Substrate mediated nitridation of niobium into superconducting Nb2N thin films for phase slip study

Abstract

Here we report a novel nitridation technique for transforming niobium into hexagonal Nb 2 N which appears to be superconducting below 1K. The nitridation is achieved by high temperature annealing of Nb films grown on Si 3 N 4 /Si (100) substrate under high vacuum. The structural characterization directs the formation of a majority Nb 2 N phase while the morphology shows granular nature of the films. The temperature dependent resistance measurements reveal a wide metal-to-superconductor transition featuring two distinct transition regions. The region close to the normal state varies strongly with the film thickness, whereas, the second region in the vicinity of the superconducting state remains almost unaltered but exhibiting resistive tailing. The current-voltage characteristics also display wide transition embedded with intermediate resistive states originated by phase slip lines. The transition width in current and the number of resistive steps depend on film thickness and they both increase with decrease in thickness. The broadening in transition width is explained by progressive establishment of superconductivity through proximity coupled superconducting nano-grains while finite size effects and quantum fluctuation may lead to the resistive tailing. Finally, by comparing with Nb control samples, we emphasize that Nb 2 N offers unconventional superconductivity with promises in the field of phase slip based device applications.

Growth windows of epitaxial $\textrm{Nb}_x\textrm{N}$ films on c-plane sapphire and their structural and superconducting properties

“…The explanation that their films actually possess the γ phase and not the β phase is consistent with their observation of T c = 11.5 K, a value consistent with the T c of γ phase films in this study and those reported by Oya [26]. Finally, Gajar et al reported the growth of mixed phase films of β-Nb 2 N and Nb 4 Nb 5 , which exhibit broad superconducting transitions around 1 K [50].…”

A robust nitridation technique for fabrication of disordered superconducting TiN thin films featuring phase slip events

“…S5 in SI]. This indicates that the samples are in the 2D limit, where phase fluctuations lead to PSLs 35 and IVCs exhibit resistive steps 20 , 36 , 37 . In Fig.…”

“…We demonstrate that by tuning the disorder the superconducting-to-normal state transition in the measured IVCs changes from a single step transition to a transition embedded with multiple steps featuring the formation of PSLs. The tuning of disorder level in TiN films has been achieved by adopting a novel substrate mediated nitridation technique 18 – 20 , which employs high temperature annealing of Ti/Si 3 N 4 based metal/substrate assembly to prepare majority phase TiN thin films accompanied by TiSi 2 and elemental Si as minority phases 18 . Conventionally, TiN films are grown either by using reactive dc sputtering of Ti in presence of Ar/N 2 gas mixtures 21 – 26 or by atomic layer deposition 27 , 28 in presence of N 2 gas etc 29 – 31 .…”

Interface study of thermally driven chemical kinetics involved in Ti/Si3N4 based metal-substrate assembly by X-ray photoelectron spectroscopy

“…Here, we have probed the metal-substrate interaction in Ti/Si3N4 assembly with respect to annealing temperature (Ta) which plays an important role as it leads to the decomposition of Si3N4 into elemental N and Si, and simultaneously, it provides thermal energy for the decomposed elements to diffuse inside the metal [20,21]. The Ta has been varied in the range from 650°C to 820°C.…”