Enhanced photoemission of Ag-O-Cs composite thin films with an internal electric field

Ag-O-Cs thin films with internal field-assisted structure were fabricated, and enhanced photoemission was observed when the internal electric field wa s applied to the thin films. The increase of photoelectronic quantum yield, corresponding to the applied 30 V bias, was about 15.7%, while the thin fi lms were irradiated by the light with wavelength of 510 nm. From an analysi s of the electric potential distribution in the Ag-O-Cs thin films with the applied internal electric field, it is found that the interfacial barrier between the Ag nanoparticles and the Cs2O matrix is decreased and the vacuu m level at the surface is degraded. The calculated barrier curves for vario us applied biases are illustrated to show the thinning effect of internal e lectric field on the interfacial barrier width. The theoretical lowering of interfacial barrier height is obtained as 0.08 and 0.22 eV when the thin f ilms are stimulated by applied bias of 1 and 30 V, respectively. Further, a group of formulas as well, based upon the electric potential distribution in the Ag-O-Cs thin films, is deduced to describe the relationship between the applied bias and the degradation of the surface vacuum level. The enhan ced photoemission of Ag-O-Cs thin films is attributed to the field-induced variations in the energy band structure which are considered to result in t he increased probabilities for the photoexcited electrons to travel through the interfacial barrier and escape into the vacuum. (C) 2001 American Inst itute of Physics.