First principles studies of an Si tip on an Si(100)2 × 1 reconstructed surface

Abstract

We present a systematic study of the interaction between a silicon tip and a reconstructed Si(100)2×1 surface by means of total energy calculations using Density Functional Theory. We perform geometry optimisation to obtain the reconstructed Si surface using the Local Density Approximation and the Generalized Gradient Approximation methods and compare our results with those obtained experimentally.We then study the effects of the tip of a scanning probe of an Atomic Force Microscope (AFM) on the behaviour of atoms on the reconstructed surface when the tip translates at distances close to it. Our results show that at certain positions of the tip relative to the surface and depending on the direction of the scan, the Si dimer on the surface flips, resulting to a local reconstruction of the surface into p(2×2) or c(4×2) configurations. These configurations exhibit energy lower by 0.05 eV/dimer compared to the Si(100)2×1 structure.

A First Principles Simulation Framework for the Interactions between a Si(001) Surface and a Scanning Probe

“…Throughout the calculations, total energy and atomic forces are calculated using density functional theory [22], which is implemented in the CASTEP code [23]. Results reported in [17] showed that in general both local density approximation (LDA) [24] and generalised gradient approximation (GGA) [25] for the exchange-correlation term for this system led to the same conclusion. Therefore in the present work we employ only the LDA method.…”

“…The first mode is concerned with calculations at a fixed tip-surface distance of 4 Å-the vertical distance from the apex atom to the plane that contains adatoms, shown in Figure 1(a). At this tip-surface distance the interaction between them is dominated by the covalent chemical interaction which is responsible for atomic resolution and image contrast [16,17,26]. The tip scans above dimers along the dimer line throughout the whole surface in steps of 0.5 Å.…”

“…From an AFM imaging point of view, it has been shown that in lateral scans the variations of the energy and the force have the same trend and the energy or the force distribution can be considered as a qualitative prediction of the AFM image in the frequency shift mode [16,17]. In (H and Si atoms) of the tip.…”

“…The tip-surface interaction has attracted much attention from the theoretical community aiming at explaining surface behaviour of different configurations of Si(001) surface [13][14][15][16][17][18]. Earlier theoretical work in this area has shown how covalent chemical interactions between the dangling bonds of the apex atom of a Si tip and the surface atoms introduce dominant forces which are responsible for atomic resolution and image contrast.…”

“…By reducing the tip-surface distance to about 4 Å, its chemical interaction increases rapidly and atoms on the surface are clearly imaged. In addition it was shown how the direction of scanning plays an important role in observing atoms on the surface [17].…”