Abstract
Thin films of CsBr deposited onto metals such as copper are potential photocathode materials for light sources and other applications. We investigate desorption dynamics of Br atoms from CsBr films grown on insulator (KBr, LiF) and metal (Cu) substrates induced by sub-bandgap 6.4 eV laser pulses. The experimental results demonstrate that the peak kinetic energy of Br atoms desorbed from CsBr/Cu films is much lower than that for the hyperthermal desorption from CsBr/LiF films. Kelvin probe measurements indicate negative charge at the surface following Br desorption from CsBr/Cu films. Our ab initio calculations of excitons at CsBr surfaces demonstrate that this behavior can be explained by an exciton model of desorption including electron trapping at the CsBr surface. Trapped negative charges reduce the energy of surface excitons available for Br desorption. We examine the electron-trapping characteristics of low-coordinated sites at the surface, in particular, divacancies and kink sites. We also provide a...
Highlights
Surface electronic excitation is important in many fundamental and applied processes
Photoemission from Cu substrates coated with a thin CsBr film and irradiated with an ultraviolet laser light displayed a quantum efficiency (QE) enhancement greater than 50.25 Maldonado et al report that a 5 nm CsBr thin film on Nb substrates enhances the QE following activation at 257 nm by a factor of several hundred[26] and significant QE enhancement was achieved from Cr and Mo photocathodes coated with CsBr.[27,28]
We have presented the results for photoinduced desorption from KBr and CsBr films grown on an insulator and metal substrates
Summary
Surface electronic excitation is important in many fundamental and applied processes These include laser desorption and ablation,[1,2] surface photochemistry,[3] selective materials modification,[4,5] photocatalysis, photolithography,[5] and photoemission.[6] Surface excitation of semiconductors and insulators may create both electron−hole pairs and surface excitons, which play a significant role in particle desorption.[7−9] Alkali halides are well studied due to their relatively simple crystalline and electronic structures and sensitivity to ultraviolet light, gamma, X-ray, and particle irradiation. Using a combination of experiment and theory we describe the mechanisms of laser desorption from hybrid metalalkali halide systems and propose a model that rationalizes the observed effects
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