Abstract: A thin film of material such as metal is deposited on the surface of a substrate by placing a substrate (22) into a chamber (10) containing holder (12) cooled by heat exchanger 18. A beam (56) of U.V. light from the illumination source (42) is projected through monochromator (43), mask (46) and lens (16) onto a selected area (58) of the substrate at an energy level exceeding the photoemission threshold of the surface. A slow electron (60) is ejected from the surface into the capture zone (62). A compound AB such as iron pentacarbonyl from supply (30) is leaked into the chamber (10), enters the capture zone (60) to form a highly reactive deposition fragment A.sup.- which attaches to the surface and a dissociation fragment which is evacuated through outlet (14). The deposited fragment may further dissociate to form metal deposit.