Selective Epitaxial Growth of Ca₂NH and CaNH Thin Films by Reactive Magnetron Sputtering under Hydrogen Partial...

Calcium compounds with N and H are promising catalysts for NH₃ conversion, and their epitaxial thin films provide a platform to quantitatively understand the catalytic activities. Here we report the selective epitaxial growth of Ca₂NH and CaNH thin films by controlling the hydrogen partial pressure (P_H) during reactive magnetron sputtering. We find that the hydrogen charge states can be tuned by P_H: Ca₂NH containing H^- is formed at P_H < 0.04 Pa, while CaNH containing H⁺ is formed at P_H > 0.04 Pa. In situ plasma emission spectroscopy reveals that the intensity of the Ca atomic emission (∼422 nm) decreases as P_H increases, suggesting that Ca reacts with H₂ and N₂ to form Ca₂NH at lower P_H, whereas at higher P_H, CaH 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.