Passivated Implanted Planar Silicon (PIPS) detectors are commonly used for alpha particle detection. The efficiency of alpha particle detection from uranium hexafluoride, which has a low specific activity, might be improved by altering the detector to increase the UF6 surface residence time. To this end, we have investigated coating the detector with gold and absorbing variously-functionalized alkylthiols to form self-assembled monolayers (SAMs) on the surface. We discuss optimization of the metal coating thickness to minimize energy spreading in the alpha spectrum, while maintaining SAM quality. Monte Carlo simulations (using the AASI program) of the alpha spectrum are combined with surface analysis techniques (reflection-absorption infrared spectroscopy (RAIRS), x-ray photoelectron spectroscopy (XPS), and contact angle goniometry) to arrive at an optimized architecture. Chemical compatibility testing of sample structures is executed, in collaboration with Argonne National Lab, in a custom chamber that allows exposure to radiological species. The chamber has the ability for QCM (quartz crystal microbalance) and RAIRS studies of the surface, and is equipped with a mass spectrometer for monitoring gas-phase products. It can operate in pressures between ultra-high vacuum (UHV) and up to ~100 Torr of UF6. We will report our progress and results of these chemical compatibility studies of the SAM surface toward UF6 attack.

Optimized surface functionalization with self-assembled monolayers for enhanced alpha detection from uranium hexafluoride (UF6)

2019 Spring National Meeting

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