Magnesium hydride film formation using subatmospheric pressure H2 plasma at low temperature

MgH2 films were prepared using pure hydrogen plasma under subatmospheric pressures ranging from 13.3 to 53.3 kPa (100-400 Torr). The prepared films were characterized by scanning electron microscopy, x-ray diffraction (XRD), and temperature programmed desorption measurements. The ratio of MgH2 to Mg in the prepared films was evaluated, as the degree of Mg hydrogenation, by XRD analysis. The plasma was found to be indispensable for the preparation of thick MgH2 film near normal hydrogen pressure. Hydrogen plasma exposure treatment after Mg film formation had only a very small effect on thick MgH2 film formation, despite the use of subatmospheric pressure hydrogen plasma with high H atom density. Simultaneous supply of Mg and atomic hydrogen was found to be important in preparing thick MgH2 films. Therefore, the surface reaction between Mg and H appears to play an important role in the growth process. The flux ratio (Gamma(H)/Gamma(Mg)) of atomic H and Mg required to prepare highly hydrogenated Mg was found to be more than 100. The resulting degree of hydrogenation of the prepared MgH2 film was as good or better than that of commercial powders. MgH2 film prepared on Si substrate exhibited growth with (211) preferred orientation as the deposition rate was decreased, and a columnar structure along the growth direction. The deposition rate reached 2.9 mu m/min while still maintaining a high degree of hydrogenation. (C) 2016 American Vacuum Society.