Abstract
By means of total energy calculations within the framework of the local density approximation (LDA), the interactions between a silicon Si(001) surface and a scanning probe are investigated. The tip of the probe, comprising 4 Si atoms scans along the dimer lines above an asymmetric p(2 × 1) surface, at a distance where the chemical interaction between tip-surface is dominant and responsible for image resolution. At that distance, the tip causes the dimer to toggle when it scans above the lower atom of a dimer. The toggled dimers create an alternating pattern, where the immediately adjacent neighbours of a toggled dimer remain unchanged. After the tip has fully scanned across the p(2 × 1) surface, causes the dimers to arrange in a p(2 × 2) reconstruction, reproducing the images obtained in scanning probe experiments. Our modelling methodology includes simulations that reveal the energy input required to overcome the barrier to the onset of dimer toggling. The results show that the energy input to overcome this barrier is lower for the p(2 × 1) surface than that for the p(2 × 2) or c(4 × 2) surfaces.
Highlights
When silicon is cleaved in the (001) direction, each atom on the surface has two dangling bonds
Depending on the buckling direction of the dimers, the following three reconstructed surfaces can be obtained: 1) p(2 × 1) surface which has all dimers buckled in the same direction; 2) p(2 × 2) surface with neighbouring dimers in each row buckled in the opposite direction and neighbouring dimers in a line normal to the dimer row are buckled in the same direction, and ; 3) c(4 × 2) surface with neighbouring dimers buckled in alternating directions both along and normal to the dimer row
In this paper we presented a modelling framework that employes total energy calculations to study the interactions between a Si tip and surface
Summary
When silicon is cleaved in the (001) direction, each atom on the surface has two dangling bonds. A number of research groups have performed experimental studies to explain the behaviour of atoms on the Si(001) surface induced by a scanning probe [3,10,11,12] In such experiments they focused on three parameters that were known to affect the arrangement of atoms on the work surface, namely the bias voltage, the tunnelling current and the tip-sample interaction. Scanning probe trajectories are simulated by advancing the tip in a stepwise manner as a real life tip would and perform quasistatic calculations to obtain force, energy landscape and surface reconstruction as explained in detail These are key features of our modelling framework that can allow more faithful representation of real life scanning probe trajectories and by doing so provide better insight into the tip-surface interactions to inform imaging experiments. We extend our study to two additional surface reconstructions, namely the p(2 × 2) and c(4 × 2) surfaces, to provide a complete investigation and elucidate an understanding of how the probe manipulates atoms on the surface which have led to the observations made in experiments such as those by Sugimoto et al [19,20,21]
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