Role of lateral forces on atom manipulation process on Si(111)- (7×7) surface in dynamic force microscopy

We investigated the role of lateral force components on the lateral manipulation of intrinsic Si adatoms toward a vacancy site on a Si(111)-$(7\ifmmode\times\else\texttimes\fi{}7)$ surface using noncontact atomic force microscopy at room temperature. Lateral atom manipulation was accomplished via constant-height scans using a set of tips with varying chemical reactivities. We determined the vertical and lateral force as well as the interaction energy profiles associated with the lateral manipulation of a Si adatom on a Si(111)-$(7\ifmmode\times\else\texttimes\fi{}7)$ surface. Our results demonstrate that lateral forces do not play a decisive role in the manipulation process while the vertical force component is key for the manipulation process, and the ability to manipulate the Si adatom depends primarily on the chemical nature of the tip apex. Our results further reveal that the tips that exhibit high chemical reactivity with Si adatoms have a sharper interaction energy profile above Si adatoms than tips with less chemical reactivity, indicating the stronger atom-trapping ability of the chemically reactive tips. This characteristic property gives tips the ability to create localized reductions in the energy barrier required for adatom movement, thereby enabling thermally induced adatom hopping toward the tip. These findings can enhance our understanding of the underlying mechanisms involved in the lateral manipulation of intrinsic adatoms of semiconductor surfaces, as well as adsorbate atoms/molecules forming covalent bonds with tip-surface systems, i.e., chemisorption systems.