The Research of Schottky Barrier Gas Sensor Based on Single SnO₂Nanowire

Gas sensor is a kind of device that can detect gas with different types and different concentration,and transform these parameters into electrical signal. It is widely used in environmental investigation,national security, food processing, medical diagnosis and various other industrial applications. With thedevelopment of science and technology, higher requirements are put forward for various performanceindicators of gas sensors, which need the developing nanotechnology to improve performance, such asimproving the sensitivity of measurement of gas and reducing working temperature. Among the severalvarieties of gas sensors available in the market, oxide semiconductor sensors are the most popular owing totheir high sensitivity, long service life, and lower-cost. Semiconducting metal oxides such as tin oxide（SnO₂）, zinc oxide （ZnO）, and tungsten oxide （WO₃） are routinely employed as active materials in thesesensors. The performance of gas sensors has a direct relation to exposed superficial area of sensitivematerial. Nanowire has relatively high specific surface area, various surface states, higher oxidative activity,so it has high sensitivity, and lower working temperature than block material. Besides, Nanowires gassensor can decrease the size and reduce energy consumption, so nanowire is the ideal candidate structuralmaterials for the designing of next generation of sensor. Nanosenser based on Schottky barrier showsexcellent performance in gas sensors, it is an important method to improve gas sensitivity using Schottkycontact instead of ohmic contact. Schottky barrier gas sensors based on single nanometer materialsgradually get the researchers’ attention.In this thesis, the gas sensing properties of single SnO₂nanowire based on the Schottky barrierwas discuss. Through the test of gas sensing properties of H2S, it demonstrated ultra-high sensitivity ofH2S at room temperature. The sensitivity of H2S with a concentration of100ppm comes up to1238, andhave a good repeated stability. SnO₂nanowires are prepared by the method of sol-gel and thermalevaporation. The structure and morphology are characterized, and we get that the nanowires we obtainedhave a structure of single crystal rutile. Electric field assembly technique was used to prepared single SnO₂nanodevice. Through testing the I-V properties, we get that both ends of nanowire are formed the schottky contact with the gold electrodes, constituting back-to-back Schottky barrier structure. We also analysisedthe possible air sensitive mechanism. In this back-to-back Schottky barrier structure, the current of devicewas controlled by reverse schottky barrier, the height of barrier was regulated by adsorption and desorptionof oxygen, current changed exponentially with the changed of barrier height, which is the main reason whyour device have high gas detection sensitivity at room temperature. SnO₂nanowires have more surfaceoxygen space defects. The O₂^-adsorbed on oxygen vacancy translate into O-, O-have higher reactivitythan O₂^-, which is the second reason to explain our device have high gas detection sensitivity at roomtemperature.In Chapter1we introduced the research progress of one-dimensional nanomaterials gas sensor.Focusing on the gas sensor based on single nanowires Schottky barrier, as well as gas sensors at roomtemperature. Based on these we selected the topic and purpose of this thesis, and the main contents.In Chapter2we describe the specific methods and the detailed experimental procedure of SnO₂nanowires by the method of sol-gel and thermal evaporation. The SnO₂nanowires was successfullysynthesized by controlling the growth conditions. The structure and surface morphology of SnO₂nanowireswere characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmissionelectron microscopy （TEM） and high-resolution transmission electron microscopy （HR-TEM）. Single SnO₂nanowire gas sensors were successfully prepared via the electric field assembly method.In Chapter3we studied the gas sensing properties of single SnO₂nanowires through the testingof sensing properties for H2S at different temperature. The sensitivity of H2S with a concentration of100ppm comes up to1238. The mechanism of gas sensor was discussed by analyzing the transport mechanismof the Schottky barrier. And a series of assisted experimental was done to prove it. The gas sensormechanism of single nanowires with begeneration of high sensitivity and high selectivity room temperaturenanometer sensor based on single nanowires was also discussed.