Computer modelling of nanoscale diffusion phenomena at epitaxial interfaces

Abstract

Abstract. The present study outlines an important area in the application of computer modelling to interface phenomena. Being relevant to the fundamental physical problem of competing atomic interactions in systems with reduced dimensionality, these phenomena attract special academic attention. On the other hand, from a technological point of view, detailed knowledge of the fine atomic structure of surfaces and interfaces correlates with a large number of practical problems in materials science. Typical examples are formation of nanoscale surface patterns, two-dimensional superlattices, atomic intermixing at an epitaxial interface, atomic transport phenomena, structure and stability of quantum wires on surfaces. We discuss here a variety of diffusion mechanisms that control surface-confined atomic exchange, formation of alloyed atomic stripes and islands, relaxation of pure and alloyed atomic terraces, diffusion of clusters and their stability in an external field. The computational model refines important details of diffusion of adatoms and clusters accounting for the energy barriers at specific atomic sites: smooth domains, terraces, steps and kinks. The diffusion kinetics, integrity and decomposition of atomic islands in an external field are considered in detail and assigned to specific energy regions depending on the cluster stability in mass transport processes. The presented ensemble of diffusion scenarios opens a way for nanoscale surface design towards regular atomic interface patterns with exotic physical features.

Atomic Scale Design, Structure and Stability of Quantum Nanowires Located on Epitaxial Interfaces and Free‐Standing in Space

“…This is clearly seen in Figure b, where the density of defects initiating the nanowire rupture is higher compared to nanowire with the B‐type initial ordering, Figure b. Let us note that in the vicinity of these defects, both A‐ and B‐type nanowires develop a twisted atomic arrangement which propagates over their entire length at a later stage . Similar helical nanowire structures have been observed in real physical experiments and molecular dynamic simulations as well …”

“…The simulation results for a thick nanowire at 200 K reveal much longer mean lifetime, 5.72 × 10 4 MCS, compared to the lifetime of a monatomic free‐standing nanowire which disintegrates immediately at the same temperature. At low values T , in the region of 10 K, the 1D nanowire has a mean lifetime of about 2.0 × 10 3 MCS, while the 3D nanowire is practically unbreakable up to the time limit of the simulation experiment (5.0 × 10 7 MCS) . We have also observed a lifetime enhancement of 3D free‐standing nanowire as a result of reduced attractive atomic interactions.…”

“…This transition has a strong impact on the nanowire lifetime and thermal stability. It is important to stress that the stabilization effect resulting from enhanced nanowire flexibility is valid in the case of 1D nanowire on homo‐ and heteroepitaxial interfaces, and 3D free‐standing nanowire, too …”

“…What is the relation between thermodynamic properties, fine atomic structure, and atomic ordering which determine the peculiar electronic properties of the nanowires? Making an attempt to unravel some of these complex questions, we give in the present paper a general overeview of our recently published results, extended by new findings and interpretation of thermal instability, spontaneous breakdown, and complete disintegration of metal nanowires . Introducing a new atomistic physical model via multi‐step hole‐mediated mechanism of nanowire rupture, we discuss in detail important structural properties, morphological shape, geometry, and rupture kinetics of four general types of nanowires: 1) one‐dimensional (1D) monatomic nanowires; 2) two‐dimensional (2D) flat nanowires located on epitaxial interfaces; 3) 1D nanowires free‐standing in space; and 4) three‐dimensional (3D) nanowires free‐standing in space, Figure .…”