Combined light and electron scattering for exploring hydrogen in thin metallic films

Abstract

We present a method, combining optical transmission with electrical resistance, to study the hydrogen uptake in thin transition metal films. The change in optical transmission is used to determine the hydrogen concentration, while the change in resistance serves as an indicator for the ordering of hydrogen. We identify phase boundaries and regions of high and low orders as well as changes in the ordering temperature. As a demonstration of this approach we compare the hydrogen uptake of 50 and 10 nm single-crystal vanadium films. The ordered phase is found to be extended to higher temperatures in the thinner sample.

Hydrogen induced changes in the optical properties of Pd capped V thin films

“…The calibration parameter value found was 1.19 ± 0.01 (similar to the one found in Ref. [13] for 140°C). With it the atom concentrations at 750 mbar are 0.74 ± 0.02 at 22°C and 0.61 ± 0.02 at 140°C.…”

“…T 0 is the transmission of the film before hydrogenation, and T is the transmission under hydrogenated conditions. The use of the Beer-Lambert law is based on that the transmission do reflect the changes in the density of states close to the Fermi level, which from the results in PdH y [12] and VH x [13] appears to be insensitive to the structural order of the hydrogen, this is highly useful in the current context. Besides, by taking the ratio between T and T 0 , the effect of neglecting boundary reflections in the context of Beer-Lambert law is diminished.…”

“…Simultaneously, transmission of normally incident non-polarized radiation, in the wavelength range from 350 to 950 nm, and electrical resistance were measured as hydrogen was allowed into the chamber slowly. The hydrogen concentration, x = [H]/[V], in the V film was initially determined using a resisto-optical method, which combines results of these two measurements, as proposed by Gremaud et al [12] and Prinz et al [13].…”

Using light transmission to watch hydrogen diffuse

“…Vanadium exhibits a much stronger affinity for hydrogen, as compared with palladium, whereby the concentration in palladium can be safely neglected38. Hydrogen causes changes in the electronic structure, giving rise to changes in the optical transmission, which can be used to determine the concentration910 (for further details see the Methods section). The optical transmission is monitored as a function of time using a charge-coupled device, with a lateral resolution of about 20 μm, whereby the concentration of hydrogen as a function of both position and time can be determined.…”

“…The relation between hydrogen concentration and electronic structure is complex25, so we have resorted to a phenomenological approach of the conversion of optical transmission to hydrogen concentration, as described by Prinz et al 9…”