Oxidation of thin film binary entropy alloys

In recent years, material science has put significant effort into understanding the behavior of multiple principle element alloys (MPEAs), notably the category high entropy alloys (HEAs). Most of these studies have been conducted on the micro to macro scales, yet the nanoscale remains relatively unexplored. Additionally, investigating the structural changes caused by amorphous oxidation for thin film MPEAs is particularly new, with no fundamental theory having been found. By studying ambient oxidation of thin film binary entropy alloys, we show how the Hume-Rothery rules affect the oxide formation and in particular the requirement of an increased temperature prior to the formation of polycrystalline oxides for these systems, compared to their single metal counterparts

Synthesis and Characterization of Boron Thin Films Using Chemical and Physical Vapor Depositions

Boron as thin film material is of relevance for use in modern micro- and nano-fabrication technology. In this research boron thin films are realized by a number of physical and chemical deposition methods, including magnetron sputtering, electron-beam evaporation, plasma enhanced chemical vapor deposition (CVD), thermal/non-plasma CVD, remote plasma CVD and atmospheric pressure CVD. Various physical, mechanical and chemical characteristics of these boron thin films are investigated, i.e., deposition rate, uniformity, roughness, stress, composition, defectivity and chemical resistance. Boron films realized by plasma enhanced chemical vapor deposition (PECVD) are found to be inert for conventional wet chemical etchants and have the lowest amount of defects, which makes this the best candidate to be integrated into the micro-fabrication processes. By varying the deposition parameters in the PECVD process, the influences of plasma power, pressure and precursor inflow on the deposition rate and intrinsic stress are further explored. Utilization of PECVD boron films as hard mask for wet etching is demonstrated by means of patterning followed by selective structuring of the silicon substrate, which shows that PECVD boron thin films can be successfully applied for micro-fabrication

Control of YH₃ formation and stability via hydrogen surface adsorption and desorption

Yttrium is known to form two hydrides: YH2, a metal, and YH3, which is dielectric. However, the stability of YH3 is not fully understood, especially in the context of thin films, where the yttrium layer must be coated to protect it from oxidation. In this work, we show that the stability of a YH3 thin film depends on the capping layer material. Our investigation reveals that YH3 appears to be stabilized by hydrogen that is adsorbed to the capping layer surface. This is evidenced by the YH3-YH2 transition temperature, which was found to be correlated with the desorption temperature of hydrogen from the surface. We posit that surface-adsorbed hydrogen prevents hydrogen from diffusing out of the thin film, which limits YH3 dissociation to the solubility of hydrogen in the YH2/YH3 thin film