Surface Dipole Formation and Lowering of the Work Function by Cs Adsorption on InP(100) Surface

The Cs adsorption on InP(100) surface is studied with Synchrotron Radiation Photoelectron Spectroscopy. The charge transfer from Cs to the InP substrate is observed from the Cs induced In4d and P2p components, and this charge transfer results in surface dipole formation and lowering of the work function. The Cs4d intensity saturates at coverage of one monolayer (ML). However, a break point is observed at 0.5 ML, which coincides with the achievement of the minimum work function. This break point is due to the different vertical placement of the first and the second half monolayer of Cs atoms. Based on this information, a simple bi-layer structure for the Cs layer is presented. This bi-layer structure is consistent with the behavior of the charge transfer from the Cs to the InP substrate at different Cs coverages. This, in turn, explains why the work function decreases to a minimum at 0.5 ML of Cs and remains almost constant beyond this coverage. The depolarization of the surface dipoles is attributed to the saturation of charge transfer to the surface In atoms and the polarization of the Cs atoms in the second half monolayer induced by the positively charged Cs atoms in the first half monolayer

Photoemission Study of Cs-NF3 Activated GaAs(100) Negative Electron Affinity Photocathodes

GaAs based negative electron affinity photocathodes activated with Cs and NF{sub 3} are used as polarized electron sources for linear accelerators. It is generally believed that the activation layer consists of CsF. The activation layers of Cs-NF{sub 3} on GaAs photocathodes are herein investigated using synchrotron radiation photoelectron spectroscopy (SR-PES). F1s, N1s and other core levels are recorded at photon energies ranging from 70eV to 820eV. Surprisingly, a significant amount of nitrogen is observed in the activation layers. Two distinct species of nitrogen are observed, one of which decreases along with the Fluorine signal as the yield of the photocathode decays with time

CsBr Photocathode at 257nm: A Rugged High Current Density Electron Source

There is a continuing need for high intensity electron sources that will operate in demountable vacuum and can be externally modulated. Materials with wide bandgap, e.g. diamond, are rugged but need photon energies exceeding the bandgap to emit efficiently and this rules out the use of CW lasers. We have found that a photocathode of CsBr is both adequately intense(>150A/cm{sup 2}) and rugged and can be excited with photons of energy of 4.8eV(257nm). This is below the energy gap of CsBr(7.3eV) but such operation can be explained by the presence of intraband states about 4eV below the conduction band minimum