InN NEMS and Heterojunction Devices For Sensing Applications

Recent research trends in chemical and biological sensing have been geared toward developing molecular sensor devices that are fast, inexpensive, miniaturized, have low power consumption and are portable. The performance of these devices can be dramatically improved by utilizing multimodal detection techniques, new materials and nanofabrication technologies. To develop such sensor devices, we utilized Indium Nitride (InN) nanowires (NWs) to fabricate nanoelectromechanical system (NEMS) based sensors and Graphene/InN NW heterojunctions, and InN thin films to fabricate Graphene/InN thin film heterojunction based sensors. InN NWs, which exhibit interesting properties including high carrier density, superior electron mobility, strong surface charge accumulation, and chemical inertness, were synthesized using Chemical Vapor Deposition (CVD) technique by Vapor-Liquid-Solid (VLS) mechanism. A novel method for synthesis of high quality InN nanowires, at temperatures well above their decomposition temperature, has been demonstrated by utilizing controlled oxygen flow into the growth chamber. Detailed structural and chemical analyses indicate that the nanowires consist of pure InN, with no evidence of In2O3 detected by any of the characterization methods. It is proposed that the oxygen, pre-adsorbed on the Au catalyst surface, assists in accelerating the decomposition of NH3 at the growth temperature by providing high concentration of atomic nitrogen to assist in the growth, and prevent decomposition of the InN nanowires, without getting incorporated in them. The proposed role of oxygen is supported by improved material quality at higher oxygen flow rates. In a related research effort, Indium Nitride based heterojunction sensor devices were investigated. We designed and fabricated graphene/InN heterojunction devices that are suitable for gas sensing because of a tunable barrier height controlling the conductivity across the heterojunction in presence of different analyte gas and vapor molecules. Electrical characterization of the device demonstrated good rectifying behavior across the graphene/InN heterojunction. Preliminary sensing experiments carried out with trace amount of water and acetone vapors, as well as, NH3 and NO2 gases showed highly promising results. It is observed that this sensor offers better sensitivity than simple graphene or InN based conductometric sensors, primarily because of the presence of a tunable Schottky barrier formed between graphene and InN that can be modulated by different analyte gas molecules, which affects the junction current exponentially. To explore promising alternative device approaches addressing the challenges posed by continuous shrinking of Si based device dimensions in integrated circuits, we investigated for the first time an InN NW/graphene heterojunction based vertical threeterminal active device, a variable barrier transistor or barristor, where the interfacial current between two terminals were controlled by an insulated gate. A very promising on/off ratio exceeding 100 was achieved by adjusting the gate voltage to control the graphene/InN NW heterojunction Schottky barrier, which underlines the promise of these devices in low power device and sensing applications

Detection of acetone vapours using solution-processed tin oxide thin-film transistors

Abnormal concentrations of volatile organic compounds (VOCs) in human breathe can be used as disease-specific biomarkers for the non-invasive diagnosis of medical conditions, such as acetone for diabetes. Solution-processed bottom gate top contact metal oxide thin-film transistors (TFTs) are used to detect acetone vapours, as part of a proof-of-concept study. The effect of increasing annealing temperature (T) and channel length (L) on electrical and sensing performance are explored. Drain current (Ids) increases following exposure as acetone undergoes a redox reaction with the adsorbed oxygen species on the semiconductor surface, which results in free electrons being released back into the conduction band. Responsivity (R) is maximized at negative bias (Vgs < 0). For L = 50 μm, the peak R of the TFT annealed at 450 °C is three times greater than that of the TFT annealed at 350 °C, with Vgs = − 37.5 V and − 33 V, respectively

Review—Non-Invasive Monitoring of Human Health by Exhaled Breath Analysis: A Comprehensive Review

Exhaled human breath analysis is a very promisingfield of research work having great potential for diagnosis of diseases in non-invasive way. Breath analysis has attracted huge attention in thefield of medical diagnosis and disease monitoring in the last twodecades. VOCs/gases (Volatile Organic Compounds) in exhaled breath bear thefinger-prints of metabolic and biophysicalprocesses going on in human body. It’s a non-invasive, fast, non-hazardous, cost effective, and point of care process for diseasestate monitoring and environmental exposure assessment in human beings. Some VOCs/gases in exhaled breath are bio-markers ofdifferent diseases and their presence in excess amount is indicative of un-healthiness. Breath analysis has the potential for earlydetection of diseases. However, it is still underused and commercial device is yet not available owing to multiferrious challenges.This review is intended to provide an overview of major biomarkers (VOCs/gases) present in exhaled breath, importance of theiranalysis towards disease monitoring, analytical techniques involved, promising materials for breath analysis etc. Finally, relatedchallenges and limitations along with future scope will be touched upon.will be touched upon

Investigation of Different Materials as Acetone Sensors for Application in Type-1 Diabetes Diagnosis

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Acetone detection using thin tungsten oxide (WO3) film based gas sensor

Acetone being a volatile organic compound is found in human breath. Non-invasive breath analysis for detection of diabetes has gained remarkable attention for the past few years. Human breath has ample of volatile organic compounds pertaining to numerous diseases in the body. Acetone in breath has been proven to be an important biomarker for diagnosis of diabetes through breath. Here, tungsten oxide (WO3) thin films of nanometer thickness have been used for this purpose. The detector films are sputtered over silicon dioxide layer and corresponding connections are made over the film to measure the resistance change. Acetone, being a reducing gas, reduces the resistance of the film as it comes in contact. Different concentrations in parts per million (ppm) have been tested on these nanometer films having thickness of 100 nm over a chip size of 5 mm x 5 mm, as low as 1.2 ppm. Optimum temperature has also been computed to be 300 oC. The topography of film has been characterized by atomic force microscopy (AFM) and a mean grain size of 24.1 nanometers has been observed

Nanostructured Metal Oxide-Based Acetone Gas Sensors: A Review.

Acetone is a well-known volatile organic compound that is widely used in different industrial and domestic areas. However, it can have dangerous effects on human life and health. Thus, the realization of sensitive and selective sensors for recognition of acetone is highly important. Among different gas sensors, resistive gas sensors based on nanostructured metal oxide with high surface area, have been widely reported for successful detection of acetone gas, owing to their high sensitivity, fast dynamics, high stability, and low price. Herein, we discuss different aspects of metal oxide-based acetone gas sensors in pristine, composite, doped, and noble metal functionalized forms. Gas sensing mechanisms are also discussed. This review is an informative document for those who are working in the field of gas sensors

双金属Zn-Fe金属有机框架的制备及其丙酮气敏特性研究

采用溶剂热法制备了双金属Zn-Fe金属有机框架结构(Zn-Fe MOF),利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和X射线衍射仪(XRD)对其微观形貌和晶相进行表征分析。结果表明:制备的双金属Zn-Fe MOF为纳米球结构,其直径约为150 nm。同时,制备了基于双金属Zn-Fe MOF材料的气体传感器件,研究了其对丙酮的气敏特性。测试结果表明:基于双金属Zn-Fe MOF的气体传感器对丙酮的最佳工作温度为210℃。在最佳工作温度下,对浓度为1×10-6的丙酮气体响应可达到2,响应/恢复时间分别为6 s/13 s,且具有较好的重复性和长期稳定性。最后,对基于双金属Zn-Fe MOF气体传感器的气敏机理进行了讨论。国家自然科学基金项目(51205274);;山西省人才专项项目(2016[36]);;山西省自然基金项目(2016[39]);;山西省高校科技创新研究项目(2016[37]);;山西省归国留学择优项目([2014]95);;山西省归国留学基金项目(2013-035);;山西省科技重大专项项目(20121101004);;山西省高等学校特色重点学科建设项目(晋教财[2012]45号

Development of Highly Sensitive and Selective Breathing Sensors Using Molecular Imprinted Filtering for Diabetic and Alcoholic Patients

Wellness sensor technology is an emerging diagnostic test research field, which mostly deal with the point of care of the patients in the recent days. Due to the lack of awareness from the patients, most diseases cannot be detected in due time. This led to worse conditions, such as diabetic and alcoholic syndrome. Therefore, many research groups have been working to develop portable sensor devices that can track serious diseases. These include diabetic and alcoholic biomarkers in breathing. These devices have very high selectivity and reliability. However, the major limitation of biomarkers is that it deals with the bio-molecular based sensing mechanism. Extensive challenges exist in the selectivity and reliability of breathing sensors. These require development of proper materials and effective detection methods. Thus, selection of proper materials, correct sensing parameters, effective device architecture and simple fabrication processing are substantially critical. The goal of this work is to develop graphene based breathing sensors with high selectivity and sensitivity using a novel molecular imprinted filtering technique. The sensors have various applications including Point of Care Testing (POCT) device for personalized home and clinical use in early detection of diabetic and alcoholic patients. Different fabrication procedures were used to optimize the sensor performance. The optimized results demonstrate that a proper biomarker molecule imprinting process could selectively detect diabetes and alcohol. The graphene layer was optimized by maintaining spray coating time, pattern and distance between the substrate and spray coater. Graphene adhesion to the substrate was also improved using polyvinyl pyrrolidone. The molecular imprinting filter made on top of the graphene layer improved the performance of acetone and ethanol molecule detection, indicated by the change of resistance in the graphene layer. The sensors showed poor performance for long-time exposure (\u3e 10 second) due to ambient molecules and moisture. However, the sensor characteristics were significantly improved for short exposing time (3-4 second) due to the optimization in the thickness of the filtering layer and sensing layer

A low cost MEMS based NDIR system for the monitoring of carbon dioxide in breath analysis at ppm levels

The molecules in our breath can provide a wealth of information about the health and well-being of a person. The level of carbon dioxide (CO2) is not only a sign of life but also when combined with the level of exhaled oxygen provides valuable health information in the form of our metabolic rate. We report upon the development of a MEMS-based non-dispersive infrared CO2 sensor for inclusion in a hand held portable breath analyser. Our novel sensor system comprises a thermopile detector and low power MEMS silicon on insulator (SOI) wideband infrared (IR) emitter. A lock-in amplifier design permits a CO2 concentration of 50 ppm to be detected on gas bench rig. Different IR path lengths were studied with gases in dry and humid (25% and 50% RH) in order to design a sensor suitable for detecting CO2 in breath with concentrations in the range of 4 to 5%. A breath analyser was constructed from acetal and in part 3D printed with a side-stream sampling mechanism and tested on a range of subjects with two data-sets presented here. The performance of the novel MEMS based sensor was validated using a reference commercial breath-by-breath sensor and produced comparable results and gave a response time of 1.3 s. Further work involves the detection of other compounds on breath for further metabolic analysis and reducing the overall resolution of our MEMS sensor system from ca. 250 ppm to 10 ppm