Photoemission measurements were performed on thick silver films vapor deposited under ultrahigh-vacuum conditions onto cold or warm substrates and on samples subsequently annealed. Laser powers were adjusted so that linear photoemission is produced with 4.5-eV (above-threshold) photons and quadratic photoemission with 2.3-eV (below-threshold) photons. Coldly deposited films were found to produce two-photon photoelectron yields three orders of magnitude greater than annealed films. By contrast, only a small enhancement was found for one-photon photoemission produced by the cold films over those of annealed or room-temperature films.

• Received 18 July 1989

DOI:https://doi.org/10.1103/PhysRevB.40.9997