Dr. Wen-Shan Zhang, Heidelberg University, Germany

Ultra-Low Voltage Scanning Electron Microscopy and Its Application in Evaluation of Charge Transport Ability

Prior to conventional scanning electron microscopy (SEM), ultra-low voltage SEM can significantly minimize the electron beam-damage during the investigation of beam-sensitive materials, such as low-dimensional materials, soft matters, polymers, organic-inorganic hybrid materials etc. It is also a very powerful tool to study ultra-thin top surface layers in terms of chemical and physical changes. Moreover, the surface charging, which is accompanied frequently but undesirably during conventional SEM imaging, is now used in our study on purpose. In the ultra-low energy regime (typically 10-100 eV), the semiconductive materials are charged deliberately with well-selected electron microscopic parameters for the desired charging sign and dose. The charge-carrier mobility can be compared among various materials. Even a subtle mobility anisotropy resulted from different crystalline angular orientations can be visualized by the dynamic charging map. With respect to extracting intrinsic mobility, this method fills the gap between computational approaches, which are yet limited within highly crystalline systems, and the experimental device fabrication, which introduces a number of extrinsic factors.