Piezotronic Effect on Ultrasensitive Chemical and Biochemical Sensors

非技术描述：传感器有许多应用，如监测家庭炉灶或壁炉附近的一氧化碳，检测机场安检的爆炸物，监测工业工厂中的有害化学蒸气，以及跟踪空气污染源。用纳米材料制成的传感器已经被证明比用大尺寸材料制成的传感器更灵敏。这项研究项目将压电半导体纳米材料(即在机械力作用下可以产生电荷的材料)结合到传感器设计中，最终目标是实现超高灵敏度。本研究项目对这些纳米材料传感机理的基本认识有望进一步推动传感器的设计。该项目的研究生和本科生在纳米材料的生长和表征以及传感器设备的制造和测试方面进行培训。研究成果被纳入了两门现有的课程：纳米材料与纳米技术和先进纳米材料，这丰富了佐治亚理工学院的材料科学课程。外展活动包括通过佐治亚理工学院校园的现有项目让K-12教师参与研究。技术描述：化学和生化纳米传感器的典型功能部件是由纳米线制成的场效应晶体管结构。纳米线暴露在气体分子中后的电流变化导致了灵敏度的增加。这些纳米线传感器的高灵敏度源于高比表面积和大量可用的分子结合部位来改变纳米线的电导。欧姆接触通常应用在半导体纳米线/纳米管和这些传感器中的金属电极之间。相反，本项目将重点放在纳米线传感器的肖特基接触上，因为与欧姆接触的纳米线传感器相比，肖特基接触具有超高的灵敏度和快速的响应。结合压电子效应，载流子通过金属-半导体势垒或p-n结的传输受压电电荷的调制。具体地说，局域压电电荷改变了界面附近自由载流子的再分布和能带结构，进而影响了载流子的输运性质。利用电子全息术和原位透射电子显微镜对金属/半导体界面的压电性电荷/电势进行了定量测绘。这项研究通过提供金属-半导体界面的关键微结构和电学性质，为这些纳米材料的传感机制提供了基本的理解。

Nontechnical Description: Sensors have numerous applications such as monitoring carbon monoxide near home furnaces or fireplaces, detecting explosives for airport security, monitoring harmful chemical vapors in industrial plants, and tracking air pollution sources. Sensors fabricated using nanomaterials have been demonstrated to be more sensitive than sensors made of large-size materials. This research project combines piezoelectric semiconductor nanomaterials (i.e., materials that can generate electric charges when subjected to mechanical forces) in the sensor designs with the ultimate goal to achieve ultrahigh sensitivity. The fundamental understanding on sensing mechanisms of these nanomaterials developed in this research project is expected to further advance the sensor designs. Graduate and undergraduate students in this project are trained in the growth and characterization of nanomaterials as well as sensor device fabrication and testing. The research findings are incorporated into two existing courses: Nanomaterials and Nanotechnology and Advanced Nanomaterials, which enriches the materials science curriculum at Georgia Tech. Outreach activities include involving K-12 teachers in research through the existing programs on the Georgia Tech campus. Technical Description: The typical functioning component of chemical and biochemical nanosensors is a field-effect transistor structure made of nanowires. The current change in the nanowires after exposing to gas molecules gives rise to the sensitivity. The high sensitivity of these nanowire-based sensors results from the high surface-to-volume ratio and a large number of available molecular binding sites to the nanowires to change its conductance. Ohmic contacts are typically applied between the semiconducting nanowire/nanotube and the metal electrodes in these sensors. Instead, this project focuses on the Schottky contact in nanowire sensors because of the ultrahigh sensitivity and fast-response compared to the nanowire nanosensors with the Ohmic contact. Combining the piezotronic effect, the transport of charge carriers across a metal-semiconductor barrier or p-n junction is modulated by piezoelectric charges. Specifically, the localized piezoelectric charges alter the free charge carrier redistribution and band structures near the interface, and further impact the charge carrier transport properties. Electron holography and in-situ transmission electron microscopy (TEM) are used to quantitatively map the piezoelectric charges/potentials at the metal/semiconductor interface. This study provides fundamental understanding of the sensing mechanisms of these nanosenor materials, by providing key microstructural and electrical properties at the metal-semiconductor interfaces.