Combinedab initioand LEEDI∕Vstudy of submonolayer adsorption of In on W(110)

Abstract

The atomic structure of various indium adlayers at submonolayer coverages on W͑110͒ is investigated by a density functional theory ͑DFT͒ approach as well as by analysis of low-energy electron diffraction intensities ͑LEED I / V͒. Single-atom adsorption is studied by DFT, with the result that adsorption at the pseudo-fourfold coordinated sites of the W͑110͒ is most preferable, followed by bonding to the pseudo-threefold and twofold short-bridge sites. Both theory and experiment reveal that for the ͑3 ϫ 1͒ structure, which corresponds to a coverage of 0.33 monolayer ͑ML͒, indium atoms occupy exclusively pseudo-fourfold coordinated sites, while for the ͑1 ϫ 4͒ phase ͑0.75 ML coverage͒ and ͑1 ϫ 5͒ phase ͑0.80 ML coverage͒, pseudo-threefold and twofold short-bridge sites are also occupied. According to DFT, the ͑1 ϫ 4͒ structure is the most stable one, closely followed by the ͑1 ϫ 5͒ structure. Analysis of DFT studies on free monolayers of In reveals the significant influence of In-In bonding on the formation of these adlayer structures. The low-coverage ͑3 ϫ 1͒ structure is energetically the least favorable one, in agreement with the experimental finding that the ͑3 ϫ 1͒ structure is only metastable and transforms with increasing time or upon annealing into islands of ͑1 ϫ 4͒ patterns. In order to investigate whether the ͑3 ϫ 1͒ structure might be stabilized by contaminants, DFT calculations were also performed for coadsorbing hydrogen and oxygen with indium on W͑110͒. However, the ͑3 ϫ 1͒ structure always remains metastable. Furthermore, we find that phase separated regions of oxygen patches and ͑1 ϫ 4͒ In islands are stabilized by about 1 eV/atom relative to mixed ͑3 ϫ 1͒ In+ O configurations. This is in very good agreement with the experimental observation that the ͑3 ϫ 1͒ → ͑1 ϫ 4͒ transition can be triggered by additional oxygen.

Surface Structure and Temperature‐Reversible Phase Transition of Sn on W(110) Surface

“…Sn atoms were adsorbed on both the threefold hollow sites and fourfold hollow sites, which is also consistent with the optimized models of Mo(110)‐(1 × 4)‐Sn [ 19 ] and W(110)‐(1 × 4)‐In structure. [ 14 ] Only one Sn atom (Sn1) adsorbs on the fourfold hollow position, whereas the remaining two Sn atoms (Sn2 and Sn3) adsorb on the threefold hollow site. The nearest‐neighboring distance between Sn and W is 2.89 Å, which is almost identical to that in the (1 × 3) structure.…”

“…[7] W is a refractory metal used for thin-film growth owing to its immiscibility with other metals. Growth modes of different adsorbate species, such as Fe, [8,9] Co, [10] Cu, [11] Au, [12] Ag, [13] In, [14] and Sn, [15] have been investigated on the W(110) surface. Sn and In grow on W(110) by adopting large superstructures because of their size mismatch, [14,15] whereas monolayers (MLs) of adsorbate species such as Fe, Cu, Co, and Au can grow pseudomorphically on W(110) surface.…”

“…Growth modes of different adsorbate species, such as Fe, [8,9] Co, [10] Cu, [11] Au, [12] Ag, [13] In, [14] and Sn, [15] have been investigated on the W(110) surface. Sn and In grow on W(110) by adopting large superstructures because of their size mismatch, [14,15] whereas monolayers (MLs) of adsorbate species such as Fe, Cu, Co, and Au can grow pseudomorphically on W(110) surface. [8][9][10][11][12] Stöhr et al reported different surface structures on In/W(110) at the submonolayer.…”

“…[ 8–12 ] Stöhr et al reported different surface structures on In/W(110) at the submonolayer. [ 14 ] The fourfold hollow sites are most favorable for W(110)‐(1 × 4)‐In structure because of their minimum adsorption energy for In‐adsorption, but this would have resulted in a strong compression of In distances along [11] direction by 18% compared with the nearest‐neighbor bulk distance. Therefore, the adsorption of In atoms in the threefold site provides a reasonable compromise between optimum chemical adsorption and considerable stress within the In‐adlayer.…”

“…Therefore, the adsorption of In atoms in the threefold site provides a reasonable compromise between optimum chemical adsorption and considerable stress within the In‐adlayer. [ 14 ] However, Sn forms various surface structures on the W(110) surface in the submonolayer range. [ 15 ] A detailed low‐energy electron diffraction (LEED) study reveals (3 × 1), (1 × 3), and (1 × 4) structures with increasing Sn coverage.…”