Abstract: A Mg—Ca sacrificial anode according to the present invention is disclosed, which is capable of providing a melts protection effect during a dissolution of Mg by adding Ca, which is a low melting point modification element, to Mg and obtaining characteristics which are equal to or better than a conventional Mg alloy group sacrificial anode in view of an open circuit potential and an anode efficiency.

Abstract: A method for modifying an (oxide) material of a substrate surface to a nitride material by radiating reactive ion particles having a certain amount of energy onto the substrate surface is disclosed. The thin film deposited on the surface-modified substrate has improved material properties. In particular, a surface treatment using ion beam is executed on an Al.sub.2 O.sub.3 substrate to initially form an AlN thin film, and then a GaN thin film is deposited on said AlN thin film. From this, it is possible to obtain a high quality GaN thin film having a better material property, compared with a GaN thin film according to the prior art.