A hydrogen-free amorphous dielectric insulating film having a high material density and a low density of tunneling states is provided. The film is prepared by e-beam deposition of a dielectric material on a substrate having a high substrate temperature Tsub under high vacuum and at a low deposition rate. In an exemplary embodiment, the film is amorphous silicon having a density greater than about 2.18 g/cm3 and a hydrogen content of less than about 0.1%, prepared by e-beam deposition at a rate of about 0.1 nm/sec on a substrate having Tsub=400° C. under a vacuum pressure of 1×10−8 Torr.