Enhanced quantum efficiency from hybrid cesium halide/copper photocathodes

Abstract

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Quantum efficiency enhancement in CsI/metal photocathodes

“…directly emitted from the substrate metal d band and easily escape the CsI overlayer into the vacuum (mean free path for a <2 eV electron is roughly 20 nm in CsI). Photoemission from the electron dense d-band is likely an important contribution to the QE enhancement for CsI on Cu and Au as previously suggested [9]. When the work function is decreased to near 2 eV, Cu 3d and Au 5d electrons can be directly emitted following excitation by 4.66 eV photons.…”

“…This feature dominates the kinetic energy spectra and photoelectron yield in fully laser activated CsI/metal systems. Table 1 The results of hybrid CsI/metal photocathodes strongly contrast those of CsBr/metal [6][7][8][9][10] as CsI/metal photocathodes have significantly higher quantum efficiencies following laser activation. Fig.…”

“…Recently, much higher QE enhancement and significantly greater work function reduction has been found for a CsI thin film, compared to a CsBr film, on Cu single crystal substrates [9]. Direct photoemission from the Cu 3d band, for the CsI thin film, and electrons emitted from the intraband states were considered as possible contributions although several key mechanistic questions remain.…”

“…In order to overcome limitations of metal photocathodes, several approaches have been explored. These include incorporation of nanostructured features, such as gratings and nanohole arrays, to couple light efficiently into the metal and induce surfaceplasmon enhanced electric fields [2][3][4], utilizing ultrathin oxide layers to reduce work function [5], and deposition of alkali halide films to increase QE [6][7][8][9][10]. Alkali halide thin film deposition has been proven to be one of the most effective ways to lower work function and increase QE of metal photocathodes.…”

Photoemission simulation for photocathode design: theory and application to copper and silver surfaces

“…Furthermore, O and H are very well know contaminants on photocathode surfaces. Li is modelled to study the effect of alkali metals since they are used as coating agent in order to increase the quantum efficiency of photocathodes [48]. The adsortion of these three species on the copper (111) surface has been extensively discussed in the literature [49][50][51].…”