Electronic effects in the formation of apparently noisy scanning tunneling microscopy images of Sr on Si(111)-7x7


The potential-energy surface (PES) for Sr adsorption on Si(111)-7x7 is calculated within density-functional theory. The main diffusion paths and corresponding energy barriers are determined for a Sr atom on reconstructed Si(111) surface. Comparison of simulated and experimental scanning tunneling microscopy (STM) images of apparently noisy patches in halves of 7x7 unit cells shows good agreement with respect to bias and polarity dependence. It was found that Sr thermal motion alone cannot account for the apparently noisy STM image patches. The origin of the peculiar intensity distribution in those images is due to charge transfer from the Sr atom to Si adatoms in the 7x7 reconstruction. Thus, electronic effects complement the picture and enable to understand the observations. With this knowledge in hand, the contradiction between experimental apparently noisy STM image patches and calculated PES for other adsorbates is readily explained.



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Zhachuk, R; Olshanetsky, B; Coutinho, J; Pereira, S

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We thank the Novosibirsk State University for providing us with computational resources. We acknowledge financial support by FCT Portugal (Grant No. SFRH/BPD/38291/2007) and by Russian Foundation for Basic Research (Grants No. 10-02-00199 and No. 08-02-01101)

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