Extremely High Quantum Photoyield from Cesiated Polycrystalline Diamond Films

Abstract

An extremely high quantum photoyield, as high as 70% at the photon energy of 10 eV, was observed from cesiated polycrystalline diamond films. The threshold photon energy of 5.5 eV or less was observed. The results suggest that the cesiated polycrystalline diamond surface has a true negative electron affinity. In contrast, a quantum photoyield of 17% at the photon energy of 10 eV was observed for a hydrogenated polycrystalline diamond film. The threshold photon energy of 5.5 eV or less was also observed, as in the cesiated one. It seems that the hydrogenated polycrystalline diamond surface has an effective negative electron affinity.

UV photoemission efficiency of polycrystalline CVD diamond films

“…For a particular electron energy the electron escape length is also fixed. For positive 6 electron affinity surfaces the escape length is the inelastic mean free path of electrons, while for samples with negative electron affinity the escape depth is determined by the diffusion length of electrons, which was reported to be on the order of 50 nm [7] and can be as high as few micrometers. The presence of grain boundaries in the polycrystalline film may reduce the electron escape length.…”

“…Several techniques are currently used for lowering the electron affinity. Deposition of Cs combined with pre-exposure to oxygen results in a true negative electron affinity of the surface and, consequently, an electron escape probability of nearly unity [7]. However this activation technique has only limited use due to an extremely high chemical reactivity of cesiated surfaces.…”

“…al [7] and the optical constants for diamond film were approximated from references [19] and [20] to fit the experimental data: n=(1, 1.05, 1.1, 0.9, 1.2, 1. …”

“…Other attractive features of diamond are chemical and mechanical stability under harsh external conditions, heat dissipation properties and radiation hardness [6]. It has also been shown that hydrogenated and cesiated diamond surfaces exhibit negative electron affinity (NEA) [7], [8], which is a very important parameter for cold electron emitting and photoemissing applications.…”

“…Since late 1980s tremendous progress has been made in growing diamond films and their application in electron emitters. However, only limited success was achieved in applying and characterizing thin diamond films as effective UV photoconverters [7], [9]- [12]. The efficiency of hydrogen-4 activated diamond reflective photocathodes in the range 140-210 nm was studied by Laikhtman et.…”