[en] This program was initiated because of the considerable need that has developed recently in high temperature plasma diagnostics for efficient x-ray photocathodes that are well characterized as to the electron energy distribution of the emitted electrons and as a function of the incident x-ray photon energy. Quantitative theory and measurement for x-ray photocathode systems has been essentially non-existent. This model approach for the characterization of x-ray photocathodes (first as applied to metals), our experimental method for obtaining high resolution electron energy distributions, and some preliminary results have been presented in two initial published reports which are attached here. A systematic study was made on a large number of semi-conductor and metal systems (of a large range in band-gap-electron affinity or work function values) in order to test the models and to suggest some superior x-ray photocathode materials for immediate application. These measurements are being made with energy resolution of about 0.04 eV. All materials are vacuum-deposited as ''infinitely thick'' systems (about 2000 A) upon gold substrates. The results are averaged over six samples from two vacuum deposited batches