Thin‐Film Metal Hydrides

Abstract

The goal of the medieval alchemist, the chemical transformation of common metals into nobel metals, will forever be a dream. However, key characteristics of metals, such as their electronic band structure and, consequently, their electric, magnetic and optical properties, can be tailored by controlled hydrogen doping. Due to their morphology and well-defined geometry with flat, coplanar surfaces/interfaces, novel phenomena may be observed in thin films. Prominent examples are the eye-catching hydrogen switchable mirror effect, the visualization of solid-state diffusion and the formation of complex surface morphologies. Thin films do not suffer as much from embrittlement and/or decrepitation as bulk materials, allowing the study of cyclic absorption and desorption. Therefore, thin-metal hydride films are used as model systems to study metal-insulator transitions, for high throughput combinatorial research or they may be used as indicator layers to study hydrogen diffusion. They can be found in technological applications as hydrogen sensors, in electrochromic and thermochromic devices. In this review, we discuss the effect of hydrogen loading of thin niobium and yttrium films as archetypical examples of a transition metal and a rare earth metal, respectively. Our focus thereby lies on the hydrogen induced changes of the electronic structure and the morphology of the thin films, their optical properties, the visualization and the control of hydrogen diffusion and on the study of surface phenomena and catalysis.

Hydrogenography of Mg Ni1−H gradient thin films: Interplay between the thermodynamics and kinetics of hydrogenation

“…Furthermore, the diffusion of hydrogen in the MgH 2 phase is very slow, and unless high temperatures are used, a blocking layer of the hydride forms that prevents further hydrogenation of Mg [1]. Many attempts have been made to destabilize MgH 2 and improve its kinetics by alloying it with transition metals [2][3][4][5][6][7][8] or transition metal oxides [9,10]. The complex hydride Mg 2 NiH 4 is one of the most promising: it has a hydrogen capacity of 3.6 wt.% and a desorption enthalpy DH ¼ À64 kJ (mol H 2 ) À1 [3].…”

Applications of high throughput (combinatorial) methodologies to electronic, magnetic, optical, and energy-related materials

“…Much of the hydrogenography work has been reviewed. 324 Similar to IR emissivity, hydrogenography can also detect metal to metal transitions during hydrogenation of films; 325 this feature makes hydrogenography useful for studying other classes of materials, such as hydrogen separation membranes. 326 Hydrogenography has also been utilized as a switchable mirror technology, taking advantage of the change in transmissivity that results from hydrogenation, as well as other applications.…”

Hydrogen-mediated long-range magnetic ordering in Pd-rich alloy film

“…[15][16][17][18] Based on these findings, we expected to observe appreciable magnetic modulation in Pd-rich magnetic alloy thin film; such materials would be useful for fabricating gas sensors. [19][20][21] Thus, in this study, the effect of hydrogenation on the magnetic properties of Co 14 Pd 86 was investigated. Reversible and appreciable modulation of the magnetism was demonstrated and analyzed for discussion.…”