用扫描探针技术解决氧化物异质结构中的局部不均匀性及其对局部2DEG形成的影响
Local inhomogeneities resolved by scanning probe techniques and their impact on local 2DEG formation in oxide heterostructures
摘要：
二维电子气（2DEG）形成过程中的横向不均匀性直接影响其电子性质。了解它们的起源是基本解释以及高质量设备的重要因素。本文利用原位局域电导原子力显微镜（LC-AFM）和散射型扫描近场光学显微镜（s-SNOM）研究了在具有部分TiO 2终端的STO（100）单晶上生长的LaAlO 3/SrTiO 3（LAO/STO）界面处掩埋二维电子气的局域形成。使用具有不同程度的化学表面终止的衬底，我们可以将所得的界面化学与不均匀的2DEG形成联系起来。在LC-AFM记录的电导率图中，在地形特征处观察到显著缺乏电导率，指示局部SrO/AlO 2界面堆叠顺序，而在显示TiO 2/LaO界面堆叠顺序的区域中可以探测到显著的局部电导率。这些结果可以通过s SNOM证实，在光信号中显示出类似的对比度分布，其可以与材料的局部电子特性相关联。低温电导率测量结果进一步证实了这一结果，该测量结果显示，随着绝缘SrO端接区域部分的增加，5 K下的剩余电阻不断增加。因此，我们可以将样品的宏观电学行为与其纳米级结构相关联。使用适当的参数，2DEG映射可以进行没有任何可见的改变样品的属性，证明LC AFM和S SNOM是可行的和无破坏的技术，用于识别本地2DEG形成。此外，以这种方式应用LC AFM和s SNOM打开了令人兴奋的前景，将宏观低温传输与其纳米级起源联系起来。
英文摘要：
Lateral inhomogeneities in the formation of 2-dimensional electron gases (2DEG) directly influence their electronic properties. Understanding their origin is an important factor for fundamental interpretations, as well as high quality devices. Here, we studied the local formation of the buried 2DEG at LaAlO3/SrTiO3 (LAO/STO) interfaces grown on STO (100) single crystals with partial TiO2 termination, utilizing in-situ local conductivity atomic force microscopy (LC-AFM) and scattering-type scanning near-field optical microscopy (s-SNOM). Using substrates with different degrees of chemical surface termination, we can link the resulting interface chemistry to an inhomogeneous 2DEG formation. In conductivity maps recorded by LC-AFM, a significant lack of conductivity is observed at topographic features, indicative of a local SrO/AlO2 interface stacking order, while significant local conductivity can be probed in regions showing TiO2/LaO interface stacking order. These results could be corroborated by s SNOM, showing a similar contrast distribution in the optical signal which can be linked to the local electronic properties of the material. The results are further complimented by low-temperature conductivity measurements, which show an increasing residual resistance at 5 K with increasing portion of insulating SrO terminated areas. Therefore, we can correlate the macroscopic electrical behavior of our samples to its nanoscopic structure. Using proper parameters, 2DEG mapping can be carried out without any visible alteration of sample properties, proving LC AFM and s SNOM to be viable and destruction-free techniques for the identification of local 2DEG formation. Furthermore, applying LC AFM and s SNOM in this manner opens the exciting prospect to link macroscopic low temperature transport to its nanoscopic origin.
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