Local variation of the work function of Cu(1 1 1) surface deduced from the low energy photoemission spectra

We have investigated the photoemission spectra very close to the vacuum level of the Cu(1 1 1) surface with high resolution, using a tunable laser as the incident ultraviolet light source. The incident photon energy was tuned very close to the work function of the sample surface. A small emission peak was found ∼100 meV below the vacuum level cutoff that corresponds to the work function. The origin of the small peak is attributed to the emission from the areas whose local work function is depressed below the work function of the majority area. Variation of the spectrum caused by surface roughening and oxygen adsorption suggests that the areas with lower work function are the step edges.