Nanoscale Au-ZnO heterostructure developed by atomic layer deposition towards amperometric H2O2 detection

Nanoscale Au-ZnO heterostructures were fabricated on 4-in. SiO2/Si wafers by the atomic layer deposition (ALD) technique. Developed Au-ZnO heterostructures after post-deposition annealing at 250 degrees C were tested for amperometric hydrogen peroxide (H2O2) detection. The surface morphology and nanostructure of Au-ZnO heterostructures were examined by field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), etc. Additionally, the electrochemical behavior of Au-ZnO heterostructures towards H2O2 sensing under various conditions is assessed by chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that ALD-fabricated Au-ZnO heterostructures exhibited one of the highest sensitivities of 0.53 mu A mu M(-1)cm(-2), the widest linear H2O2 detection range of 1.0 mu M-120mM, a low limit of detection (LOD) of 0.78 mu M, excellent selectivity under the normal operation conditions, and great long-term stability. Utilization of the ALD deposition method opens up a unique opportunity for the improvement of the various capabilities of the devices based on Au-ZnO heterostructures for amperometric detection of different chemicals

Nanocomposite Films for Gas Sensing

Nanocomposite films are thin films formed by mixing two or more dissimilar materials having nano-dimensional phase(s) in order to control and develop new and improved structures and properties. The properties of nanocomposite films depend not only on the individual components used but also on the morphology and the interfacial characteristics. Nanocomposite films that combine materials with synergetic or complementary behaviours possess unique physical, chemical, optical, mechanical, magnetic and electrical properties unavailable from that of the component materials and have attracted much attention for a wide range of device applications such as gas sensors.NRC publication: Ye

Synthesis and gas sensing properties of inorganic semiconducting, p-n heterojunction nanomaterials

En aquesta tesis utilitzant principalment Aerosol Assited Chemical Vapor Deposition, AACVD, com a metodologia de síntesis d'òxid de tungstè nanoestructurat s'han fabricat diferents sensors de gasos. Per tal d'estudiar la millora en la selectivitat i la sensibilitat dels sensors de gasos basats en òxid de tungstè aquest s'han decorat, via AACVD, amb nanopartícules d'altres òxids metàl·lics per a crear heterojuncions per tal d'obtenir un increment en la sensibilitat electrònica, les propietats químiques del material o bé ambdues. En particular, s'han treballat en diferents sensors de nanofils d'òxid de tungstè decorats amb nanopartícules d'òxid de níquel, òxid de cobalt i òxid d'iridi resultant en sensors amb un gran increment de resposta i selectivitat cap al sulfur d'hidrogen, per a l'amoníac i per a l'òxid de nitrogen respectivament a concentracions traça. A més a més, s'han estudiat els mecanismes de reacció que tenen lloc entre les espècies d'oxigen adsorbides a la superfície del sensor quan interactua amb un gas. I també s'ha treballat en intentar controlar el potencial de superfície de les capes nanoestructurades per tal de controlar la deriva en la senyal al llarg del temps, quan el sensor està operant, a través d'un control de temperatura.En esta tesis utilizando principalmente Aerosol Assited Chemical Vapor Deposition, AACVD, como metodología de síntesis de óxido de tungsteno nanoestructurado se han fabricado diferentes sensores de gases. Para estudiar la mejora en la selectividad y la sensibilidad de los sensores de gases basados en óxido de tungsteno estos se han decorado, vía AACVD, con nanopartículas de otros óxidos metálicos para crear heterouniones para obtener un incremento en la sensibilidad electrónica, las propiedades químicas del material o bien ambas. En particular, se han trabajado en diferentes sensores de nanohilos de óxido de tungsteno decorados con nanopartículas de óxido de níquel, óxido de cobalto y óxido de iridio resultante en sensores con un gran incremento de respuesta y selectividad hacia el sulfuro de hidrógeno, para el amoníaco y para el óxido de nitrógeno respectivamente a concentraciones traza. Además, se han estudiado los mecanismos de reacción que tienen lugar entre las especies de oxígeno adsorbidas en la superficie del sensor cuando interactúa con un gas. Y también se ha trabajado en intentar controlar el potencial de superficie de las capas nanoestructuradas para controlar la deriva en la señal a lo largo del tiempo, cuando el sensor está trabajando, a través de un control de temperatura.In this thesis, using mainly Aerosol Assited Chemical Vapor Deposition, AACVD, as a synthesis methodology for nanostructured tungsten oxide, different gas sensors have been manufactured. To study the improvement in the selectivity and sensitivity of gas sensors based on tungsten oxide, they have been decorated, via AACVD, with nanoparticles of other metal oxides to create heterojunctions to obtain an increase in electronic sensitivity, in the chemical properties of the material or at the same time in both. Particularly, we have worked on different tungsten oxide nanowire sensors decorated with nanoparticles of nickel oxide, cobalt oxide and iridium oxide resulting in sensors with a large increase in response and selectivity towards hydrogen sulfide, for ammonia. and for nitrogen oxide respectively at trace concentrations. In addition, the reaction mechanisms that take place between oxygen species adsorbed on the sensor surface when it interacts with a gas have been also studied. Furthermore, efforts have been put on trying to control the surface potential of the nanostructured layers to control the drift in the signal over time, when operating the sensors, through temperature control

Colorimetric Plasmonic Gas Sensor

학위논문(석사)--서울대학교 대학원 :공과대학 재료공학부,2019. 8. 장호원.Plasmonics 분야는 지난 수십 년 동안 많은 관심을 받았으며 다양한 응용 분야에 적용 가능성을 보여주었습니다. 다양한 응용 분야 중 특히 가스 감지를 목적으로 하는 플라즈몬 (plasmonics)에 대한 연구가 활발히 진행되고 있다. 가스 센서의 감도, 선택도 및 내구성을 향상시키기 위해 가스 센서의 광 센서로서 플라즈몬을 사용하는 것에 대한 많은 연구가 이루어졌습니다. 광학 센서는 전압을 가할 필요가 없으며 전자기적으로 노이즈에 영향을 받지 않으며 가열 메커니즘을 필요로 하지 않으므로 반도체식 센서에 비해 더 높은 신뢰도를 보인다. 본 연구에서, 플라즈몬 공명의 전자기 강화와 결합 된 광학 간섭의 개념을 기반으로 가스 검출을 위한 센서를 설계하였다. 센서의 플라즈몬 층과 빛의 상호 작용에 의해 야기 된 국부적 인 표면 플라즈몬 공명 (LSPR)과 표면 플라즈몬 분극 (SPP)은 다양한 색의 센서를 제조하는데 이용되었다. 색상은 Lumerical software Finite Difference Time Domain (FDTD) 솔루션을 통해 시뮬레이션 하였다. Reflectance 를 위해 Si 기판 위에 Al layer를 thermal evaporator로 증착 하였다. 이후 e-beam evaporator를 이용해 WO3 박막 또는 WO3 nanorods 구조체를 제작하였다. 최종적으로 Au 필름을 증착하여 plasmonic 효과를 분석하였다. 센서의 플라즈몬 층에서 발생하는 공진은 환경 변화에 매우 민감하다. 따라서, 촉매로서 귀금속으로 장식 된 나노 구조 금속 산화물은 기체의 흡착 및 탈착을 위한 유전체 매체로 사용되었다. 가스의 흡착으로 인해 센서의 광학적 특성에 변화가 생길 것으로 예상하였으며, 그 결과 산란, 흡수 및 투과 스펙트럼에서 피크 시프트가 발생할 것으로 기대한다. 이러한 피크 시프트와 색 변화가 플라즈몬 센서의 가스 감지 능력을 판별하는 파라미터로 사용된다.The field of plasmonics has been of much interest over the past few decades, showing potential for use in various applications. Of these applications, the use of plasmonics in gas sensing is currently being investigated. In order to enhance the sensitivity, selectivity, and durability of gas sensors, many studies have focused on the use of plasmonics as optical sensors for gas sensing. Because optical sensors require no contact measurements, are electromagnetically noise independent, and do not require a heating mechanism they can be more reliable compared to electrical sensors. In this study, the concept of optical interference coupled with the electromagnetic enhancement of plasmon resonances is used to design a sensor for the colorimetric detection of gases. The localized surface plasmon resonance (LSPR) and surface plasmon polariton (SPP) caused by the interaction of light with the plasmonic layer of the sensor is utilized in fabricating sensors of various structural colors. The structural colors were simulated through Lumerical software Finite Difference Time Domain (FDTD) Solutions then fabricated for comparison. The resonances that occur at the plasmonic layers of the sensors are extremely sensitive to changes in its environment. Therefore, nanostructured metal oxides decorated with noble metals as catalysts were used as the dielectric medium for the adsorption and desorption of gases. The adsorption of gas is expected to bring about a change in the sensors optical properties, which in turn causes a peak shift in the scattering, absorption, and transmission spectra. These peak shifts and the possible color change associated with these shifts are used as the response for our plasmonic sensor.Table of Contents Abstract i Contents iii List of tables vi List of figures vii Chapter 1. Introduction 1.1 Background 2 1.2 Objectives of this study 5 Chapter 2. Literature review 2.1 Classification of gas sensing methods 9 2.2 Fundamentals of optical gas sensors 12 2.2.1 Types of optical gas sensors 12 2.2.2 Plasmonic gas sensors 14 2.3 Optical Interference 16 2.3.1 Thin film optical interference theory 16 2.3.2 Structural colors 17 Chapter 3. WO3 thin film with Au plasmonic layer on Al mirror layer for the detection of NO2 3.1 Introduction 19 3.2 Sensor fabrication 21 3.2.1 Thin film plasmonic sensor 21 3.3 Characterization 22 3.4 Finite Difference Time Domain (FDTD) simulation 24 3.5 Gas sensing measurement 25 3.5.1 Optical response 25 3.6 Conclusion 28 Chapter 4. Au/Pd decorated WO3 Nanorods on Al mirror layer for the detection of H2 and NO2 4.1 Introduction 30 4.2 Sensor fabrication 34 4.2.1 Resistive sensor with nanorods 34 4.2.2 Plasmonic sensor with nanorods 35 4.3 Characterization 36 4.4 Gas sensing measurement 38 4.4.1 Resistive response 38 4.4.2 Optical response 42 4.5 Conclusion 45 Chapter 5. Summary 5.1 Summary 47 References 48 Abstract (in Korean) 58Maste

Photoelectrochemical Water Splitting of Modified Tungsten Oxide Nanostructures via Vapour Deposition

Semiconductor photocatalysts have been used for water splitting for several decades. By utilizing solar energy, splitting water into H2 and O2 is considered to be a promising way for generating renewable energy. The aim of this project was to synthesize and study different nanostructured photoelectrode materials for photoelectrochemical (PEC) water splitting. Tungsten(VI) oxide (WO3) is a promising photoanode material which is active under visible light illumination. Flat WO3 films and nanostructured WO3 films were deposited via aerosol-assisted chemical vapour deposition (AACVD). The morphology, structure and PEC properties of the films were compared, with nanostructured WO3 films showing improved performance compared to flat WO3 films (~ 0.41 mA/cm2 ) with an average photocurrent density of ~ 0.68 mA/cm2 at 1.23 V vs. RHE (reversible hydrogen electrode). Nanostructured WO3 modified with Au, Ag and Pt nanoparticles (NPs) were deposited via AACVD on nanostructured WO3 films, and deposition parameters optimized. The band gap of metal NP-modified WO3 films appeared narrower than that for WO3 alone. The size, morphology and density of metal nanoparticles were controlled by deposition temperature and precursor amount with (0.1 mg) Au/WO3 and (100 μL) Ag/WO3 both having the highest photocurrent density amongst all samples at 0.96 mA/cm2 at 1.23 V (vs. RHE), which was 1.5 times that of undecorated WO3. Pt/WO3 showed 1.33 times PEC enhancement. Highly uniform, dense, amorphous TiO2 and Al2O3 films were synthesized via atomic layer deposition (ALD). Precursor vapour pressure, dose/purge times, gas flow rate and deposition temperature were optimised. The growth rate of TiO2 deposition was in the range of 0.5 – 0.7 Å/cycle. For Al2O3, a stable ALD process with a growth rate of 1 – 1.4 Å/cycle was observed. Heterojunction films composed of WO3, metal NPs, TiO2 and Al2O3 thin films were constructed together in specific sequence in order to optimise PEC water splitting performance. Ag/WO3 films with and without ALD layers had higher PEC performance and were more stable than undecorated WO3 films after 24 h, however the use of ALD layers wasn’t considered to be fully successful, and the parameters need further optimization

Aerosol-Assisted Chemical Vapour Deposition (AACVD) of Silver Nanoparticle Decorated Tungsten Oxide Nanoneedle for Use in Oxygen Gas Sensing

Semiconducting metal oxides (SMOX) gas sensors, such as tungsten oxide (WO3), have been developed in depth for use in toxic gas detection, such as nitrogen oxides (NOx). With the addition of catalytic nanoparticles, like Ag, Pt, Pd and etc., the sensing properties, the three ‘S’ (sensitivity, selectivity and stability), can be significantly improved. This thesis details a two-step synthesis method for the fabrication of Ag nanoparticle decorated WO3 nanoneedle by using different silver metal precursors, including silver nitrate (AgNO3), silver 2-aminoethanol (Ag-EA), silver 1-aminopropan-2-ol (Ag-AP) and silver 2-methyl-2-aminopropan-1-ol (Ag-AMP), in a vapour deposition process. A series of experiments were conducted to investigate the parameters that affect the growth of the materials microstructure including deposition temperature, deposition time, flow rate of N2 carrier gas and concentration of precursor solution. Physical property characterization techniques including UV/Vis, XRD, XPS, SEM and TEM, have been systematically applied for all WO3 and Ag-decorated WO3 samples and sensor materials. Oxygen sensors’ have been considered as the critical component of Engine Management System for several decades. Gas sensing performance was carried out toward different O2 concentration between 1 and 20% at various operating temperatures. The sensing response revealed that the decoration of Ag nanoparticle on WO3 sensors significantly improved sensing properties as compared to undecorated WO3 sensors. An optimal gas response with silver-decorated WO3 is enhanced 400% compared to an undecorated WO3 sensor at an optimum operating temperature at 350 °C towards 20% oxygen at a relative humidity level ~ 85% by using AgNO3 as a precursor. An enhancement was also observed for the Ag decorated WO3 sensors fabricated using organometallic silver precursors, with a dramatically increasing in baseline resistance for these Ag@WO3 sensors. Sensing mechanisms, are proposed to explain the enhancement in sensing response

Multilayer Thin Films

This book, "Multilayer Thin Films-Versatile Applications for Materials Engineering", includes thirteen chapters related to the preparations, characterizations, and applications in the modern research of materials engineering. The evaluation of nanomaterials in the form of different shapes, sizes, and volumes needed for utilization in different kinds of gadgets and devices. Since the recently developed two-dimensional carbon materials are proving to be immensely important for new configurations in the miniature scale in the modern technology, it is imperative to innovate various atomic and molecular arrangements for the modifications of structural properties. Of late, graphene and graphene-related derivatives have been proven as the most versatile two-dimensional nanomaterials with superb mechanical, electrical, electronic, optical, and magnetic properties. To understand the in-depth technology, an effort has been made to explain the basics of nano dimensional materials. The importance of nano particles in various aspects of nano technology is clearly indicated. There is more than one chapter describing the use of nanomaterials as sensors. In this volume, an effort has been made to clarify the use of such materials from non-conductor to highly conducting species. It is expected that this book will be useful to the postgraduate and research students as this is a multidisciplinary subject

Fabrication and gas sensing properties of pure and au-functionalised W03 nanoneedle-like structures, synthesised via aerosol assisted chemical vapour deposition method

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 nanoneedle