An infrared imaging high-throughput combinatorial method for investigating new phase formation and hydrogen storage capacities of thin films
Jason Hattrick-Simpers, Leonid A. Bendersky, Edwin J. Heilweil, H. Oguchi, Ichiro Takeuchi
We have refined and expanded on the capabilities of rapid screening, which utilizes infrared (IR) emissivity imaging. A complete procedure for using infrared emissivity to characterize the hydrogen storage properties of thin-film samples is described. The infrared system consists of a pressurized and sample heated optical cell that allows infrared images to be acquired as the sample is hydrogenated/dehydrogenated. The raw image data is normalized to an inert reference sample measured simultaneously to remove spurious effects produced by changes in the sample chamber environment (i.e. changing temperature, pressure, etc.). This procedure allows for the clear identification of hydrogen absorption and desorption processes as demonstrated by combined measurements of IR emissivity and X-ray diffraction on a single composition sample. Infrared measurements on Pd thickness gradient samples identify the critical thickness which blocks the infrared emission below. As an example, the change in infrared emissivity from a Mg-Ni composition spread sample with a gradient Pd capping layer was monitored during hydrogenation/dehydrogenation. A systematic trend in infrared emission intensity showed a clear dependence of hydrogenation on the Mg-Ni composition and Pd thickness. Additionally, the capability of infrared imaging to detect phase formation was demonstrated by monitoring the formation of a Mg-Si phase on the surface of a Mg thin-film grown on a silicon substrate during annealing.