Studies of YBa2Cu3O6+x degradation and surface conductivity properties by Scanning Spreading Resistance Microscopy

TL;DR

This study investigates the surface degradation and conductivity properties of YBa2Cu3O6+x thin films using SSRM, revealing inhomogeneity, oxygen diffusion effects, and the influence of voltage on conductive regions, with implications for device analysis.

Contribution

The paper introduces SSRM analysis of YBCO surface degradation and inhomogeneous conductivity, linking it to oxygen diffusion and surface layer variations, which is novel in this context.

Findings

Surface conductivity decreases over time due to oxygen out-diffusion.

Conductive regions are highly inhomogeneous and voltage-dependent.

Surface degradation involves varying oxygen concentration and layer thickness.

Abstract

Local surface conductivity properties and surface degradation of c-axis oriented YBa2Cu3O6+x (YBCO) thin films were studied by Scanning Spreading Resistance Microscopy (SSRM). For the surface degradation studies, the YBCO surface was cleaned by ion beam etching and the SSRM surface conductivity map has been subsequently repeatedly measured over several hours in air and pure nitrogen. Average surface conductivity of the scanned area was gradually decreasing over time in both cases, faster in air. This was explained by oxygen out-diffusion in both cases and chemical reactions with water vapor in air. The obtained surface conductivity images also revealed its high inhomogenity on micrometer and nanometer scale with numerous regions of highly enhanced conductivity compared to the surroundings. Furthermore, it has been shown that the size of these conductive regions considerably depends on the applied voltage. We propose that such inhomogeneous surface conductivity is most likely caused by varying thickness of degraded YBCO surface layer as well as varying oxygen concentration (x parameter) within this layer, what was confirmed by scanning Auger electron microscopy (SAM). In our opinion the presented findings might be important for analysis of current-voltage and differential characteristics measured on classical planar junctions on YBCO as well as other perovskites.