YBa2Cu3O6 +x降解及表面导电性能的扫描扩展电阻显微镜研究
Studies of YBa2Cu3O6+x degradation and surface conductivity properties by Scanning Spreading Resistance Microscopy
摘要：
利用扫描扩展电阻显微镜（SSRM）研究了c轴取向YBa 2Cu 3 O 6 +x（YBCO）薄膜的局域表面电导特性和表面退化。对于表面降解研究，YBCO表面通过离子束蚀刻进行清洁，随后在空气和纯氮气中重复测量SSRM表面电导率图超过几个小时。在这两种情况下，扫描区域的平均表面电导率随着时间的推移而逐渐降低，在空气中更快。这可以通过两种情况下的氧气向外扩散以及与空气中的水蒸气发生化学反应来解释。所获得的表面电导率图像还揭示了其在微米和纳米尺度上的高度不均匀性，与周围相比具有高度增强的电导率的许多区域。此外，已经表明，这些导电区域的大小在很大程度上取决于所施加的电压。我们建议，这种不均匀的表面电导率是最有可能引起的退化YBCO表面层的厚度变化，以及在此层内的不同的氧浓度（x参数），这是由扫描俄歇电子显微镜（SAM）证实。在我们看来，所提出的研究结果可能是重要的分析的电流-电压和微分特性测量的经典平面结上的YBCO以及其他钙钛矿。
英文摘要：
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.
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