Structural and electronic properties of rare earth silicide nanowires on Si(557)

Abstract

We report on the atomic structure and electronic properties of self-organized dysprosium and erbium silicide nanowires on Si͑557͒, studied using scanning tunneling microcopy and angle-resolved photoelectron spectroscopy. The nanowires were prepared by deposition of different rare earth amounts and subsequent annealing for silicide formation. Due to the stepped structure of the Si͑557͒ surface, nanowires form along the step edges, showing a variety of structurally and electronically different types, depending on the preparation conditions. At submonolayer dysprosium coverages, different chainlike structures dominate, showing one-dimensional dispersion with half-metallic properties. These nanowire regions are separated by 7 ϫ 7 reconstructed Si͑111͒ facets or submonolayer dysprosium silicide patches on these facets. At monolayer coverages, in contrast, mainly nanowires with lengths exceeding 1 m and widths of a few nanometers are found, forming on the ͑111͒ facets of the Si͑557͒ surface. Their electronic properties are characterized by a two-dimensional band structure with strong dispersion both parallel and perpendicular to the nanowires and clear metallic behavior, and it is demonstrated that they are formed from hexagonal DySi 2 monolayers. In the case of thicker silicide layers, metallic nanowires form again on the Si͑111͒ facets, but with clear structural and electronic characteristics of hexagonal Dy 3 Si 5 multilayers. At these coverages, additional structures are found, which show an intense signal in the photoelectron spectroscopy data. Related experiments on the growth of erbium silicides indicated the formation of very similar nanowire structures.

Rare-earth silicide thin films on the Si(111) surface

“…formation of nanowires was found, consisting of RESi 2 monolayer or RE 3 Si 5 multilayer stripes on the Si(111) terraces with widths of a few nanometers. On the Si(001) surface, besides the formation of strongly anisotropic 4 × 2 and 7 × 2 reconstructions, the growth of silicide nanowires is observed, which have cross sections on the nanometer scale, but lengths sometimes exceeding micrometers [13][14][15][16][17][18][19]. The nanowires are assumed to consist of the same hexagonal RESi 2 material as the silicide monolayers studied here.…”

“…For submonolayer coverage, a variety of structures with different periodicities was found [8][9][10][11][12]. Furthermore, the rare-earth silicides are the basis for the self-organized formation of nanowires on several Si substrates with other orientations [13][14][15][16][17][18][19].…”

Self-organized atomic nanowires of noble metals on Ge(001): atomic structure and electronic properties

“…Interestingly, their electronic character here depends on the substrate used. While on Si(001) these broad metallic nanowires exhibit a quasi-1D band structure [30], the corresponding structures grown on Si(557) will induce Si(111) facets and exhibit a 2D band structure [31]. In YSi 2 nanowires, charge-order fluctuations reminiscent of a CDW, albeit shortranged, have recently been observed [32].…”

Energy surfaces of rare-earth silicide films on Si(111)

“…Furthermore, these hexagonal disilicides formed on Si(1 1 1) were also found in nanowires growing in a self-organized way on the Si(0 0 1) [7,8] and Si(5 5 7) [9,10] surfaces. For all trivalent rare-earth metals very similar silicides are formed because of their chemical similarity.…”

“…1c by the respective reconstructions and the local silicide coverage in monolayers. The shape of the terrace edges varies from straight edges along the [1 10] directions for the monolayer silicide to rounder edges for the multilayer silicide, which can be related to the density of lateral dangling bonds [2,9,10]. It should be noted that the preparation conditions have a strong influence on the formation of the silicides.…”