High-Resolution Model for Noncontact Atomic Force Microscopy with a Flexible Molecule on the Tip Apex
High-Resolution Model for Noncontact Atomic Force Microscopy with a Flexible Molecule on the Tip Apex
复制标题
尖端带有柔性分子的非接触式原子力显微镜高分辨率模型
DOI：
10.1021/jp511214e
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发表时间：
2015-01-22
影响因子：
3.7
通讯作者：
Zhao, Yong
中科院分区：
文献类型：
--
作者：
Guo, Chun-Sheng;Van Hove, Michel A.;Zhao, Yong
使用带有co分子功能化尖端的非接触原子力显微镜（NC-AFM）进行的实验可以清晰地成像共轭分子内的化学结构。在这里，我们描述了一个基于从头算方法的AFM尖端和样品分子之间相互作用力的详细模型，该模型产生了原子尺度的图像，与我们考虑的实验图像非常吻合。我们的模型的关键因素是明确地包括由于样品施加的侧向力导致的尖端CO分子倾斜对图像的影响。在此模型的基础上，我们具体讨论了在AFM图像中看到的畸变。正如最近报道的那样，AFM图像中的畸变源于内在效应，即p电子轨道的不同程度，以及外在效应，特别是CO倾斜。我们发现固有畸变与扫描高度相关，归因于尖端样品重叠区域的集成电子密度远离原子或键位置（垂直投影）。这种固有畸变在原子力显微镜图像中占主导地位，尽管由于CO倾斜导致的外部畸变可能会使原子位置发生更大的位移。
Experiments using noncontact atomic force microscopy (NC-AFM) with CO-molecule-functionalized tips have distinctly imaged chemical structures within conjugated molecules. Here we describe a detailed model based on an ab initio approach of the interaction force between the AFM tip and the sample molecule that yields atomic-scale images, which agree very well with the experimental images we considered. The key ingredient of our model is to explicitly include the effect on the image due to the tilt of the CO molecule at the tip apex resulting from the lateral force exerted by the sample. On the basis of this model, we specifically discuss the distortion seen in AFM images. As reported very recently, the distortion in AFM images originates from an intrinsic effect, namely, different extents of p-electron orbitals, as well as from an extrinsic effect, specifically CO tilt. We find that intrinsic distortion is scanning height dependent, attributing to the integrated electron density in the tip-sample overlapping region moving away from (the vertical projection of) the atom or bond positions. This intrinsic distortion is dominant in AFM images, although the atomic positions could be displaced even more by the extrinsic distortion due to CO tilt.