Negative Photoelectron Diffraction Replica in Secondary Electron Angular Distribution

Photoelectron diffraction (PD) is an element selective local structure analysis method. Atomic arrangements around photoelectron emitter atom can be deduced from the position of forward focusing peaks (FFPs) and diffraction rings around them. We have measured $2\pi$-steradian Ge 3p and a series of secondary electron patterns from the Ge(111) surface at a kinetic energy of 600 eV by varying photon energy. The destruction of PD patterns due to the defocusing effect by inelastic plasmon excitations was observed at 40 eV off from the elastic peak. Moreover, we found that the secondary electron patterns at over 160 eV off from the elastic peak are a complete negative contrast replica of 600-eV PD. The contrast was about one-fourth of that of the original PD. The mechanism of this new phenomenon can be explained by the decrease in isotropic secondary electron beam intensity caused by the absorption process of time- and space-reversal PD.