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

• Optical transmission of a Pd/V layers is measured [350–950 nm range] at 22 and 140 °C.
• Pd caped crystalline V films are optically characterized as function of H absorption.
• Spectral dependence of the dielectric function of hydrogenated V film is calculated.
• Changes due to H absorption in absorption coefficients of V and Pd films are calculated.
• H concentration in V thin films is calculated from change in absorption coefficient.

Optical properties of 50 nm thick single crystal vanadium films deposited on double side polished MgO substrates have been obtained from spectrophotometric measurements. The films were coated with a polycrystalline Pd layer (5 nm thick) to protect them from oxidation and to favor absorption of atomic hydrogen. Electrical resistance was recorded while hydrogen pressure was increased slowly up to 750 mbar keeping temperature constant. Simultaneously, under normal incidence of non-polarized radiation [350–950 nm], transmittance spectra of this Pd/V/MgO system were measured. These were numerically inverted to obtain the spectral behavior of the Pd, V, PdHy and VHx dielectric functions at 22 and 140 °C, and at 750 mbar. Hydrogen concentration in V film was first determined from a resisto-optical method. Finally, we demonstrate the possibility to determine the concentration in the Pd and the V layers independently, solely using the changes in the optical transmission.