Infrared laser deposition of high-quality CsBH₄ epitaxial thin films stable under atmospheric conditions

Abstract

We have demonstrated the growth of CsBH4 (001) epitaxial thin films utilizing an infrared laser deposition technique. The thin film exhibited the coherent growth with a tensile strain from the substrate, resulting in its crystallinity superior to other kinds of metal borohydride thin films reported in earlier studies. Moreover, the notable chemical stability of CsBH4 enabled surface morphological and optical characterizations even under atmospheric conditions, which is a challenge to other metal borohydride thin films. The optical transition energy values estimated from a Tauc plot were found smaller than the theoretical ones previously reported, and DFT calculations suggested a partial deficiency of Cs+ or [BH4]− created in the thin films.