Size induced metal insulator transition in nanostructured Niobium thin films: Intragranular and intergranular contributions

Abstract

With a reduction in the average grain size in nanostructured films of elemental Nb, we observe a systematic crossover from metallic to weakly-insulating behavior. An analysis of the temperature dependence of the resistivity in the insulating phase clearly indicates the existence of two distinct activation energies corresponding to inter-granular and intra-granular mechanisms of transport. While the high temperature behavior is dominated by grain boundary scattering of the conduction electrons, the effect of discretization of energy levels due to quantum confinement shows up at low temperatures. We show that the energy barrier at the grain boundary is proportional to the width of the largely disordered inter-granular region, which increases with a decrease in the grain size. For a metal-insulator transition to occur in nano-Nb due to the opening up of an energy gap at the grain boundary, the critical grain size is ~ 8nm and the corresponding grain boundary width is ~ 1.1nm.

References in corpus (1)

• Size dependence of the Tc and the superconducting energy gap in nanocrystalline thin films of Nb

Cited by in corpus (3)

• Upper critical field in nanostructured Nb: Competing effects of the reduction in density of states and the mean free path
• Competing effects of surface phonon softening and quantum size effects on the superconducting properties of nanostructured Pb
• Superconducting transition in Nb nanowires fabricated using focused ion beam