标题： WO3-x纳米结构的异常气体传感器响应和半导体到绝缘体转变：氧空位的作用 显示英文标题

标题： Unusual gas sensor response and semiconductor-to-insulator transition in WO3-x nanostructures : The role of oxygen vacancy

摘要： 三氧化钨-x薄膜在受控氧分压下通过热丝化学气相沉积法生长，具有花瓣状和层状纳米结构。这些合成的三氧化钨-x纳米结构经X射线衍射和拉曼光谱分别证实具有单斜晶体结构，并含有大量氧空位（VO）。这些三氧化钨-x纳米结构在室温下对氨气和二氧化氮气体表现出传感器响应。然而，传感器响应随温度和分析气体类型而变化。对于氨气，传感器在低于150 0C的温度下表现出电阻增加，类似于p型半导体，而在较高温度下电阻降低，类似于n型半导体行为。另一方面，在低于150 0C时，这些传感器对二氧化氮表现出n型行为，但在较高温度下则像p型半导体。在通过在甲烷气氛下退火引入额外氧空位后，对这些三氧化钨-x纳米结构进行了25至300 oC温度范围内的温度依赖性输运研究。花瓣状三氧化钨-x纳米结构在100 - 212 0C温度范围内，在加热和冷却循环中分别显示出电阻的突然变化，表明绝缘体到半导体和半导体到绝缘体的转变。在层状三氧化钨-x纳米结构中，电阻在300 0C时从半导体到绝缘体发生翻转，并在冷却至30 0C时保持绝缘状态。三氧化钨-x纳米结构中的氧空位解释了异常的气体传感行为和绝缘体-半导体转变。 显示英文摘要

摘要： WO3-x thinfilms featuring petal-like and lamella-like nanostructures are grown under controlled oxygen partial pressures using hot filament chemical vapor deposition. These synthesized WO3-x nanostructures exhibit monoclinic structure and contain a significant amount of oxygen vacancies (VO) as confirmed by X-ray diffraction and Raman spectroscopy, respectively. These WO3-x nanostructures demonstrate sensor response to both NH3 and NO2 gases even at room temperature. However, the sensor response varies with temperature and analyte gas type. For NH3, the sensors exhibit an increase in resistance behaving like a p-type semiconductor at temperatures below 150 0C while the resistance decreases at higher temperatures, resembling n-type semiconductor behavior. On the other hand, below 150 0C, these sensors display n-type behavior towards NO2 but act like p-type semiconductor at higher temperatures. Further temperature dependent transport studies were performed in these WO3-x nanostructures in the temperature range from 25 to 300 oC, after inducing additional VO in the films through annealing under CH4. The petal-like WO3-x nanostructures display an abrupt change in resistance, indicating insulator-to-semiconductor and semiconductor-to-insulator transitions during heating and cooling cycles respectively, in the temperature range of 100 - 212 0C. In lamella-like WO3-x nanostructures, the resistance is flipped from semiconductor-to-insulator at 300 0C and remains insulating state when cooled down to 30 0C. The abnormal gas sensing behavior and insulator - semiconductor transition is discussed in terms of VO in WO3-x nanostructures.