Tunnelling in aluminium/aluminium-oxide/palladium junctions: hydrogen-induced variations

The tunnel current of aluminium/aluminium-oxide/palladium (Al/Al2O3/Pd) junctions, obtained by means of sapphire sputtering, has been measured in air and in hydrogen-nitrogen atmosphere at various H2 concentrations ranging from 2 to 100% and at room temperature. It has been found that the tunnel current undergoes a significant change as a consequence of Pd work function lowering induced by the hydrogen. The ratio between the tunnel current in H2 and in air has a value in the range 102¿106, depending on the oxide thickness. The increase of the current occurs in some hundreds of milliseconds if the hydrogen is emitted at atmospheric pressure.