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Photoelectron emission (PEE) by potassium (0.002-3 mole liter-I) and sodium (0.013-0.21 and 7.2 mole liter-I) in liquid ammonia at -60'C was studied from 1.55 to 5.4 eV. The PEE spectrum is composed of the previously reported band with its maximum about 3.2 eV and a new band peaking about 4.6 eV. The highly asymmetric low-energy band is assigned to PEE by solvated electrons. Its interpretation by a recent model for PEE by solutions results in a linear dependence of the range of quasifree electrons in solution on photon energy. The quantum yield appears to be proportional to the square root of the analytical metal concentration up to 0.1 mole liter-I. The 4.6 eV symmetric PEE band is interpreted as the result of bound-bound transitions (similar to f3 band for F centers) followed by autoionization. Experimental methods are outlined. and their details are available in an unpublished report.

A model for the physical vapor deposition of compound semiconductor films that describes film growth from component molecular beams is presented. Constitutive relationships are used in the model to account for incomplete adsorption from the incident molecular beams, emission of adsorbed components into vacuum, and surface reactions of the elemental species. The model predicts film composition and growth rate as a function of incident fluxes and substrate temperature. It is applicable for important binary and ternary alloy semiconductors including the li-VI and Ill-V compounds over the range of deposition conditions yielding both stoichiometric and two-phase films. In this paper the model equations and the behavior predicted by the model are described for a number of material systems including (CdHg)Te, (CdZn)S, and CulnSe,.

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Vacuum sublimation of cadmium sulfide for manufacture of thin film solar cells was analyzed. The sublimation unit consisted of a two chamber cylindrical source bottle having a rate control orifice and exit nozzle. Coupled heat and mass balance equations were solved using appropriate rate equations for flow in the free molecular-to-viscous transition regime. The model equations predicted that heat traqsfer has a significant effect on sublimation rate. Experiments were carried out over a range of temperatures with several rate control orifices and exit nozzles. Quantitative agreement between measured rates and those calculated from the model equations was obtained. R. E. ROCHELEAU SCOPEThe economic utilization of solar energy through direct conversion of sunlight to electricity requires development of efficient photovoltaic cells and low cost manufacturing technologies. Thin film solar cells using cadmium sulfide are leading candidates. At the laboratory scale, cells are made by vacuum coating cadmium sulfide on a substrate. The vacuum coating process involves sublimation of cadmium sulfide powder from a heated chamber and condensation onto a cooler substrate. The laboratory process has been sufficiently well developed so that cells having conversion efficiencies over 9% can be made in small quantities.Design of a commercial scale process and equipment is analogous to chemical reactor design. Ideally, design of the commercial scale unit is based on analysis of laboratory experience, followed by unit operations experimentation. For this paper we have analyzed the laboratory scale sublimation of cadmium sulfide that is used for CdS/CuZS solar cells fabrication. The sublimation system consisted of a two compartment cylindrical chamber having a rate control orifice and exit nozzle. Mass and energy balances were derived. The coupled balance equations were solved numerically using appropriate rate equations. The fluid mechanical situation involved flow through orifices and short pipes in the free molecular-to-viscous transition regime. The rate expression was developed for congruent dissociative evaporation of a binary compound in a form such that available thermochemical data could be used to evaluate the properties of the gas.Experiments were carried out in which the rate of sublimation was measured over a range of wall temperatures for several sets of orifice and exit nozzle dimensions. Predictions based on the model equations were compared to measured rates and the model was verified to a paint where design of a unit operations scale system could be carried out. CONCLUSIONS AND SIGNIFICANCEUnsteady state mass and energy balances on a charge of solid cadmium sulfide subliming in a nearly closed cylindrical chamber and effusing through a small orifice have been written and numerically solved. The results show that heat transfer from the chamber walls to the subliming surface significantly affects the rate of effusion. The magnitude of this effect depends on the orifice dimensions, geometry of the chamber, and the surf...