8 masks for PolyMUMPs devices. This could save more than 60% of the fabrication cost. Finally, the fabricated devices have high Q because of the high resonant frequency and small damping factor as well as high sensitivity. The high density (ρ = 19 g.cm^-3) makes it the best candidate for accelerometer and gyroscope mass proof. The existing accelerometers and gyroscope either fabricated with piezoelectric film or with thermal bubbles. These devices have very low response in time. Another version of accelerometers and gyroscopes is operating as variable capacitors. This type of devices is fabricated with PolyMUMPs process, which makes it very complicated and expensive. On the other hand, their response time is very fast. Using WN_x to fabricate accelerometers and gyroscope, gives the advantage of single mask easy process and fast response time. The high density of WN_x leads to higher sensitivity device. Higher elasticity modulus leads to stiffer spring and longer lifetime in term of stiction, the most killing factor for NEMS and MEMS. The high conductivity leads to faster response in charging and discharging the sensing capacitance, which lead to a better operation than the existing classical devices. The amorphous metal WN_x gives the advantage of fractureless springs and material, even distribution of the internal stress in the spring, higher elasticity than Si and wider temperature range for operation. All these characteristics give the amorphous WN_x advantage to be the one of the best candidates for accelerometers and gyroscope fabrication.

In the last years there is an intense research for the development of hydrogen or hydrocarbon-based fuel cells because of the feasibility to generate electrical energy from the reaction of these gases with oxygen. As a result, the exhaust gases of the cell have a high concentration of water vapor and CO₂. However, due to an improper operation of the devices, the exhausts could contain rests of the fuel or byproducts of the catalytic reaction. For this reason, gas sensors are required to monitor the proper operation of the fuel cell.
In this work we will show the use of Pt/TaO_x/SiO₂/SiC Metal Insulator Semiconductor (MIS) capacitors to detect hydrogen, CO and saturated and unsaturated hydrocarbons in atmospheres with extremely high concentrations of water vapor (up to 40% by volume ratio of water vapor to nitrogen) and temperatures between 200 and 400#730;C. The TaOx layer is nominally 20nm thick, while the porous Pt contact has a thickness of about 40nm. The sensors gas response has been measured as the gate voltage change (#8710;V=V_G(gas)-V_G(N₂)) under constant capacitance conditions and referred to the value when in N₂ gas.
The obtained results indicate that, in absence of other gases involved in the fuel cell, the capacitors are almost insensitive to the presence of water vapor, while the addition of hydrogen to the water vapor gives rise to a diminution of the response to hydrogen with increasing water vapor concentration, saturating above 30%.
In this work we will report the response of the MIS capacitor to the different gases and mixtures of interest for this application and we will correlate the results with the most recent approaches to heterocatalysis on Pt surfaces in order to propose suitable sensing mechanisms.

The scaling of silicon-based CMOS technology has hit a limit both in terms of the thickness of SiO₂ based dielectric schemes, which are now limited by quantum tunneling, and secondly with respect to carrier injection from the drain into the Si channel. The first problem has been overcome by the use of high-k dielectrics, like zirconia and hafnia among many others. The issue of carrier injection necessitates the use of materials with high electron and hole mobilities, the most promising amongst them being Germanium having electron and hole mobilities of 3000 and 900 cm²/Vs respectively. Zirconia is known to form a stable interface with germanium unlike hafnia and hence can be used as high-k dielectric on Ge as a potential combination to replace conventional SiO₂/Si for CMOS applications.
For the first time, in this interesting study we correlate growth stress in the ZrO₂ films to their crystallinity and dielectric permittivity. Our results showed that compressive growth stress alone can change the ZrO₂ films relative permitivity from 5 to 23. And effect of further increase in stress was also studied.
We reported electrical and structural characterization of ZrO₂ /n-Ge [100] by reactive-direct current sputtering. As zirconia has phase dependent anisotropic dielectric permitivity. For the first time a clear selection of phase in thin film was achieved by precise control of growth temperature, stress and film thickness. Amorphous, tetragonal and monoclinic phases of zirconia were studied.
The best EOT of 8 Å at 5 nm oxide thickness was achieved in sputter deposited zirconia. A novel stack was proposed to reduce leakage current density in MOS capacitor structures, which showed promising leakage current reduction by an order of magnitude.

The ability for sensor or electronics devices to adapt or withstand complex environment is important for enabling their practical applications. Flexible sensors and electronics produced by roll-to-roll manufacturing process represent advanced approaches to the versatility of applications in terms of sensing environment and device durability. This report describes recent results of an investigation of nanomaterials that can be printed and processed on flexible substrates such as polyethylene terephthalate and polyimide. Size and composition controlled metal or alloy nanoparticles have been synthesized by wet chemical processes. The demonstration of the controllable printing and sintering of the nanoparticle inks on the flexible substrates by thermal and laser sintering techniques provide promising leads to establishing printable nanomaterials for flexible sensors and electronics. The morphological, structural, and electrical properties of the flexible devices are characterized using different techniques in correlation the detailed laser-sintering parameters with both pulsed and continuous-wave lasers. Results on the device strain-performance characteristics will also be discussed in correlation with the device durability and application.

Nanostructural magnetic materials have the potential to revolutionize current data storage technologies, magnetoelectronics, and biotechnology. The surface and size effects have been one of the main topics among scientists. The ferromagnetic(FM)/antiferromagnetic(AFM) core/shell systems are gaining increasing attention due to their appealing novel properties and promising application. Many valuable phenomena, such as giant magnetoresistance and interfacial exchange bias effect, have been found. In this work, the manganese oxide coated Ni particles were prepared in a two-step process. The first step is the manufacture of Ni nanoparticles. The second step is the coating process, which is to cover the above precipitates manganese oxide. Detailed synthesis process is omitted here. Nanostructural characteristics are obtained by XRD and TEM observation. The TEM image of manganese oxide coated Ni particles clearly exhibits the core/shell structure with the core size of about 15~20 nm coated by 9 nm thick shell. No Ni-oxide phase is found, indicating the dependability of the processing method. Magnetization curves for the manganese oxide coated Ni particless were performed with maximum magnetic field 50 kOe at different temperatures after the zero field cooling(ZFC). The hysteresis loop below 5 kOe and the unsaturation of magnetization at higher field reflect the cooperative contribution of ferromagnetic and superparamagnetic characteristics in the sample. For T=300 K, the typical non-hysteretic superparamagnetic behavior is obtained, which is related to the small size effect of Ni nanoparticles. Basically, these curves can be fitted by the contribution of two kinds of magnetizations: M(H)=M_sp(H)+chi;H, where M_sp is a superparamagnetic one that follows a Langevin-like function, and chi;H is the linear component. The comparison between the ZFC and Field cooling(FC) hysteresis loops were also measured at 5 K for the Ni/MnO particles. It can be seen that the ZFC and FC loops are completely overlapped for both samples. There exists no exchange bias behavior, probably because of the weak ferromagnetic characteristic of Ni cores and poor interfacial coupling effect between FM core and AFM shell, even though the distinct core/shell structure has been exhibited. The magnetization measurements show that the total magnetization of each particle is the result of cooperation of the core and shell magnetic moments. Even though the interaction between them is too weak to cause exchange bias effect, but the typical two step magnetization behaviors have been presented in the annealed Ni/MnO particles. Through the analysis of M-T curves, we find out that the synthesized MnO-coated Ni particles , with the perfect nanostructure, are without any magnetic impurity phases.

Volatile organic compounds (VOCs) sensors are the imperative technology of modern life for environmental monitoring. There are no ending quests for low cost, high sensitivity, high reproducibility and high selectivity sensors. In this study, we demonstrated a VOCs sensor chip adopting the proposed methodology that the optical property of poly(3-hexylthiophene) (P3HT)/poly(methyl methacrylate)(PMMA) blend is sensitive to VOC vapor due to morphological evolution and hence can be served as an indication of the presence of VOCs. The P3HT/PMMA served as a representative blend, and the sensitivity of the P3HT/PMMA blend was optimized with respect to P3HT molecular weight, P3HT/PMMA blending ratio, and blend concentration. The present work utilizes P3HT/PMMA blend to sense various VOCs by detecting the variation of optical properties. In order to increase the specific surface area, the electrospinning technique was used to fabricate P3HT/PMMA VOCs sensing chips and it exhibit high optical absorbance and high sensitivity. A series of VOCs, such as toluene, chlorobenzene, ethanol, acetone, etc., were chosen to test the applicability of the sensor, and the results reveal high performance without disruption by water vapor. The measurements of the detection limit show that the concentration over explosive limits can be detected by the sensor within several minutes. The low cost, high sensitivity, high sensing accuracy, quick response, and real-time P3HT/PMMA VOC sensor chip developed in the present work signi#64257;cantly extends the current VOC sensing technology and can be extensively used to e#64256;ectively prevent humans and the environment from potential damages of VOCs.

Nanogenerators that harvest energy from mechanical vibration are an attractive area of nanotechnology fields. Recently, composite-type nanogenerator consisting of piezoelectric nanostructures and multi-walled carbon nanotubes (MWCNTs) is one of the excellent candidates for the future energy harvesting because they can apply the great electrical and mechanical properties of MWCNTs. Researches on the composite-type nanogenerators are focused on obtaining highest output power and understanding the role of the MWCNTs in the nanogenerators. However, the role of the MWCNTs is not fully understood because previous reports are based on the simply mixed MWCNTs and piezoelectric nanostructures in the polymer matrix. The interconnected growth of piezoelectrics onto MWCNTs provides not only key information to understand a systematic role of MWCNTs in nanogenerator property but also effective transfers of stress occurred in the MWCNT and piezopotential created in the piezoelectrics.
We report a successful growth of Pb(Zr_x,Ti_1-x)O₃ (PZT) nanoparticles (NPs) interconnected with MWCNTs (PZT NPs-CNT) through injection method of sol-gel solution into a filter for squeezing them and annealing for crystallizing them. The injection method helps to minimize the remaining sol-gel solution after coating onto MWCNTs. High resolution transmission electron microscope analysis of PZT NPs-CNT reveals that the PZT NPs have a diameter of 20minus;30 nm and are polycrystalline with a tetragonal structure which atomically connected with the MWCNTs. Energy dispersive x-ray spectroscope of PZT NPs-CNT confirms the presence of lead, zirconium, titanium and carbon. In order to form the flexible thin film, the PZT NPs-CNT was mixed with poly-tetrafluroethylene of 5minus;30 % as binder and milled until 150 mu;m in thickness. The thin films were then attached to the Au/Cr coated polyimide film. By periodic banding movements, the open-circuit voltage and short-circuit current of the PZT NPs-CNT reaches about 0.2 V and 10 nA, respectively. In order to analyze the role of the MWCNTs in the nanogenerator, we controlled the ratio of the CNT and PZT NPs from 0.1 to 0.8, which can vary the internal resistance and conductance. We will discuss the role of the MWCNTs by measuring the output powers of weight-ratio-controlled PZT NPs-CNT.

Copper is a promising material that can be used as conductive layer in printed electronics due to its high electrical conductivity and low cost compared to other metals. However, copper patterns printed are prone to oxidation and corrosion, and copper oxides degrade the electrical properties of the copper patterns. Coating the copper patterns by organothiol self-assembled monolayers (SAMs) is one of effective methods for oxidation and corrosion protection. However, the SAMs coating layer may not withstand high temperature. Although, thermal stability is also an important feature because it can limit their practical applications, only a few works have studied the effects of the temperature on the SAMs coating layer. In this work, we studied the thermal stability of organothiol SAMs coating on the copper surface. Moreover, mechanisms of SAMs decomposition were also investigated. The organothiol SAMs were coated on copper sheets prepared by electro-polishing followed by oxygen plasma treatment. Three types of organothiol molecules including 1-octanethiol (OTT), 2-ethylhexanethiol (2-EHT) and 2-phenylethanethiol (2-PET) were investigated. These chemicals are similar in terms of the number of carbon atoms but different in chemical structure. Contact angle, SEM, AFM, and potentiodynamic polarization are used to analyze hydrophilic and hydrophobic features, morphology, roughness, and corrosion inhibition efficiency, respectively. Mechanisms of SAMs decomposition were studied by FT-IR and XPS analyses. The copper surfaces coated by each organothiol SAMs were annealed at temperature ranging from 25 to 250°C. It was found that OTT SAMs were decomposed at 80°C while 2-EHT SAMs were decomposed at 140°C. In contrast, decomposition of 2-PET SAMs were occurred between 140°C and 250°C, because 2-PET molecule consists of aromatic rings that are more stable than other functional groups in OTT and 2-EHT structures. It is apparent that in all cases, decomposition of organic chain groups were occurred and followed by decomposition of thiolate bond.

Using copper as conductive material in printed electronics has gained considerable attention in recent years due to its high electrical conductivity and low cost compared to other metals. However, copper patterns printed are prone to oxidation and corrosion especially in environment containing chloride ion, and it affects the electrical properties of the copper patterns. Organothiol self-assembled monolayers (SAMs) coating is one of effective methods to protect the copper patterns from corrosion and oxidation. The condition used during SAMs formation affects quality of the organothiol-SAMs coating layer and hence corrosion protection efficiency. However, only a few works have studied the effects of the condition used during SAMs formation on the properties of the SAMs coating layer obtained. The aim of this work was to study the effects of concentration of organothiol molecules and temperature used during SAMs formation on wettability, packing density, roughness and corrosion inhibition efficiency of the SAMs coating layer. The organothiol-SAMs were coated on copper sheets prepared by electro-polishing followed by oxygen plasma treatment for 15 s. Three types of organothiol molecules including 1-octanethiol (OTT), 2-ethylhexanethiol (2-EHT) and 2-phenylethanethiol (2-PET) were investigated. These chemicals are similar in terms of the number of carbon atoms but different in chemical structure. Temperature ranging from -15 to 50 °C, and concentration of organothiol molecules ranging from 0.005 to 0.02 M in isopropanol alcohol (IPA) were studied. Contact angle analysis, SEM/EDX, AFM and potentiodynamic polarization are used to analyze the properties of the SAMs coating layer obtained. It was found that the condition used during SAMs formation strongly affects the quality of the SAMs coating layer. Organothiol molecules of 0.01 M provided the SAMs coating layer with highest corrosion inhibition efficiency. Higher concentration used yielded the SAMs with higher porosity or lower packing density. In contrary, with lower concentration used, the organothiol molecules could not fully cover the copper surface. The SAMs formed at 40 °C with OTT and 2-EHT, and at 0 °C with 2-PET were the most favorable condition with the water contact angle of 124.79°, 130.66° and 120.58°, respectively, and the corrosion inhibition efficiency of 96.24%, 99.37% and 98.90%, respectively.

Although the Au nanoparticle (Au NPs)-based chromatic lead ions detection allows straightforward observation often with high sensitivity and specificity, solution-phase chromatic sensors in general still have several limitations which practically deter its widespread use. Driven by actual need, we have developed a fast, sensitive and portable sensor strip for naked-eye chromatic assaying of Pb²⁺ utilizing electrospun Nylon-6/Polyvinylidene fluoride (N6/PVDF) nano-fibers/nets (NFN) membranes assemble L-glutathione conjugated Au NPs probes (Au@GSH). A basic principle here is that the Au@GSH on the N6/PVDF NFN membranes can aggregate to trigger the red shift from 550 nm to 600nm and a color change of pink to purple on the strip upon incubation with Pb²⁺. Benefiting from large specific surface areas, high porosity and Steiner Tree networks structure of the NFN membranes, the strips exhibited excellent stability, rapid response (10 min), wide detection range (10 to 100 mu;g/dl) and low naked-eye detection limit of 10 mu;g/dl at room temperature. Additionally, the sensing responses are visualized quantitatively by employing a chromatic framework that translates measured spectra into numeric color values which is directly related to color perception. Furthermore, the NFN-based strip displayed excellent anti-interference ability to other 10 possible interfering metal cations and 28-fold higher sensitivity than paper-based one upon exposure to a synthetic mixture. The result clearly demonstrated that this is promising sensing system which could act as a first step toward remediation of lead poisoning in future.

Nanocomposites based on inorganic nanoparticles incorporated in polymer matrixhave received much attention recently due to their electrical and optical properties and the wide range of potential applications [1]. Among inorganic nanoparticles, zinc oxide (ZnO) present appealing features such as electrical and optical properties, it is biocompatible and can be prepared by simple chemical routes [2]. As polymer matrix, polyaniline (PANI) is a widely studied conducting polymer due to good environmental stability and tunable conductivity [3]. In the present work, we obtained nanocomposite films based on PANI/ZnO, which were obtained by the Layer-by-Layer (LBL) method aiming at applications in chemical sensors. PANI was purchased from Sigma Aldrich and ZnO particles were synthesized by the hydrothermal method at 150°C during 30 minutes. The films with 3, 5 and 7 bilayers of PANI/ZnO were deposited onto interdigitated platinum electrodes. The samples were characterized by UV-vis spectroscopy, scanning electron microscopy and electrical measurements, in air with different concentrations of ammonia. UV-vis spectroscopy and scanning electron microscopy confirmed the homogeneous adsorption of bilayers of PANI/ZnO onto the substrates. The electrical measurements yielded satisfactory differentiation for distinct concentrations of ammonia, indicating the potential application of nanocomposites based on PANI / ZnO as gas sensors.
Acknowledgments: This work was supported by CNPq, CAPES, FAPESP and Embrapa.
References:
1. Dhingra, M., et al., Polyaniline mediated enhancement in band gap emission of Zinc Oxide. Composites: Part B, v. 45 p. 1515-1520, 2013.
2. HUANG, R.H., et al., Improvement of proton exchange membrane fuel cells performance by coating hygroscopic zinc oxide on the anodic catalyst layer. Journal of Power Sources, v. 227, p. 229-236, 2013.
3. Ahmed, F., el al., Preparation and characterizations of polyaniline (PANI)/ZnO nanocomposites film using solution casting method. Thin Solid Films, v. 519 p. 8375-8378, 2011.

The use of electronic tongue devices based on polymeric materials to evaluate and distinguish liquids has grown largely in the last decade due to its sensitivity and versatility. These sensors are generally obtained by the deposition of an active layer onto an electrode to interact with the analytes. For this, several film fabrication techniques have been used, emphasizes to the Layer-by-Layer (LbL) technique. In addition, the development of new materials for modifying the sensing units of the electronic tongue is crucial to improve the sensibility and sensitivity of the sensor. Therefore, in this study we focus on the production of materials whose properties are varied significantly by the interplay among their constituents. More specifically, we incorporate gold nanoparticles (AuNP) in the polymeric matrix of poly(allylamine hydrochloride) (PAH) to enhance the properties of tetrasulfonated nickel and cupper phthalocyanine (NiTsPc and CuTsPc) in LbL films. Characterization of the surface morphology, roughness and other physicochemical properties of nanostructured films were carried out by UV-Vis and Infrared spectroscopy, scanning electron microscopy, atomic force microscopy and electrical measurements. The UV-vis absorption spectroscopy revealed that both the Au@PAH/TsPc LbL films grow linearly with the number of deposited bilayers. According to FTIR data, the LbL film growth might be driven by electrostatic interactions between the NH₃⁺ and SO₃^minus; groups from PAH and TsPc, respectively. The electrical behavior of LbL films was evaluated by measuring the electrical impedance, from 1 Hz to 1 MHz, and the results revealed an improvement of resistivity response due the presence of gold nanoparticles. The results demonstrated that the growth of Au@PAH/MTsPc LbL films was successfully achieved and therefore these films could be used in sensing and biosensing applications.
Acknowledgements: We thank financial support from FAPESP (Proc. 2013/23880-3), CNPq, CAPES, MCTI and EMBRAPA from Brazil.

Zinc oxide (ZnO) pure or doped are one of the most promising metal oxide semiconductors for gas sensing applications due to the well-know high surface-to-volume area and surface conductivity. ZnO has been proved to be an excellent gas-sensing material for different gases such as CO, O₂, NO₂ and ethanol. In this context, ZnO pure or doped exhibiting different morphologies and a high surface/volume ratio can be a good option regarding the limitations of the current commercial sensors. Different studies showed that the sensitivity of metal-doped ZnO (e.g. Co, Fe, Mn,) enhanced their gas sensing properties. Motivated by these considerations, the aim of this study consisted on the investigation of the role of Co ions on structural, morphological and the gas sensing properties of nanostructured ZnO samples.
ZnO and Zn1-xCo_xO (0 < x < 5 wt%) thin films were obtained via the polymeric precursor method. The gas sensing properties as sensitivity, response time and long term stability, were investigated for a 33 to 930 ppb concentration range of ozone at different working temperatures. The gas sensing property was probed by electrical resistance measurements. The long-range and short-range structures around Zn and Co atoms were investigated by X-ray diffraction and X-ray absorption spectroscopy, while the microstructural characteristics of thin films were analyzed by a field-emission scanning electron microscope (FE-SEM).
XRD patterns of Zn_1-xCo_xO samples were indexed to the wurtzite ZnO structure and any second phase was observed even at a higher cobalt content. Co-K edge XANES spectra revealed the predominance of Co³⁺ ions. FE-SEM images showed that particle size decreases in function of cobalt content (40 - 30 nm). Gas sensor measurements pointed out that ZnO and Co-doped ZnO samples exhibit a good gas sensing performance concerning the reproducibility and a fast response time (around 10 s). The sensitivity value (R_gas/R_o) of ZnO was 45.0 when exposed to 33 ppb ozone at 250°C. Nevertheless, the Co addition contributed to reduce the sensitivity to ozone gas.

Poly(vinylidene fluoride) (PVDF) has received much attention in recent years as a material for an organic sensor, due to its unique electric properties such as piezo-, pyro-, ferroelectric responses against external stimuli. Those properties are caused by characteristic structures, which are several forms like alpha (TGTG), beta (TTTT), and gamma(TTTGTTTG') phases. The electronegativity difference between fluorine and hydrogen attached to the backbone makes dipole moment along the perpendicular direction to chain axis. In alpha phase, however, all dipole moments cancel each other and make the net moment zero. On the other hand, the beta formed one shows strong net dipole moment when all dipoles are aligned in the same direction. In a preceding research, beta formed PVDF crystal shows well defined hysteresis P-E loop as a ferroelectric material, and large displacement in a electric field as a piezoelectric material. To achieve highly beta formed crystal, there are two basic principles in the applications. One is mechanical stretching. All trans conformation of beta formed crystal has the longest unit length, that's why elongational stress can induce the phase transformation from alpha to beta. And from the ferroelectric property, strong electric field makes the dipole moments aligned to the filed direction causing the structure to be beta formed.
In this study, we introduced some processes to manufacture the highly beta formed PVDF nanocomposite and to simplify the process. Nanotubes made from different atoms are added to the composite to increase an elongational effect, and the external electric field gets the dissolved solution stretched and electrically repulsed into the spinning jet, promoting the beta phase transformation. The rapidly rotating roll collects the spun fibers, causing further stretching effect. WAXD(Wide Angle X-ray diffraction) and FTIR(Fourier Transform Infrared Spectroscopy) were chosen to verify the amount of beta formed crystals in each samples.

We examined the influence of confining gold nanoparticles templated within hierarchically structured thiol functionalized liquid crystalline brush block copolymers (LCBBCs) gelled in ionic liquids on the overall nanoscale morphology, mechanical and electrochemical properties of the nanocomposite ion gels. In the first step, gold nanoparticles (AuNPs) were prepared by in situ reduction of the gold ions and stabilized by direct anchoring through the coordination bonds with the thiol functionalized LCBBCs. The resulting LCBBC/AuNPs nanocomposites comprised a hierarchical structure in which polymer-coated AuNPs were dispersed in a microsegregated LCBBCs matrix that further contained both LC and block copolymer ordering. In the second and final step, these LCBBC/AuNPs nanocomposites were solubilized in ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, to form nanocomposite ion gels. The hydrophilic PEO unit is soluble in IL, while LC domains and AuNPs were insoluble in IL and formed junctions within the LCBBC/AuNPs nanocomposites ion gel network, which predominantly provides mechanical robustness to the ion gels. At 5 wt% concentration, strong LCBBC/AuNPs nanocomposites ion-gels exhibit interesting characteristics including excellent mechanical strength (~ 10³ Pa), good optical properties with higher ionic conductivity (~ 10^-2 Scm^-1) and long-term electrochemical stability over the large potential range than plain polymer ion gels as well as other controls. Thus, self-assembled nanocomposite ion gels by virtue of their architecture and functionality encompassed tunable morphological, optical, thermal and mechanical properties are attractive new materials, offers a promising and versatile approach to design nanocomposite ion gels for templating various nanoparticles with multiple functionalities for applications in catalysis, electrochemical devices, photonic, and opto-electronics.

In recent years, there is a strong preference toward bimetallic systems due to their superior properties. Transition metal integrated main group clusters (i.e. [PtPb₁₂]^2-, [Ni₂Sn₁₇]^4-, [Ni₂Ge₉(PPh₃)]^2-, [Ni₆Ge₁₃(CO)₅]^4-, etc.) have strong potentials to be used as precursors to bimetallic nano-catalysts, in photovoltaic devices, light emitting diodes or in laser applications. Therefore, it is very important to investigate the spectroscopic properties of these clusters to improve currently used systems or develop new ones for applications in nanotechnology. In this study, optical and vibrational properties of the Nickel-Germanium clusters have been investigated via UV-Vis, FTIR, Fluorescence and Raman Spectroscopy. Also, frequency and Time-Dependent (TD) electronic transition calculations have been performed to complement the experimental results. The spectroscopic and computational findings toward evaluation of their potential future applications will be presented.

The growing demand on new technologies in recent years is toward miniaturization of devices into nanometer size with enhanced performances. Currently, nanomaterials, especially bimetallic systems, are subject of intense research due to their unique properties. Transition metal integrated main group clusters (i.e. [PtPb₁₂]^2-, [Ni₂Sn₁₇]^4-, [Ni₂Ge₉(PPh₃)]^2-, [Ni₆Ge₁₃(CO)₅]^4-, etc.) have a wide variety of application area including nanocatalysis, photovoltaic devices, light emitting diodes or laser applications. Therefore, it is essential to perceive the spectroscopic properties of these clusters in order to develop new ones with superior properties for various applications in nanotechnology. In this study, optical and vibrational properties of transition metal integrated lead clusters have been investigated. Experimental findings from UV-Vis, FTIR, Fluorescence and Raman Spectroscopy supported with frequency and Time-Dependent (TD) electronic transition calculations will be presented.

The surface plasmon resonance band of gold nanomaterials embedded in metal oxide heterostructure films is used both as an energy harvesting device structure as well as an optical beacon for the detection of emission gases, CO, NO₂ and H₂, at temperatures ranging between 500 and 800^oC. A summary of previous experiments detailing the sensing characteristics will be provided. Challenges for the detection of emission gases include high levels of sensitivity, the selective detection of the gas of interest within a catalytically active environment as well as surmounting future integration challenges. Recent work will be detailed which shows the implementation of plasmonic based sensing arrays for the detection of emission gases. Variations in nanoparticle size, shape, geometric arrangement as well as the metal oxide matrix chemistry are being varied to produce next generation sensing arrays with enhanced selective sensing properties. Coupled with these recent studies is the novel design of plasmonic arrays that are being developed for their energy harvesting capabilities. Studies will be detailed on these next generation plasmonic structures that include their energy harvesting characteristics and subsequent detection of emission gases without the need of an external white light excitation source.

This presentation will be focused on the development of a novel thermally stable surface enhanced Raman scattering (SERS) substrate. Specifically, these substrates can withstand high temperatures in air for an extended period of time without the loss of their enhancement capabilities. To accomplish this, we utilized a bottom-up approach, where the polyol reduction process was used to synthesize silver nanowires (NW) that were roughly 90 nm wide to act as the SERS active moiety. Subsequently, the NW were coated with a thin protective layer of Al₂O₃ via atomic layer deposition (ALD) or surface sol-gel process (SSP). After heating these SERS substrates at 400°C for 24 h in air, it was found that the coated samples maintained a significant enhancement of the Raman signal, with further heating resulting in effectively no change in the SERS spectrum. The stability imbued by the ALD coating stems from limiting surface oxidation along with impeding aggregation that occurs at the higher temperature, which would otherwise lead to the destruction of the nanomorphology and complete loss of the SERS capabilities. These highly stable SERS substrates highlight the potential application of SERS in investigation of high-temperature chemical reactions and catalytic processes.

Improvements in conventional fossil energy technologies requires increased ability to monitor gas species in extreme conditions such as high temperatures, high pressures, highly reducing or oxidizing atmospheres, and corrosive gases. Optical waveguide sensors with metal oxide thin films that measure optical changes as a result of changing external conditions represent a promising step forward in sensor development. The fuel stream of solid oxide fuel cells (SOFCs) is a promising target for improvements in gas sensing technology, with high operating temperatures and reducing gas streams. This talk reports on the optical gas sensing response of La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM), which has already stability as an anode material in SOFC systems. The near-IR transmission and resistivity response to varying hydrogen levels (1-100%) in a nitrogen background is reported. LSCM shows a large response to reducing gas streams with good recovery and stability. Simultaneous resistivity measurements allow for correlation of optical sensing response to traditional chemi-resistivity sensing literature. The effect of operating temperature on the resistivity and optical response is also reported. These results show high promise for incorporation of well-studied correlated conducting oxide systems into novel waveguide sensors.

The performance of graphene-based ultraviolet (UV) photodetectors fabricated on gallium nitride (GaN) substrates is investigated under ambient and irradiated conditions. For harsh environment applications, UV photodetectors must be robust and handle conditions such as high temperatures, chemically corrosive or radiative environments. GaN is a candidate harsh environment material platform due to its wide bandgap (3.4 eV). GaN devices can operate at higher temperatures, handle higher power requirements and tolerate higher energy/radiative conditions. III-V nitrides (e.g. GaN) can be alloyed with ternary elements for heterostructured devices with potential cut-off wavelength control based on ternary element amounts. The integration of GaN with nanomaterials such as graphene can provide additional functionality.
The metal-semiconductor-metal (MSM) UV photodetector architecture consists of interdigitated comb finger electrodes (typically metal) patterned on a semiconductor substrate. When biased, MSM photodetectors should exhibit linear behavior and low dark currents. For GaN-based UV photodetectors fabricated on silicon wafers, devices can suffer topside illumination losses due to opaque metal electrodes, reducing external quantum efficiency. Enhancement of photodetector performance can occur with use of semi- or transparent electrodes.
Graphene has outstanding electrical, optical, and mechanical properties. A two-dimensional material consisting of carbon atoms arranged in a honeycomb configuration, graphene exhibits room temperature ballistic transport, high charge carrier mobilities and high current carrying capability. Additionally, graphene has absorption of 2.3% across the visible spectrum and a flat absorption spectrum from 300 to 2,500 nm, with potential for optical and optoelectronics applications. Specifically, graphene can be used as a transparent, conductive electrode material.
Although graphene was first isolated using mechanical exfoliation, the development of chemical vapor deposition (CVD) techniques and transfer methods has allowed large area integration for sensor applications. Using CVD-growth graphene and transfer techniques, graphene-based UV photodetectors are fabricated on GaN substrates, with graphene forming the metal portion of the MSM photodetector. The photodetector behavior is characterized using a UV light source under ambient and irradiated conditions (Cs-137 source). Raman spectroscopy is used to investigate the structural disorder of the graphene photodetectors. Recent studies have shown that graphene encapsulation can protect materials from electron beam irradiation damage as well as improve 1/f noise in graphene devices. As such, graphene may prove to be a radiation tolerant material that can be used in combination with GaN for extreme harsh environment applications.

During the last decade, the capture and storage of CO₂ is presented as an important method to control the CO₂ emission. CO₂ chemical sensing in soil and water may contribute significantly to safe CO₂ storage and is also relevant to horticulture. Contrary to commonly used electrochemical CO₂ sensing systems, fibre Bragg gratings (FBG) enable sensing over large distances and at several locations and is a low maintenance and sensitive distributed chemical sensor system on a well known optical platform. The FBG is a one dimensional periodic array of high and low refractive index sections in the core of the fibre. Light is reflected on this grating, and the reflected wavelength depends on the periodic distance in the grating and thus changes with deformation of the fibre.
In order to use the FBG for chemical sensing applications, chemically responsive coatings are developed and applied to the FBG. The coating should expand and/or contract upon a change in CO₂ partial pressure in aqueous environment. The swelling of the material must be carefully tuned, because high swelling will result in coating delamination from the glass fiber, and low swelling will not give enough response. The coating should maintain its mechanical strength in all circumstances to be able to stretch the glass fiber and thus cause a difference in reflected wavelength.
Here we present a responsive polymer coating that fulfils these requirements. Upon the presence of CO₂, the pH of the water will change, which is measured with the coated FBG. The monomer solutions are processed using coating application equipment. The polymer coatings are mechanically stiff, have a good adhesion to the fibres and have proven to be durable so far. In order to reach these properties, a process for the application of the coating to the fibre was optimised and includes fibre stripping and cleaning, application of an adhesion promoter, application of the responsive coating and a post-treatment. The coated FBG is packaged with a semipermeable membrane which is permeable for gasses and water, but is impermeable for ions. The package protects the fragile coated FBG and in addition optimizes the sensor response. The packaged sensor was immersed into an aqueous solution and exposed to 100 % CO₂ (1 bar)(resulting in decreasing pH) followed by 100 %N₂ (to increase pH again) in several test cycles. Automatic measurements of the FBG wavelength response were performed in time. Using a detection resolution of 0.5 pm, fully reversible responses in the order of 200 pm with a good signal to noise ratio are measured with a response time of less than 3 hours.

We describe a new transport mechanism that supports the localized collection of airborn analytes at higher rates when compared to diffusion based standard commonly used. It combines advanced aerosol science with novel nanosensor designs.^[1][2][3]
Background: The detection of single molecular binding events has been a recent trend in sensor research introducing various sensor designs where the active sensing elements are nanoscopic in size. While it is possible to detect single binding events, the research has not yet addressed the question of how to effectively transport airborne analytes to these point-like sensing structures. Currently, diffusion-only-transport is used and it becomes increasingly unlikely for an analyte molecule to “find” and interact with sensing structures where the active area is shrunk in size, trading an increased sensitivity with a long response time.
Approach: Instead of using diffusion-only-transport, we introduce various analyte charging methods and electrodynamic nanolens based analyte concentration concepts to transport airborne analytes to nanoscopic sensing points to improve the response time of existing gas sensor designs. We demonstrate localized collection of analytes over a wide range of molecular weights ranging from 3×10¹⁷ to 1×10² Daltons, including (i) microscopic analyte particles, (ii) inorganic nanoparticles, all the way down to (iii) small organic molecules. We also demonstrate first experimental results towards an programmable active matrix based analyte collection approach referred to as “Airborn Analyte Memory Chip/Recorder” for “offsite” analyte analysis, which (i) takes samples of the particles or molecules in an Aerosol at specific points in time, (ii) transports the analyte sample to a designated spot on a surface, (iii) concentrates the analyte at this spot to achieve an amplification, (iv) repeats this sequence until the recording matrix is full, and (v) reads out the analyte matrix on the chip.
Implications: In all cases we find that the collection rate is several orders of magnitudes higher than diffusion-only-transport. The collection scheme is integrated on an existing surface-enhanced Raman spectroscopy based sensor. The process is able to detect analytes at 9 parts per million within 1 second. As a comparison, 1 hour is required to reach the same signal level when diffusion-only-transport is used. The novel “Airborn Analyte Memory Chip/Recorder” achieved by this approach could be a commodity item that is placed in an environment that a user would like to keep a record from. The information is retrieved on an as needed basis. Offsite analysis of the chip storing the information would make this approach more economical than an online monitoring system for all kinds of threads.
[1]Jun Fang et al., Advanced Functional Materials (in press) (2014).
[2]En-Chiang Lin et al., Advanced Materials 25(26), 3554-3559 (2013).
[3]En-Chiang Lin et al., Nature Communications 4-1636 (2013).

High temperature compatible harsh environment sensors can enable improved process control for higher-efficiency, lower emission power generation applications. Such sensors can also have broad impacts across an array of other industries and applications including nuclear power generation, aviation, aerospace, and industrial manufacturing. Optical based sensor platforms are attractive because they (1) eliminate many common failure modes of electrical based sensors such as the need for electrical wiring and interconnects at the sensing location, (2) reduce the risk of explosions due to an electrical spark when deployed in explosive atmospheres, and (3) allow for increased functionality due to compatibility with broadband wavelength interrogation and distributed sensing methodologies. As a result, a recently established sensor material effort at the National Energy Technology Laboratory has placed an emphasis on the research and development of new optical based functional sensor layers along with prototype sensor demonstration on evanescent wave absorption spectroscopy-based sensor devices for extreme temperature applications. An overview of the current research efforts will be presented including new experimental results of gas sensing at temperatures ranging from 300-800^oC coupled with theoretical modeling of both materials and functionalized sensors to explain measured sensing responses. Future research directions for improved materials and sensor development will be highlighted.

Surface enhanced Raman spectroscopy (SERS) using metallic nanorod substrates has been generally limited to the laboratory setting due to rapid nanostructure degradation in ambient. Beyond just ambient, the extension of SERS to high temperature or reactive environment has not been possible due to even faster degradation of nanostructures in extreme conditions. Aluminum (Al) may be a unique candidate for SERS sensing in extreme conditions due to the formation of a stable surface passivation layer of aluminum oxide while maintaining moderate enhancement in SERS. However, existing theory and atomistic simulations indicate that the growth of Al nanorods using physical vapor deposition should be impossible. Here, through the use of oxygen (O) as a surfactant, we realize the controllable growth of Al nanorods using PVD and illuminate the mechanism enabling the growth of Al nanorods using PVD. It is proposed and experimentally validated that the concentration of O in the vacuum chamber during growth dictates the coverage of kink sites and step edges during growth. The binding of O at the Al kink or step edge increases the local kinetic barriers for a diffusing adatom. As diffusion from the top terrace dictates the diameter of nanorods grown from PVD, the diameter of Al nanorods can be controlled through modification of vacuum level during growth. When grown through this mechanism, Al nanorods have a protective shell of ~2nm of Al oxide. Through long term thermal annealing in ambient, it is shown that this oxide layer is stable at ~2nm in thickness to at least 475K and that the morphology remains unchanged up to 1275K, at which point the nanorods are fully crystalline Al₂O₃.
Taking the nanorods to technological application, SERS, for the detection of trace amounts of N-719 dye, is performed using the Al nanorods as substrates. Freshly fabricated Al nanorods produce moderate enhancement factors of ~10³. The order of enhancement factor is maintained after annealing the Al nanorods in ambient for 30 days or at 475K for one day prior to use. Beyond enhancement and stability, Al is also attractive as an alternative to noble metal nanostructures due to its relative abundance and low cost. Our results indicate that the controllable growth of Al nanorods would enable a new breed of resilient SERS sensors.

The ability of Ag plasmonic nanostructure for surface-enhanced Raman spectroscopy (SERS)-based chemical sensing and measurements in harsh environments is a long-recognized challenge due to their tendency to coalesce or to Ostwald ripen at elevated temperatures, which diminishes SERS enhancement. We have fabricated thermally robust SERS substrates with Ag nanoparticles that maintain their discret size and distribution upon exposure to high temperature. Nanoparticles were immobilized on a porous anodized aluminum oxide (AAO) template via in situ growth from electroless-deposited Ag seeds and heated up to 500 0C for 360 min. The substrates were characterized at room tempreture with SERS, SEM and UV-VIS spectroscopy after heat treatment. Trapping nanoparticles within the pores of AAO prevented the coalescence of colloids at elevated temperatures, thereby preserving their LSPR and SERS activity. The feasibility of this thermally robust SERS-based sensor is demonstrated using both aqueous Rhodamine 6G (R6G) solution (as low as 10^-7 M) and toluene vapor (#65374;2-3%) as modal analytes.

Extensive emissions and fuel economy directives are stimulating the development of ever more sophisticated energy conversion systems, sensors and catalyst systems with improved performance and self-evaluation capabilities. For the development of such systems, deeper insights are required to understand the often complex interplay between the chemical state of the material and its electrical, optical, thermal and mechanical properties. Examples, illustrating how information gained about the defect, electronic and transport structure of oxide materials can be used to optimize properties, are presented. Particular emphasis is focused on means for in-situ monitoring of the status of fuel cell electrodes, catalysts and traps.

With the device miniaturization, functional surface nanostructures become the foundation of modern and future devices. Comparing to planar nanostructures, three-dimensional (3D) nanostructures have extremely large surface areas and high structure densities, hence the realization of 3D nanostructures presents an important task for nanotechnology research. To address this point, template-based 3D nanostructuring techniques with scalable, parallel and fast fabrication processes have been developed in our group. Using these techniques, different 3D semiconductor nanostructures are achieved with advantageous features including perfect regularity of large-scale nanostructure arrays, high density, scalable and parallel fabrication processes, and cost-effectiveness, which are highly desirable for device applications. More importantly, the obtained 3D nanostructures have high structural controllability, which makes these 3D nanostructures as good systems for optimizing their properties. An addressing system of 3D nanostructures with nano-scale resolution is proposed for property investigation and device integration. Using these well-defined semiconductor nanostructures, high performance devices have been realized, mainly for energy-related applications (i.e., supercapacitors) that can be used within a wide temperature range and sensor applications. These achievements indicate the high potential and importance of the 3D nano-structuring techniques both for basic research and for device applications.
[1] Lei Y., Yang S.H., Wu M.H., Wilde G., Chemical Society Reviews, 40, 1247, 2011.
[2] Vellacheri R., Al-Haddad A., Zhao H.P., Wang W.X., Wang C.L., Lei Y., Nano Energy, 8, 231, 2014.
[3] Zhan Z.B., Lei Y., ACS Nano, 8, 3862, 2014.
[4] Wen L.Y., Mi Y., Wang C.L., Zhao H.P., Grote F., Zhan Z.B., Zhou M., Lei Y., Small, in press (DOI: 10.1002/smll.201400436), 2014.
[5] Cao D.W., Wang Z.J., Nasori, Wen L.Y., Mi Y., Lei Y., Angewandte Chemie International Edition, in press, 2014.
[6] Zhou M., Bao J., Xu Y., Zhang J.J., Xie J.F., Guan M.L., Wang C.L., Wen L.Y., Lei Y., Xie Y., ACS Nano, in press (DOI: 10.1021/nn501996a), 2014.

The air and feedstock flux entering into a high temperature engine, a blast furnace, or a coal (or gas) -fired power plant is traditionally measured by either indirectly from temperature and pressure data, or directly using a total pressure probe. Meanwhile, sophisticated and large-size laser diode based measurement system is also being implemented as a promising in-situ monitoring technique at the moment. How to shrink the system and make it portable becomes a great challenge in this case. Herein, a miniaturized and portable measurement method is proposed here that can directly detect gas concentration and flow rate in-situ and real-time simultaneously.
The example sensor candidate is based on ZnO nanorod arrays which have been studied for detection of various inflammable gases including NO₂, C₂H₅OH, CO, and H_2. Here we successfully fabricated uniform and long ZnO nanorods array gas sensor by a continuous hydrothermal flow synthesis method. The respective ZnO nanorod gas sensor has been tested using amperometric detection mode. Meanwhile a piezoresistive signal on the ZnO nanorod surface is reliably extracted dependent on gas flow induced pressure on the nanorod arrays. These signals are systematically demonstrated with a good response and dual-signal differentiation ability upon different gas flow rates and concentrations of multiple gases at high temperature up to 800^oC. The new type of ZnO nanorod array based gas flux sensors have shown high stability, high sensitivity, quick response and recovery time as well as high selectivity.

Abstract
In this study, we present a facile hydrothermal synthesis of hexagonal structured delafossite CuAlO₂ comprised of nanoparticles with typical size ~ 70 nm, thermally stable up to 1200 ° C. Phase analysis carried out using X-ray diffraction and micro-Raman scattering confirmed the single-phase structure of delafossite CuAlO₂. The field-emission scanning electron microscopy images revealed the hexagonal surface and the average nanoparticle size was estimated using transmission electron microscope. The gas sensing performance of delafossite CuAlO₂ was tested towards ozone gas. At the operating temperature, the resistance of sensor decreased upon exposure to 200 ppb of ozone. This phenomenon is explained by the gas sensing characteristics of p-type semiconductor oxide. The hexagonal structured CuAlO₂ detects ozone at a low range of 200 °C with 10 fold larger response than the earlier reported values for other delafossite structures. The results suggest that morphology plays an important role in the performance of sensor. Thus, hexagonal CuAlO₂ structures can be considered as a good candidate for ozone gas sensor application.
Keywords: CuAlO₂, delafossite, hexagonal, morphology, nanoparticle, ozone gas

The well-ordered Cu-doped SnO₂ and un-doped porous thin films with high specific surface area have been fabricated on a desired substrate using self-assembled soft templates combined with a simple physical co-sputtering deposition. The Cu-doped SnO₂ porous film gas sensor shows a significantly enhancement in the sensing performance including high sensitivity, selectivity, reproducibility, and fast response and recovery time. The sensitivity of Cu-doped SnO₂ porous sensor is one order higher than that of un-doped SnO₂ sensor with the average response and recovery times to 100ppm H₂S of about 10.1 and 42.4s, respectively, at the optimum operating temperature of 180°C. The well-defined porous sensors fabricated by the method exhibit high reproducibility due to the accurately controlled process. The facile fabrication process can be easily extended to other semiconductor oxide gas sensors fabrication with easy doping and multilayer porous nanostructure for the practical applications.

1-D Semiconductors have been preferred materials for fabrication of chemical sensors due to the ease of adsorption-induced electronic structure modification. However, at nanoscale, surface passivation leads to deterioration of the merit of their sensitivity. In this study, using first principles density functional theory combined with Boltzmann transport calculations, we have observed sensitivity of as high magnitude as semiconductor nanowires towards chemical species in ultrathin gold nanowires (AuNWs). We observe that the sensing mechanism is directed by the modification of electronic structure of the AuNW and adsorption-induced scattering. Most importantly, the sensitivity of the system shows a linear relationship with the electron affinity of the analyte species. Based on this relationship, we propose an empirical parameter, which can predict an analyte-specific sensitivity of an AuNW, rendering them as effective sensor for a wide range of chemical analytes.

Recent advances in synthesis strategies exercising appreciable control on the nucleation /growth can help to obtain exotic nanostructures and well defined morphologies. This has opened up newer possibilities to revisit and redesign materials with superior properties. The present work explains in detail a one pot hydro-/solvo- thermal synthesis route for the preparation of well defined bcc-In(OH)₃ architecture. The morphological variation such as spheres, cubes, nano-diamonds, and nanoparticles could be obtained by the simple modulation of the reaction medium polarity. Hierarchical In(OH)₃ architectures were synthesised by a hydro-/solvo- thermal route using indium chloride as the metal precursor and ethanolamine as the organic Lewis base. The polarity of the reaction medium was found to play a determining role on the final morphology of In(OH)₃ obtained. A plausible mechanism of formation for these hierarchical In(OH)₃ architectures could be postulated based on controlled experiments. Finally, transformation to porous In₂O₃ nanostructures while retaining the parent morphology could be achieved by calcining the corresponding In(OH)₃ samples. The as prepared materials were characterized and assessed for their physico-chemical properties prior to their performance evaluation as gas sensor materials.
Detection and monitoring of harmful and inflammable gases are of great importance for monitoring environment and health. Among the various air pollutants, carbon monoxide (CO) is one of the most toxic gas, which reacts rapidly with human blood haemoglobin to form carboxy-haemoglobin and damages the human body by causing a reduction in cellular respiration. A trace amount of CO inhalation causes a large number of deaths annually in the world.^1-3 Carbon monoxide sensing characteristics of the In₂O₃ nanostructures were investigated at different sensing temperatures (T_s) and at different gas concentrations (G_c). Gas sensing studies demonstrate an excellent sensing performance of the as prepared hierarchical In₂O₃ architectures in terms of high sensitivity (down to ppb level) as well as fast response (Γ_RES)/recovery (Γ_REC) time. Sensing response at room temperature and selectivity was improved substantially by the incorporation of gold nanoparticles into the In₂O₃ matrix.
References
Yamazoe, N. Sens. Actuators B 1991, 5, 7.
Kolmakov et.al. Adv. Mater.2003, 15, 997.
Guo et.al. CrystEngComm, 2013, 15, 4730-4738.

Gas sensors based on Semiconducting Metal Oxides (SMOX) are already multiply used to detect low concentrations of toxic and/or explosive gases (e.g. H₂, CO, CH₄, ethanol). They offer a low-cost, low-power-consumption alternative to sophisticated analytical equipment and can be easily deployed and operated. Originally, SMOX-based sensors date back to the pioneering work of Heiland, Bielanski and Seiyama [1]. Even if such sensors are sold nowadays in millions per year [2], there is still much research to do to understand their function and the way how the active sensor surface interacts with the surrounding atmosphere, and finally, to improve their performance.
We have prepared core@shell nanocomposites with Pd⁰ encapsulated by SnO₂ shells (Pd@SnO₂) and SnO₂ shells covered with Pd⁰ (SnO₂@Pd) via water-in-oil (w/o)-microemulsions [3-5]. Such nanocomposites as model systems and a comparison of their sensor performance are shown for the first time. Both nanocomposites exhibit high-surface, porous matrices of SnO₂ shells (>150 m²/g) with very small SnO₂ crystallites (<10 nm) and Pd nanoparticles (<10 nm) that are uniformly distributed in the porous SnO₂ matrix. Although similar by first sight, Pd@SnO₂ and SnO₂@Pd are significantly different in view of their structure with Pd inside or outside the SnO₂ shell and in view of their sensor performance. As SMOX-based sensors both nanocomposites show a very good sensor performance for the detection of CO and H₂. Especially, the Pd@SnO₂ core@shell nanocomposite is unique and shows a fast response time (tau;₉₀ < 30 seconds) and a very good response at low temperature (<250 °C), especially under humid-air conditions [6]. Extraordinarily high sensor signals are observed when exposing the Pd@SnO₂ nanocomposite to CO in humid air. Under these conditions even commercial sensors (Figaro TGS 2442, Applied Sensor MLC, E2V MICS 5521) are outperformed.
References
[1] A. Bielanski, J. Deren, J. Haber, Nature1957, 179, 668.
[2] K. Ihokura, J. Waston, The Stannic Oxide Gas Sensor: Principle and Application, CRC Press, Boca Raton 1994.
[3] D. H. M. Buchold, C. Feldmann, Nano Lett.2007, 7, 3489.
[4] H. Gröger, F. Gyger, P. Leidinger, C. Zurmühl, C. Feldmann, Adv. Mater.2009, 21, 1586.
[5] F. Gyger, M. Hübner, C. Feldmann, N. Barsan, U. Weimar, Chem. Mater.2010, 22, 4821.
[6] F. Gyger, A. Sackmann, M. Hübner, P. Bockstaller, D. Gerthsen, H. Lichtenberg, J.-D. Grunwaldt, N. Barsan, U. Weimar, C. Feldmann, Part. Part. Syst. Charact. 2014, 31, 591

Some of the volatile organic compounds (VOCs) in exhaled breath are used as bio-marker for specific diseases. Therefore, sensors for diagnostic use in exhaled human breath have attracted much attention due to their potential for fast, non-invasive, and convenient use; as well as the significant advantage of leaving no bio-hazardous waste, compared to conventional medical examination. Metal-oxide semiconductor gas sensors are good candidates for use as an exhaled-gas sensor because they chips and can easily be minimalized; however, in order to work well as breath sensors, metal-oxide semiconductor gas sensors need enhanced response and selectivity. In this work, we report remarkably improved properties of gas sensing by combining catalytic rhodium (Rh) nanoparticles (NPs) with WO₃ nanofibers (NFs). We synthesized WO₃ NFs by electrospinning, which is a facile and versatile process for producing webs of metal-oxide NFs. Rh NPs (2-4 nm) were synthesized using the polyol process. We functionalized Rh NPs inside of 1-D WO₃ NFs by mixing dispersed Rh-NP solution with W-composite precursor/polyvinylpirrolidone (PVP) solution. The Rh NPs-WO₃ NFs were obtained by calcination of the electrospinning as-spun fiber matrix at 600 °C. Addition of the Rh NPs, results in a rough surface morphology of the WO₃ NFs, and also increases their gas-sensing properties. The gas-sensing characteristics of pure WO₃ and Rh NPs-functionalized WO₃ NFs, were tested using acetone, ethanol, H₂S and toluene gases in a high humidity atmosphere (90% RH), which is similar to exhaled human breath. The results showed that Rh NPs-WO₃ NFs exhibited about 2.5 times better response for acetone than did pure WO₃ NFs. The high sensitivity to acetone by Rh NPs-WO₃ NFs was attributed to the catalytic effect of the Rh NPs. The Rh NPs-WO₃ NFs sensor also had a good enough response and recovery rate to be used as a VOC sensor for human exhaled breath. Therefore we propose that Rh NPs-WO₃ NFs have strong potential for use in sensing acetone in exhaled human breath.

In this research the use of ZnO based sensors and thin-film transistors (TFT&’s) is explored for flexible large area sensor array applications. The sensors involve the use of an addressable array made of ZnO channel transistors and diodes fabricated on flexible substrates. This allows wearable sensor system that will be integrated into a remote low energy-sensing node for health care application. In this paper we are reporting the ongoing realization and optimization of ZnO-thin-film-based metal-semiconductor junction.
Samples consist of a thin (sim; 14 nm) ZnO-based film sandwiched between a 60 nm thick bottom metal contact and a top metal contact with thickness of 200 nm, deposited on a fused silica substrate.
The ZnO thin films were fabricated by means of radio frequency (RF) sputtering, creating a randomly oriented polycrystalline film structure. The junction comprises a Schottky contact as top electrodes (Ag, Ni) and an ohmic contact for bottom electrodes (Al, Ti) to induce the diode effect. Electrodes are deposited by means of DC-sputtering and thermal evaporation. For the metal-ZnO diodes, the barrier heights are as high as 1.00 V and 0.90 V for Ag and Ni respectively and as low as 0.00 V, 0.20 V for Al and Ti respectively.
The ZnO films deposited by RF sputtering lead to a different surface termination, stoichiometry and phase composition, so the influence of sputtering parameters such as total pressure, argon and oxygen flow on the Schottky behavior and film morphology are investigated theoretically and experimentally.
The devices resistivity and mobility are measured. Sentaurus Technology-CAD is used to simulate the band diagrams and output characteristics. Ellipsometer and XRD are used for ZnO film band gap and orientation characterization.
It is possible to achieve high electron mobility for sputtered ZnO on glass and thus maintaining good electrical conductivity. The ZnO film mobility is usually equal to the respective Hall-mobility for low interface traps; however, leakage currents may lead to the underestimation of the channel mobility. Measurements showed an increase of the reverse current which could be attributed to inhomogeneous barrier heights.
The obtained data are used to optimize the junctions for the TFT fabrication.

Diodes are essential to the exponential growth in computing capabilities and serve as a basic building block of many electronic components such as transistors, solar cells, and photodetectors. Despite broad importance, diodes have not been built from metals because the electric field that is needed to achieve current rectification cannot be established inside of a metal. Here we show that the junction between oppositely charged metal nanoparticles produces an electric field that rectifies current. Unlike other diodes such as the vacuum tube or p-n semiconductor diode, these metal nanoparticle diodes achieved highest currents under conditions that areanalogous to reverse bias in other material systems. To apply these diodes to the design of computational circuitry, we built working “AND” and “OR” logic gates and, in combination with metal nanoparticle sensors and resistors, we demonstrated all-metal nanoparticle circuits that functions as an “OR” or “NOR” gate. We expect that metal nanoparticle diodes will expand material choices, simplify the design of future electronic components, and provide functionality beyond that of traditional semiconductor p-n junctions.

The zinc oxide (ZnO) compound is one of the most promising metal semiconducting oxides for multifunctional applications, especially as chemiresistors. Additionally, ZnO compound has been proved to be an excellent gas-sensing material for toxic gases, such as CO, NO_x, NO₂, and O₃. It is well established that ZnO microstructures exhibiting different morphologies and high surface/volume ratio can overcome the limitations of the current commercial chemiresistors. Herein, we investigated the influence of zinc precursor (sulfide, acetate, and nitrate) on the structural, morphological, and ozone gas sensing properties of ZnO thick films obtained by hydrothermal method at 110^oC for 4 hours. The ZnO thick films were grown directly onto a SiO₂/Si substrate with interdigitated Pt electrodes.
The crystalline phase and morphological features were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) measurements. The gas sensor measurements were carried out at room-temperature under blue light irradiation using different ozone levels (80 to 930 ppb).
X-ray diffraction measurements display a hexagonal wurtzite of ZnO with a preferential growth along [001] direction for the all samples. FE-SEM images show that the morphology of the both ZnO films obtained from zinc nitrate and acetate consists of the hexagonal nanorods of ca. 150 nm. Whereas, the ZnO film prepared from zinc sulfide was based on hexagonal disks-like structures of ca. 10 mm. Electrical measurements proved the efficiency of the ZnO films as ozone gas sensors at room temperature under blue light irradiation, displaying good gas sensing characteristics, such as a fast response (less than 25 s) and a short recovery time (less than 60 s) at a low ozone level of 80 ppb. On the other hand, the ZnO film obtained from sulfide exhibited a better gas sensing performance, with a faster response ( of ca.18.8 s) and a shorter recovery time of ca. 5.7 s, compared to ZnO films obtained from nitrate and acetate. These results point out that the zinc precursor becomes a key parameter to control of microstructural properties as well as the sensitive room-temperature ozone sensing performance under blue light irradiation of ZnO thick films obtained via hydrothermal method.

The polythiophenes can act as sensor materials of volatile organic compounds (VOCs) [1, 2], these sensors have a high demand for many applications such as environment monitoring and homeland security [3]. Langmuir-Blodgett (LB) technique was employed to produce the polymeric thin films, since it provides organized molecular architecture at nanoscale level [4]. We have mixed, amphiphilic molecules (stearic acid - SA) to poly(3-alkylthiophenes) (P3ATs): poly(3-butylthiophene), poly(3-hexylthiophene) and poly(3-octylthiophene), in order to improve deposition via Langmuir-Blodgett technique. The solutions of P3ATs/SA were fabricated with 43 molecular percentage of stearic acid that was chosen, among other films with different molecular percentages, due to good quality films and high conductivity presented. The mixed LB films were fabricated using a Langmuir trough model KSV 5000 and it was observed the deposition parameters. Film growth in hydrophobic glass was supervised using the UV-Visible optical absorption. Film morphology and roughness were analyzed through Atomic Force Microscopy. Electrical measurements, current versus voltage (I vs. V), and current versus time (I vs. t) were carried out in the IDE using Keithley 238 source-measure unit. In order to characterize the sensor behavior it was measured the current versus time with a fixed applied voltage of 5V on the presence of the VOCs: toluene, dichloromethane and tetrahydrofuran in dynamic flow, dragged by nitrogen. The electrical measurements were performed using the parallel contact that was obtained by depositing P3ATs/SA LB film on interdigitated electrodes (IDE). Thin films showed, in current versus time (I vs. t) curve, sensibility to the VOCs, with a decrease in the current value. Despite the incomplete reversibility of the process, sensors can be used several times. Even after a film have detected a VOC, the same film can detect different VOCs.
We acknowledge support from CAPES, FAPESP, CNPQ/INEO and LNLS.
[1] S. Ozawa et al. Journal of Nanoscience and Nanotechnology, 14, 9, 6624-6631 (2014).
[2] B. Li et al, Sensors and Actuators B, 123, 651 - 660 (2007).
[3] H. Kim and G Kwak. Macromolecules, 902-904 (2009).
[4] G. C. Ferreira et al. Synthetic Metals, 194, 65-70 (2014).

Ferroelectric materials have been widely used to fabricate capacitors. Nevertheless, their dielectric properties are generally closely related to the spontaneous polarization and phase transition, with resulted in a large variation in capacitance and dielectric loss at the Curie temperature, as well as fatigue and aging problem at an alternating electric field. Unusual cubic perovskite like CaCu₃Ti₄O₁₂ (CCTO) has drawn a lot of attention, because revealed an extraordinarily high dielectric constant at room temperature. Compared with other compounds, CCTO possesses much higher permittivity. There are some hypotheses to explain the origin of the giant dielectric constant in CCTO, mainly including the extrinsic and intrinsic factors. Unfortunately, the high dielectric loss hampers a practical application. In this investigation, we propose to prepare and study the CCTO doped with Na aiming to reduce the dielectric loss. CCTO was prepared by the traditional solid-state reaction technique using starting materials of CaCO₃, CuO and TiO₂ reagents. After homogenization for 6h, the mixtures were calcined at 950^oC for 10h. The powders were then ball-milled for 2h into fine powders, compacted into disk-shaped samples and then sintered at 1050^oC for 6h. The phase and microstructure developments were followed by X-ray diffraction (XRD) using a Rigaku Ultima IV diffractometer (with a monochromatic CuK_α radiation, lambda;=1.5406Å) and scanning electron microscopy (FEI), respectively. Electrical measurements were carried out with a Solartron SI 1260 impedance/gain-phase analyzer over a wide temperature range from 25 to 200^oC. No phase transition is observed in the studied temperature. Dielectric constant and dielectric loss decrease with the increase of the Na content.

The solid solutions based on (1-x)Ba(Ti_1-xZr_x)O₃ - (x)Ba_yCa_1-yTiO₃ (BZT-BCT) have attracted a significant research interest due to their high piezoelectric coefficients. Although in a small temperature range, some compounds presents piezoelectric coefficients values that exceed even the d₃₃ of soft PZT. Nevertheless, the Influence of synthesis and sintering parameters on structure and phase transitions in these “pseudo binary” materials were not completely studied. Therefore, in the present work, ceramics of (0.5)BaTi_0.85Zr_0.15O₃ (BTZ) - (0.5)Ba_0.77Ca_0.23TiO₃ (BCT) (BCT-BZT) has been prepared by the solid state reaction of BZT and BCT compounds. To complete our study, samples with the nominal formulation Ba_0.885Ca_0.115Ti_0.925Zr_0.075O₃ (BCZT) were prepared. The powders were individually calcined at 1200^oC for 2h and then mixed in the proportion of 50/50, ball-milled for 12h into fine powders, compacted into disk-shaped samples and then sintered at 1320^oC for 1min/2h/10h and at 1270^oC for 1 min. The final density of each sintered specimen was determined by the Archimedes method. The BZT/BCT phase and microstructure developments were followed by X-ray diffraction (XRD) using a Rigaku Geigerflex diffractometer (with a monochromatic CuK_α radiation, lambda;=1.5406Å) and optical microscopy (Zeiss AX10), respectively. Grain size of the ceramics was evaluated by the intercept method. Electrical measurements were carried out with a Solartron SI 1260 impedance/gain-phase analyzer over a wide temperature range from 25 to 200^oC. The dielectric spectra are characterized by dielectric peaks that correspond to the ferroelectric-to-paraelectric phase transitions. In particular, there was observed that the two preparation methods results in different structural phase transitions with the temperature. Furthermore, the sintering temperature and time affect the phase transitions, microstructure and the dielectric properties of BCT-BZT ceramics. The conclusion is that the preparation methodology, sintering temperature and time has influence in the competition between the ions to occupy the same crystallographic site, with leads to compositional fluctuations of different micro-regions in the material.

Metal oxides are a candidate for active material adequate for low -cost & high- mass-production of gas sensors. After many options, integrated sensor devices based on silicon base platform become the more feasible and reliable technology only limited but the range of available temperature excursion although, nowadays, it can be overcome using SOI based platforms which could work up to 6000C. As both, active material and sensor platform, are able to operate at high temperature, place this technology in a very good position for its application under harsh enviroments, such as boilers.
In this work, we present an innovatibe CMOS-compatible, Silicon-on-insulator (SOI) integrated smart microsensor system capable of measuring multiple targets under harsh environmental conditions.
As part of this system, we will discuss around a CO sensor based on tin oxide thin films deposited by Pulsed Laser Deposition.
Due to the small effective area of the platform, 200 microns diameter, one of the stronger drawbacks is the availability of techniques for such localized deposition of sensing material. Although different methods have already been proposed as inkjet, sputtering, localized CVD, etc. They have some drawbacks concerning, respectively, to reproducibility, material stoichiometry control or strong requirement on ambient and platform conditions.

Thin film resistors subjected to harsh conditions such as high temperature often exhibit a drift in resistivity. This drift will deteriorate the performance of devices relying on stable resistivity such as strain gauges. In this work, the electrical stability of titanium nitride thin films deposited using reactive sputtering has been investigated. The depositions were carried out in a N₂/ Ar atmosphere from a titanium target onto polished glass substrates that were not intentionally heated. The effect of three parameters on the electrical stability was studied: deposition pressure, nitrogen flow and target power. The resistivity was measured using electrical 4-point measurements on two sets of samples. The first set was used to study the stability at room temperature while the second set was used to study the stability at 200°C for up to 350 hours. Additional substrates for further analysis of the films were included in each deposition.
The deposition pressure was found to have the most dramatic impact on the film stability. The film deposited at the highest pressure (0.5 Pa) was found to be very unstable even at room temperature. As the pressure was decreased the stability was drastically improved. Furthermore, a significant increase in the X-ray diffraction (XRD) peak intensities was observed indicating an increased crystallinity of the films. Cross sectional scanning electron microscopy images showed a more dense columnar film structure of the films deposited at low pressures while the films deposited at higher pressures appeared more porous. The increased density of films deposited at low pressure was verified by direct measurement of the film masses using a high precision micro scale. Energy-dispersive X-ray spectroscopy measurements showed large amounts of oxygen in the films deposited at higher pressures despite no oxygen being added during deposition. This indicates that oxygen diffuses deeper into the more porous films after the deposition process.
The variation of nitrogen flow was done from the metallic target mode to the poisoned target mode at constant pressure. The films deposited in the metallic and poisoned modes were found to be stable at 200°C with a resistivity drift below 2 % after an initial relaxation time of 50 hours. The films deposited at intermediate nitrogen flows were not stable at 200°C showing a continuing increasing trend in the film resistance. Furthermore, the XRD spectra showed a predominant (111) texture for the unstable films. The effect of target power on film stability was also investigated. It was generally found that the films made in the region in-between the metallic and poisoned target modes yielded unstable films at 200°C.

Novel Co₃O₄ nanostructure arrays with rhombus-shaped and needle-like morphologies have been prepared by using urea and hexamethylenetetramine as hydrolysis agents through a facile fluoride-assisted hydrothermal method, respectively. The precursor Co(CO₃)_0.5(OH)middot;0.11H₂O or Co(OH)F plays a crucial role in the formation of needle-like or rhombic arrays. The as-prepared precursor can be further thermally converted to porous Co₃O₄ arrays without significantly altering the one-dimensional morphology. Both types of the Co₃O₄ nanostructure arrays can directly serve as gas sensors without complicated fabrication process, owing to the direct growth on the substrates, good ohmic contact with the electrodes and intensive contact with the substrates. The Co₃O₄ nanostructure arrays based gas sensors showed high-performance of ethanol detection. The highest sensitivity of rhombus-shaped and needle-like Co₃O₄ morphologies reached 30.4 and 89.6 for 100 ppm ethanol vapor and the optimal working temperature was as low as 160^oC and 130^oC, respectively. Meanwhile, both types of the sensors exhibited good response/recovery kinetics, outstanding selectivity and good reproducibility. The high ethanol gas sensing performance of the Co₃O₄ nanostructure arrays can be explained by a typical p-type behavior with the one-dimension structure, nano-porosity, quasi-single crystalline structure and open space. Higher sensitivity in nanostructure arrays with needle-like morphology than rhombus-shaped arrays can be mainly attributed to the different exposed crystal planes. We consider that the exposed planes simultaneously contain Co²⁺ and Co³⁺ on the surface are benefit for the gas-sensing properties.

Proton conducting polyvinylalcohol based composite membranes were fabricated to be used as ionically conducting membranes for the development of flexible solid state electrochemical capacitors. Fillers such as silica nanoparticles were uniformly dispersed in polyvinyl alcohol/phosphoric acid mixture in order to improve the mechanical properties as well as increase the overall uptake of phosphoric acid. Effect of addition of silica on polymer properties were probed using impedance spectroscopy as well as other characterization tools that include transmission electron microscopy and infrared spectroscopy. It was shown that addition of phosphoric acid affects the crystallinity of the polymer and incorporation of silica facilitates the fabrication of freestanding solid state membranes as thin as 25mu;m. The effect of ionic conductivity over a wide range of temperature ranging from - 50 °C to 100 °C was also explored. Mechanism related to space charge conduction due to the addition of nanofillers was investigated. The fabricated membranes were then used to assemble all solid state stacked electrochemical capacitors with the help of flexible binder-free carbon nanotube electrodes.

Zn₂SnO₄ has a cubic inverse spinel structure and has been attractive as a potential candidate for use in ultraviolet photo-detectors, electrodes for dye-sensitized solar cells, and gas sensors, due to its high electrical conductivity, high thermal stability, low absorption coefficient in the visible range, and high chemical sensitivity. Furthermore, low cost mass production of Zn₂SnO₄ nanofibers (NFs) can easily be achieved using the electrospinning method.
In this work, two efforts were made to enhance the selectivity and sensitivity of acetone detection by Zn₂SnO₄ NFs. First, we synthesized porous Zn₂SnO₄ NFs that had a high surface-to-volume ratio. The highly porous structure of these Zn₂SnO₄ NFs was formed via an in situ phase-separation between inorganic-metal precursor-rich regions and poly (vinyl acetate, PVAc) polymer-rich regions, during the electrospinning and following calcination steps. Second, we functionalized the Zn₂SnO₄ NFs with palladium (Pd) and graphene oxide (GO) to achieve better sensitivity and selectivity than pristine Zn₂SnO₄ NFs. The 1 wt% Pd-embedded, porous Zn₂SnO₄ NFs were fabricated by electrospinning, using a solution into which Pd was mixed as a form of salt with metal-precursor and PVAc-polymer in DMF. Then, the GO was uniformly functionalized with the 1 wt% Pd-embedded porous Zn₂SnO₄ NFs, to bring out the synergistic effects of the GO and Pd. The GO-Pd-functionalized porous Zn₂SnO₄ NFs showed vastly improved acetone detection capability, with sensitivity (R_s) of 125 at 5 ppm. This was 3.78-fold, 3.92-fold, and 6.78-fold better than the values achieved by pristine porous Zn₂SnO₄ NFs; 1 wt% Pd embedded porous Zn₂SnO₄ NFs; and GO functionalized with porous Zn₂SnO₄ NFs, respectively. We also confirmed that the new product was outstandingly selective for acetone, when compared to H₂S (R_s=5) and toluene (R_s=6.5) in high humidity atmosphere (90 RH%). This condition is similar to exhaled human breath. This work suggests significant potential for precise acetone detection in exhaled breath using the optimized, GO-Pd-functionalized, porous Zn₂SnO₄ NFs.

Sandia Octahedral Molecular Sieves (SOMS) and well-aligned SOMS micro-wires with hydrophilic dangling bond on the surface show distinguished humidity response both in static and dynamic examinations. Sandia Octahedral Molecular Sieves (SOMS) wires were synthesized using niobium pentoxide as the precursor in concentrated sodium hydroxide solution. The electrophoresis method was further utilized to align the SOMS micro-wires on substrate. The static and dynamic humidity responses of SOMS and aligned SOMS wires were examined by I-V behaviors in RH0% ~ RH100%. The high sensitivity linear dependence relation between current/resistance response and relative humidity were observed. In I-RH diagram, the slopes are 0.06 with standard error 0.007 and 0.11 with standard error 0.012 for SOMS and aligned SOMS wires, respectively. In the dynamic measurement, changing of the humidity of detecting chamber were reached by turning on and off the valve connected the chamber and the humid gas (RH70%) storage tank and were examined by the I-t behaviors. The response time was 28~35 seconds and recovery time was 12~15 seconds. The sensitivity maintain 90% after more than 10 cycles in between RH0% and RH70%, which indicates the moisture detectors have good humidity response, recovery time and reproducibility. In summary, SOMS and aligned SOMS micro-wires with high sensitivity and quick response to moisture, can be produced easily through a nature-friendly mass production process, making them a prominent candidate for humidity detector.

With the rapid development of micro-electro-mechanical systems (MEMS), many micro-machining ways were well developed and used, which made the micromation, low power consumption and intelligence of sensors possible. Carbon monoxide, one of the most common and widely distributed air pollutants, is harmful to atmosphere and human health. During the development of MEMS CO catalytic combustion micro-sensor, it was found that the sensitivity and selectivity were all very low when traditional high temperature catalyst was used. Combustible gases other than CO also respond at that temperature. In order to solve above problem, highly stable low-temperature CO oxidation catalyst under ambient condition was developed and introduced into the structure of micro-sensor. The CO oxidation process could be carried out at relative low temperature and thus promote the selectivity effectively. In addition, the resulting product become intrinsically safe instead of explosion-proof security products as traditional catalytic combustion sensor be. On the other hand, the sensitive materials (CO oxidation catalyst) were fabricated into meso-structure. The loaded amount of catalyst and contacted area between CO and the catalyst will be greatly enhanced, and much higher sensitivity could be obtained. Here, we reported a facile self-assembly approaching using P123 as template and in-suit reduction process to obtain meso-structured Mn₃O₄ supported Pd catalyst. The resulting materials displayed large surface area and high dispersion of palladium species, and showed much enhanced catalytic activities and stability for low-temperature CO oxidation under ambient condition. Complete CO conversion could be achieved at as low as -10 ^oC over 5.3 wt% Pd loaded catalyst and the catalyst exhibited no detectable deactivation even after 30 hours of reaction at 35 ^oC when 4.0 vol% H₂O was introduced into the feed gas. After applied on micro-heater chip, at the working temperature 80 ^oC, the intrinsically safe, sensitive and low-powered CO micro-sensor could be easily achieved.

The National Energy Technology Laboratory is the primary laboratory for the Department of Energy focusing on applied research, development, and demonstration of highly efficient and environmentally benign fossil energy-based power generation technologies. Advanced power generation systems including those capture and store carbon have harsh conditions that require monitoring for optimal performance. During fuel conversion, conditions can include high temperature (up to 1600 C) with either highly oxidizing (e.g. combustion turbines) or reducing conditions (coal gasifiers) Post conversion conditions are at lower temperatures (200-700 C) but have the need to measure trace level constituents in real time. As CO2 capture and storage operations are coupled to with advanced power generation, the sub surface conditions for CO2 storage require extensive monitoring including temperature (100-250 C) range, pressure (up to 10,000 psi) and strain/stress in formations where dissolved solids are very high and the pH is low. Monitoring needs within these systems are extensive and advances in real time and in situ sensing are important to monitor and maintain performance of these systems. Recent advances in sensor materials, designs, and prototypes to address measurement needs, harsh system conditions, and application to industrial commercial applications will be reviewed.

Composites of magnetostrictive (MS) and piezoelectric (PE) layers on a cantilever substrate (Sub) are candidates for ultrasensitive magnetic field sensors at room temperature and recently have shown magneto-electric (ME) coefficients of 20 kV/cmOe in resonance [1-3]. In these composites a magnetic field H causes a mechanical strain in the MS layer. On resonance this excites an oscillation of the cantilever, which is limited by damping. In the static case a static deformation follows. The deformation of the PE layer induces an electric field E and thus an electric potential difference V across the PE layer, which constitutes the sensor signal in open circuit operation. If the sensor electrodes across the PE layer are short circuited in short circuit operation the voltage vanishes and the piezoelectric charge constitutes the signal for a charge amplifier resulting in a renormalization of the balances between the strain, electric, and magnetic fields in the cantilever. Here, we present a theoretical investigation of the short circuit vs. the open circuit operation mode for FeCoBSi-AlN and FeCoBSi-PZT bilayers on Si substrates and the achievable magneto-electric coefficients in these four cases. We implemented analytic and finite element models producing nearly identical results for the resonant strain-mediated, bending-mode ME effect in thin film composites. Using these linear elastic models, we calculate the open and short circuit ME coefficients αME_Voc= dV/dH and αME_Qsc= dQ/dH of the transverse ME effect (E _|_ H ) for varying layer thicknesses in both material systems. We find pronounced operation mode and PE material-induced differences of the ME effect size and layer thickness behavior. In short circuit operation the greatest magnetoelectric response is produced near vanishing PE layer thicknesses independent of PE material choice (AlN or PZT) while the open circuit response maxima appear about near equal PE and MS layer thicknesses. In open circuit mode FeCoBSi-AlN-Si cantilevers produce about 10 times greater ME coefficients than corresponding FeCoBSI-PZT-Si cantilevers. As a surprise, this behavior is reversed in short circuit operation with an even greater ratio. This indicates greatly different contributions of the piezoelectric, dielectric, and elastic properties of the PE layer to the resonant bending-mode magnetoelectric response for different operation modes. The results are important for enhanceing the sensitivity and SNR of bending-mode magnetoelectric sensors towards, among others, detection of human heart and brain currents for medical diagnostics.
This work was supported by the German Science Foundation (DFG) within the Collaborative Research Center SFB 855 “Magnetoelectric Composite Materials - Biomagnetic Interfaces of the Future”.
[1] C. Kirchhof et al. , Appl. Phys. Let. 102, 232905 (2013)
[2] M.C.Krantz and M. Gerken, AIP Advances 3, 052131 (2013)
[3] M.C.Krantz, J.L.Gugat, and M.Gerken, AIP Advances 3, 062135 (2013)

Gas sensor based on thin films have allowed for the detection of an important set of gases in several environmental control. It becomes important to focus a research on the development of low-cost gas sensors in order to access applications where the use of conventional analytical systems is prohibitively expensive. Recently in the literature, the strontium titanate doped with iron was suggested as a good candidate for application as ozone gas sensors. Strontium titanate (ST) has been extensively explored as gas sensors. This material is widely studied due the facility to incorporate different ions in its structure. The aim of this study was the synthesis and characterization of SrTi_0.85Fe_0.15O₃ (STF) and La_0.02Sr_0.98Ti_0.85Fe_0.15O₃ (LSTF) thin films in order to verify their ozone sensing properties. The thin films were synthesized by a polymeric precursor method followed with spin-coating and heat treatment at two different temperatures 500 and 600 °C/4h. The crystalline phase and morphological features were investigated by X-ray diffraction (XRD), X-ray Absorption Near Edge Structure (XANES) and field-emission scanning electron microscopy (FE-SEM). The thickness of the films were observed around 100 nm by electronic microscopy (FEG-SEM). X-ray diffraction (XRD) technique showed that both compositions present only a single cubic phase similar to the SrTiO₃. The Ti K-edge structure X-ray Absorption Near Edge Structure (XANES) spectra of films heated at 600 °C/4h compared to 500 °C/4h indicates an increase of the local order around Ti atom caused by different heat treatment. The electrical characteristic of the thin films as a function of sample composition and temperature were evaluated regarding the response to ozone gas at 300 °C. The O₃ gas was generated by oxidizing oxygen molecules of dry air by a pen-ray UV lamp calibrated to give an O₃ concentration range 0.4 to 3.2 ppm. The samples showed a p-type semiconducting characteristic since their resistance decrease with the adsorption of oxidizing gases. The LSTF film showed the best sensor response, S = R_air/R_gas (R_gas < R_air), to ozone gas between 2 and 4, depending of the gas concentration, as well as a short response time ~4 seconds. The present study shows that thin films composed of SrTi_0.85Fe_0.15O₃ (STF) and La_0.02Sr_0.98Ti_0.85Fe_0.15O₃ (LSTF) can be synthesized by polymeric precursor method followed with spin-coating. The gas sensing measurements showed that the sensor film with La exhibited a better sensitivity as well as a short response time to ozone gas.

Ability to control thermal and electrical transport through materials in nanoform makes them highly desirable in energy conversion devices. For example, enhanced electrical transport offered by single-crystalline nanowires makes them highly useful in photovoltaic fabrication. These desirable properties, however, come with a huge drawback, the instability of nanowires. High propensity of these nanowires to react with air and moisture reduces the lifetimes of energy conversion devices fabricated from them. The problem is more pronounced if the acidic nature of rainwater is taken to account. The acidic nature of rainwater accelerates the degradation of nanowires, and further reduce the lifetimes of energy conversion devices employing nanowires as one of the component. To utilize the superior and novel properties of these materials even in acidic environments, a simple and reliable strategy for stabilizing the surfaces of compound semiconductor nanowires is presented. This strategy involves the non-conformal decoration of nanowire surfaces with boron nitride (BN) to make them hydrophobic. This hydrophobic nature makes the nanowires non-wettable to aqueous solution and imparts them stability. At the same time, this BN non-conformal decoration does not majorly alter the electrical and electronic properties of the nanowires. In this talk, experimental methods underlying the use of this strategy for stabilizing zinc phosphide (Zn₃P₂), zinc oxide (ZnO) and magnesium silicide (Mg₂Si) nanowires will be presented. Demonstration of the enhanced resistances of these nanowires to moisture- and acid-assisted degradation will be made. Pathways for extending this strategy for stabilizing other compound semiconductor nanowires, including nitrides, sulfides, silicides and antimonides, will be discussed.

Noble metal nanoparticles are extensively used for sensitizing and enhancing metal oxide chemical sensors through a catalytic spill-over mechanism. However due to earth-scarcity and high cost of noble metals, finding replacements present a great economic benefit with a significant opportunity for enhancing materials and manufacturing sustainability. In this study, a new type of β-Ga₂O₃ nanorod array based high temperature gas sensors has been successfully fabricated. The enabled gas sensors are found to be highly sensitive to carbon monoxide at 500°C, with good reversible and reproducible response characteristics. Through surface decoration of 10 nm thick perovskite-type La_0.8Sr_0.2FeO₃ (LSFO) nanoparticles, the sensitivity of β-Ga₂O₃ nanorod array gas sensors was enhanced by an order of magnitude, rivaling the Pt-decoration effect. The LSFO-Ga₂O₃ sensor also featured a faster response time compared to Pt sensitized counterparts, although the selective molecule adsorption and filtering effect originating from LSFO decoration made the sensor response slower than that of pristine Ga₂O₃ nanorod array sensors. The perovskite-type LSFO could be a promising candidate to replace noble metals for sensitizing metal oxide gas sensors at high temperature.
Reference:
Hui-Jan Lin, John Baltrus, Haiyong Gao, Chang-Yong Nam, Paul Ohodnicki, Pu-Xian Gao, 'Perovskite nanoparticle sensitizing effect on semiconducting Ga₂O₃ nanorod arrays for high temperature gas detections,' 2014, to be submitted.

High temperature gas sensors for harsh exhaust environments are of paramount importance to improve combustion efficiency and control emissions. There is an urgent demand to develop miniaturized, robust and cost-effective high temperature gas sensors with good thermal stability, high sensitivity and selectivity. This talk discusses our recent work on thermal stable nanostructure enabled resistor-configured gas sensors for in-situ and real-time reducing gas detection at high temperature above 800 ^oC with good sensitivity and selectivity. Electrospinning technique was used to fabricate metal oxide nanofibers due to its efficient and facile process to generate one-dimensional nanostructure in large scale.
Perovskite La_0.67Sr_0.33MnO₃ and CeO₂ nanofibers were first fabricated by electrospinning followed by a calcination process. Both of LSMO and CeO₂ nanofibers exhibited excellent thermal stability in terms of both morphology and chemical composition at 1000 ^oC. These two materials were employed as sensing material in resistive sensors to in-situ and real-time detect O₂ at high temperature (800 - 1000 ^oC), which showed good sensitivity, recoverability and reproducibility. In addition, CeO₂ nanofibers-based sensor also demonstrated its excellent sensitivity towards CO.
To improve the selectivity of resistor-configured gas sensors for reducing gas detection, three different approaches were used. First, impedance spectroscopy was employed to investigate the impedance profile changes of Pt-CeO₂ nanofibers in different gas atmosphere (N₂, O₂, CO, CO₂, SO₂, NO, C₃H₈) at 800 ^oC. Equivalent circuit analysis was conducted to investigate the sensing mechanisms. By operating the sensor at a high frequency (e.g., 100 kHz), the sensor can selectively detect strong reducing gas (CO and C₃H₈) and eliminate the interference from all oxidizing gas and weak reducing gas. To further improve the selectivity within the reducing gas group, p-LSMO NFs/n-CeO₂ NFs heterojunction composites were prepared by sonication and systematically investigated. The optimized LSMO-CeO₂ NFs composite with CeO₂ NFs content of 80% showed the good sensitivity as well as the improved selectivity to C₃H₈ over other reducing gases such as CO and CH₄ at high operation temperature of 800 ^oC. Lastly, Ce-Ni-O composite nanofibers were fabricated by electrospinning and subsequent calcination and showed an excellent sensitivity and selectivity towards C₃H₈ and negligible response to CO and CH₄, due to the much faster reaction kinetics between Ce-Ni-O nanofibers and propane. The sensing mechanism was proposed.
By designing novel materials and employing impedancemetric technique, nanostructure enabled gas sensors with good stability, high sensitivity and selectivity for reducing gas detection were successfully developed. These research activities open an avenue in the design of high temperature gas sensor with high performance.

Nanowire gas flow sensor is a novel form of MEMS mass flow sensor at its primary research stage. It is designed by utilizing a nanowire array and its specific electrical conductivity changes upon flow pressure on the sensor material. Piezoresistivity of the material is currently being studied as the main sensing mechanism of nanowire gas flow sensor. This study is focused on modeling and simulation of piezoresistive effect in the nanowire gas flow sensor. Finite element analysis (FEA) model constructed using COMSOL Multiphysics^® software has been used for modeling piezoresistive phenomena in nanowire array for design of new gas flow sensor. 3D FEA model of p-type silicon nanowire array has been constructed using COMSOL and tested for multiple variables such as induced stress tensor, induced voltage and electric field with varying gas flow in the channel. Initial model is constructed by a single nanowire, gas channel with symmetric boundary conditions and solved using fully coupled Fluid-structure interaction and Piezoresistivity Domain currents modules. COMSOL model and simulation is used to understand the morphology dependence of sensor activity and to support the experimental device fabrication. Given their excellent irradiation resistance reported in literature, these Si nanowire array based mass flow sensors could be used to measure the ion flux under ion irradiation extreme condition.

There is a critical need for electrically conductive thin film materials that remain very stable and nonreactive at temperatures above 1000^oC for use in wireless sensors, actuators, and other thin film based electronic devices operating in harsh environments. At these high temperatures, thermodynamic rather than kinetic factors become dominant and often film deterioration occurs by mechanisms including recrystallization, agglomeration, oxidation, and chemical interdiffusion. In this work, we have synthesized 200 nm thick nanocomposite Pt-Zr-B and Pt-Si thin film materials on both sapphire and langasite substrates using e-beam evaporation, and have characterized their structure, morphology, and chemical composition following thermal treatments in laboratory furnaces and testing within a small-scale turbine engine environment. Soft x-ray absorption spectroscopy and valence band photoemission measurements have also been performed on both types of films to probe valence band electronic structure. In the Pt-Zr-B system, fabrication of a nanolaminate architecture consisting of a ZrB₂ phase layered with a Pt phase leads to intermixed phases at high temperature, and 4-point probe conductivity measurements show that the resulting nanocomposite film structures have a conductivity of 10⁶ - 10⁷ S/m depending on the Pt-ZrB₂ layer thickness ratio. X-ray diffraction also indicates that ZrO₂ nanocrystallites are formed in the films, which help to hinder agglomeration of the Pt phase. In oxidizing environments, XPS analysis shows that boron oxide forms at the surface, which evaporates above ~800^oC. A thin amorphous alumina capping layer on top of Pt-Zr-B nanocomposite films are found to be effective in limiting boron depletion and retarding oxidation, leading to improved long-term morphological stability. In the Pt-Si system, the film compositions were varied to yield either nanocrystalline Pt₂Si or Pt-Si phases depending on the Pt-Si ratio, or an amorphous phase with high Si content. Above 1000^oC in air, Pt-oxide and Si-oxide phases form and coexist with the Pt-Si phases, and the film conductivities remain in the range 1x10⁶ to 5x10⁴ S/m. An amorphous alumina capping layer also aids long term film stability for this system.

This contribution deals with hard nanocrystalline conductive thermally stable materials MBCN (M = Ti, Zr, Hf). The materials were prepared in the form of thin films by pulsed reactive dc magnetron sputtering of M₄₅(B₄C)₅₅ targets in N₂+Ar plasma. All films exhibit very smooth defect-free surfaces (average roughness <1 nm) and low compressive stress (due to the adaptively varied discharge pressure). The materials exhibit oxidation resistance (mass change <0.01 mg/cm²) of around 600 °C at low N content and 750°C at enhanced N content (and well above 1000°C upon Si incorporation).
We focus on the complex relationships between the metal element choice (at fixed contents of the non-metal elements and fixed deposition parameters), materials structure and materials properties. The experimental results are compared with and explained by ab-initio calculations. Most importantly, we show that the transition from Ti through Zr to Hf leads to an increasing preference to form stable MB_xC_yN_1-x-y solid solutions.
At low N contents (compositions around M₄₁B₃₀C₈N₂₀) the aforementioned trend leads to a transition from x-ray amorphous TiBCN through nanocomposite ZrBCN (fcc-ZrB_xC_yN_1-x-y + fcc-ZrN or ZrC_yN_1-y + amorphous phase) to nanocomposite HfBCN (fcc-HfB_xC_yN_1-x-y + amorphous phase). This transition from almost amorphous to nanocomposite structures significantly improves material hardness (from 21 to 33-37 GPa), hardness to effective Young's modulus ratio (from 0.098 to 0.132-0.133) and elastic recovery (from 67 to 82-85%). In the form of thin films the materials combine low electrical resistivity (on the order of 10^-6 Omega;m) with optical transparency (extinction coefficient at 550 nm 0.06 and 0.014 for M=Zr and M=Hf, respectively).
At enhanced N contents (approximately from 20 to 50 at.%) the transition from TiBCN (which is homogenous) to ZrBCN and especially HfBCN (where small conductive nanocrystals are predicted to be separated by an insulating amorphous phase) dramatically increases the electrical resistivity (from the order of 10^-6 [M=Ti] to 10³ [M=Zr] - 10⁶ [M=Hf] Omega;m).
Collectively, the consistent theoretical and experimental results provide guidelines for the design of future hard, oxidation resistant, electrically conductive and/or transparent nanostructured MBCN materials for different technological applications, including the identification of the most thermally stable structures or structures which are prone to form at high temperatures.
[1] J. Houska, J. Kohout and J. Vlcek, Thin Solid Films 542, 225 (2013)
[2] M. Zhang, J. Jiang, J. Vlcek, J. Houska, J. Kohout, E.I. Meletis, Acta Materialia, in print (2014)
[3] J. Kohout, J. Vlcek, J. Houska, P. Mares, R. Cerstvy, P. Zeman, M. Zhang, J. Jiang, E.I. Meletis, S. Zuzjakova, Surf. Coat. Technol., in print (2014)

Design of radiation tolerant materials for application in extreme radiation environment is a significant scientific challenge. Numerous types of defect sinks have been applied to mitigate radiation damage. In this presentation, we will review some of our recent studies on extraordinary radiation tolerance of several types of nanostructured metallic materials, namely nanolayers, nanoporous and nanotwinned metals. We provide direct evidence, via in situ Kr ion irradiation under a transmission electron microscope, that immiscible layer interfaces in Ag/Ni multilayers can effectively absorb radiation induced dislocation loops, and thus significantly reduce the density and size of defect clusters. Similarly in situ radiation also revealed drastic different response of nanotwinned Ag and nanoporous Ag to Kr ion irradiation damage compared to their bulk counterparts. Twin boundaries in nanotwinned Ag can effectively destruct stacking fault tetrahedra. Defect migration kinetics (diffusivity of defect clusters) was determined in coarse grained and nanoporous Ag. These studies provide an important forward step towards understanding of defect-sinks enabled enhancement of radiation tolerance in nanostructured metallic materials.

Incoherent nano structured metallic multilayer (NMM) films exhibit very good irradiation resistance due to the high amount of interfaces that act as defect sinks. By increasing the amount of interfaces, e.g. making thinner layers, the irradiation resistance is enhanced. However, the manufacturing of thinner NMM is not trivial and as a result the use of NMM as coatings in industrial applications is limited. However, we can tackle this problem, by manufacturing NMM with precipitates inside the softer layer. The addition of precipitates achieves two goals: 1. strengthens the thicker NMM (that are easier to manufacture) by providing extra obstacles to dislocation motion, and 2. provides extra irradiation protection due to the additional incoherent interfaces between the precipitates and the layer. In this work, fcc/bcc bilayer thin films with spherical bcc particles inside the fcc layer were both simulated, using molecular dynamics, and synthesized, using magnetron sputtering. The experimental results confirmed the computational findings that the addition of precipitates improves the mechanical behavior of NMM, compared to similar structures without particles. Furthermore, molecular dynamics simulations showed that NMM with precipitates are more resistant to irradiation than NMM of the same thickness but without precipitates, thus verifying our original hypothesis.

Recent studies have shown that immiscibility is important to achieve enhanced radiation tolerance in metallic multilayers, as immiscible layer interface is more stable again radiation induced mixing [E.G. Fu, et al, Philosophical Magazine, 93 (2013) 883-898]. However the influence of coherency on radiation resistance of immiscible systems remains poorly understood. Here immiscible Cu/Fe multilayers with indidual layer thickness h varying from 0.75 to 100 nm were subjected to He ion irradiation. At large individual layer thickness, incoherent Cu/Fe interface enables significant mitigation of radiation damage. However, at smaller layer thickness when interface is fully coherent, the capability of coherent interfaces to remove radiation indcued defects is not as remarkable as that of incoherent interfaces. An optimized window of layer thickness was identified to achieve enhanced radiation resistance. This research is funded by NSF-DMR-Metallic Materials and Nanostructures Program.

In-situ transmission electron microscopy (TEM) method is powerful in a way that it can directly correlate the atomic-scale structure with physical and chemical properties. In this presentation, we will report on the construction and applications of the in-situ TEM electrical and optical holders. The properties at nanoscale under various physical stimuli have been studied inside TEM, including electrical, optical, and optical-electromechanical coupling properties. The in-situ atomic-scale imaging of structural transition and dynamic electrochemical processes has been achieved, including the electrically driven redox process in CeO₂ and lithium storage mechanism in several nanostructures.
Acknowledgements: Thank the contribution from Drs. Zhi Xu, Kaihui Liu, Peng Gao, Shize Yang, Xuezeng Tian, and Lifen Wang, etc.
References:
[1] P. Gao et al, J. Am. Chem. Soc. 132, 4197 (2010).
[2] S. Z. Yang et al, Adv. Mater. 24, 4676 (2012).
[3] X. Z. Tian et al, Adv. Mater. 26, 3649 (2014).
[4] L. F. Wang et al, J. Am. Chem. Soc. 136, 6693 (2014).

There are much technological interest as well as strategic opportunities in the recent years in the nanoscale multilayered composite materials due to their unusual mechanical properties such as very high flow strength, ultralight weight and stable plastic flow to large strains, as well as extreme radiation damage tolerance, and thus their great potential applications in the next generation energy technologies as
well as in transportation, defense, biomedical, aerospace and space applications. Nanoscale multilayers represent a class of novel composite nanomaterials in which there arises rare opportunities to design new materials from the ground up and to tailor their properties to suit exactly their performance requirements - the holy grail of the modern materials science. This is becoming a reality due to the confluence of two recent advances in nanoscale materials processing and characterization technologies allowing construction and
manipulation of microstructural building blocks of materials such as interfaces, grain boundaries and ultrathin films consisting of practically just a few layers of atoms. In this research, we design new nanoscale multilayered composite materials through atomic engineering of the interfaces leading to a high performance coating for both mechanical passivation as well as for radiation and strain sensing capabilities. The latter could lead to highly functional coating with real time, online, non-invasive monitoring capability of radiation and mechanical strains which could be critical for key components for instance in aerospace and space technologies/systems as well as for biomedical applications (for instance, strain monitoring for stents). As defects in nanolayers are accumulated in the interfaces, the interfaces become more and more disordered due to higher and higher concentrations of defects (dislocations, bubbles). We have preliminary evidence that dislocation density increases linearly with strain up until ~ 4% of strain. This represents an extended linear regime that we could take advantage for sensing of strains, and by extension of the same principles, of radiation damage. Preliminary evidence will be presented and initial design of novel nanolayers discussed.

Understanding radiation responses of Fe-based metals is essential to develop radiation tolerant steels for longer and safer life cycles in harsh environments involving particle irradiation. Nanograined metals have been explored as self-healing materials due to point-defect recombination at grain boundaries. The fundamental defect-boundary interactions, however, are not well understood. By means of molecular dynamics simulations, we discover that the interactions are always mediated by formation and annealing of chain-like defects, which consist of alternately positioned interstitials and vacancies. These chain-like defects are closely correlated to the patterns of defect formation energy minima on the grain boundary, which depend on specific boundary configurations. Through chain-like defects, a point defect effectively translates large distances, while only overcoming low activation energies, to annihilate with its opposite, thus grain boundaries act as highly efficient defect sinks that cannot saturate under extreme radiation conditions. The findings reported clearly show that boundary-defect interactions are not caused by biased random diffusions of point defects.
Instead, such interactions are much more complicated and involve a group of defects.

Temperature, pressure, strain, corrosion, vibration, and gases sensor instrumentation in harsh environments is key to allow the monitoring and control of several process in the aerospace industry, power generation, and industrial processes. Sensor systems capable of operating in such environments are required to improve combustion efficiency, provide cleaner emissions, reduce costs in power generation, and characterize industrial processes and improve process control. In addition, harsh environment sensor instrumentation is required to monitor the integrity of equipment using condition-based maintenance (CBM) and structural health monitoring (SHM) approaches, key aspects of modern aerospace industry and power plant operation.
This talk focuses on recent accomplishments towards enabling the stability and operation of nanoelectrode thin films for surface acoustic wave (SAW) sensor operation in high-temperature turbine engines and power plant environments up to 1100°C. The referred sensor technology, and associated interrogation system, is able to deliver wireless, battery-free, operation in turbine engines, industrial process control, and power plants harsh environments. The presentation will review the motivation and background for the materials development, together with major accomplishments in temperature sensor performance regarding stability, repeatability, and precision.
This talk will discuss: (i) electrode nanomaterial investigation, fabrication, characterization, and testing to allow consistent operation over 1000°C; (ii) fabrication and testing of SAW sensors employing high temperature langasite piezoelectric crystals and the nanoelectrode films; (iii) materials and techniques involved in sensor assembly and packaging for operation in turbine engine and power plant environments; (iv) wireless testing of sensor arrays; (v) different types of wireless interrogation techniques for the implemented harsh-environment SAW sensors; and (vi) successful field testing of wired and wireless sensors instrumented in laboratory, turbine engines, the NETL Aerothermal Facility up to 1180°C gas temperature and up to 72 psi pressure and in other power plant environments. The accomplishments of these wireless harsh-environment sensors and systems reported in this work validate this technology for implementation and commercialization in a multitude of harsh environment industrial, aerospace, and energy sector applications.

Gas sensors are applicable in a variety of applications when unobtrusive measurements are required. Existing gas sensors often degrade their measurement accuracy in the presence of high levels of interferences and cannot quantitate several components in complex gas mixtures. Thus, new sensing approaches are required with improved sensor selectivity. This technological task can be accomplished by the careful design of sensing materials with new performance properties and coupling these materials with the suitable physical transducers. In this talk, we will provide an assessment of the capabilities of new nanomaterials for selective gas sensing. These sensing materials can operate with diverse transducers based on electrical, mechanical, and optical readout principles and can provide vapor-response selectivity previously unattainable using other sensing materials. This ability for selective gas sensing provides opportunities to significantly impact the major directions in developments and application scenarios of gas sensors.

The quality of life and sustainable development of modern society are largely defined by the available amount of electric power. Everything that hallmarks the high-tech era, from advanced illumination, through smart appliances to portable and even wearable electronics, depends on electricity, which has become indispensable in people&’s daily life. Harvesting mechanical energy is an important route in obtaining economical, clean, and sustainable electric energy. Recently, the triboelectric generators have been proved as a simple, reliable, cost-effective and efficient means to harvest ambient mechanical energy. However, a breakthrough is desperately needed to boost the output power so that it can be used as an effective power source for practical applications.
In this work, we report a two-dimensional planar-structured triboelectric generators based on rotary electrification, which could produce energy from rotary surfaces with unprecedented output performance. The radial arrays of micro-sized sectors on the contact surfaces enable a high output power of 1.5 W (area power density of 19 mWcm^-2) at an efficiency of 24 %, which made a breakthrough of boosting the output power of triboelectric generators to a level at which they can be used as an effective power source for practical applications. Besides, the triboelectric generator can effectively harness various ambient motions, including light wind, tap water flow, and normal body movement. Integrated with a power management circuit, a power-supplying system can provide a constant direct-current source for sustainably driving and charging commercial electronics, immediately demonstrating the feasibility of the triboelectric generator as a practical power source. Given exceptional power density, extremely low cost, and unique applicability resulting from distinctive mechanism and structure, the radial-arrayed triboelectric generator can be applied not only to self-powered electronics but also possibly to power generation on a large scale.
References:
(* indicates co-first author)
J. Chen*, G. Zhu*, W. Yang, Q. Jing, P. Bai, Y. Yang, T. C. Hou and Z. L. Wang. “Harmonic- Resonator-Based Triboelectric Nanogenerator as a Sustainable Power Source and a Self-Powered Active Vibration Sensor”. Adv. Mater.25 (2013), 6094-6099.
J. Chen*, G. Zhu*, J. Yang*, Q. Jing, P. Bai, W. Yang, X. Qi, Y. Su and Z. L. Wang. “Personalized Keystroke Dynamics for Self-powered Human-Machine Interfacing”. Nat. Commun., under revision.
G. Zhu*, J. Chen*, T. Zhang, Q. Jing and Z. L. Wang. “Radial-Arrayed Rotary Electrification for High Performance Triboelectric Generator”. Nat. Commun.5 (2014), 3426.
G. Zhu*, J. Chen*, Y. Liu, P. Bai, Y. Zhou, Q. Jing, C. Pan and Z. L. Wang. “Linear-Grating Triboelectric Generator Based on Sliding Electri#64257;cation”. Nano Lett. 13 (2013), 2282-2289.

Emulation of tactile sensing in human skin will be an important progress for making biomimetic electronic devices such as humanoid robot, medical tools, and wearable computer [1]. Besides flexibility and bio-compatibility, such a tactile sensor should be highly sensitive to distinguish surface textures by a gentle touch in a human perceptive pressure area. Graphene is one of mostly suitable materials for this application since it has structural flexibility and proper electromechanical properties including fast restoration after mechanical stress.
In this study, we present a biomimetic graphene tactile sensor combined an artificial finger-print structure (AFPS) which is adopted for mimicking the viscoelastic characteristics of actual human skin with the structural resemblance of the finger print. Various methods for handling of soft materials are introduced to build the wearable and foldable tactile sensors. The sensor shows sensitive and reliable resistance responses for the vertical pressure of 500 ~ 8,300 Pa which belong to the gentle touching range perceived by human tactile mechanoreceptors. We further demonstrate the reproducible operation with 1,000 loading-unloading characteristics under a pressure 3 kPa at a frequency of 2.5 H#7458; and negligible resistance variation for our graphene tactile sensor. It also shows the stable piezoresistive operation after wearing of sensor on human skin.
Detection of surface texture is confirmed by the analysis of sensor outputs in frequency domain that are obtained from resistance changes due to the shear force generated by the slip test with the artificially formed surfaces having a periodic pattern. Our sensor actually distinguishes the periodic patterns (100 ~ 1000 mm) composing surface textures.
References
[1] C. Mathew Mate et al, Nature 480, 189-190 (2011).

Oscillations or acoustic vibrations ubiquitously exist in the surroundings. They create periodic strains toward materials or devices that are placed in the vicinity, which usually induce fatigue or performance instability. For flexible electronics, strain is also an inevitable factor that influences their performance. Recent discovery of the piezotronic effect revealed that when a strain is experienced by a piezoelectric semiconductor material or device, it can introduce interfacial charge redistribution and may lead to significant performance gain or new functionality. In this talk, we will discuss the coupling of piezoelectric polarization and the intrinsic electric field in a space charge region for the purpose of tuning charge transport behaviors in Wurtzite materials. Three piezotronic-enhanced or enabled applications will be introduced as successful examples. In a metal-insulator-semiconductor (Pt/Al₂O₃/ZnO) based photodetector, the Schottky barrier height can be actively modulated by the piezopolarization under compressive strains. The responsivity and detectivity of the SP photodetector were increased by 2.77 times and 2.78 times, respectively under a compressive strain of -1.0%. The piezotronic effect has also been applied to the ZnO/PbS quantum dot (QD) heterojunction for engineering the interfacial band structure and depletion region. This method escalated the solar energy efficiency by 30% when a relatively small strain -0.25% was applied to the QDSC under low-intensity illumination. The enhancement of short circuit current and efficiency was mostly due to the expansion of depletion region in PbS, as a result of piezoelectric polarization-induced charge redistribution at the ZnO/PbS interface. The strain-induced piezopolarization can direct interact with electrochemical processes, which is denoted as the piezocatalysis effect. By straining a ferroelectric PMN-PT beam in water, we experimentally demonstrated that piezoelectric potential can raise the energy of electrons at the surface of piezoelectric material (or electrode) to such a level that is sufficient to drive proton reduction reactions within its immediate vicinity. Theoretical calculations revealed that the piezocatalysis behavior is heavily dependent on the strain and material&’s dielectric properties. A piezocatalyst can realize self- or remotely-activated electrochemical processes from ambient oscillations or applying acoustic waves, respectively. Such capabilities could be particular useful for pollution or corrosion control in systems located in remote or exotic locations, such as electricity, water and fuel transportation infrastructures. In addition, using piezoelectric polarization to adjust the energetics of surface charges may realize a new route for engineering the catalytic properties of conventional catalysts via mechanical straining.

Designing, fabricating, and integrating arrays of nanodevices into a functional system are the key to transferring nanoscale science into applicable nanotechnology. We report large-array three-dimensional (3D) circuitry integration of piezotronic transistors based on vertical zinc oxide nanowires as an active taxel-addressable pressure/force sensor matrix for tactile imaging. Using the piezoelectric polarization charges induced at a metal-semiconductor interface under strain to gate/modulate the transport process of local charge carriers, we designed independently addressable two-terminal transistor arrays, which convert mechanical stimuli applied to the devices into local electronic controlling signals. By combining the top-down microfabrication techniques with bottom-up synthesis and assembly of ZnO NWs, integration of 92×92 (8464) piezotronic transistors is achieved on an area as small as 1 cm² (234 taxels per inch), enabling a more than 100-fold increase in taxel area density as compared with other recent reports on tactile imaging devices. Built on flexible substrates, the device matrix can detect shape change of itself, achieving shape-adaptive tactile imaging and multidimensional active sensing. Sustainability of the device matrix in water and corrosive solution has been investigated, demonstrating the applicability and reliability of the device under humid and reactive environments. Cyclic bending is further performed to show the physical stability and durability of the device under large bending radii and repetitive operations. The 3D piezotronic transistor array is expected to have significant applications in human-electronics interfacing, implantable biosensors, prosthesis, robotics and nanoelectromechanical systems.
Reference:
Xiaonan Wen*, Wenzhuo Wu* and Zhong Lin Wang, “Taxel-addressable matrix of vertical-nanowire piezotronic transistors for active and adaptive tactile imaging”, Science, 340, 952-957, 2013.
*Authors with equal contributions

Surface acoustic wave (SAW) devices are promising as high temperature (HT) sensors, owing to advantages such as robustness, passive operation and wireless interrogation making them usable in harsh environments (temperature/ pressure/ chemically aggressive) as well as mounted on moving pieces [1]. One of the key challenges faced herein is the choice of interdigital transducer (IDT) material that is stable with long lifetime and high reliability up to operating temperatures of about 1000 °C [2]. Degradation of IDTs can occur by different effects such as agglomeration, corrosion, cracking, delamination, material transport along with stress driven mechanisms like high temperature creep which become significantly operative at ~ 0.4 T_m.
As alternative to commonly used IDT materials like Pt, Pd or Ir, we study refractory metal films of W, Mo and their multilayers which have been deposited by magnetron sputtering onto the HT-stable piezoelectric substrates - langasite: LGS (La₃Ga₅SiO₁₄) and CTGS (Ca₃TaGa₃Si₂O₁₄). The microstructural characterization of the films has been carried out using (HT) X-ray diffraction, X-ray reflectivity, texture measurements, Auger electron spectroscopy, scanning and transmission electron microscopy and stress measurements. It is observed that the multilayers exhibit improved properties as compared to single layer films which has been attributed to the significant role of the interfacial structure. Thus, a fine tuning of the microstructure, and in turn the film properties, by altering the interface of the multilayers was possible. TRIM [3] calculations show that the highly energetic backscattered sputtering gas neutrals have predominant effect on this interfacial structure. The high temperature characteristics were studied by following the evolution of stresses in the films upon thermal excursions by in-situ substrate curvature measurements. All the films are stable upon annealing to 800 °C for 12 h in vacuum, exhibiting no degradation in the surface quality, no intermixing of the W-Mo layers and an almost 10 % reduction of the electrical resistivity. The results will be discussed in relation to depositions on LGS and CTGS considering the thermal compliance of the film-substrate composites and correlating it with microstructural studies.
Financial support by German BMBF (InnoProfile-Transfer grant 03IPT610Y) is gratefully acknowledged.
References:
[1] O. Elmazria, T. Aubert: U. Schmid, J.L. Sanchez-Rojas, M. Leester-Schaedel (Eds.), Proceedings SPIE 8066, Smart Sensors, Actuators, and MEMS V, 806602 (2011).
[2] J.W. Mrosk, C. Ettl, L. Berger, P. Dabala, H.J. Fecht, A. Dommann, G. Fischerauer, J. Hornsteiner, K. Riek, E. Riha, J. Auersperg, E. Kieselstein, E. Born, B. Michel, M. Werner, A. Mucha, IECON '98 - proceedings of the 24th annual conference of the IEEE industrial electronics society, 4:2386 (1998).
[3] Ziegler J F, Biersack J P, Litmark U. ‘‘The Stopping and Ranges of Ions in Solids&’&’, (Pergamon, 1985).

The catalytic combustion micro-sensor with fast response, high sensitivity and low power consumption has been expected for practical application. In order to get a stable and detectable signal, the sensor film coated on micro-heater requires not only high sensitivity for target gas but also large specific area. Generally, the heating area of a micro-heater chip is only about one percent of that in traditional (0.01 mm2). It&’s a challenge to fabricate desired porous film on such small surface area micro-heater.
Here we present a simple, versatile and effective reverse micro-emulsion & pyrolysis protocol for in-situ growth mesoporous Pd-Pt/Al₂O₃ film on the MEMS micro-heater chip. PdO-Pt nano-particles with narrow size distribution homogeneously dispersed throughout the Al₂O₃ support. Most importantly, the obtained worm-like catalyst network has both high specific area and highly crystalline, which is favorable for catalytic combustion applications. After coated on a MEMS micro-heater and assembled as methane catalytic combustion sensor, it demonstrated a very short T90 response time of less than 9 s for all the methane concentrations, a high signal output of about 4.5 mV for pre-alarm 10% LEL methane concentration, high enough signal noise ratio in practical detecting, and, even more importantly, a low power consumption of 25 mW, which was about one fifth of that for traditional.