Hopping Al atom on Si(111) 7 × 7 surface studied by scanning tunneling microscopy

Abstract

Adsorption of Al atoms on the Si(111) 7 × 7 surface was investigated by STM at room temperature. The adsorbed Al atom displaced a Si center adatom on the surface, and the expelled Si atom diffused inside a half unit cell. The adsorbed Al atom hopped among center adatom sites with a frequency of about 0.01s 1 Introduction Study of atom adsorption and diffusion on the Si surface [1, 2] is of both scientific and technological importance. Information for adsorption site, diffusion path and potential energy barrier is expected from atomically resolved experiments and simulations. On a Si(111) 7 × 7 surface that has the dimer-adatom-stacking fault (DAS) structure, a complex potential energy surface for Si atom adsorption and diffusion exists [3,4]. On the other hand, reconstructed Al adsorbed structure [5] and dynamical adsorption process of the Al atoms [6] were reported for the Si(111) surface. However, the behavior of a single Al atom on the surface is not yet understood. To investigate the adsorption process of the Al atom with three valence electrons on the Si (four valence electrons) surface is of interest from scientific viewpoint because the nature of the Si(111) 7 × 7 surface will be revealed.In this article, we study adsorption and diffusion of Al atoms inside a half unit cell of the Si(111) 7 × 7 surface, especially hopping phenomena of a single Al atom, by using a scanning tunnelling microscope (STM) at room temperature. Adsorption site, atomic exchange with a Si adatom, hopping rate are investigated.

Electronic effects in the formation of apparently noisy scanning tunneling microscopy images of Sr onSi(111)−7×7

“…Such motion originates fuzzy or apparently noisy patches in the STM images that have been found earlier for other adsorbates such as Si, Pb, Tl, Sn, Ag, and Y. [4][5][6] Several theoretical studies have been dedicated to adatom adsorption and diffusion on Si͑111͒-7 ϫ 7. In the pioneering work by Cho and Kaxiras, the authors used a 4 ϫ 4 supercell to mimic the local 2 ϫ 2 arrangement of adatoms in the Si͑111͒-7 ϫ 7 reconstruction.…”

Impact of strain and surface reconstruction on long-range diffusion of Ge atoms on Ge(111) surface

“…With increasing tensile strain, the diffusivity across the dimer rows is further frustrated (according to both experiments and first principles calculations [6,7]) while that along the dimer rows is enhanced (according to calculations of Shu et al [6]) or does not change (according to experiments of Zoethout and co-workers [7]). * zhachuk@gmail.com Experimental studies of surface diffusion on Si(111)-7× 7 also revealed an interesting phenomenon -the mobility of adsorbed atoms inside the Si(111)-7 × 7 half unit cells (HUCs) was in many cases found to be high at room temperature, while under the same conditions, hops between neighboring HUCs were rare [8][9][10][11][12][13][14][15][16][17]. This is somewhat unexpected since Si(111)-7×7 HUCs contain a high density of dangling bonds, to which adsorbed atoms can connect strongly.…”