Hydrogenation-induced gigantic resistance decrease of palladium films deposited by high pressure magnetron sputtering

Abstract

We demonstrate a pronounced decrease in the electrical resistance of highly disordered palladium (Pd) films deposited under a high working Ar pressure using a compact film coating system. The resulting resistance change ratio of up to $1/335$ is predominant among those reported previously. Film characterization suggests two primary mechanisms responsible for this significant resistance reduction: atomic force microscopy observation indicates improved electrical contacts among Pd grains, and X-ray diffraction measurement demonstrates hydrogenation-induced crystallization of Pd. These findings offer a simple scheme to enhance hydrogen sensor performance and can contribute to a more comprehensive understanding of the hydrogenation process in Pd.

Figures (4)

• Figure 1: Sheet resistance ($R_\mathrm{S}$) as a function of elapsed time for Pd(7.5 Pa). The dotted horizontal line indicates the value of initial resistance ($R_0$). The resitance change ratio with respect to $R_{\rm fin}= 188$$\Omega$/sq is also written.
• Figure 2: (a),(b) Sheet resistance change ratio ($\Delta R_\mathrm{S}$/$R_0 \equiv (R_s -R_0)/R_0$) as a function of elapsed time for Pd(2.5 Pa) and Pd(20 Pa) (a), and for Pd(5.0 Pa) and Pd(10 Pa) (b). (c) Working Ar pressure ($P_{\rm Ar}$) dependence of $\Delta R_\mathrm{S}/R_0$. (d) $\Delta R_\mathrm{S}/R_0$ plotted against initial resistivity ($\rho_0$). We classified the data into two groups (see text).
• Figure 3: (a)-(d) AFM images of the surfaces of Pd(20 Pa) (a),(c) and Pd(5.0 Pa) (b),(d) taken before (a),(b) and after (c),(d) the hydrogen exposure, respectively. Grains with a typical size are indicated by white dotted circle, whose diameters are 13 nm (a), 22 nm (b), 33 nm (c), and 18 nm (d), respectively. (e),(f) XRD patterns of Pd(20 Pa) (e) and Pd(5.0 Pa) (f). Blue and red data represent the results obtained before and after the hydrogen exposure, respectively. Intensity is normalized by the peak from sample stage at $2\theta \sim 44^\circ$.
• Figure 4: (a)-(c) Magnetic field ($H$) dependence of Hall resistivity ($\rho_{yx}$) for Pd(5.0 Pa) (a), Pd(10 Pa) (b) and Pd(20 Pa) (c). Blue and red data represent the results obtained before and after the hydrogen exposure, respectively.