A study on the interaction between hydrogen and Pd/SiO$_{2}$/Si*

The surface electrical resistance of Pd/SiO$_{2}$/Si and Pd/Al$_{2}$O$_{3}$ were monitored by a two-probe technique during the H$_{2}$ exposure to clarify the interaction of H$_{2}$ and ultra thin Pd film($<$2nm). In this work, the Pd/SiO$_{2}$/Si structure has a sensitivity of 30 to 1{\%} H$_{2}$/Ar presence within 1.4 s at RT, where the sensitivity was defined as the ratio of the surface resistance change to the original resistance, ($R-R_{0})$/$R_{0}$. However, the sensitivity of ultra thin Pd film observed in Pd/Al$_{2}$O$_{3}$ was less than 2. Compared to Pd/Al$_{2}$O$_{3}$, the non-linear relationship of $I-V$ of Pd/SiO$_{2}$/Si reveals a possible Schottky barrier and that electrons actually go through the Si substrate. When the thickness of Pd film in Pd/SiO$_{2}$/Si is decreased to less than 2 nm, Si substrate will demonstrate a large change of the charge concentration during the interaction between the Pd film and H$_{2}$. This change amplified displays the change of the work function of Pd films and together with an already accelerated response due to a thinner Pd film, Pd/SiO$_{2}$/Si provides an excellent H$_{2}$ detecting capability.