Nb3 Ge superconductive films grown with air

Claim 1

A control method of preparing a superconducting film having a critical temperature T c of at least about 19° K. which comprises providing a vacuum chamber with a substrate having at least one substantially smooth surface on which said film is to be deposited, said substrate being at least substantially inert under the conditions of deposition, providing said chamber with a source of niobium and germanium, means for monitoring of niobium flux and germanium flux individually, providing said chamber with a source of air, protecting said substrate surface with a movable protective means which prevents niobium and germanium flux from contacting it, reducing the pressure in said chamber to produce an evacuated chamber with a residual pressure no greater than about 10 -5 mm Hg, heating said substrate to a temperature ranging from 750° C. to 1100° C., vaporizing said niobium and germanium to produce an impinging flux composition ranging from about 1 part to about 3 parts of niobium to about 1 part of germanium, allowing said residual pressure to stabilize at a level no greater than about 10 -5 mm Hg, introducing by a controlled leak of air into said evacuated chamber an incremental air pressure which raises said stabilized pressure in said chamber at least about 0.1 × 10 -5 mm Hg, removing said protective means from said substrate, and impinging said substrate with said niobium and germanium composition forming an adherent superconductive Nb 3 Ge film thereon ranging in composition up to about 2 atomic % from stoichiometric composition, for a constant rate of impingement of said niobium and said germanium on said substrate with increasing substrate temperature from 750° C. to 1100° C. said incremental air pressure increasing up to 5 × 10 -4 mm Hg and said amount of niobium decreasing down to about 1 part, said film having at least a thickness sufficient to form a continuous film.