What is the orientation of the tip in a scanning tunneling microscope?

IF 8.7 2区 工程技术 Q1 CHEMISTRY, PHYSICAL
Gábor Mándi , Gilberto Teobaldi , Krisztián Palotás
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引用次数: 19

Abstract

The atomic structure and electronic properties of the tip apex can strongly affect the contrast of scanning tunneling microscopy (STM) images. This is a critical issue in STM imaging given the, to date unsolved, experimental limitations in precise control of the tip apex atomic structure. Definition of statistically robust procedures to indirectly obtain information on the tip apex structure is highly desirable as it would open up for more rigorous interpretation and comparison of STM images from different experiments. To this end, here we introduce a statistical correlation analysis method to obtain information on the local geometry and orientation of the tip used in STM experiments based on large scale simulations. The key quantity is the relative brightness correlation of constant-current topographs between experimental and simulated data. This correlation can be analyzed statistically for a large number of modeled tip orientations and geometries. Assuming a stable tip during the STM scans and based on the correlation distribution, it is possible to determine the tip orientations that are most likely present in an STM experiment, and exclude other orientations. This is especially important for substrates such as highly oriented pyrolytic graphite (HOPG) since its STM contrast is strongly tip dependent, which makes interpretation and comparison of STM images very challenging. We illustrate the applicability of our method considering the HOPG surface in combination with tungsten tip models of two different apex geometries and 18,144 different orientations. We calculate constant-current profiles along the 11¯00 direction of the HOPG(0 0 0 1) surface in the |V|1V bias voltage range, and compare them with experimental data. We find that a blunt tip model provides better correlation with the experiment for a wider range of tip orientations and bias voltages than a sharp tip model. Such a combination of experiments and large scale simulations opens up the way for obtaining more detailed information on the structure of the tip apex and more reliable interpretation of STM data in the view of local tip geometry effects.

扫描隧道显微镜中尖端的方向是什么?
尖端的原子结构和电子性质对扫描隧道显微镜成像的对比度有很大影响。这是STM成像中的一个关键问题,迄今为止尚未解决的是精确控制尖端原子结构的实验限制。定义统计稳健的程序,以间接获得尖端结构的信息是非常可取的,因为它将为更严格的解释和比较来自不同实验的STM图像打开。为此,我们引入了一种统计相关分析方法来获取STM实验中使用的局部几何形状和取向信息。恒流地形的实验数据和模拟数据之间的相对亮度相关性是关键。这种相关性可以对大量模拟的尖端取向和几何形状进行统计分析。假设在STM扫描过程中有一个稳定的尖端,并基于相关分布,可以确定在STM实验中最有可能出现的尖端方向,并排除其他方向。这对于高取向热解石墨(HOPG)等衬底尤其重要,因为其STM对比度强烈依赖于尖端,这使得STM图像的解释和比较非常具有挑战性。结合两种不同顶点几何形状和18144种不同取向的钨尖模型,说明了该方法在HOPG表面的适用性。在偏置电压|V|≤1V范围内,计算了HOPG(0 00 1)表面< 11¯00 >方向的恒流分布,并与实验数据进行了比较。我们发现,在更大的尖端取向和偏置电压范围内,钝尖端模型比尖尖端模型与实验具有更好的相关性。这种实验与大规模模拟的结合,为获得更详细的叶尖结构信息和从局部叶尖几何效应角度更可靠地解释STM数据开辟了道路。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Progress in Surface Science
Progress in Surface Science 工程技术-物理:凝聚态物理
CiteScore
11.30
自引率
0.00%
发文量
10
审稿时长
3 months
期刊介绍: Progress in Surface Science publishes progress reports and review articles by invited authors of international stature. The papers are aimed at surface scientists and cover various aspects of surface science. Papers in the new section Progress Highlights, are more concise and general at the same time, and are aimed at all scientists. Because of the transdisciplinary nature of surface science, topics are chosen for their timeliness from across the wide spectrum of scientific and engineering subjects. The journal strives to promote the exchange of ideas between surface scientists in the various areas. Authors are encouraged to write articles that are of relevance and interest to both established surface scientists and newcomers in the field.
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