Polarization effects in noncontact atomic force microscopy: A key to model the tip-sample interaction above charged adatoms
Polarization effects in noncontact atomic force microscopy: A key to model the tip-sample interaction above charged adatoms
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DOI：
10.1103/physrevb.83.035411
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发表时间：
2011-01-20
影响因子：
3.7
通讯作者：
Loppacher, Christian
中科院分区：
文献类型：
--
作者：
Bocquet, Franck;Nony, Laurent;Loppacher, Christian
讨论了原子力显微镜（AFM）针尖与带电吸附原子表面之间的短程静电力（偶极力）的影响。偶极力具有微观特征，其起源于尖端和表面最前面原子的极化率。在大多数非接触式AFM实验中，其他作用力（如结合力）占主导地位。然而，在Gross等人[Science 324，1428（2009）]提出的实验中，其中确定了吸附在薄介电层上的单个金原子的电荷状态，结合力可忽略不计，因为尖端-样品距离相对较大。我们开发了一个模型，模仿上述实验的实验尖端样品的几何形状。该模型包括货车德瓦耳斯和远程静电相互作用，以及短程静电相互作用的基础上的自洽描述的电子极化效应的中性和带电的吸附原子。该模型是基于计算的静电能量的尖端样品的几何形状。我们的非接触式AFM成像以及偏置光谱曲线的计算与Gross等人提出的实验结果吻合良好。它表明，短程偶极力是主要负责以上带电物种的形貌成像中观察到的对比度。然而，它是长程电容力，这是负责的偏置光谱中的电荷状态的检测。我们讨论了我们的研究结果对未来的实验，旨在通过开尔文探针力显微镜检测单电荷的影响。
We discuss the influence of short-range electrostatic forces, so-called dipolar forces, between the tip of an atomic force microscope (AFM) and a surface carrying charged adatoms. Dipolar forces are of microscopic character and have their origin in the polarizability of the foremost atoms on tip and surface. In most experiments performed by noncontact AFM, other forces such as binding forces dominate the interaction. However, in the experiments presented by Gross et al. [Science 324, 1428 (2009)], where the charge state of individual gold atoms adsorbed on a thin dielectric layer was determined, binding forces are negligible as the tip-sample distance is relatively large. We develop a model which mimics the experimental tip-sample geometry of the aforementioned experiments. The model includes van der Waals and long-range electrostatic interactions, as well as the short-range electrostatic interaction based on the self-consistent description of electronic polarization effects on neutral and charged adatoms. The model is based on a calculation of the electrostatic energy of the tip-sample geometry. Our calculations of noncontact AFM imaging as well as of bias spectroscopic curves are in good agreement with the experimental ones presented by Gross et al. It is demonstrated that the short-range dipolar force is mainly responsible for the contrast observed in topography imaging above charged species. However, it is the long-range capacitive force which is responsible for the detection of the charge state in bias spectroscopy. We discuss implications of our findings on future experiments which aim to detect single charges by means of Kelvin probe force microscopy.