Hydrogen Loading System for Thin Films for Betavoltaics

Abstract Betavoltaics are direct conversion energy devices that are ideal for low power and long-lasting, uninterruptable applications. Betavoltaics operate similarly to photovoltaics where a radio isotope irradiates beta particles into a semiconductor p-n junction that converts the kinetic energy into electrical energy. Betavoltaics are limited by their power output from the radio isotope. However, the source power density can be increased by the selection of solid-state substrates. While tritium absorbing substrates can be simulated to estimate tritium absorption levels and surface emission energies, their viability has to be physically evaluated. A state-of-the-art hydrogen loading system developed by our research group was used to evaluate different film types to understand how they perform during the hydrogen/tritium loading process. The hydrogen loading system utilizes the Sievert technique, where the temperature and volume is constant and pressure drop of the system is used to determine hydrogen uptake of a film substrate. The hydrogen loading system procedure was verified using 250 nm thick palladium films at three loading temperatures. Results clearly show uptake of hydrogen by the thin palladium films accurate to the ideal stoichiometric ratio of one hydrogen atom to host palladium atom.