Measurement Condition on True Atomic Resolution Imaging of Noncontact Atomic Force Microscope

在这个项目中，我们研究了Si尖端与Si(111)√<3>×√<3>-Ag表面之间的力相互作用，使用在超高真空（UHV）下操作的非接触原子力显微镜（AFM），利用Si和ag吸附尖端。利用Si尖端，在Si(111)√<3>×√<3>-Ag表面上的AFM图像显示出三种类型的对比，这些对比取决于尖端与样品表面之间的距离。在样品尖端距离约0.1 ~ 0.3nm处，AFM图像显示蜂窝结构。在样品尖端距离约0 ~ 0.05nm处，图像呈现出由三个亮点组成的三角形周期性结构，对比度相对较强。另一方面，在0.05-0的距离。在Lnm下，图像对比度似乎是上述两种对比度的综合。当尖端远离样品表面时，尖端与样品之间的相互作用力主要是物理键合作用，如尖端尖端Si原子与样品表面Ag三聚体之间的库仑力和/或范德华力。另一方面，在接触前，由于尖端顶端的Si原子悬空键与表面的Si- ag共价键轨道之间的杂化，导致尖端-样品相互作用力主要由化学键相互作用主导。利用ag吸附的针尖，可以获得不同的图像对比度，且不受偏差的影响。首次用原子分辨率观察到表面上的单个银原子。这些实验结果表明原子力显微镜鉴定原子种类是可能的。

In this project, we investigated the force interactions between a Si tip and Si(111)√<3>×√<3>-Ag surface, susing noncontact atomic force microscopy (AFM) operating in ultrahigh vacuum (UHV) by using Si and Ag-adsorped tips. By using Si tip, AFM images on Si(111)√<3>×√<3>-Ag surface showed three types of contrasts which depended on the distance between a tip and a sample surface. At the tip-sample distance of about 0.1 -0.3nm, AFM image showed the honeycomb arrangement. At the tip-sample distance of about 0- 0.05nm, the images showed the periodic structure of the triangle consisting of three bright spots with relatively strong contrast. On the other hand, at the distance of 0.05-0.lnm, the image contrast seemed to be the synthesis of the above two types of contrasts. When the tip is far from the sample surface, the tip-sample interaction force is dominated by physical bonding interaction such as the Coulomb force and/or the van der Waals (vdW) force between the tip apex Si atom and Ag trimer on the sample surface. On the other hand, just before the contact, the tip-sample interaction force is dominated by the chemical bonding interaction due to hybridization between the dangling bond out of the tip apex Si atom and the orbit of Si-Ag covalent bond on the surface. By using Ag-adsorbed tip, different image contrast was obtained and no its deitance dependence was observed. For the first time, individual Ag atoms on the surface was observed with atomic resolution. These experimental results suggest that the identification of the atom species is possible by using AFM.