Segregation phenomenon of substrate copper atoms onto rf sputter-deposited titanium film was observed using Auger electron spectroscopy and x-ray photoelectron spectroscopy. When the specimens were heated, Cu atom diffused onto the surface of Ti film from the substrate with the diffusion constant bigger than that of the bulk diffusion by three;orders of magnitude. The surface concentration of Cu saturated at about 5%. If the segregated layer was removed by sputtering, the saturated Cu concentration on the surface was easily reformed by heating. The saturation concentration was constant at heating temperatures between 710 and 850 K. This was interpreted to mean that the saturated surface composition is thermodynamically achieved and is easy to reproduce. The binding energy of Cu 2p(3/2) of the segregated Cu was 0.24 eV higher than that of the pure metal. The amount of the charge transfer from Cu to Ti was assumed to vary linearly with the chemical shift, and the decrease in the work function due to the segregation layer of Cu was estimated to be 0.62 eV. Therefore, surface segregation is postulated to be a method to reproducibly decrease the work function and is potentially useful to manufacture materials for a field emitter.