Interplay between electronic and atomic structures in the Si(557)-Au reconstruction from first principles

Abstract

The quasi-one-dimensional Si͑557͒-Au reconstruction has attracted a lot of attention in recent years. We study here the interplay between the electronic and structural degrees of freedom in this system. Our calculations are in good agreement with recent experimental data obtained using scanning tunneling microscopy and spectroscopy both at room and low temperatures. Together with the quite successful description of the experimental band structure, these results give further support to the current structural model of the Si͑557͒-Au surface. We consider in detail the energetics and variation of the band structure as a function of the buckling of the step edge and its implications to explain the observed metal-insulator transition. Finally, we present the results of a first-principles molecular dynamics simulation of several picoseconds performed at room temperature. As expected, we find a strong oscillation of the step-edge atoms. The dynamics associated with other vibrational modes is also observed. Particularly apparent are the oscillations of the height of the restatoms and adatoms and the associated fluctuation of the Si-Au-Si bond angles along the gold chain. This mode, together with step-edge buckling, has a strong influence on the insulating and/or metallic character of the surface.

Systematic investigation of the structure of the Si(553)-Au surface from first principles

“…In previous investigations, we found that this was crucial to reduce the number of dangling bonds in the final structures and to facilitate the appearance of the so-called honeycomb-chain structure. 9 The honeycomb chain was proposed by us 7,9,11,16,18 and by other authors 3,5 as one of the key ingredients of the reconstructions induced by gold on Si͑111͒ vicinal surfaces, and the results presented here seem to confirm this idea. We have developed a compact notation that allows us to label and identify all of the structures.…”

“…13,38 These bands are half filled and exhibit, as the temperature is lowered, a metal-insulator transition that is accompanied by a periodicity doubling along the steps in the STM images. [12][13][14]16 The Si͑553͒-Au surface, which has a smaller terrace width, shows two bands similar to those observed in the case of the Si͑557͒-Au system. It also shows a strongly dispersing one-dimensional band with a fractional ͑ϳ1 / 3͒ filling.…”

“…18 The importance of the HC structure for the gold induced reconstructions on vicinal Si͑111͒ was recently emphasized by Crain et al 3 It is known to form the step edge of the Si͑557͒-Au surface. [9][10][11]16 It is also a key ingredient of the most recent proposals for the structure of the Si͑111͒-͑5 ϫ 2͒-Au reconstruction. 5,7 The HC structure was initially proposed to explain the low coverage reconstructions induced by some alkali metals ͑Li, Na, and K͒, Mg, and Ag on Si͑111͒.…”

“…46 and in our previous calculations. 7,16,18,22 Different basis sets were used for the silicon atoms ͑see below for more details͒. For the fastest calculation, a single-͑SZ͒ basis of numerical atomic orbitals 43,47,48 was used.…”

“…In the case of vicinal substrates, the average terrace width can be controlled by the miscut angle, which provides a route to tuning interwire distances and interactions. 3 Some examples of quasi-one-dimensional reconstructions that have attracted much attention in recent years are the Si͑111͒-͑5 ϫ 2͒-Au, [3][4][5][6][7] Si͑557͒-Au, [8][9][10][11][12][13][14][15][16] Si͑553͒-Au, [17][18][19][20][21][22][23][24] and Si͑111͒-͑4 ϫ 2͒-In ͑Refs. 25-37͒ surfaces.…”