A detailed picture of the behavior of cesium oxide as a low work-function coating on III-V semiconductors and on silver has been obtained. Measurement of required cesium and oxygen exposure for optimum photoyield shows that the compound normally formed is close to CS2O, with variations in required exposure for very thin and very thick layers. By making simultaneous Kelvin work-function, photoyield-threshold, and thickness measurements, it was possible to establish that the CS2O, an n-type semiconductor, forms a heterojunction or Schottky barrier with its substrate. This provides a band bending which produces a gradual lowering of the vacuum level with increasing thickness to an ultimate work function of 0.6 eV. The photoyield and dark current from the substrate are limited by the interfacial barrier at the heterojunction. This barrier is 1.00±0.05 eV for a silver substrate and 1.23±0.03 eV for GaSb. The band-bending distance in the CS2O is about 50 Å and the hot electron scattering distance is 9 Å. These data have been used in an improved calculation of the maximum Γ escape probability and requisite CS2O thickness for electron emission from III-V semiconductors of different bandgaps. Electron emission from CS2O induced by an oxygen overpressure was also measured. CSOH is compared with CS2O as a work-function lowering coating.

Calculations show that very nearly bulk quality material is required for high-efficiency semitransparent III-V photocathodes. For narrow-band response, this can be obtained by epitaxially growing a thin layer of a semiconductor whose bandgap is slightly less than that of the substrate. Cathodes made by growing GaAsSb on GaAs have given quantum efficiencies comparable with front surface values, peaking out at 0.54% at 1.35 eV near the onset of absorption in the GaAs substrate. Preliminary results demonstrating semitransparent yield at 1.06 μ of 0.013% are also shown.

We describe the construction and performance of a new electron spectrometer for analysis of low kinetic energy electrons, 0–2000 eV. The design of the analyzer is based on computer calculations and combines many favorable properties of both the retarding and the deflection energy analyzer. The energy analyzer consists of a set of electrodes with cylindrical symmetry and a planar retarding field grid followed by an electrode system with postmonochromatic action. Therefore a differential spectrum is obtained directly. The performance of the analyzer is discussed in terms of resolution, sensitivity, luminosity, and signal-to-background. The resolution achieved is 0.5%, with a resolution of 30 meV, making it possible to resolve and study electronic vibrational levels in atoms and molecules. A few spectra of nitrogen and argon are shown as representative of the performance of the new analyzer.

Auger electron spectroscopy has been used to measure quantitatively the amount of carbon contamination on GaAs–Cs–O photosurfaces. It appears that approximately one monolayer of carbon is sufficient to reduce the photoyield to zero.

Photoelectric measurements on cleaved p+ InP show that a process of cesiation and oxidation can produce a work function lower than the InP bandgap. Efficient photoemission results, with luminous efficiencies of 450 μA/lumen or better, and a threshold at 1.24 eV (1 μ).