Enhanced resolution imaging of ultrathin ZnO layers on Ag(111) by multiple hydrogen molecules in a scanning tunneling microscope junction
Enhanced resolution imaging of ultrathin ZnO layers on Ag(111) by multiple hydrogen molecules in a scanning tunneling microscope junction
复制标题
DOI：
10.1103/physrevb.97.195417
复制
发表时间：
2018-05
影响因子：
3.7
通讯作者：
Shuyi Liu;A. Shiotari;D. Baugh;M. Wolf;T. Kumagai
中科院分区：
文献类型：
--
作者：
Shuyi Liu;A. Shiotari;D. Baugh;M. Wolf;T. Kumagai
扫描隧道显微镜(STM)结中的分子氢被发现可以提高STM成像的横向空间分辨率，被称为扫描隧道氢显微镜(STM)。本文报道了用扫描隧道显微镜对在Ag(111)衬底上外延生长的2层和3层厚的氧化锌薄膜的原子分辨率成像。这种提高的分辨率可以在相对较大的尖端到表面的距离处获得，并且解决了3ML厚的氧化锌比2ML厚的氧化锌更有缺陷的结构。为了阐明增强成像的机理，用扫描隧道显微镜和原子力显微镜相结合的方法研究了氢分子结(HMJ)的电学和力学性质。结果表明，HMJ在电导和频移曲线的尖端到表面的距离依赖关系中表现出多个扭结特征，这在无氢结中是不存在的。基于一个简单的模型，我们认为结包含多个氢分子，并且分子的顺序挤出导致电导和频移曲线上的扭结特征。该模型还定性地再现了氧化锌薄膜的增强分辨率图像。
Molecular hydrogen in a scanning tunneling microscope (STM) junction has been found to enhance the lateral spatial resolution of the STM imaging, referred to as scanning tunneling hydrogen microscopy (STHM). Here we report atomic resolution imaging of 2- and 3-monolayer (ML) thick ZnO layers epitaxially grown on Ag(111) using STHM. The enhanced resolution can be obtained at a relatively large tip to surface distance and resolves a more defective structure exhibiting dislocation defects for 3-ML-thick ZnO than for 2 ML. In order to elucidate the enhanced imaging mechanism, the electric and mechanical properties of the hydrogen molecular junction (HMJ) are investigated by a combination of STM and atomic force microscopy. It is found that the HMJ shows multiple kinklike features in the tip to surface distance dependence of the conductance and frequency shift curves, which are absent in a hydrogen-free junction. Based on a simple modeling, we propose that the junction contains several hydrogen molecules and sequential squeezing of the molecules out of the junction results in the kinklike features in the conductance and frequency shift curves. The model also qualitatively reproduces the enhanced resolution image of the ZnO films.