By measuring the very low energy photoelectron spectra of Cu single crystal surfaces with a high resolution, we have observed the energy loss structure due to image charge interaction. The structure appears as a spike at zero-kinetic-energy in the Cu(001) spectra. We have proposed that the requirement for appearing the energy loss structure is the absence of unoccupied states at the vacuum level of the Γ‾ point to which zero kinetic energy electrons can return. This result demonstrates that the very low energy photoelectron spectroscopy is a useful tool in analyzing the electron dynamics just outside of the solid surface.
