Structure and morphology of Ni monolayers on W(110)

Scanning tunneling microscopy (STM) is employed to investigate the structur al and morphological properties of Ni monolayers (ML) deposited on W(110) a t room temperature. We observe almost perfect layer-by-layer growth for the first three atomic layers. At a coverage of about 6 ML, a transition to th ree-dimensional growth is found. The analysis of STM images in the submonol ayer regime indicates that the coalescence of the islands triggers the form ation of a 8 x 1 coincidence structure. In contrast to the preferential ori entation expected from the twofold symmetric substrate, the islands in the first atomic layer have an irregular shape. Elongated Ni islands are observ ed in the second layer. The anisotropic island shape is ascribed to the ani sotropic diffusion due to anisotropic strain in the underlying first layer. The edges of the Ni islands are oriented along the closed packed [110] dir ections of the growing Ni(111)film for Ni coverages above 5 ML. (C) 1998 El sevier Science B.V. All rights reserved.