Electrical resistivity of epitaxial molybdenum films grown by laser ablation deposition

The results of electrical resistivity measurements at room and low temperatures, and also of reflection high energy electron diffraction analysis of thin (less than 110 nm) Mo films, grown by laser ablation deposition are presented. The films deposited under ultrahigh vacuum conditions on sapphire (1̄012) substrates at temperatures of 20–750 °C are monocrystalline, with a [001] axis perpendicular to the substrate. It is shown that the ratio of room temperature to residual resistance which characterizes structural perfection, is in the range 12–32 for the films 70 nm thickness. It increases abruptly at film growth temperatures of 200–370 °C and changes weakly at further temperature increase. The analysis of data on the size (thickness) effect of the Mo films deposited at 750 °C revealed that the effective electron mean free path is in the range 0.1–1 μm for the films 15–110 nm thickness. Surface scattering was found to be the basic channel of electron scattering at helium temperatures, with the specular coefficient q∼0.3 and residual bulk electron mean free path ∼100 μm. At low temperatures T<25 K, the temperature dependent part of the resistance is approximated by ρ(T)−ρ0=ATn. The power degree smoothly varies from 3.2 in high quality films deposited at 750 °C, where the effective electron mean free path exceeds film thickness to 4.5 in the films deposited onto cold unannealed substrates, where the effective electron mean free path is comparable with film thickness.