Metastable and stable overstructures of In on W(1 1 0)

The growth of indium on W(1 1 0) at submonolayer coverages was studied by low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). At room temperature with increasing coverage three indium-induced overlayer structures – (3 × 1), (1 × 4) and (1 × 5) are observed. The (3 × 1) structure corresponds to an overlayer with 1 indium atom per overlayer unit cell and an ideal coverage of 0.33 ML. The (1 × 4) structure is interpreted as a slightly distorted In(1 1 1) layer with In [ 1 1 ¯ 0 ] aligned parallel to W[0 0 1] (Nishiyama–Wassermann orientation). The atom density in the (1 × 4) overlayer matches that of a close-packed In(1 1 1) layer within 2%. The (1 × 5) structure is interpreted as a compressed monolayer, where the areal density of In exceeds that of an In(1 1 1) monolayer by 8%. Upon annealing or aging at room temperature the In atoms of the (3 × 1) structure agglomerate into islands with the high-coverage (1 × 4) structure. This transition can also be induced by exposure to oxygen. Obviously oxygen first adsorbs onto the free W(1 1 0) surface and compresses In atoms into densely-packed islands of (1 × 4) periodicity rather than oxidizing the indium adlayer.