Development Of Opaque Photocathodes Deposited Onto Microchannel Plates

Atomic layer deposition (ALD) techniques are being used to manufacture microchannel plate (MCP) imaging electron multipliers. The MCP substrates arc borosilicate microcapillary arrays, which are more robust than traditional lead glass MCPs, allowing them to be produced in large formats (400 cm(2)) with high open area ratios (up to 85%). The application of resistive and secondary emissive layers using ALD allow custom nanofabrication and optimization of parameters such as gain and resistance. The UV quantum efficiency of bare ALD MCPs exceeds conventional MCPs and application of opaque alkali halide photocathode layers have been investigated. The robust nature of ALD MCPs means they can also withstand the processing temperatures required for high temperature deposition of III-V materials, such as Gallium Nitride (GaN), for UV photocathodes with high QEs in the Near-UV (similar to 200-300nm). Here we discuss the status of the QE of bare ALD MCPs and the results of our opaque photocathode deposition effort onto ALD MCPs. Initial trials of opaque bialkali depositions have been successfully completed showing detection efficiencies commensurate with the highest efficiency semitransparent cathodes. GaN has been grown by molecular beam epitaxy onto sapphire substrates in order to optimize the deposition parameters. These results are being used as a diagnostic for refining depositions of GaN directly onto ALD MCPs.