Resistivity size effect in epitaxial VNi2 layers

Epitaxial VNi2 layers are deposited onto MgO(001) and their resistivity rho measured as a function of layer thickness d = 10.5-138 nm to quantify the resistivity size effect. The layers exhibit resistivity minima at both stoichiometric V:Ni = 1:2 composition and 700 degrees C growth temperature, which is attributed to electron scattering at V-Ni antisite defects and is described using the ordering parameter within the framework by Rossiter. A cube-on-cube epitaxy of the fcc parent structure on MgO(001) leads to two possible layer orientations for orthorhombic VNi2(010) and VNi2(103), resulting in considerable atomic disorder at domain boundaries, consistent with relatively small x-ray coherence lengths of 8 and 14 nm in-plane and along the growth direction of a 33.5 nm thick layer. In situ rho vs d measurements yield a bulk resistivity of rho(o) = 46 +/- 2 mu Omega cm and a benchmark quantity of rho(o)lambda = (138 +/- 5) x 10(-16) Omega m(2), where lambda is the bulk electron mean free path. Air exposure causes a minor resistivity increase due to 2 +/- 1 nm thick surface oxide that perturbs the surface potential. Resistivities at 77 K are Delta rho = 16 +/- 3 mu Omega cm below those at room temperature. This Delta rho is thickness independent and is close to the previously predicted 13.9 mu Omega cm bulk resistivity for VNi2 along [100]. However, the measured bulk resistivity is well above this prediction, which is attributed to electron scattering at domain boundaries/atomic disorder. Consequently, the theoretically predicted superior directional conduction cannot be experimentally confirmed in this study. The overall results indicate that VNi2 is only a promising compound for narrow interconnects if a synthesis scheme can be developed that results in a strong atomic order, a negligible domain boundary density, and a [100] crystalline orientation along the transport direction.

Automated summary

The epitaxial VNi2 layers deposited on MgO(001) exhibit a resistivity size effect, with a minimum resistivity observed at stoichiometric composition and specific growth temperature. The atomic disorder at domain boundaries in the layers affects the resistivity, and the thickness has a limited impact on the resistivity. The theoretically predicted superior directional conduction in VNi2 cannot be confirmed experimentally in this study. This research provides guidance for the application of VNi2 compound.