Energy distribution and quantum yield for photoemission from air-contaminated gold surfaces under ultraviolet illumination close to the threshold

Abstract

The kinetic energy distributions of photo-electrons emitted from gold surfaces under illumination by UV-light close to the threshold are measured and analyzed. Samples are prepared as chemically clean through Ar-Ion sputtering and then exposed to atmosphere for variable durations before Quantum Yield measurements are performed after evacuation. During measurements the bias voltage applied to the sample is varied and the resulting emission current measured. Taking the derivative of the current-voltage curve yields the energy distribution which is found to closely resemble the distribution of total energies derived by DuBridge for emission from a free electron gas. We investigate the dependence of distribution shape and width on electrode geometry and contaminant substances adsorbed from the atmosphere, in particular to water and hydrocarbons. Emission efficiency increases initially during air exposure before diminishing to zero on a timescale of several hours, whilst subsequent annealing of the sample restores emissivity. A model fit function, in good quantitative agreement with the measured data, is introduced which accounts for the experiment-specific electrode geometry and an energy dependent transmission coefficient. The impact of large patch potential fields from contact potential drops between sample and sample holder is investigated. The total quantum yield is split into bulk and surface contributions which are tested for their sensitivity to light incidence angle and polarization. Our results are directly applicable to model parameters for the contact-free discharge system onboard the LISA Pathfinder spacecraft.

Effective decrease of photoelectric emission threshold from gold plated surfaces

“…During phase 1, work function measurements were not made frequently enough to track its evolution through the initial decay period or with sufficient fidelity to see the required ∼ 0.2 eV increase in its value to explain the variation. The measurements quoted earlier for the work function derive mainly from measurements done after the yield had stabilised and these are similar to other results 19,23,24,36 .…”

“…Once liberated, the electrons then need to migrate to the surface and this process is characterised by the inelastic scattering mean free path (IMFP), λ s , 35 which will degrade the emitted electron energy spectrum. On reaching the surface the electron escape probability will be dependent on the electron energy including possible quantum tunnelling effects 36 . Finally, any finite spectral line width from the UV illumination source will cause additional broadening.…”

“…The model 1. The basic concept A signficant lowering of the work function of gold (from 5.1 eV to 4.4 eV and below) occurs by the chemisorption of a tightly bound monolayer of polar molecules, such as water 19 ,and/or hydrocarbons, which exist in both polar and non-polar forms 36,42. Using such a model, equations 5, 6, 7, 8 and 9 encompass the functional dependencies of photoelectric yield and electron energy distribution on photon energy, angle of incidence, scattering and surface patchiness which are needed for photon ray-tracing, photoelectron production and electron propagation simulations.…”

A pulsed, mono-energetic and angular-selective UV photo-electron source for the commissioning of the KATRIN experiment

“…Factors such as the Schottky effect in combination with surface roughness as well as impurities caused by adsorbed gas molecules modify the Fermi level at the photocathode, which typically reduces the observed or effective work function [24]. In the case of our electron gun, both factors are believed to contribute significantly to the observed work function.…”

Anti-Fowler Temperature Regime in Photoemission from <i>n</i>-Type Semiconductors with Surface Accumulation Layer

“…Due to the absence of quantization parallel to the surface, the electrons in such a well constitute a quasi-two dimensional metallic-like degenerated electron gas. Therefore, the electron concentration within the AL can be larger than the bulk concentration (as for example in InN) by 2 or 3 orders of magnitude and reach concentrations up to 21 3 10 cm − , which is only around one order of magnitude lower the electrons concentration in metals [7]. In addition, it is known the photoemission intensity from quantum-well states in thin metallic films is considerably greater than the corresponding value of the bulk metal (see for example references [8] and [9]).…”