Selective Epitaxial Growth of Ca 2 NH and CaNH Thin Films by Reactive Magnetron Sputtering under Hydrogen Partial Pressure Control.

Calcium compounds with N and H are promising catalysts for NH 3 conversion, and their epitaxial thin films provide a platform to quantitatively understand the catalytic activities. Here we report the selective epitaxial growth of Ca 2 NH and CaNH thin films by controlling the hydrogen partial pressure ( P H 2 ) during reactive magnetron sputtering. We find that the hydrogen charge states can be tuned by P H 2 : Ca 2 NH containing H - is formed at P H 2 < 0.04 Pa, while CaNH containing H + is formed at P H 2 > 0.04 P a. In situ plasma emission spectroscopy reveals that the intensity of the Ca atomic emission (∼422 nm) decreases as P H 2 increases, suggesting that Ca reacts with H 2 and N 2 to form Ca 2 NH at lower P H 2 , whereas at higher P H 2 , CaH x is first formed on the target surface and then sputtered to produce CaNH. This study provides a novel route to control the hydrogen charge states in Ca-N-H epitaxial thin films.