A preliminary gas detection study was conducted on as-grown multi-walled carbon nanotubes and anodized aluminum oxide (MWNTs/AAO) template. The material demonstrated room temperature gas sensitivity and p-type semiconductor characteristics. Plasma-etched MWNTs/AAO templates were employed to construct capacitive gas sensors. The capacitances of the sensors were sensitive to both reducing and oxidizing gases at room temperature. Single-walled carbon nanotubes (SWNTs) dispersed in binder andamp;aacute;-terpineol were applied on sensor platforms to form resistive gas sensors. The sensors demonstrated excellent sensitivity to low concentrations of reducing and oxidizing gases at room temperature, which suggests the p-type semiconducting behavior of SWNTs. The sensor recovery was found to be incomplete at room temperature in flow of nitrogen and air, thus possible solutions were investigated to enhance sensor performance. The sensor operating principles and suggestions for possible future work are discussed. The room temperature and air background functionality of the sensor suggest that SWNT is a promising gas sensing material for application in ambient conditions.

The detection of low level concentrations of particles in a gaseous environment is of importance to many fields, especially Homeland Security. The ability to identify ppb concentrations of explosives and their degradation products can aid in the detection of improvised explosive devices (IEDs), ammunition dumps, or hidden explosives. One method of accomplishing this task is through the use of an array of chemiresistors in an electronic nose device. For this study, chemiresistors were constructed using 3-D silica nanospring mats with a contiguous film of ZnO nanocrystals and ZnO nanocrystals decorated by metallic nanoparticles. Samples with an average grain size of 15nm were found to be the most responsive and upon exposure to a gas flow of 20% O2 and 80% N2 with ~200 ppm of acetone and an operational temperature of 400 oC produced a relative change in conductance by a factor of 400. The addition of metal nanoparticles onto the surface of the ZnO nanocrystals produced a relative change in conductance by a factor of 1100. Under optimum conditions, sensing elements of this design exhibited well-defined spikes in conductance upon exposure to explosive vapors (TNT, TATP) at the ppb levels. The use of a pattern recognition system allowed discrimination between three analyte chemicals.

The birth of nanotechnology era has revolutionized materials science, catalysis and field of optoelectronics. Novel and unique phenomena emerge when material dimensions are reduced to ultra-small size regime and enter nanometre (2-100 nm) realm. Such novel materials are expected to replace bulk materials, offering lower cost of manufacturing and enabling progress in many areas such as solar cell, drug delivery, quantum communication and computing, catalysis and sensing applications. With the progress in nanomaterial synthesis and fabrication, the need for the state-of-art characterization techniques became obvious; such techniques help to establish a complete understanding of the nature and interactions of nanosized materials. In this thesis, the first part focuses on the synthesis of gold and ruthenium clusters, namely Au8, Au9, Au101, Ru3, Ru4 and AuRu3, using the well-established synthetic protocols in the literature. Apart from the standard lab-based characterization techniques such as nuclear magnetic resonance (NMR), UV-visible spectroscopy (UV-vis) and Fourier Transform Infra-red (FTIR), a less explored but useful technique far infra-red (far IR) spectroscopy, available at the Australian Synchrotron (AS), was employed to investigate the vibrational modes in these clusters. Peaks in the experimental far IR spectra were assigned unambiguously to specific vibrations by comparing with the ones generated via DFT calculations with the help of collaborators, group of Professor Gregory Metha, University of Adelaide. For the Au9 cluster, three significant gold core vibrations are observed at 157, 177 and 197 cm-1 in the experimental spectrum. In the case of the Ru3 cluster, only a single ruthenium core vibration is identified within the spectrum, at 150 cm-1 with the calculated force constant, k = 0.33 mdyne/Å. The Ru4 cluster exhibits two metal core vibrations at 153 and 170 cm-1 with force constants of 0.35 and 0.53 mdyne/Å, respectively. Substitution with a gold atom yielding a mixed metal AuRu3 cluster shifts the core transitions toward higher wavenumbers at 177 and 299 cm-1 with an increase in force constants to 0.37 and 1.65 mdyne/Å, respectively. This is attributed to the change in chemical composition and geometry of the metal cluster core. A combination of the DFT calculations and high quality synchrotron-based experimental measurements allowed the full assignment of the key transitions in these clusters. Next, these clusters were fabricated into heterogeneous catalysts by depositing on different metal oxide nanopowders. Synchrotron X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) studies were performed at the Australian Synchrotron and the Photon Factory synchrotron in Japan to investigate the electronic structure of Au8, Au9 and Au101 on TiO2 catalysts. The XPS analysis reveals that “as-deposited” Au8 and Au9 retain some un-aggregated clusters while Au101 show bulk-like gold. These findings are in line with TEM observations, where the aggregates (large particles, > 2 nm) of Au8, Au9 and Au101 are hardly seen under HRTEM. UV-visible diffuse reflectance spectroscopy (UV-vis DRS) studies show the absence of localised surface plasmon resonance (LSPR) peaks in these “as-deposited” clusters, suggesting they are below 2 nm in size. Importantly, the XAS spectrum of “as-deposited” Au9 clusters estimates that 60% of pure, un-aggregated Au9 clusters and 40% of bulk gold in the sample. Upon calcination under O2 and combined O2 and H2 (O2-H2), Au8, Au9 and Au101 clusters form larger nanoparticles (> 2 nm) with the appearance of LSPE peak in UV-vis DR spectra. In addition, majority of the phosphine ligands (that stabilise the gold core) dislodge and form phosphine oxide-like species by interacting with oxygen on the TiO2 surface. The third part focused on testing the catalytic performance of the supported Au8, Au9, Au101, Ru3, Ru4 and AuRu3 clusters on different TiO2, SiO2, ZnO and ZrO2 in benzyl alcohol oxidation. Au101-based catalysts display the highest catalytic activity with a turn-over frequency (TOF) up to 0.69 s-1. The high catalytic activity is attributed to the formation of large Au nanoparticles (> 2 nm) that coincides with the partial removal of capping ligands. Au8 and Au9 clusters which contain NO3- counter anions are found to be inactive in benzyl alcohol oxidation. Further work shows that the presence of NO3- species diminishes the catalytic activity. Monometallic ruthenium clusters, Ru3 and Ru4, are found to be inactive yet the bimetallic AuRu3 clusters are active in benzyl alcohol oxidation, suggesting the synergistic effect between ruthenium and gold metal. Investigation of catalytic testing parameters reveals that tuning selectivity of the product is possible through manipulating the reaction temperature. Finally, a joint experiment with Prof. Wojtek Wlodarski’s group at RMIT, Melbourne was undertaken to test the sensing ability of Au9 clusters for hydrogen detection. Au9 clusters were deposited onto radio-frequency (RF) sputtered WO3 films at two different concentrations; 0.01(S1) and 0.1(S2) mg/mL. It was found that the optimal temperatures for sensor S1 and S2 were 300 °C and 350 °C, respectively. The sensor with lower Au9 concentration (S1) displays a faster response and recovery time, and a higher sensitivity toward H2. HRTEM studies reveal that the sensor S1 contain a significant population of sub-5 nm Au nanoparticles which might be responsible for a faster rate of H2 adsorption and dissociation. The key finding in this study suggest that the addition of catalytic layer such as ultra-small Au9 clusters results in improved sensitivity and dynamic performance (response and recovery time) of H2 sensors. In summary, this thesis demonstrated that cluster-based nanomaterials have wide range of applications spanning from catalysis to sensing. Further improvements in material synthesis and use of multiple complimentary characterization techniques allowed better understanding of the nature of the key active species (metal nanoparticles) assisting design of catalysts and sensors with enhanced performance.

No description available.

<p>Graphene is a novel carbon material with great promise for a range of applications due to its electronic and mechanical properties. Its two-dimensional nature translates to a high sensitivity to surface chemical interactions thereby making it an ideal platform for sensors. Graphene's electronic properties are not degraded due to mechanical flexing or strain (Kim, K. S., et al. nature 07719, 2009) offering another advantage for flexible sensors integrated into numerous systems including fabrics, etc. </p><p>We have demonstrated a graphene NO2 sensor on a solid substrate (100nm SiO2/heavily doped silicon). Three different methods were used to synthesize graphene and the sensor fabrication process was optimized accordingly. Water is used as a controllable p-type dopant in graphene to study the relationship between doping and graphene's response to NO2. Experimental results show that interface water between graphene and the supporting SiO2 substrate induces higher p-doping in graphene, leading to a higher sensitivity to NO2, consistent with theoretical predications (Zhang, Y. et al., Nanotechnology 20(2009) 185504). </p><p>We have also demonstrated a flexible and stretchable graphene-based sensor. Few layer graphene, grown on a Ni substrate, is etched and transferred to a highly stretchable polymer substrate (VHB from 3M) with preloaded stress, followed by metal contact formation to construct a flexible, stretchable sensor. With up to 500% deformation caused by compressive stress, graphene still shows stable electrical response to NO2. Our results suggest that higher compressive stress results in smaller sheet resistance and higher sensitivity to NO2. </p><p>A possible molecular detection sensor utilizing Surface Enhanced Raman Spectrum (SERS) based on a graphene/gallium nanoparticles platform is also studied. By correlating the enhancement of the graphene Raman modes with metal coverage, we propose that the Ga transfers electrons to the graphene creating local regions of enhanced electron concentration modifying the Raman scattering in graphene.</p> / Dissertation

This dissertation describes the fabrication and operation of porous silicon gas sensors. The first chapter describes the motivation behind gas sensor research and provides the reader with background knowledge of gas sensors including the terminology and a review of various gas sensors. The following two chapters describe both how the porous silicon gas sensors are created and how they have been tested in the laboratory. Chapter 4 describes the steps required to create arrays of gas sensors to provide for a selective device through the application of patented selective coatings. Chapter 5 proposes a physical model that leads to a numerical solution for predicting the operation of the gas sensor. The next chapter builds from this model to analyze and optimize the experimental methods that are used to test both this and other gas sensors. The final chapter of this dissertation describes the prototype gas sensor system that has most recently been created, the company that was formed to further the development of that system, and the future applications of the porous silicon gas sensor.

The use of breath odours in medical diagnosis dates back to classical times, though in its modern form the technique is only a few decades old. There are several breath tests in common clinical use, though all of them involve administration of a known or labelled exogenous compound. More recently, over the last twenty years, interest has focussed on analysis of endogenous metabolites in breath, but despite a large number of published studies reporting a number of disease markers, there has been little or no impact on clinical practice. Nonetheless, breath analysis offers a number of potential advantages over current biochemical methods. One major advantage of breath analysis is its non-invasive nature, which has led to significant interest in its use at point-of care for monitoring chronic diseases such as diabetes and the chronic infections ubiquitous in cystic fibrosis. However, breath analysis classically involves the use of expensive laboratory based analytical equipment which requires extensively-trained personnel and which cannot readily be miniaturised. Systems based on simple gas sensors might offer a way of overcoming these limitations. In recent years, Cranfield University has developed an instrument called the single metal oxide sensor gas analyser (SMOS-GA, more commonly referred to as the “Breathotron”) as a proof of concept for sensor-based breath analysis. In this project the Breathotron has been used in conjunction with selected ion flow tube mass spectrometry (SIFT-MS) and thermal desorption gas chromatography mass spectrometry (TD-GC-MS) to determine the changes in the concentrations of volatile organic compounds (VOCs) in breath in a number of experimental situations which a relevant to the diagnostic monitoring of diabetes mellitus. Studies conducted on clinically healthy volunteers were: an oral glucose tolerance test (OGTT); a six minute treadmill walking test; and a bicycle ergometer test. Additionally Breathotron and analytical data were also obtained during a hypoglycaemic clamp study carried out on hypoglycaemia-unaware Type I diabetics. The principle breath volatiles determined analytically were: acetone, acetaldehyde, ammonia isoprene though data on a number of others was also available. In general, it proved difficult to establish any reproducible relationship between the concentration of any compound measured and blood glucose concentration any of the experimental interventions. It was notable, though, that statistically significant associations were observed occasionally in data from individual volunteers, but even these were not reproduced in those trials which involved repeated measurements. This remained true even where spirometry data were used to derive VOC clearance rates. This may explain previous reports from smaller studies of an association between glucose and breath acetone concentration. It seems probable that any experimentally-induced changes in breath VOC concentration or clearance were of much smaller magnitude than background variability and was consequently not detectable. These observations were mirrored in the sensor-derived results. Multivariate analysis across all trials where Breathotron data were obtained suggested clustering by individual volunteer rather than glycaemic status. This suggests that that there exists a “background” breath volatile composition, dependent perhaps on such factors as long-term diet, which is independent of our experimental intervention. The Breathotron was also used as a platform to assess the performance of three different types of mixed metal oxide sensor in vitro. Calibration curves were generated for acetone, ammonia and propanol covering the physiological range of concentrations and with a similar water content to breath. Close correlations were obtained between concentration and the amplitude of the sensor response. Sensor response reproducibility was also determined using acetone at a concentration of 10ppm with dry and humidified test gas. There were significant differences between sensor types in overall reproducibility and in response to humidity. These results suggest that had there been substantial changes in breath VOC composition as a result of our experimental interventions, any of the types of sensor used would have been capable of responding to them. In summary, these results do not support the efficacy of breath VOC analysis as a means of non-invasive diagnostic monitoring.

En esta tesis doctoral, se ha investigado y desarrollado un nuevo método de CVD asistido por aerosol (AACVD), que permite el crecimiento de nanoestructuras de WO3 intrínsecas y funcionalizadas con Au. Así mismo se han depositado capas policristalinas de SnO2 para aplicaciones de detección de gases. La síntesis de materiales nanoestructurados, la fabricación de dispositivos y sus propiedades de detección de gases, han sido estudiadas. El método AACVD fue utilizado para la síntesis y la deposición directa de capas activas encima de sustratos de alúmina y también sobre substratos micromecanizados (microhotplates), lo que demuestra la compatibilidad entre la tecnología de silicio y la deposición de la capas activas nanoestructuradas. En la tesis se ha demostrado que las capas nanoestructuradas de WO3 funcionalizadas con oro tienen una sensibilidad mejor que las intrínsecas frente a algunos gases relevantes y al mismo tiempo se ha producido un cambio de selectividad. / In this doctoral thesis, it has been investigated and developed the Aerosol Assisted Chemical Vapour Deposition (AACVD) method for direct in-situ growth of intrinsic and Au-functionalised nanostructured WO3, as well as SnO2-based devices for gas sensing applications. The nanostructured material synthesis, device fabrication and their gas sensing properties have been studied. AACVD method was used for synthesis and direct deposition of sensing films onto classical alumina and microhotplate gas sensor substrates, demonstrating the compatibility between the microhotplate fabrication process and the sensing nanostructured layer deposition. The effect of Au nanoparticles on the gas sensor’s response was measured and presented in this thesis. The test results revealed that the addition of Au nanoparticles to the WO3 nanoneedles has increased the sensor’s response towards the tested gases (i.e. EtOH). It was therefore demonstrated that the Au-functionalisation has an enhancing effect on the gas sensing properties of WO3 nanoneedles

With the development of economy, more and more cars appear in the roads. Many drivers ignore thedanger about driving after drinking so that drunk driving causes a large number of traffic accidents allaround the world. By now, alcohol has killed a lot of people in the world. To reduce accidents causedby drunk driving, make certain the alcohol content in driver's body would help a lot, and it is related toalcohol concentration measuring and relevant instrument.In this thesis work, the design of a simple alcohol meter was present. The designed system iscomposed of a gas sensor (TGS-822) working circuit, microcontroller PIC16F690 and LCD display.The system collects the electronic signals caused by resistance changes in gas sensor (TGS-822) froma built-in Analog-to-Digital Converter (A/D) in microcontroller PIC16F690, programs withPIC16F690, and displays alcohol concentration in LCD display finally. The measuring concentrationrange of the designed alcohol meter is from 50PPM to 5000PPM. This paper describes the datacollection, processing and display of the designed alcohol meter in detail. And lastly, the authordiscussed about the advantages and disadvantages of the designed alcohol meter, it could beconsidered as a guideline for further work.

Submitted by Ranilson Angelo da Silva null (ranilsonangelo@yahoo.com.br) on 2016-10-03T13:42:06Z No. of bitstreams: 1 Tese Doutorado_Ranilson_Final.pdf: 16582757 bytes, checksum: de5b3924045b0020ea737e76aa06ee18 (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-10-05T19:07:16Z (GMT) No. of bitstreams: 1 silva_ra_dr_araiq.pdf: 16582757 bytes, checksum: de5b3924045b0020ea737e76aa06ee18 (MD5) / Made available in DSpace on 2016-10-05T19:07:16Z (GMT). No. of bitstreams: 1 silva_ra_dr_araiq.pdf: 16582757 bytes, checksum: de5b3924045b0020ea737e76aa06ee18 (MD5) Previous issue date: 2016-06-29 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A eficiência dos materiais semicondutores óxidos metálicos utilizados em dispositivos sensores, depende fortemente de parâmetros morfológicos e estruturais. É de grande interesse que os materiais apresentem um elevado grau nos parâmetros de medidas que definem um bom sensor, como: sinal, sensibilidade, seletividade. Devido a isso, métodos de sínteses adequados têm grande influência no desempenho dos dispositivos, já que interferem diretamente na morfologia e estrutura dos materiais semicondutores. Através dessa perspectiva, nesse trabalho, morfologias do composto semicondutor óxido metálico ZnO foram superficialmente modificadas com o intuito de realizar melhorias para aplicações em sensores de gás e de radiação luminosa (fotocondução) na faixa do ultravioleta. Dois métodos de sínteses foram utilizados: i) evaporação térmica por redução carbotérmica e ii) hidrotermal assistido por micro-ondas, responsáveis por obter morfologias tipo tetrapés e estrelas multipontas, respectivamente. Processos de evaporação térmica por redução carbotérmica tem a grande vantagem de obter estruturas com morfologias unidimensionais, em contrapartida, o método hidrotermal assistido por micro-ondas pode sintetizar uma enorme gama de diferentes morfologias com a vantagem de ser um processo rápido e de baixos custos energéticos. Técnicas como microscopia eletrônica de varredura, microscopia eletrônica de transmissão, difração de raios-X, espectroscopia ultravioleta visível e infravermelho, foram utilizadas para caracterizar o material em seu aspecto morfológico e estrutural. Análises em gases como NO2, CO e H2, e da radiação eletromagnética na região ultravioleta, foram realizadas com a finalidade de se obter parâmetros relevantes como, sinal do sensor (para aplicação em sensor de gás) e responsividade (para aplicação em fotocondução), e verificar a performance do ZnO puro e decorado nesses dois seguimentos de aplicação. Através dos resultados e possível observar que houve boa uniformidade das partículas metálicas aderidas à superfície do ZnO. Com relação as respostas do sensor de gás para os materiais puros e decorados houve um aumento do sinal para decoração com Ag na presença do gás H2. Na presença do gás NO2 o material puro obteve um maior sinal, para ambas morfologias. Já para o gás CO, somente é observado uma resposta do sensor para as estrelas multipontas decoradas com platina. A responsividade das amostras de tetrapés foram elevadas em comparação as amostras de estrelas multipontas com valor da ordem de 0,8 A/W. Os resultados obtidos são de fundamental importância para contribuição científica e levanta margem para um foco ainda mais profundo para o desenvolvimento de dispositivos sensores de alto desempenho. / Efficiency of the metal oxide semiconductor materials used in sensor devices, relies heavily on morphological and structural parameters. Is of great interest that the materials have a high degree in the measurement parameters that define a good sensor, such as signal sensitivity, selectivity. Methods suitable synthesis have great influence on the performance of the devices, since they directly affect the morphology and structure of the semiconductor materials. Therefore, in this work, morphologies of the compound semiconductor metal oxide ZnO were surface modified in order to make improvements for applications in gas sensors and light radiation (photoconduction) in the ultraviolet range. Two methods of synthesis were used: i) thermal evaporation by carbothermal reduction and ii) hydrothermal assisted by microwave, responsible for obtaining morphologies type tetrapods and stars multi-point, respectively. Thermal evaporation processes by reduction carbothermic, has the great advantage of obtaining structures with one-dimensional morphology, however, the hydrothermal method assisted by microwave can synthesize a wide range of different morphologies with the advantage of being a quick process and lower costs energy. Techniques such as scanning electron microscopy, transmission electron microscopy, X-ray diffraction, ultraviolet–visible spectroscopy and infrared, were used to characterize the material in its morphological and structural aspect. Analysis of gases such as NO2, CO and H2, and electromagnetic radiation in the ultraviolet region were performed in order to obtain relevant parameters as sensor signal (for use in gas sensor) and responsivity (for use in photoconduction) and check the performance of ZnO and decorated ZnO, in these two application segments. From the results it is observed that there was good uniformity of metal particles adhered to the surface of ZnO. In relation the responses of the gas sensor for pure and decorated material, there was an increase signal for decoration with Ag in the presence of H2 gas. In the presence of NO2 gas, there was a higher signal to both morphologies of pure ZnO. For CO gas, a response to the multi-point stars decorated with platinum is observed. The responsivity of the tripods samples was high compared with multi-point stars, with value of the order of 0.8 A / W. The results are of fundamental importance for scientific contribution and raises margin for an even deeper focus to developing high-performance sensor devices.