Surface-dependent transport properties of nanostructured materials

In this project, the research team will study the correlations between surface structural characteristics and the electrical/transport properties of nanostructures. The researchers aim to gain control of such properties via rational synthesis and surface functionalization/treatment of nanostructures. They will focus on Si, ZnO and Ag nanowires, as representative systems for semiconductors, metal oxides and metals, respectively. These materials are selected as they attract intense interest due to their wide range of applications. The researchers will use several techniques to prepare nanomaterials including the generic oxide-assisted growth method (that the researchers developed), metal-assisted chemical etching method (that the researchers developed) to grow well-aligned SiNW arrays with predetermined properties inherited from the parent Si wafers, the vapor-liquid-solid (VLS) method, and the vapor-solid deposition in an AAO template. Cleaning, passivation, and functionalization of surfaces will be used to modify the surface structure, and tune the electrical and transport properties. The researchers will characterize systematically and comprehensively the structural, optical, and electronic and transport properties of the as-prepared and surface-modified nanostructures using a range of state-of-the-art analytical tools. They will include ultra-high transmission electron microcopy (TEM; particularly the researchers will use the sub-Angstrom resolution TEM newly established in Beijing National Center of Electron Microscopy in Tsinghua University) to characterize micro-structural, compositional and electronic properties (using EELS); scanning tunneling microscopy/scanning tunneling spectroscopy to study atomic structure and electronic properties; I-V transport and field-effect transistor measurements to investigate electrical and transport properties; near-field scanning optical microscopy (NSOM)/AFM/PL/UV-Raman to study structural, defect and optical properties. Significantly, the research team will focus on performing several characterizations concurrently on the same single nano-object to establish direct correlation between nanomaterial size, structure, and transport properties. The identification of nano-objects with specific structure and properties and their characterization will form a base for controllable design and for engineering new structures and their assembly into functional units. The researchers will establish the correlation of surface cleaning, passivation, and functionalization of NWs with device performances. Such study will lead to a better understanding of surface effects in NWs, and establishing feasible approaches to utilize nanostructures in some practical devices, such as sensors, solar cells, LEDs, photodetectors, photoswitches, etc. While their studies will focus on Si, ZnO and Ag nanowires, the researchers expect detailed understanding of these nanowires will generate knowledge that can be transferable to the surface and transport properties of nanostructures in general.