A semiconductor comprises a compound adsorbed on a surface of the semiconductor, the compound having at least one lone electron pair and substantially not undergoing in oxidation-reduction reactions, wherein the presence of the compound negatively changes a flat band potential of the semiconductor with reference to that when the compound is absent. By preliminary trial run one can determine precisely whether an application will benefit or suffer from hardware prefetch. These allow air bubbles, which accumulate between an outer shell of the annular collar and a bore of a housing, to escape to a bore for a non-return valve and hence directly into the open.