In Situ Research On Structual Evolution And Electrical Transport Properties Of Semiconductor Nanomaterials Under Field Loading By Electron Microscope

The structure and properties of materials will be influenced significantly by anychange of external environment (such as force, thermal field, electric field, etc.) whenthe size down to nanometer. It is meaningful to investigate the evolution of structureand properties of nano-materials under field loading since nano-materials arefundamental building blocks for all kinds of nano-devices. In this paper, STM-TEMnano-manipulating system is used to conduct the in-situ research of structureevolution and electrical properties on typical semiconductor nano-materials underfield loading, including stress field and electrical field, in high resolution transmissionelectron microscopy (HRTEM). The main achievements are following:1. In-situ studied the structure evolution and transport properties of semiconductornano-structure under bending strain;(1) The structure evolution and electrical properties of <100> orientated p-typeindividual Si nanowire (NW) under bending strain has been investigated. NWs werecut from <100> p-type Si single crystal film by using Focused Ion Beam (FIB)technology. Bending strain were loaded to single Si NW by STM-TEMnano-manipulating system in HRTEM, while the current-voltage (I-V) curves wererecorded simultaneously. Result shows that the conductivity of Si NWs is improvedlargely by bending strain when stain is lower than2%, the largest improvement isbeyond600%. When strain approach to2%, the improvement of conductivity of SiNWs also nearly approach the saturation point. The current reduces a little sometimeswhen strain exceeds3%which may be resulted from plastic deformation.(2) Researched the electrical properties of individual epitaxial InGaAs and GaAs NWunder bending strain. Selected, fixed and bent of single InGaAs and GaAs NW werecarried out by STM-TEM nano-manipulating system in HRTEM, and the electricalproperties of NWs were recorded with the bending process. Results indicate that thesetwo kinds of semiconductor NWs show different electrical behaviors under bendingstrain. With the increasing strain, the conductivity of InGaAs NWs increase firstlythen decrease while the conductivity of GaAs NWs raise continuously.2. Explored the structure evolution and electrical properties of individual core-shellNW (core: semiconductor NW, shell: amorphous carbon layer) under electrical field;(1) Selected and fixed an individual semiconductor NW by STM-TEM nano manipulating system to form a metal-semiconductor-metal structure with two W tips.The NW was used as template to form an uniform amorphous carbon layer on thesurface by Electron Beam Induced Deposition (EBID), then different voltage wereapplied to the core-shell nano-structure to research the influence of current-causedthermal effect on InAs, InGaAs and SiC NWs. Results show that all of the NWs couldbe melted under electrical field but the critical voltage are quite different, which maybe concerned with the melting point and the band gap of NWs.(2) A novel in-situ method of synthesizing individual carbon nanotube (CNT) hasbeen developed in TEM. Voltage was applied on the core-shell nano-structurementioned as above, the NW was melted, simultaneously, the amorphous carbon layeron the surface of NW crystallized and formed as multi-wall CNT. The electricalproperties of CNT was tested, and results reveal that the CNT have a high capabilityof electron transport.