Epitaxial growth of Ni on MgO(002)1×1: surface interaction vs. multidomain strain relief

Abstract

The growth of Ni films by d.c. magnetron sputtering onto MgO (100) substrates was investigated with the aim of producing epitaxial smooth Ni layers for magnetic multilayer applications. Growth temperatures ranging from 20 to 700°C for 200 nm thick Ni films were examined. At a reduced temperature, 20°C, a complex texture dominated by 〈022〉 orientated grains co-existing with 〈14̄1〉 and traces of 〈002〉 texture was obtained. However, at 100–200°C, smooth, single-crystal layers with a complete 〈200〉 texture were obtained, as demonstrated by analyses of {200}, {2 2 0} and {111} X-ray diffraction pole figures. All higher deposition temperatures produced a 〈751̄〉 texture that was fourfold degenerate and twinned that gradually became better defined at higher temperatures. This change in texture also marked a transition to a faceted surface, as shown by atomic force microscopy (AFM). The increase in deposition temperature between samples allows the initially nucleated Ni islands to rearrange to the 〈002〉 texture. However, at even higher temperatures, the mobility of the Ni atoms is higher, and thus, the Ni can rearrange further and grow with a 〈751̄〉 texture. This texture accommodates both the strong Ni metal–metal bonds, as well as placing each interfacial Ni atom in such a position that a minimal mismatch between the two crystal lattices occurs. Thus, the (75̄1) plane Ni atoms can be said to form a c(3×1) surface lattice on the MgO surface. The surface feature size, extracted from the measurements of the power spectral density, and surface roughness both showed increased values by an order of magnitude as the crystallographic orientation changed from being single 〈002〉 to multiple 〈751̄〉 domained.