MS-3-P-2381 Ag induced low-dimentional structures on the Si(110) surface

Metal adsorption on Si(110) surface received significantly less attention in comparison with other low-index Si surfaces [Si(111) and Si(100)}. This is due to the complicated surface reconstruction and complexity of big surface domains preparation. The increasing interest to this surface analysis is caused not only from fundamental point of view [1] but also by possible applications of Si(110) surface for electronic circuits. Anisotropic structure of Si(110) surface can be used for nanowires growth. P-doped (110) oriented Si samples with the help of Ni-free instrument were mounted on tantalum sample holder, degased at 600C during 24 hours and processed with argon-ion-sputtering. In the final stage of surface preparation the samples were flashed at 1200C. The Ag/Si(110) evaporation was perfomed using a Knudsen-cell type of evaporator. As it was shown previously [2], the initial sites of Ag adsorption on Si(110)-16x2 surface are situated along terrace's borders. It was shown that it should be about 13-14 Ag atoms in the unit cell of 16x2-Si(110)-Ag structure at 0.21 ML Ag surface coverage. With annealing temperature increasing up to 630C we observed new atomic phase (4,6)x(-3,1) on Si(110) surface. Experimental results are presented in Fig.1 (a,b). Uniformly distributed terraces separated by dark rows are visible on the STM images. The surface profile height measured across the STM image changes in the range of 0.1 nm what is smaller than the step's height (0.19 nm) of 16x2-Si(110) surface. So the observed pattern is caused by the surface electronic effect. For correct interpretation of obtained results, STM image was superimposed on unreconstructed Si(110) surface (Fig.2). It's clear that the unit cell of experimentally observed structure is (4,6)x(-3,1). In the surface area restricted by unit cell sizes there are 43 atoms of substrate. Therefore should be 43x0.21=9 Ag atoms in unit cell of structure induced by silver adsorption at 0.21 monolayer coverage. It's resonable to suggest that Ag atoms saturated the Si(110) dangling bonds to minimize an adsorption energy (Fig.3). Based on this fact it's possible to build a model of (4,6)x(-3,1) surface reconstruction (Fig.4). Dotted line shows surface cell corresponding to structure (4,6)x(-3,1) of clean Si(110) surface. A solid line indicates unit cell of Si(110)-Ag-(4,6)x(-3,1) after Ag adsorption. As can be seen from Fig.4 there are 10 atoms of Ag in unit cell of Si(110)-Ag-(4,6)x(-3,1) and  it is in good accordance with experimental results. The appearence of Ag-Si(110)-4x1 surface structure with increasing of Ag coverage up to 0.42 ML and 490C-550C anneleaning temperatures was also demonstrated.

1 B.Z. Olshanetsky et.al., Surf. Sci., 67, 581 (1977)2 N.S. Maslova et. al., JETP Letters, 84, 320 (2006).