Beyond the Chemical Shift: Visualization and Characterization of Low-dimensional Electron System by Core-Level Photoelectron Spectro-microscopy
Chung-Lin Wu1*
1Department of Physics, National Cheng-Kung University, 701 Tainan, Taiwan
* presenting author:CHUNG-LIN WU,
The main impact of core-level photoelectron spectroscopy in its application to material science is the utilization of the chemical shift; different species and bonding information are often easily identified from their core-level binding energy positions. In this talk, there is additional, important environment-coupled information of low-dimensional electron system available from a detailed study of the binding energy shift of the main characteristic core-level line using spatial resolved photoelectron spectro-microscopy. I will show how the environment modifies the electronic structures of oxide heterojunctions, graphene, and ZnO nanostructures in their core-level spectra significantly. By monitoring the core-level shifting of the buried layer of oxide heterojunctions under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top oxide layer, and demonstrate a generic approach to use this top oxide layer as a nonvolatile modulation of the electric transport behaviors at oxide heterointerface. In addition, precise C 1s core-level characterization shows graphitic and contaminated carbon states of graphene. The main C 1s core-level shift is found to represent the graphene doping level and type, which strongly depends on the supporting substrate. We also achieved a direct visualization of the piezoelectric potentials in a single bent ZnO microwire (MW) using the core-level spectro-microscopy. Using radial-line scan across the bent section of ZnO MW, the characteristic core-level shifts were directly related to the electric-mechanical couplings in this piezoelectric ZnO micro-/nano-wire system. These cases show that the spectro-microscopic technique allows imaging and identification of environment-induced couplings in the low-dimensional electron system.

Keywords: Low-dimensional Electron System, Core-Level Photoelectron Spectro-microscopy, Oxide Heterojunctions, Graphene, ZnO