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

We have demonstrated the growth of CsBH4 (001) epitaxial thin films utilizing an IR laser deposition technique. The thin film exhibited 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. 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.