Alkali semi-metal films and method and apparatus for fabricating them
Methods and systems for fabricating a film, such as, for example, a photocathode, having a tailored band structure and thin-film components that can be tailored for specific applications, such as, for example photocathode having a high quantum efficiency, and simple components fabricated by those methods.
1. An apparatus for fabricating a thin film component, comprising:
a deposition subsystem configured to deposit a pre-synthesized semi-metal compound material on a substrate; wherein the apparatus comprises a pre-synthesized semi-metal compound material source providing a target material; the pre-synthesized semi-metal compound material source comprising an evaporation crucible into which pre-synthesized semi-metal compound material is loaded; the pre-synthesized semi-metal compound material comprising at least two alkali materials and a semi-metal material; the pre-synthesized semi-metal compound material being polycrystalline; the pre-synthesized semi-metal compound material having crystallite size from about 15 nm to about 30 nm.
2. The apparatus of claim 1 wherein the thin film component is a photocathode.
3. The apparatus of claim 2 further comprising a characterization member configured to measure a quantum efficiency of the photocathode in real time of photocathode deposition.
4. The apparatus of claim 3 , wherein the characterization member comprises:
a light source for generating a light of a wavelength;
an anode; and
an electric circuit coupled between the anode and the photocathode for measuring a photocurrent in response to the light from the light source to obtain the quantum efficiency.
5. The apparatus of claim 4 , wherein the anode comprises a metallic ring configured to stay remote from a photocathode source material and proximate the deposited photocathode.
6. The apparatus of claim 1 , wherein the deposition subsystem comprises one of a sputtering apparatus, a thermal evaporation apparatus, e-beam apparatus, and a hot wall evaporation apparatus.
7. The apparatus of claim 1 , further comprising a feedback member coupled to the deposition subsystem and a member chosen from at least one of a characterization member or a thickness sensing member; said feedback member configured to adjust a parameter, the parameter being at least one of temperature of the deposition subsystem, temperature of the substrate or deposition rate in accordance with measurements by the member.
8. The apparatus of claim 1 wherein the at least two alkali materials comprise a first alkali material and a second alkali material.
9. The apparatus of claim 8 wherein the first alkali material comprises potassium (K), the second alkali material comprises cesium (Cs).
10. The apparatus of claim 9 wherein the semi-metal is antimony, and where in the pre-synthesized semi-metal compound material comprises K 2 CsSb.
11. The apparatus of claim 1 wherein the thin film component is a photovoltaic component.
12. The apparatus of claim 1 wherein the pre-synthesized semi-metal compound material is a powder.