Monitoring, verification and accounting is an integral part of determining CO₂ sequestration well integrity. As part of a two year project funded by the DOE National Energy Technology Laboratory, GE Global Research has developed MEMS-based sensors for highly accurate, real time distributed measurements of pressure within the harsh environment of CO₂ sequestration cavities. The downhole sensors are interrogated at the surface via fiber optics.
In a previous project, a single MEMS sensor was successfully field tested in a geothermal well at 200°C and 120 bar and exhibited a ±0.1% accuracy or better, but provided only a single point pressure measurement and required a second sensor for temperature calibration [1]. The new interrogation scheme multiplexes sensors by both wavelength and resonant frequency so that multiple measurements of pressure and temperature can be obtained along a single fiber. A high power laser pulse excites the resonant sensor and the ringdown signal is measured to determine the resonant frequencies. The measurement can be made at a single wavelength without feedback electronics.
A sensor package was designed and demonstrated that can be spliced into a downhole cable with a fiber bypass and the signals from two sensors were simultaneously measured. The pressure and temperature dependence of the sensor resonances were measured in CO₂ from ambient into the supercritical regime. The sensor was also interrogated via a wireless remote monitor using the GE Predix^TM cloud-based industrial internet. Wavelength division multiplexers and fiber power splitters were tested up to 250°C over a period of months with no change.
This material is based upon work supported by the Department of Energy, National Energy Technology Laboratory, under Award Number DE-FE0010116. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
[1] S. Palit et al., "Subsystem design and validation for optical sensors for monitoring enhanced geothermal systems," Proc. 37^th Workshop on Geothermal Reservoir Engineering, Jan. 30-Feb. 1 (2011) SGP-TR-194.

Opportunities exist for increasing efficiency of utility scale fossil-based power generation systems and enabling adoption of new technologies through sensors and controls that would allow for embedded sensing at the highest value locations. Relevant technologies include advanced boilers, oxy-fuel combustion systems, gas turbines, gasifiers, and solid oxide fuel cells, all of which involve extremely high temperatures and reducing, oxidizing, and/or corrosive environments. Similar needs can be identified in a broad range of other applications and industries including aerospace, aviation, automotive, and manufacturing processes for semiconductors, metals, glass, and chemicals. A number of sensor technologies are currently under development for applications in such extreme high temperature and harsh environment conditions including chemi-resistive, electrochemical, and surface acoustic wave based devices. Optical based sensors are also under development and they are known to display a number of unique and inherent advantages which include: (1) the lack of electrical wiring or connections at the sensing location, (2) compatibility with broadband wavelength and distributed interrogation, and (3) the elimination of potential safety hazards associated with electrical sparks when deployed in flammable atmospheres.
Advanced materials can play an important role in enabling new sensor devices of all types with unique functionality and improved stability in harsh operating conditions. In support of this need, the in-house research team at the National Energy Technology Laboratory has recently established a new advanced sensor material program focused on research and development of new sensing materials in parallel with demonstration on fabricated sensors under relevant high temperature conditions. The research program has therefore placed a particular emphasis on understanding optical responses of materials to parameters of interest under relevant testing conditions. A brief overview of the program and research team capabilities will be presented. Recent breakthroughs of the on-going research and development efforts will also be discussed.

Films of gold nanoparticles (AuNPs) are generally unstable and can sinter to an electrically conductive mass at temperatures less than 150 °C. Here we show how such sintering can be resisted up to temperatures as high as 300 to 350 °C using a mixture of AuNPs and a suitable organic molecule with high stability and boiling point, such as phthalocyanine or oleylamine. A paint made from such mixtures possesses dual functionalities: it rapidly changes from non-conductive to conductive, and also changes from optically absorbing to reflective, upon sintering at high temperatures. The paint may therefore be used as a sensor in sensitive high temperature environments, where an increase in conduction and/or reflection indicates that the temperature or incident radiative flux has risen above a critical point.
The sintering of the AuNP/molecule mixture was examined by measuring the electrical resistance of a sample deposited between gold electrodes on an insulated substrate while heating. The sintering event is characterised by a rapid and significant drop in resistance accompanied by a visible colour change from virtually black to lustrous gold. Our results show that the temperature of the sintering event for these mixtures correlates with the combustion temperature of the organic molecule, as confirmed by thermogravimetric analysis. This is significant, as we have previously shown that the sintering temperature of AuNPs is dependent on the rate of heating [1], whereas the sintering of these AuNP/molecule mixtures is more dependent on the thermal properties of the molecule and whether it is covalently bonded to the gold nanoparticle or not. Therefore, the sintering temperature of a sensor could be adjusted by selecting a molecule with the desired thermal properties. We propose that this type of tuneable ‘smart&’ coating could be used in a variety of packaging and sensing applications in extreme environments.
1. Coutts, M. J.; Cortie, M. B.; Ford, M. J.; McDonagh, A. M. Rapid and Controllable Sintering of Gold Nanoparticle Inks at Room Temperature Using a Chemical Agent. J. Phys. Chem. C 2009, 113, 1325-1328.

Metal oxide nanomaterials have served as a foundation for chemical sensor development studies for nearly 20yrs. Recent work has shown that the surface plasmon resonance band of gold nanomaterials embedded in metal oxide nanocomposite 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. Challenges for their detection 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 selective detection of emission gases. Coupled with these recent studies is the novel design of plasmonic arrays that are being developed for their energy harvesting capabilities. First of a kind studies will be detailed on these structures that include their energy harvesting characteristics for devices operating with plasmonic resonances that range between 800 and 1600nm. Enhancement in the sensitivity of plasmonic based devices will be further detailed through the introduction of multi-pole based resonance structures serving as the optical beacon for emission gases of interest.

The use of nanomaterials for environmental sensing under extreme and harsh conditions is often hampered by the thermodynamic drive toward decomposition, coarsening, degradation, etc. over time. We are taking advantage of just this tendency to measure and record temperature and heating duration. The original motivation behind the development of our sensors was the need to determine temperature profiles during explosive events. However, the sensors can also be used for other heating events, such as fires, accidental over-heating, etc. The sensors themselves consist of pre-cursor materials such as carbonates, hydroxides, etc. Under heating, these materials undergo irreversible transitions such as decomposition, nucleation, grain growth, and phase transitions. Such changes can be optically monitored using luminescent lanthanide dopants. The spectral properties of these dopants are highly sensitive to their local environment. Spectral analysis in combination with phase transition modeling can then be used to determine temperature and heating duration. This approach can also be combined with in-situ two-color thermometry and other approaches to provide correction factors due to thermodynamically-induced changes over time.

Pressure sensitive paints (PSPs) are effective, non-intrusive tools used in a wide range of applications spanning from environmental monitoring to defense and aerospace engineering. Traditional PSPs consist of O₂-sensitive organic chromophores dispersed in a binder. When exposed to O₂, the emission of the chromophore is quenched proportionally to the O₂ partial pressure, allowing one to measure the O₂ concentration in gas mixtures remotely through simple optical detection, and to map the gas flow on complex surfaces such as the fuselage of an aircraft.
Recently, colloidal nanocrystals (NCs) have been proposed as potential O₂-sensing materials for PSPs, as they combine efficient emission with large surface-to-volume ratios. This latter aspect is amplified in bi-dimensional colloidal quantum wells that further exhibit enhanced emission efficiency when exposed to harsh oxidative environments¹. However, O₂ detection using organic- or NCs-based PSPs requires quantitative measurement of the emission intensity and sophisticated calibration procedures that are rendered further more difficult by the typically complex experimental geometry. A disruptive advancement would be the realization of PSPs capable of detecting and quantifying pressure variations through a ratiometric spectral response based on the different sensitivity to O₂ of co-existing emissive states, one acting as an O₂ probe and the other as internal intensity calibration. A few examples of inorganic/organic hybrid PSPs, containing mixtures of reference emitters and an O₂-sensitive dyes, were reported. To date, however, no ratiometric PSP based on a single type of emitter has been demonstrated.
Here, we demonstrate the first example of ratiometric PSPs based on a single type of two-color emitting NCs. Specifically, we use CdSe/CdS Dot-in-Bulk (DiB) NCs exhibiting electrochemically tunable dual-color luminescence², arising from simultaneous radiative recombination of excitons localized in the NC core and shell regions. Since red-emitting core excitons are separated from the outer environment by the thick shell, the core emission is unaffected by chemical agents that instead severely quench the green shell luminescence. As a result, by lowering the O₂ pressure from 1 bar to 10^-3 bar the intensity of the green emission undergoes a four-fold increase, whereas the red luminescence remains unvaried, with the consequent transition of the total emission color from red to yellow to green. Spectroscopic experiments under controlled atmosphere demonstrate the ability of DiB NCs to reproducibly and reliably probe O₂ across a pressure range of over 4-orders of magnitude. The reversible sensing response is ascribed to the occupancy of surface electron trap states, which are activated by the presence of electron withdrawing agents such as O₂.
1. Lorenzon, M et al Nat Comm 2015, 6.
2. Brovelli, S.et al Nano Lett 2014, 14, (7), 3855-3863.

Increased energy efficiency of industrial high temperature processes can be achieved by instrumenting equipment with sensor arrays to measure process parameters and materials performance. Unfortunately, in the high temperature (800^oC-1300^oC) harsh conditions of interest to several industry sectors, most thin film sensor elements, electrodes, interconnects, and packaging materials rapidly degrade, making sensors and devices unstable and short lived. At these temperatures, the challenge is to develop thin films (< 500 nm thick) that remain morphologically stable and electrically conducting under conditions where thermodynamics rather than kinetics determine the film nanostructure and performance. This talk reviews work performed at UMaine that has investigated the electrical conductivity of a wide range of multilayered Pt-ceramic nanocomposite film architectures grown on sapphire, langasite, and silica substrates as a function of annealing treatments in air and under vacuum. The multilayered films are comprised of an interfacial diffusion barrier (Al₂O₃), adhesion layer (Zr, Ni, or Y), electrically conductive Pt-based nanocomposite layer that contains either an oxide (ZrO₂, HfO₂, Al₂O₃), silicide (PtSi, Pt₂Si, Pt₃Si), or boride (ZrB₂, BN) stabilizing phase, and an oxidation resistant capping layer (Al₂O₃ or SiAlON). For the conducting Pt-ceramic layer, nanolaminate growth via e-beam evaporation or inclusion of a ceramic phase by co-evaporation helps retard agglomeration of Pt grains and stabilize the film morphology. The application of these Pt-ceramic nanocomposite films as electrodes on wireless surface acoustic wave (SAW) sensors will be discussed, and results of electrical conductivity experiments up to 1300^oC will be reported. The film architectures are being transitioned to Environetix Technologies Corporation, a spin-off company from the UMaine research. The Pt-ceramic nanocomposite films also have applications in several other high temperature technologies that involve sensors, actuators, and other electronic devices.

1) Photocatalytic and degradation mechanisms of anatase TiO₂: a HRTEM study
The photocatalytic process for degradation of methylene blue with TiO₂ (P25) was directly observed using HRTEM. It was found that: 1) the pristine anatase TiO₂ nanoparticles exhibited a perfect crystal lattice with a clear lattice image; 2) after adsorption and degradation, there were many methylene blue crystals as 1 nm molecular adsorbed at the surface of TiO₂ nanoparticles, which therefore resulted in a fuzzy HRTEM image; 3) when the TiO₂ was exposed in air for a period of time, the methylene blue molecules disappeared and the TiO₂ lattice image again became integrated as the pristine one; 4) however, if the TiO2 nanoparticles became deactivated after degradation of methylene blue for more than 20 cycles, the lattice image was fuzzy fully and could not recover even it was exposed in air for a long time. We propose that there exists a surface lattice driving force forming on the surface distortion leads to the TiO₂ lattice image from fuzzy to integrate, and it decides the photocatalytic ability.
2) Characterization of oxygen vacancy associates within hydrogenated TiO2: a positron annihilation study
We introduce a novel method for characterizing the oxygen vacancy associates in hydrogenation modified TiO2 by using PALS. It was found that a huge number of small neutral Ti3⁺-oxygen vacancy associates, some larger size vacancy clusters, and a few voids of vacancy associates were introduced into hydrogenated TiO2. The defects blurred the atomic lattice HRTEM images and brought about the emergence of new Raman vibration. X-ray photoelectron spectroscopy (XPS) measurement indicated that the concentration of oxygen vacancies was 3% in the TiO2 lattice. The photoluminescence (PL) spectroscopy, photocurrent, and degradation of methylene blue indicated that the oxygen vacancy associates introduced by hydrogenation retarded the charge recombination and therefore improved the photocatalytic activity remarkably.
3) A new approach to measure the percentage of anatase TiO₂ exposed (001) facets: Raman spectroscopy
We introduce a novel approach for quantitatively measuring the percentage of exposed {001} facets in anatase TiO2 by using Raman spectroscopy. Comparing to XRD, Raman peaks originate from the vibration of molecular bonds, that is, vibrational mode Eg and A1g peaks, which are related to different crystal planes. Therefore, it provides a high sensitivity and accuracy for measuring the percentage of the exposed facets from the micro perspective of molecular bonding with less measurement errors. With the photocatalytic experiments, we found that 50% was the optimal percentage of the exposed {001} facets for the highest efficiency, which seemed more reasonable than the value of 70% obtained from XRD.

Organic-inorganic hybrid nanocomposites are considered a new generation of high performance materials because they combine both the advantages of inorganic materials (stiffness, high thermal stability, barrier properties, optical, catalytic, electrical and thermal conductivity among others) and organic polymers (flexibility, dielectric, toughness, lightweight, processing). Each part of a nanocomposite has a synergistic function in its performance and has much better combination properties than a single material. We report on the thermo-mechanical properties and morphology of polyacrylic-nanosilica (SiO₂) composites prepared in-situ via emulsion polymerization, using a semi-continuous mode. The latex emulsion thus obtained was stable for at least six months. Moreover, this process produced controlled molecular weight in the final latex and low formation of agglomerates. Films drawn from the latex exhibited excellent optical transparency, suggesting good dispersion of the nanosilica, and confirmed by scanning electron microscopy (SEM). There was an increase in glass transition temperature, T_g, suggesting a modification of molecular dynamics; hydrophobic behavior, as probed by water contact angle, was also promoted. Moreover, the Young&’s modulus of the nanostructured latex films increased up to 57% with only 3 wt% nanosilica, therefore denoting a reinforcing effect of the nanoparticles.

It has been reported that the addition of liquid rubbers, like poly(dimethylsiloxane) (PDMS), to epoxy resins alter the final morphology, increase the toughness and influence the curing kinetics. Due to immiscibility, there is phase separation of the elastomeric phase during curing giving rise to microdomains embedded in the epoxic matrix. The resultant heterogeneous morphology obtained after the reaction controls to an important extent the properties of the epoxy composite. Here we report a method to obtain well-dispersed rubber nanodomains of silyl-diglycidyl ether terminated polydimethyl siloxane (PDMS-DGE) in diglycidyl ether of bisphenol-A (DGEBA) epoxy by using a prepolymerization step. Light scattering and optical microscopy showed that initial mixing of pre-polymerized rubber produced phase separation with micron-scale droplet formation. However, as the curing reaction proceeded, the rubber domains decreased below optical resolution, light scattering intensity reached a maximum and then decreased. Finally, rubber nanodomains of about 100 nm size were formed at the end of curing reaction, as revealed by transmission electron microscopy (TEM). The pre-polymerization step induced a two-fold increase in gel time, t_gel, due to lesser active groups available for reaction. Strikingly, tensile modulus and toughness increased, suggesting rubber-epoxy interaction. The final nanocomposite also exhibited higher thermal stability and char formation.

Surface acoustic wave (SAW) devices have been used in different areas of key technologies like highly precise frequency filters, delay lines, resonators, oscillators and RF-ID-tags for over 3 decades. In recent years, they have exhibited promising application 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]. Several research works have focused on noble materials (such as Pt and Pd based) for the interdigital transducer (IDT). However, a major cause of degradation of these IDTs is due to effects such as agglomeration, cracking, delamination along with stress driven mechanisms like high temperature creep which become significantly operative above ~ 0.4 T_m. Thus, obtaining stable electrodes with long lifetime and high reliability up to operating temperatures of about 1000 °C is still a challenge [2].
We study refractory metal films of W, Mo and their multilayers which have been deposited by magnetron sputtering onto Si (100) as a reference material [3] and onto the high temperature 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, scanning and transmission electron microscopy and stress measurements. The applicability of the unstable LGS substrate under vacuum annealing, a topic not intensively investigated so far, has been addressed to by application of a diffusion barrier layer. Further on, the applicability of these electrodes materials in air is shown up to a temperature of 400 °C and under vacuum up to 800 °C. The thermomechanical stress in these films has been studied in order to design compliant passivation films to allow its use up to 700 °C in air.
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 SPIE8066, 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] G.K. Rane, S. Menzel, T. Gemming, J. Eckert, Thin Solid Films, 571, Part A (2014) 1-8.

Hydrogen gas is attracting match attentions as a next-generation clean energy resource. However, it is dangerous gas because it is explosive between 4 and 74% in air. Therefore, immediately detectable hydrogen gas sensor is required for safety. Pt catalyst loaded WO₃ (Pt/WO₃) is a one of the promising candidate material as the hydrogen gas sensor because it shows the gasochromism which is the reversible color change from light yellow to blue under a hydrogen gas atmosphere. In addition, this material can also detect hydrogen by the electrical conductivity change.
Hydrogen gas sensor of Pt/WO₃ thin film requires small particles, porosity and low crystallinity in order to show higher sensitivity. Therefore, we solved these requirements by the transition doping to WO₃ with the sol-gel process. And, we investigated the relationship between the film structure and the hydrogen sensing property.
Ti-doped Pt/WO₃ films were prepared by the above new sol-gel process. Tungsten hexachloride, titanium tetrachloride and hydrogen hexachloroplatinate were dissolved to ethanol. Mixture of starting materials solutions were spin-coated on alkaline-free glass substrates and dried at 150 0C for 5 minutes. These as-deposited films were heat-treated at the several temperature for 10 minutes in the electric furnace. In this study, 0, 1, 5 and 10 mol% Ti-doped films were prepared, respectively. Structure and surface morphologies of films were evaluated by XRD measurement and SEM observation. The hydrogen gas sensing properties of films were evaluated by the optical absorbance change under the hydrogen gas atmosphere.
From X-ray diffraction patterns, all films were indexed as single phase of WO₃. From the SEM observation, the crystallite size of WO₃ became smaller with increasing the amount of Ti-doping. In case of non-doped Pt/WO₃ film heat-treated at 700 0C, the average crystallite size was 90 nm. Also, the average crystallite size of 10 mol% Ti-doped Pt/WO₃ film heat-treated at 700 0C was 40 nm. We thought that oxygen vacancies were also formed to maintain to an electrical neutral because a part of W⁶⁺ ion sites were substituted to Ti⁴⁺.
The hydrogen gas sensing properties of thin films heat-treated at 750 0C were evaluated by optical absorbance change under 1% hydrogen gas exposure. 10 mol% Ti-doped film showed large absorbance change, immediately. In contrast, the hydrogen gas response of the non-doped film declined due to the high temperature heat-treatment. The absorbance change value of the 10 mol% Ti-doped film was nine times larger than that of the non-doped film. Therefore, Ti-doped Pt/WO₃ is promising new hydrogen gas sensor for a high temperature operation.

Pollutions in air and water supply are receiving keen attention since the exact nature, concentration, and health effects now just begin to be revealed. While methods for monitoring airborne pollutions, such as particulate matter, have already been established, monitoring pollutants in water is still difficult mainly due to much greater diversity in low volatility chemicals present in low concentration. Systems which are capable of detecting a wide range of waterborne chemical pollutants and producing easily detectable signals are therefore of great interest.
The use of fluorescent polymers such as poly(p-phenyleneethylene)s (PPEs) for fluorescence-based sensing has been explored extensively. Due to highly sensitive quenching response of PPEs towards analytes with certain electronic structures, thin films of PPEs have been successfully applied in sensing analytes in the gas phase. Reports on PPE-based platforms, which are functional in aqueous environment, are, however, relatively rare.
Recently, our group has reported a simple synthesis of water-dispersible polymer nanoparticles in a one-pot reaction between sodium polysulfides and organic polyhalides. The method allows for the preparation of well-defined nanoparticles with controlled size and narrow size distribution.
Herein, we report our investigations toward preparing water-dispersible fluorescent polymer nanoparticles for aqueous-phase sensing of electron-poor analytes. Specifically, interfacial cross-linking of functionalized PPEs with aqueous polysulfides is optimized to yield fluorescent nanoparticles which are readily dispersible in water. We expect that this platform would allow for the sensing of analytes in aqueous environment through the fluorescence quenching and, by varying the electronic structure of PPEs employed, a selective range of pollutant sensing would be possible.

Gas detection is important for controlling industrial, and vehicle emissions, agricultural residues, and environmental control. In last decades, several semiconducting oxides have been used to detect dangerous or toxic gases. The excellent gas-sensing performance of these devices have been observed at high temperatures (~250^oC), which forbids the use for the detection of flammable and explosive gases. In this way, ultraviolet light activated gas sensors have been a simple and promising alternative to achieve room temperature sensitivity. Among the semiconductor oxides which exhibit a good performance as gas sensor, the zinc oxide (ZnO) and tin oxide (SnO₂) have been highlighted. Nevertheless, their poor selectivity is the main disadvantage for application as gas sensor devices. Recently, heterostructures combining these two semiconductors (ZnO-SnO₂) have been studied as an alternative way to enhance the gas sensor performance (sensitivity, selectivity, and stability). In this work, we investigated the influence of mass ratio Zn:Sn on the properties of ZnO-SnO₂ nanocomposites prepared by hydrothermal treatment for 4 hours at 200^oC. The crystalline phase, surface, and morphological features were characterized by X-ray diffraction (XRD), high-resolution transmission electron (HR-TEM), and X-ray photoelectron spectroscopy (XPS) measurements. The gas sensor measurements were carried out at room-temperature under ultraviolet (UV) light irradiation using different ozone levels (0.06 to 0.61 ppm). The XRD measurements indicate the presence of ZnO and SnO₂ crystalline phases, without the evidence of solid solution formation. HR-TEM analysis revealed that a good contact between the SnO₂ nanoparticles and the ZnO nanorods, which are very important since interface characteristics between nanostructures is considered a challenge to development new and efficient heterostructures. Electrical measurements proved that the best ozone gas-sensing performance is obtained for ZnO:SnO₂ (50:50) nanocomposite under UV light irradiation. Its sensitivity was of ca. 6 times higher when compared to SnO₂ pure, a traditional ozone gas sensor. These results demonstrate the potential of ZnO-SnO₂ heterojunctions for the detection of ozone gas at room-temperature when irradiated with UV light irradiation.

Zinc oxide (ZnO) pure or doped are one of the most promising metal oxide semiconductors for gas sensing applications due the well-known high surface-to-volume area and surface conductivity. It was show that ZnO is an excellent gas-sensing material for different gases such as CO, O₂, NO₂ and ethanol. In this context, pure and doped ZnO 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 its 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 Zn_1-xCo_xO (0 < x < 5 wt%) thin films were obtained via the polymeric precursor method. The sensitivity, selectivity, response time and long-term stability gas sensing properties were investigate when the sample was exposed to different concentration range of ozone (O₃), hydrogen (H₂) and nitrogen dioxide (NO₂) at different working temperatures. The gas sensing property was probed by electrical resistance measurements. The long and short-range order structure around Zn and Co atoms were investigate by X-ray diffraction and X-ray absorption spectroscopy. X-ray photoelectron spectroscopy measurement were performed in order to identify the elements present on the film surface as well as to determine the sample composition. Microstructural characteristics of the films were analyzed by a field-emission scanning electron microscope (FE-SEM).
Zn_1-xCo_xO XRD patterns 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 Co²⁺ ions. XPS characterization revealed that Co-doped ZnO samples possessed a higher percentage of oxygen vacancies than the ZnO samples, which also contributed to their excellent gas sensing performance. 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). Furthermore, the Co addition contributed to reduce the working temperature for ozone detection and improve the selective sensing properties.

Mesoporous zinc oxide (ZnO) powders were prepared by the homogenous precipitation method. ZnO nanoparticles were synthesized from a solution of zinc acetate di-hydrate (Zn(CH₃COO)₂^.2H₂O) as zinc source and ammonium carbonate ((NH₄)₂CO₃) as precipitant agent, dissolved in a mix of methanol (CH₃OH), ethanol (CH₃CH₂OH) and de-ionized water (H₂O). Other parameters, such as molarity (0.1, 0.35, and 0.5 M), saturation (%), temperature (30, and 70°C), and time (30, 60, and 120 min). After mixing under magnetic stirring a white colloidal precipitate was obtained, and then separated by centrifugation at 4500 rpm for 6 min. Then, the resultant past is thrice washed with methanol and dried to 100°C for 1 h. Finally is calcined at 400°C for 2 h in a conventional drying chamber. All powders were analyzed by X-ray Diffraction (XRD) for analyzing their structure. The particles morphology (size and shape) was analyzed from the Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) images. In order to test the sensing properties of the ZnO powders, 12 mm diameter pellets were manufactured at different pressing conditions. The pellets were measured in propane (C₃H₈) atmosphere at different C₃H₈ concentrations and measuring temperatures.

Metal nanoparticles encapsulated with functionalized alkanethiolates exhibit unique electrical properties for exploitation in chemical/bio sensors, whereas nanofibrous membranes with controllable porosity provide a flexible platform for chemical and biological interfacing. In this report, gold nanoparticles encapsulated with thiolates terminated with carboxylic acid are printed or assembled on a nanofibrous membrane as interfacial tunable network structures on microelectrodes. The nanocomposite materials are characterized by electrochemical techniques such as cyclic voltammetry and impedance spectroscopy. The ionic fluxes across the nanocomposite membranes depend on the detailed interparticle interactions and structures, as well as the porosity in the membrane. The physical (e.g., swelling or deswelling) and chemical (e.g., protonation, deprotonation, or electrostatic binding) changes in the nanostructure are determined. The results have implications to the design of functional nanocomposite materials for selective electrochemical detection of biomolecules such as cancer biomarkers.

Monitoring of endocrine disruptors substances (DE) such as pesticides are generally based on chromatographic methods. In this sense, development of sensor materials for monitoring these substances, presents several advantages such as lower cost and time of analysis as well as offering the possibility of in-situ monitoring. Conductive polymer-based materials (CPs) and carbon nanotubes (CNTs) are being increasingly used in the development of sensors. The CPs main characteristic is its electrical conductivity can be regulated in wide range, through interactions with electron donors and receivers, which makes them attractive as transducers or active materials. Among the different conducting polymers the Polypyrrole (PPy) is one of the most studied in the development of sensors. In turn, the CNTs have the ability to promote electron transfer reactions, increase reaction speed and decreased oxidation potentials. Thus, CPs composites with CNTs has been developed and exhibit synergistic properties like increased sensitivity and selectivity in relation to separate materials. In this work, self-assembled films based on PPy and CNTs composites were produced, characterized and evaluated in pesticides determination. Initially, polypyrrole (PPy) and its respective composites with functionalized carbon nanotubes (CNT) were chemically polymerized using ammonium persulfate as oxidant. Nanostructured films were produced by self-assembly technique (SA) by the deposition of alternated layers of Polypyrrole (or CNT composite) and Polystyrene Sulfonated. The films were characterized by UV-visible and Fourrier Transformed Infrared spectrometry analysis (FTIR), as well as, electrochemical techniques of cyclic voltammetry (CV) and Electrochemical Impedance spectroscopy (EIS). The applicability of the sensors was evaluated for determination of pesticides Clorotalonil and Diuron. The analyses were performed using cyclic and square wave voltammetry analysis. The results showed an increase of sensibility of modified sensor.

A method is proposed that combines electrostatic and molecule diffusion calculation to determine the capacitive of dielectric sensitive coatings. Simulation were conducted to test the validity of this approach on the capacitive gas sensors by COMSOL Multiphysics. An evident agreement of the calculated capacitive of the films observed between the proposed approach and the previous studies. Besides, the capacitive and sensitive using a complex experiment are consistent with those from direct finite element simulation. The discovery suggest that simulation can serve as an alternative tool for extracting the capacitive of films in gas sensors. The significance of the simulation is that it not only verifies the potential value of GO as sensing material, but also provides a usable method to sulfur dioxide detection. Although sulfur dioxide sensors are dealt with in this paper, the simulation can be used for the optimization of capacitive sensors for other user-defined.

Piezoelectric single crystals of the langasite family enable novel sensing mechanisms in harsh environments. Depending on the transducer configuration, the resonant frequency of these devices reflects mechanical and electrical properties even of nanometer-scale films deposited on the transducer. Applications include gas sensors and the determination of phase transformations of nanomaterials.
Langasite-type crystals exhibit piezoelectrically excited bulk acoustic waves up to temperatures of about 1400 °C and relatively low acoustic losses, which are dependent on the specific crystal structure. Consequently, they are robust sensor devices operating in harsh environments. Resonance frequencies in the low megahertz range enable robust and precise data acquisition.
In this work, structure and property interrelationships of CTGS (Ca₃TaGa₃Si₂O₁₄) and LGS (La₃Ga₅SiO₁₄) are reviewed, including the high-temperature defect chemistry and atomistic transport processes in the crystals. Further, the acoustic loss mechanisms are correlated with the transport kinetics. The effect of defects on the electromechanical properties such as mechanical stiffness, piezoelectric and dielectric constant, effective viscosity and electrical conductivity are evaluated. Thereby, the electromechanical properties are extracted from resonance spectra using a one-dimensional physical model. Above about 600 °C in langasite, the electrical conductivity is a noticeable contribution to the total acoustic loss. In contrast, the loss in CTGS is less affected by the conductivity.
Further, the mechanical displacement of vibrating membranes and cantilevers is characterized by laser vibrometry and found to be consistent with displacements extracted from electrical impedance data. In addition, the damping of the piezoelectric devices is determined using laser vibrometry. Comparing CTGS and LGS, the former shows significantly lower losses at high temperatures which is caused to some extent by its fully ordered structure.
Further, the shape stability of small langasite structures is confirmed up to at least 1350 °C. Issues like gallium evaporation, which could affect the performance of these crystals in harsh environments, can be suppressed by appropriate packaging. Resonators can also be protected by thin alumina films which almost completely eliminate gallium loss.
Modeling to describe the thermal transport and to optimize the device structure is done. Thermal diffusivities are determined and included in the model. Associated experimental work includes the preparation of freestanding bulk acoustic resonators with low thermal masses.
Finally, high-temperature sensing applications of bulk acoustic resonators are briefly discussed. Examples are the in-situ determination of the carbon monoxide content in hydrogen containing atmospheres at 600 °C and of the phase transformation of nano-sized molybdenum disulfide.

Hydrogen gas can degrade electrical properties in electroceramic materials such as dielectrics, piezoelectrics, PTCRs and varistors. The degradation resistivity due to hydrogen gas in barium titanate was investigated by I-V tests, which showed resistivity degradation due to hydrogen gas primarily modifying the interfaces. ALD coatings were offered as a solution to be a barrier against hydrogen gas. Three ALD layers of ZnO, Al₂O₃, and HfO₂ with different thickness were coated on the capacitors and their merit as a gas barrier was evaluated by I-V tests at high temperatures in hydrogen atmosphere. TEM analysis was applied to examine the ALD layers before and after the I-V tests and it suggested crystallizations was the main reason of ALD failure above T₀.

Platinum-silicon (Pt_xSi_y) thin films with silicon molar fractions (f_Si) in the range 0.00-0.75 were grown on r-sapphire substrates by electron beam co-evaporation. Phase, morphology, and electronic properties were analyzed on as-deposited films and as a function of annealing environment for films processed at 1000 °C in vacuum (10^-8 Torr) and in air furnaces. Co-evaporation is presented as a means to grow pure Pt₃Si films, in addition to the Pt₂Si and PtSi phases familiar to the conventional self-aligned silicide technology. As-deposited films, nominally 200 nm thick, are conductive in the range of 0.1-4.0×10⁶ S/m and a distinct film morphology accompanies each of the three silicide phases. Vacuum annealed Pt_xSi_y films, independent of phase or composition, are morphologically and electrically stable after 6 hr at 1000 °C—beyond temperatures and times where self-aligned platinum silicides routinely agglomerate; this superior thermal stability is attributed to the smaller grain size and smoother surfaces/interfaces of co-evaporated Pt_xSi_y films over those of conventional solid-state reacted Pt-Si films. Unlike vacuum treatments, annealing in air at 1000 °C results in major evolution of film morphologies within 6 hr of processing. During this time, all crystalline silicide phases present in as-deposited Pt_xSi_y films degrade resulting in structures consisting of amorphous silica and recrystallized cubic-Pt. Segregation of Pt and SiO₂ in Pt₂Si- and PtSi-grown films leads to a loss of electrical conductivity within 6 hr. Oxidized Pt₃Si films, however, remain conductive for 45 hr at 1000 °C due to the formation of a nanocrystalline Pt network stabilized by an amorphous silica matrix. Pt-Si co-evaporation with low Si content (f_Si < 0.15) was also used to incorporate finely dispersed Pt₃Si crystallites into the Pt films. After several hours of air annealing at 1000 °C, small (< 0.5 mu;m) amorphous silica precipitates decorate a larger agglomerating Pt network and serve to delay the rate of agglomeration, thus prolonging the life of the conducting Pt film, consistent with a solute-induced drag (Zener pinning) mechanism. The sheet resistance of patterned PtSi electrodes is known to be independent of the linewidth, even for electrodes as narrow as 150 nm. Since several sensing technologies depend on electrically conductive components that are stable at reduced device dimensions while in aggressive environmental conditions, the heightened thermal stability of platinum silicides fabricated by co-evaporation elevates them as a potentially versatile material of choice for such high temperature applications.

The current trend in miniaturization of micro/nanoelectronics demands for materials with better mechanical and electrical properties. In particular, interconnects play a critical role and their electrical and mechanical integrity is crucial to reliability of advanced micro/nano-devices. Current issues with miniaturization of copper as the only current interconnect material including electro-migration and increased resistance dictates the need for highly conductive material that can safely be integrated with current semiconductor manufacturing. A hybrid material made with combination of copper and CNT is proposed as a better solution that can overcome some of these issues and offer better electrical and thermal performance. This study offers a multi-scale modeling approach in order to provide a preliminary understanding of the mechanical behavior of this hybrid material under different loading conditions. Molecular dynamics simulation (MDS) was used to evaluate the cohesive zone model (CZM) of the CNT/Cu interface at the nano-scale. Then, using the CZM extracted from the MDS, finite element analysis was conducted to evaluate the mechanical behavior of the micro-scale CNT/Cu-composite through silicon via (TSV) interconnect under bending and thermal loading conditions. From the results, CNT/Cu composite-TSV could be mechanically reliable since CNT/Cu separation does not take place prior to plastic deformation of Cu in bending, and separation does not take place when a standard thermal cycling is applied. Moreover, more study is recommended in order to alleviate the increased plastic deformation in Cu at the CNT/Cu interface in both loading conditions.

The most common flexible substrates so far used are the polymers such as PET, PI and PMMA etc. They are able to endure extremely large strains, but suffer from many shortages such as poor mechanical strength, poor wear resistance, low thermal stability etc. The paper reports a new type of flexible surface acoustic wave (SAW) based strain sensors on ultra-thin glass substrate which has excellent flexibility and transparency, high mechanical reliability and thermal stability, and high corrosion and wear resistance.
SAW devices were made on the ultra-thin glass substrate (~100 mu;m) using ZnO thin film piezoelectric layer (2-3 mu;m) and aluminum (Al, 100 nm) interdigitated transducers (IDTs). Material characterization by XRD and SEM showed that ZnO films have a single strong peak at 34.3° in the XRD curve corresponding to the (0002) crystal orientation, and the crystal have large grain size, showing high quality ZnO films.
The transmission property of the flexible SAW devices was characterized using network analyzer. All the devices show one well-defined resonant peak at a frequency in the range of 110-140 MHz depending on the wavelength and ZnO thickness. The amplitude of the transmission signals is over 30 dB, showing excellent properties for potential electronic and sensing applications. The performance of the devices improves as the ZnO thickness increases and when they were annealed at temperature up to 300 °C. The flexible glass based SAW devices exhibit a similar power transmission performance.
The resonant frequency of a SAW device changes when it is bent due to the change of wavelength (IDT pitch distance) and acoustic velocity under deformation. This is the working principle of SAW based strain sensors. These SAW strain sensors work well under various applied strains, and the resonant frequency shift is linearly correlated to the strain applied. The sensitivity of the strain sensors is about 88 Hz/mu;ε for the as-made devices, and increases to 138 Hz/mu;ε after annealed at 200 °C. The largest strain the device can withstand is ~3000 mu;ε, which is 3-5 times larger than other SAW strain sensors based on rigid substrates. The sensors also show the best sensitivity when the strain applied angle is 45 ° with the wave propagation direction. A theoretical model was then developed with the consideration of wavelength and acoustic velocity changes induced by deformation, and the theoretical calculated sensitivities fit very well with the experimental results under different alignment angles. The strain sensors were subjected to repeatability and stability test under various strains and temperatures. It showed the sensitivity of the sensors is not affected by the environmental temperature (20-80 °C), and the performance of the sensors remains stable after up to 8000 cyclic test at a strain of 2300 mu;ε without noticeable deterioration, demonstrated excellent performance and reliability of the flexible broadband strain sensors.

There continues to be high demands for sensors that are capable of in situ monitoring environmental and physical parameters in advanced fossil fuel-based power plants. Currently, there is no existing sensor technology to satisfy the needs for such in situ detection or monitoring. In this presentation, we report the development of a new type of coaxial cable sensor which is a Fabry-Pérot interferometer operating on microwave signals. This sensor is being developed using metal conductors and ceramic insulations and air gap reflectors to achieve high temperature applicability. The sensor, named as “metal-ceramic coaxial cable Fabry-Pérot interferometer (MCCC-FPI)”, has been demonstrated for temperature monitoring up to 600^oC and it&’s principle of operation is discussed.

Logging-while-drilling (LWD) is a technique to transmit real time measurement results about geologic and geophysical properties of oil well borehole, which are widely used to ensure safety margins and optimize completion. The economics behind geosteering or high-cost drilling can cost-justify using LWD sensors to acquire data in real time, and usually piezoacoustic receivers are designed to measure one or more acoustic-wave properties to obtain subsurface formations. This abstract focuses on the simulation and optimization of a piezocomposite acoustic receiver based on the Finite element method (FEM) simulation and experimental measurement.
Compared with the traditional piezo acoustic receiver design, a piezocomposite PZT/polymer acoustic receiver is proposed here, there are several advantages of the composite logging device, such as higher voltage output, better mechanical properties under harsh environment (temperature of 250 °C, pressure of 20,000psi or even higer), improved sensitivity, etc. COMSOL Multiphysics® was used to study the working modes also acoustic responses of the piezocomposite receiver. The finite element modeling results and our past work experience with ceramic polymer composites indicate several ways to improve the design of the logging receiver.
To achieve a higher voltage output, the PZT/polymer composite structure could be used to lower the dielectric constant and the ratio of the width of PZT and polymer could be reduced since there are wasted spaces in the polymer part. Less space in the polymer gap between neighboring PZT plates will provide a higher stress transferred from polymer to PZT and thus better electric signal output. In addition, more PZT ceramic plates can be packed in the receiver if there is less polymer there. Also with better packaging techniques, there is no need for anti-corrosive rubber protection since the polymer to be used is also anti-corrosive. Meanwhile a d33 mode PZT operation (at the hoop resonance) to replace the current d31 mode PZT receiver can also lead to improved sensitivity since the piezoelectric d33 coefficient is more than twice higher than the piezoelectric d31 coefficient.
The thickness (along the radial direction) to width (along the arc direction) ratio, or aspect ratio, of the polymer gap between the neighboring PZT plates is also studied. In an ideal case, the incoming pressure (stress) signal should be transmitted mostly to the PZT ceramics (due to much higher elastic modulus of PZT plates). However if the aspect ratio is too large, the stress in the polymer region will not be effectively transferred to the PZT plates, reducing the overall transducer performance. In general, one should have the aspect ratio much smaller than 1 based on our simulation results.
A new PZT/polymer composite receiver is proposed and our study provides some optimization methods for the logging device design, the new receiver has a better sensitivity, signal to noise ratio (SNR) and output voltage.

The large surface to volume ratio combined with the ability to control both thermal and electrical transport through nanomaterials makes them highly desirable for use in various applications. Devices based on nanomaterials, such as photovoltaics, thermoelectrics, sensors etc., have been reported to have higher efficiencies than their bulk counterparts. For example, nanowires offer enhanced electrical transport along their axis and reduced thermal transport in the other two directions, which makes them highly useful in thermoelectric fabrication, However, these properties also lead to their instability. Nanowires have high propensity to react with air and moisture, which decreases the lifetimes of devices fabricated from them. The problem is exacerbated when these devices have to be used in extreme environments such as low pH or at high temperature.
In this work, a novel strategy is presented to utilize the superior and unique properties of nanowires even in extreme conditions. This strategy involves non-conformally decorating the surfaces of inorganic nanowires to make them hydrophobic, which in turn leads to the increased stability of the nanowires. In this talk, we also show that the nonconformal decoration reduces the thermal conductivity of the material without detrimentally influencing the electrical properties. The methods for stabilizing nanowires of zinc phosphide (Zn₃P₂), a good solar cell material, and magnesium silicide (Mg₂Si), a well-known thermoelectric material, will be presented. Demonstration of enhanced resistances, lower thermal conductivities and unchanged electrical properties of these nanowire systems will be made. Pathways for extending this strategy for stabilizing other compound semiconductor nanowires, including nitrides, sulfides, silicides and antimonides, will be discussed.

Overcoats for the protection of thin film sensors have historically focused on inhibiting the growth of native oxide films on the surfaces of the metallic strain elements and not on the passivating nature of the oxide. Our approach to improving the high temperature stability of the active strain elements comprising PdCr and NiCr thin film strain gages, was to enhance the oxygen diffusion barrier properties of the native oxide formed on the surface. The premise here was to prevent Cr depletion in these devices due to the selective oxidation of Cr, and in the process, produce a more compliant Cr₂O₃ layer that would protect the underlying metal from oxidation. SEM studies of the Cr₂O₃ scales showed a plate-like morphology, whereby individual platelets were anchored at one edge. This morphology was largely responsible for the improved stability during strain testing, since the oxide plates were able to accommodate severe bending stresses while protecting the underlying material from oxidation. In addition to SEM examination, the Cr₂O₃ scales were characterized by XRD and XPS to determine extent of crystallinity and chemical bonding in the oxide. High temperature stability of the thin film strain gages was improved as were the drift rates at temperature.

A number of electrical components and devices work in extreme environment such as high temperature, high pressure, strong vibration, corrosive chemicals, etc. A common practice to protect them is to shield them in materials that are mechanically and chemically resistant to these harsh conditions. In this scenario, epoxy bonding is inevitable and it is crucial to have high bonding strength. One example is the acoustic transducers used in oil drilling. The temperature can reach 200 °C and the pressure can reach 20,000 psi. The piezoelectric ceramic parts cannot withstand these conditions so different packaging materials are used such as polyether ether ketone (PEEK).
Here a novel epoxy bonding technique is presented that has demonstrated ultrahigh bonding strength. Though epoxy resin is degassed before applying, which gets rid of air bubbles generated in the mixing process, there is trapped air when two surfaces are closed together. This trapped air has minuscule effect for applications in ambient environment, but under extreme environment, it compromises the bonding strength majorly. We devised a vacuum system that contains a motorized stage with the bonding parts attached. After the epoxy is applied and the system is pumped to vacuum, a computer controls the motor to move the bonding parts closed together. Since the entire operation is in vacuum, it leaves no trapped air and results in increased bonding strength.
Another technique to improve the bonding strength utilizes the finding that a uniform epoxy resin layer between 50 µm and 150 µm results in the optimal bonding strength. Here we applied spacers such as optic fiber (100 µm in diameter) or glass fiber fabric (150 µm in thickness) in between the bonding surfaces. These spacers ensure that the epoxy resin layer is of uniform thickness.
The above novel bonding technique has been proven to increase the bonding strength by experiments. Acoustic transducers bonded with this technique passed the high pressure, high temperature tests resembling the oil drilling conditions.

Three-dimensional (3-D) integration of functional nanostructures or nanostructure arrays into applicable platforms or devices usually in a macro-scale represents the need for meeting ever-increasing demands of human beings for cost-effectiveness, structure sophistication, multi-function enabling, while simplified and efficient practical operations. Such an integration process generally involves a diverse array of nanostructured entities that include various dissimilar nanoscale building blocks such as nanoparticles, nanowires, and nanofilms made of metals, ceramics, or polymers in the nanoscale form. In this talk, I will highlight our latest research progress on the two-dimensional (2-D) and 3-D metal and semiconducting metal oxide based nanostructure integrations toward applicable ultrahigh efficiency, robustness, and improved functionality at high temperature. Specifically, examples through design in nanostructure integration, scalable nanomanufacturing, and gaseous species sensing utilizing electrical, electrochemical and optical modes will be used as the connecting dots to display a nanomaterials roadmap linking from scalable 2-D/3-D integration toward practical nanotechnology applications in harsh environment.

High temperature gas sensors for harsh exhaust environments are of paramount importance to improve combustion efficiency and control emissions. In the past decades, various sensors have been developed for monitoring combustion process. Among them, resistor-type gas sensors have been extensively studied for high temperature environment due to its simplicity in fabrication, low cost and user-friendliness. However, for resistive high temperature gas sensors, besides stability and sensitivity, selectivity is the major challenge issue that impedes the real application of resistive gas sensors. This talk will first review recent progress in high temperature gas sensing and its current challenges, and then discuss our recent work on exploring various strategies to improve the high temperature gas sensing selectivity.

Metal oxide semiconductor nanostructures represent an important class of gas sensor materials, due to their high surface-to-volume ratio, significant surface band structure bending upon gas molecule exposures, good mobility of charge carriers (electrons or holes) and good structural stability under the operating conditions.¹ Their usually surface-dominant sensing processes entail the important roles played by nanostructure size, defects, morphologies, and surface absorbate energetics and dynamics.² The behind structural, chemical, and electronic characteristics in sensor nanomaterials form the basic metrics for designing better metal oxide based chemical sensors for various energy and environmental applications. Our recent work has suggested that nanowire decoration with trace amount of nanoparticles of either noble metal (e.g., Au and Pt) or perovskite (e.g., La,Sr)CoO₃ and La,Sr)FeO₃) could significantly enhance various metal oxide nanowire array (nano-array) sensing performance in terms of sensitivity, selectivity, response and recovery. Specifically in this contribution, gold nanoparticles decorated ZnO nano-array gas sensors on different substrates (e.g., ITO/glass, Si and GaN) are found to work effectively for detection of NO and NO₂ (NO_x) at a large temperature range from room temperature to 600 ^oC. A multi-mode gas sensing platform was achieved by utilization of three gas detection signals including electrical resistance, electrochemical impedance and ultraviolet (UV) light excited photocurrent. In addition to electrical resistance mode, UV excited photocurrent mode offers a significant enhancement over the sensitivity and reversibility, which could be associated with the catalytic Au effect and the mixed gaseous nature in NO_x. Besides, a good differentiation between NO_x and O₂ has been achieved using the Au decoration and UV excitation sensing mode. The mixed gaseous conditions at different concentrations shift the extent of enhancement of sensitivity, selectivity, response and recovery as revealed in the acquired three signal data sets based on this Au/ZnO nano-array sensing platform. It is suggested that correlating/differentiating these signals with/from the multi-component gases from the standard signals of individual component gases may allow this single sensor platform to detect the concentrations of multiple component gases simultaneously.
References:
Zhang, Yuan, et al. "Decoration of ZnO nanowires with Pt nanoparticles and their improved gas sensing and photocatalytic performance." Nanotechnology 21.28 (2010): 285501.
Joshi, Rakesh K., et al. "Au decorated zinc oxide nanowires for CO sensing." The Journal of Physical Chemistry C 113.36 (2009): 16199-16202.

With the ever present threat of terrorist attacks and the continued innovation of IED&’s for this purpose, there is a greater need for explosives detection at trace levels. This work describes the fabrication and characterization of metal oxide nanowires for chemical sensing, and in particular, the detection of energetic materials at trace levels. Recently, a number of oxide nanowires, based on zinc oxide and copper oxide, have been incorporated into our solid-state gas sensors as catalysts. These nanowire catalysts produced a dramatic increase in sensor response, and improved selectivity for target molecules. These responses were attributed to a large increase in surface area available for catalyst/analyte interaction. Zinc oxide and copper oxide nanowires were grown by hydrothermal and gas phase reactions and characterized by XRD, XPS and FE-SEM to determine extent of crystallinity, oxidation state and morphology. Results indicated that energetic materials such as TATP and 2-6 DNT could be detected at the part per billion level. Other possibilities for oxide nanowires as catalysts in chemical sensing are discussed as well.

Oxide semiconductors such as Gallium Indium Zinc Oxide (GIZO) combine unique advantages in processing with robust electrical performance in thin-film transistors (TFTs). Large area deposition at temperatures below 200 °C allows to fabricate active matrices on unconventional light-weight substrates, with field-effect mobility above 10 cm²/Vs and operating voltage below 10 V. The technology already found application in transparent display technology with high pixel densities. Here we investigate for the first time the radiation hardness of this material class by subjecting high mobility oxide TFTs to X-ray irradiation (Mo tube source, 35kV) with doses up to 2000 Gy and subsequently monitoring the devices performance. TFTs with different combinations of semiconductors (GIZO, Zinc Tin Oxide (ZTO)) and dielectric layers (SiO₂, Ta₂O₅-SiO₂) were tested. A statistical analysis of the obtained data demonstrates stable sub-threshold slopes and mobilities in the range of 10 to 20 cm²/Vs, with degradation of less than 5% per kGy of absorbed X-ray dose. During irradiation we observe a negative shift of threshold voltage (V_T) which is in agreement with charge trapping in the dielectric layer as observed in Si-based electronics. At room temperature the charges quickly neutralize and the TFT recovers original V_T. The results demonstrate stable operation of high mobility oxide TFTs in radiation harsh environments and indicate that these new semiconductor materials and devices have a large potential for applications which require large-area and light-weight properties, e.g. in space applications.

The detection and control of H₂ emission is substantial for ecological balance, industrial safety and efficiency. Industrialization and technological advancements forces the development of fast responding hydrogen sensors with higher sensitivity and selectivity. Semiconductor oxide based sensors are the most investigated and widely used ones for detection of hydrogen gas. Recently, TiO₂ has received a great deal of attention as a semiconductor oxide based hydrogen sensor material owing to it&’s high stability at elevated temperatures and in harsh environments, low cost, non-toxic properties. The possibilities of nanoporous structure formation on the surface of Ti or doping Ti with suitable elements opened up new horizons for increasing the sensing and selectivity characteristics of titania based hydrogen gas sensors. In addition, instead of using metallic Ti foil, deposition of TiO₂ sensor material in the form of thin films on different substrates expands the scope of it&’s application in functional hydrogen sensor devices.
In the present study, hydrogen sensing properties of nanoporous titania and titania-alumina sensor platforms were investigated. Metallic Ti and TiAl thin films were deposited on ceramic substrates using modified cathodic arc based technique. Dense and well adherent coatings that are required for obtaining durable nanoporous structures during anodic oxidation process were produced. These structures were anodized in ethylene glycol based solution both for oxidation and nanoporous structure formation. For obtaining well ordered nanostructures anodization parameters were optimized. Sensing properties of both titania and doped titania structures towards hydrogen gas were investigated and evaluated. The nanotubular TiAl oxide sensor exhibited promising sensing performance towards H₂ gas concentrations and quick response and recovery behaviour with high stability.

Carbon fibers composites are one of the most important family of structural materials for the development of frontier technologies in aircraft and aerospace, automotive, as well as wind energy industries and the manufacturing of lightweight but strong chassis for many objects.
In the last years, several researches have been focused on the application and integration of sensors on these composites in order to have feedback information from carbon-fiber based structural elements during their use in high stress and vibration conditions. In this work, we propose a different approach to this problem by directly turning carbon fiber composite into an active sensing material by functionalizing it with zinc oxide (ZnO) nanowires.
Carbon fibers have been coated by a brush-like layer of ZnO nanowires using a seeded solvothermal growth. Both single carbon fibers or large bundles can be functionalized in such a way.
Exploiting the electrical conductivity of carbon fibers and the multiple functional properties of ZnO nanostructures, we demonstrated that the intersection at the crossing of two functionalized carbon fibers can act as piezoelectric transducer, as well as a photo-sensor or a gas sensor.
These results can be the considered as the basis to transform a typical carbon fiber texture into an integrated array of micron-scale sensors to be used in the harsh environments in which these composites are often required.

Environmental sensing needs are particularly important in oil and gas extraction environments. In particular, deep water and ultradeep water offshore platforms often require a suite of sensing applications to mitigate safety and economic risks associated with large distances from the shore and production shutdowns, respectively. Often, sensors need to be positioned in remote and difficult to access locations, exposed to harsh conditions and carry mechanical load.
Aluminium alloy 6082 (AA6082) has the highest strength among members of AlMgSi family of alloys. It is a strong material and finds structural applications such as stairs, handrails and bridges. Because of its corrosion resistant properties, good weldability and its particularly high strength to weight ratio, AA6082 is an attractive material to complement steel housing of sensors used in oil and gas platforms.
Compared to other AlMgSi such as AA6061 which it has largely replaced, the creep properties of AA6082 have not been as widely studied. Understanding creep properties of AA6082 is especially important as occurrence of fire on platforms may significantly affect the structural integrity of sensors. This paper will discuss the creep behaviour of AA6082 after thermal aging. Effects of aging temperature and time on the creep behavior were investigated. We propose an empirical model to describe the relationship between creep strain with aging temperature and time. We also attempt to analyze our results in the framework of the various creep models in light of recent work by Kassner and Langdon.

Carbon fibers are used as sensing elements in CFRP due to their electrical conductivity. In some more advanced studies, in CRFP, the carbon fibers were used for both strain sensing and damage sensing. The basic theory, in such studies, was that the movement of carbon fiber could be detected by ER (ER) measurement. During loading, the extent of contact between carbon fibers in a CF tow is altered, and the ER changes from its initial value. In this work, interfacial properties of carbon fiber/polymer composites were evaluated by such ER measurements. During the wetting process of CF tows by the polymer resins, the change in ER was recorded and analyzed. The test results for different carbon fibers and polymer resins exhibited different trends. The ER change was associated with the different wetting conditions, and the interfacial properties were predicted by these ER measurements. CF tow/epoxy exhibited the poorest carbon tow wettability, the smallest change in resistance and the poorest IFSS and ILSS. For the four systems studied, the relative change in each of these quantities for the materials of a given composite was roughly proportional to the other measured quantities. This may have some very significant practical importance. It may point the way to use quick easy tests to screen and predict other behaviors for composites of different materials and/or processes. Perhaps a simple resistance change test might be used to predict and select good candidate materials, surface processing techniques for high strength composite applications. The proportional relationship between interfacial adhesion and ER change was obtained by trend fitting line analyses. Mechanical properties related to interfacial properties might potentially be predicted by ER measurement and studies of wetting behavior, using empirical formulas and correlations.

Radiation immune high magnetic field sensing is critical for the safe and reliable operation of particle accelerators and for other applications. The potential for the use of Terbium Gallium Garnet, Tb₃Ga₅O₁₂ (TGG) for magneto-optical sensing in radiative environments is studied. Long-term radiation stability of the TGG crystals was analyzed by observing the changes in optical, magneto-optical and magnetic properties of TGG crystals as they are exposed to radiation (neutron doses as high as 5×10¹⁵ n/cm²). The characterization of the effects of radiation has allowed for the development of a damage compensated Faraday Effect magnetic field sensor. This sensor provides more than an order-of-magnitude improvement in radiation damage survivability over commercially available Hall Effect magnetic field sensors currently used in particle accelerators. Also, a novel interrogation instrument with significantly enhanced dynamic range/stability is presented.

Surface-enhanced Raman spectroscopy(SERS) enabled by noble metal nanostructures such as Ag and Au has long been exploited for chemical sensing and identification at readily attainable limits of detection of ppm-ppt. Structural and morphological instability of metal nanostructures due to Ostwald ripening poses a major challenge, however, for robust SERS in high-temperature environment such as advanced coal gasifiers and gas turbines. We report an experimental study on the use of anodized aluminum oxide (AAO) with highly aligned nanoporous air channels as support for thermal stabilization of Ag and Pd nanoparticles. We show that Ag and Pd nanoparticles immobilzed throughout the AAO pore structure exhibit excellent thermal stability in size and distribution and, more imporyant, possess strong SERS activity after heat treatment at high temperatures, in sharp contract to their counterparts anchored to planar silicon substrates. Specifically, Ag nanoparticles on AAO air channels were fabricacted via in-situ growth from electroless-deposited Ag seeds and subsequently heated at 5000C for up to 5 days. Pre-synthesized colloidal Pd nanoparticles were immobilized on AAO air channels through a polymer-mediated process for strong electrostatic particle-support interactions and then heated at up to 8000C for 1 hour. The heat-treated AAO/Ag and AAO/Pd were used for SERS measurements (at RT) of Rhodamine 6G solution (~10^-7 M) and toluene vapor (~2-3 vol%), and benzenethiol (~0.1 wt% in ethanol), respectively. Parallel investigation of Ag and Pd nanoparticles anchored to planar substrates was carried out for comparison. The SERS results will be interpreted in accordance with detailed characterization before and after heat treatment using scanning electron microscopy and X-ray photoelectron spectroscopy.

In almost all cases, phenol is damaging not only to individual species and populations, but also to the natural biological communities. Disturbingly, with plenty of discharging sources, such as chemical plants, pharmaceutical plants and petroleum refineries, phenol is one of the most serious and persistent organic pollutants widely existed in ambient environment, especially in the surface water. As a common environmental disaster due to its high toxicity, considerable effort has been committed to remove the phenol from ambient environment, especially from wastewater.
Here, we report a unique route that creatively harnessed the b-cyclodextrin enhanced triboelectricfication for self-powered phenol detection as well as electrochemical degradation. A detection sensitivity of 0.01/mu;M was demonstrated in the sensing range of 10 mu;M to 100 mu;M. Additionally, the b-cyclodextrin enhanced triboelectricfication was designed to harvest kinetic impact energy from wastewater waves to electrochemically degrade the phenol in a self-powered manner without using an external power source. At a fixed wave velocity of 1.4 m/s and initial phenol concentration of 80 mg/L, the generated power is capable of cleaning up to 90% of the phenol in the wastewater in 320 min. Given the compelling features, such as being self-powered, environmentally friendly, extremely cost-effective, simple, device reusable, high detection sensitivity and degradation efficiency, the b-cyclodextrin enhanced triboelectricfication renders an innovative approach for ambient phenol detection and electrochemical degradation.
References: (* indicate co-first author).
1. Z. Li*, J. Chen*, J. Yang ,Y. Su, X. Fan, Y. Wu, C. Yu and Z. L. Wang. Energy & Environ. Sci. 8 (2015), 887-896.
2. J. Chen*, G. Zhu*, J. Yang, Q. Jing, P. Bai, W. Yang, X. Qi, Y. Su and Z. L. Wang. ACS Nano 9 (2015), 105-116.
3. J. Chen*, G. Zhu*, T. Zhang, Q. Jing and Z. L. Wang. Nat. Commun.5 (2014), 3426.
4. J. Chen*, G. Zhu*, W. Yang, Q. Jing, P. Bai, Y. Yang, T. C. Hou and Z. L. Wang. Adv. Mater.25 (2013), 6094-6099.
5. J. Chen*, J. Yang*, Z. Li, X. Fan, Y. Zi, Q. Jing, H. Guo, Z. Wen, K. C. Pradel, S. Niu and Z. L. Wang. ACS Nano 9 (2015), 3324-3331.