Nanogaps controlled by liquid nitrogen freezing and the effects on hydrogen gas sensor performance

A practical strategy for the reduction of nanogap width has been investigated using liquid nitrogen freezing of Pd-sputtered elastomeric substrates. Two types of hydrogen gas sensors, in which no pre-strain and 25% elongation were applied to Pd films on the elastomeric substrates, showed extremely low detection limits of less than 300 and 200 ppm, respectively, after liquid nitrogen freezing and recovery to room temperature. For the non-strained sensors, the nanogap width was measured to be about 90 nm, whereas it was more reduced to 25 nm on the elongated sensors. Both sensors exhibited perfect On-Off switching, fast response, and good reversibility, which are based on the nanogap open-close mechanism upon exposure to hydrogen gas. These results provide a valuable clue for reducing nanogap width, thereby improving the hydrogen-sensing capabilities of nanogap-based On-Off hydrogen sensors.