Asymmetric coherent tilt boundaries formed by molecular beam epitaxy

Abstract

We describe a novel system inwhich low-angle, asymmetric tilt boundaries organise spontaneously under conditions of molecular beam epitaxial growth. In the cases studied, the (1072) surfaces of hexagonal rare earths grow coherently but tilted on the (21 1) surfaces of BCC transition metals. The main driving forces are interfacial coherency and the relief of long-range epitaxial strain.

Morphology and microstructure of epitaxial Cu(001) films grown by primary ion deposition on Si and Ge substrates

“…The formation of asymmetric tilt boundaries during growth has previously been reported for close packed metals deposited on bcc substrates 29,30 and during the relaxation of strained SiGe alloys. 28 In these studies, a single direction was observed for the tilted layer, in a direction opposite to the substrate miscut angle.…”

“…These dislocations can be decomposed into three components: an edge component that relieves the misfit strain, a screw component that produces a rotation of the Cu crystal in the plane of the Ge substrate, and a ''tilt'' component that rotates the Cu crystal out of the plane of the substrate. 28,29 In the ideal situation, where long- range stresses are eliminated by the formation of the tilt boundary, we expect a tilt of the Cu͑001͒ axis away from the Ge͑001͒ toward the Cu͗111͘ direction by approximately &⑀ radians and a rotation of Cu͑001͒ in the plane of the film by ⑀ radians where ⑀ is the lattice mismatch between Cu͑001͒ and the surface unit cell of Ge͑001͒, ⑀ϭ0.10. The observed tilt is in reasonable agreement with this simple model, although we do not observe discrete rotations of the crystals, only a distribution of film texture about the ͗111͘ directions.…”

Annealing effects on (0 0 1) Ni films grown on MgO

“…2.1 nm). Another possibility for the observed reconstruction could be the formation of an asymmetric, coherent tilt boundary [14] as has been observed in other systems or even miss-cut of the MgO surface. Some authors have reported surface nano-patterning with formation of nano-wires attributed to substrate miss-cut when annealing sub-monolayers of Fe epitaxially grown on W substrates [15].…”

Strains and rotations in thin deposited films

“…One example of each of the three interface types in figure 2 substrates [14]. Very thin films were observed by X-ray diffraction to be homogeneously strained to be commensurate with the substrate, but this coherency strain was relieved in thicker deposits.…”

“…Rigid body rotations of hetero-epitaxial films away from the nominal orientation relationship were first reported by Igarishi in 1971 [6]: he attributed the rotations to dislocations in the interface with Burgers vector components inclined to the interface, thereby producing a small-angle tilt wall superposed on an underlying misfit array. Since that time numerous observations of rotated films have been reported and their consequences discussed [7][8][9][10][11][12][13][14][15]. This paper focuses on two aspects of coherency strains and rotations in a thin film, B, deposited on a substrate A: characteristic distances and partitioning.…”