研究目的
To provide a detailed explanation for 'sub-atomic' contrast observed on Si(111)-7×7 using a simple model based on Lennard-Jones potentials and a flexible tip, and to understand the origin of the contrast.
研究成果
The simulations demonstrate that 'sub-atomic' contrast on Si(111)-7×7 can arise from a flexible tip exploring an asymmetric potential created by the surrounding surface atoms, without needing to consider electronic orbital structure. The contrast is influenced by backbonding atoms and rest atoms, highlighting the role of multi-atom effects. However, the model cannot reproduce certain features like repulsive halos, requiring more sophisticated ab-initio modeling for full interpretation.
研究不足
The model does not include chemical interactions or changes in chemical reactivity, which limits its accuracy at close tip-sample separations. It also assumes identical properties for all atoms, not accounting for known differences in chemical reactivity at different sites on the Si(111)-7×7 surface. Electrostatic forces are not included, and the tip termination is generic, not specific to the experimental setup.
1：Experimental Design and Method Selection:
The study uses a simulation method based on Lennard-Jones potentials with a flexible tip model, as proposed by Hapala et al., to model constant height force images. The method involves scanning the sample laterally and approaching the tip to the sample in steps, allowing probe relaxation at each step.
2：Sample Selection and Data Sources:
The Si(111)-7×7 surface geometry is imported from previous density functional theory simulations. Artificial surface slabs are constructed using different elements of the unit cell (e.g., only adatoms, adatoms with backbonding atoms, adatoms with rest atoms) to examine contrast contributions.
3：List of Experimental Equipment and Materials:
Not applicable as this is a simulation-based study; no physical equipment is used.
4：Experimental Procedures and Operational Workflow:
Simulations are performed by scanning with step sizes Δx, Δy =
5：1 ?, approaching the tip in steps of Δz = 05 ? from an initial separation z0 = 15 ?. The probe position is relaxed at each step, and force fields and Δf grids are calculated using specified cantilever parameters (kcant = 1800 N/m, f0 = 30 kHz). Data Analysis Methods:
Simulated images are compared to experimental data; qualitative comparisons are made to understand contrast evolution and origins.
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