Morphology of Ni ultrathin films on Mo(110) and W(100) studied by LEED and STM

[摘要] The morphology of ultrathin Ni films on Mo(110) and W(100) has been studied by low-energy electron diffraction and scanning tunneling microscopy. Ni films grow pseudomorphically on Mo(110) at 300 K for a coverage of 0. 15 ML. A (8 x 1) structure is found at 0.4 ML, which develops into a (7 x 1) structure by 0.8 ML. The film undergoes a structural change to fcc Ni(111) at 6 ML. The growth mode switches from layer-by-layer to Stranski-Krastanov between 4 ML and 6 ML. Annealing at around 850 K results in alloying of submonolayer films with the substrate, while for higher coverages the Ni agglomerates into nanowedge islands. Ni films grow pseudomorphically on W(I 00) up to a coverage of around 2 ML at 300 K, above which there is a structural change from bcc to hcp Ni with the epitaxial relationship (11 (2) over bar0)(Ni)parallel to(100)(w). This is accompanied by the formation of orthogonal domains of uniaxial strain-relieving dislocations from the third layer of the film. For coverages up to I ML the growth proceeds by formation of two-dimensional islands, but shifts to three-dimensional growth by 2 ML with rectangular islands aligned along the < 011 > substrate directions. Annealing at around 550 K results in agglomeration of Ni into larger islands and increasing film roughness. (c) 2007 Elsevier B.V. All rights reserved.

[发布日期] 2007-12-01

[关键词] scanning tunneling microscopy;molybdenum;tungsten;nickel;epitaxy