Measurement Condition for Atomic Resolution imaging on Reactive Surfaces Using Atomic Force Microscopy

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In this project, we investigated the force interactions between a Si tip and Si(111)<square root>3x<square root>3-Ag surface as well as between a Si tip and Ag (111) surface, using noncontact atomic force microscopy (AFM) operating in ultrahigh vacuum (UHV). AEM images on Si(111)<square root>3x<square root>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 0.05-0.1nm, 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 timer 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. Furthermore, atomic resolution imaging of pure metallic surface of Ag (111) was achieved, suggesting that noncontact AFM has potential for investigation of pure metallic surface.