Recoil effects of photoelectrons in a solid

High-energy-resolution C0.2em0ex1s photoelectron spectra of graphite were measured at excitation energies of 340, 870, 5950, and 79400.3em0exeV using synchrotron radiation. On increasing the excitation energy, i.e., increasing kinetic energy of the photoelectron, the bulk origin C0.2em0ex1s peak position shifts to higher binding energies. This systematic shift is due to the kinetic-energy loss of the high-energy photoelectron by kicking the atom and is clear evidence of the recoil effect in photoelectron emission. It is also observed that the asymmetric broadening increases for the higher-energy photoelectrons. All these recoil effects can be quantified in the same manner as the M\"ossbauer effect for γ-ray emission from nuclei embedded in crystals.