A charge particle simulation study on the kinetic energy and probing depth dependence of X-ray photoemission electron microscope
Chia-Chi Liu1*, Yen Huang1,2, Tzu-Hung Chuang1, Deng-Sung Lin2,3, Der-Hsin Wei1,2
1National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2Graduate Program of Science and Technology of Synchrotron Light Source, National Tsing Hua University, Hsinchu, Taiwan
3Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:Chia-Chi Liu, email:liu.cc@nsrrc.org.tw
Probing surface/interface with X-rays excited electrons is a well-accepted detection approach in surface science. However, when the specimen of interest has a finite dimension, the legitimate question to ask additionally is where the photo-excited electrons are coming from. Photoemission electron microscope (PEEM) records full-field images by applying a strong electric field with a cathode lens that collects photo-excited electrons emitted from the sample surface, where X-rays are commonly used as the probing light source. To probe an object of interest positioned under the surface, both soft X-rays and hard X-rays can be employed. However, the emission profile of the buried object at the sample surface is not an invariant, as the spatial and angular distribution of the photoelectrons differ from that at its burial depth. These variations are induced by the inelastic collisions and the energy loss during the propagation of the photoelectrons, and are highly related to the kinetic energy of the photoelectrons. In this study, we employ numerical calculation and charge particle simulation to determine how the quality of PEEM images is affected by the factors mentioned above (with two kinetic energies studied, 1 eV and 6.5 keV), and how well an aperture can correct the image distortion. Finally, we discuss the origins of image deterioration when imaging a buried object with either the soft X-ray PEEM (1 eV) or the hard X-ray PEEM (6.5 keV).

Keywords: Photoemission electron microscope (PEEM), X-ray PEEM