Preparation and properties of niobium thin films

الملخص EN

Niobium thin films have been prepared by thermal evaporation techniques in a UHV system using an electrostatically focussed electron beam evaporator.

The starting material was MARZ grade niobium, with 99.999% purity, and in discs 12 mm diameter by 3 mm.

Deposition was, in general, on to thermally oxidised silicon slices with deposition rates of the order of 2 AS~X.

Film properties were examined as a function of film thickness, deposition rate and substrate temperature during deposition.

The critical temperature (Tc) was assessed by four-probe assessment of the sheet resistivity ratio at room temperature and in liquid nitrogen.

These indicated a critical temperature close to the bulk value of 9.2 K appropriate to niobium and, in all cases, the films were superconducting in liquid helium (4.2 K).

Films of thicknesses < 500 A° revealed Tc values <9.2 K and the film resistivity was significantly greater than should have been expected.

This was thought to be due to incomplete coalescence of the nucleation processes and a contribution to surface scattering in electron transport.