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arXiv 1104.5522cond-mat.mtrl-sci
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离子轰击诱导SrTiO $_{3}$表面的金属-绝缘体转变

Metal-insulator transition on SrTiO$_{3}$ surface induced by ionic-bombardment

Heiko Gross, Namrata Bansal, Yong-Seung Kim, Seongshik Oh

摘要:

SrTiO $_{3}$由于其与多种复合氧化物薄膜具有良好的晶格匹配性,是生长各种复合氧化物薄膜最常用的绝缘单晶衬底之一。在这里,我们表明,一种常见的薄膜加工技术,氩离子铣削,创建高导电层的表面上的STO,不仅在室温下,而且在低温下,在该温度下的热扩散被完全抑制。在真空环境中对单晶STO衬底进行了系统的\emph{in situ}四点电导测量。绝缘STO的金属性的演变遵循基于氧空位掺杂效应的简单模型。在低温下,离子铣削产生了一个薄但比氩气渗透深度厚得多的稳态氧空位层,从而形成高度同心的金属状态。然而,在室温附近,发生了显著的热扩散,金属态连续地扩散到体中,仅在表面上留下低浓度的电子载流子。实验和模型之间的差异分析也提供了证据vacany集群,这似乎发生在任何空位形成过程中,并影响所观察到的电导。这些观察结果表明,使用高能方法,如离子铣削STO基板上处理的膜的传输特性需要谨慎。另一方面,如果适当控制,离子轰击可以用作在STO表面上产生用于器件应用的选择性导电层的方式。

英文摘要:

SrTiO$_{3}$ is one of the most popular insulating single-crystal substrates for various complex-oxide thin film growths, because of its good lattice match with many complex oxide films. Here, we show that a common thin film processing technique, argon ion-milling, creates highly conducting layer on the surface of STO, not only at room temperatures but also at cryogenic temperatures at which thermal diffusion is completely suppressed. Systematic \emph{in situ} four-point conductance measurements were taken on single-crystal STO substrates inside vacuum environment. The evolution of metallicity out of insulating STO follows simple models based on oxygen vacancy doping effect. At cryogenic temperatures, ion milling created a thin - but much thicker than the argon-penetration depth - steady-state oxygen-vacant layer, leading to a highly-concentric metallic state. Near room temperatures, however, significant thermal diffusion occurred and the metallic state continuously diffused into the bulk, leaving only low concentraion of electron carriers on the surface. Analysis of the discrepancy between the experiments and the models also provided evidence for vacany clustering, which seems to occur during any vacancy formation process and affects the observed conductance. These observations suggest that the transport properties of films processed on STO substrates using energetic methods such as ion milling need to be taken with caution. On the other hand, if properly controlled, ionic bombardment could be used as a way to create selective conducting layers on the surface of STO for device applications.

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