Successive change in work function of Al exposed to air

Aluminum surface freshly shaven with a steel knife showed significant changes in work functions from 3.25 to 3.60 eV within one day. Successive changes of the work functions were measured in air using the open counter. XPS spectra showed no change fundamentally when the fresh Al surface was exposed to air for 1 min and 24 h. Molecular orbital calculations by use of the DV-X α method predicted an appearance of an additional local density of state near the Fermi edge when an Al-Al distance becomes large. Based on the experimental results and calculations, we proposed formation of an interface between an Al matrix and a surface oxide or oxyhydroxide, which has a stress induced density of state. This state appears at the beginning of air exposure and disappears after the lapse of time because such stress is released after rearrangement of surface and interface structures.