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

Abstract

Ag–O–Cs thin films with internal field-assisted structure were fabricated, and enhanced photoemission was observed when the internal electric field was 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 films were irradiated by the light with wavelength of 510 nm. From an analysis 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 vacuum level at the surface is degraded. The calculated barrier curves for various applied biases are illustrated to show the thinning effect of internal electric 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 films 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 enhanced 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 the increased probabilities for the photoexcited electrons to travel through the interfacial barrier and escape into the vacuum.