Epitaxial Growth of Thin Films

Abstract

This chapter gives an introduction to the epitaxial growth of thin films on solid substrates. The term epitaxy refers to the growth of a crystalline layer on (epi) the surface of a crystalline substrate, where the crystallographic orientation of the substrate surface imposes a crystalline order (taxis) onto the thin film. This implies that film elements can be grown, up to a certain thickness, in crystal structures differing from their bulk. If film and substrate have the same crystal lattices, but different lattice constants, the film will be under strain, that is, it will have a slightly different lattice constant than in its own bulk. Both effects, together with the electronic hybridization at the interface, lead to novel properties.One distinguishes homo-and heteroexpitaxy, where the former refers to the growth on one element on a crystal surface of its own and the latter refers to the more general case, where film and substrate materials are different. Note that the first distinguishes itself from crystal growth, as we will see in more detail later.We start this chapter by giving examples from technology, illustrating where thin epitaxial films are used and outlining potential applications that become reality once we are able to grow the respective thin film sequences. We then contrast thin film and crystal growth, respectively, with kinetics and thermodynamics of growth. We introduce the deposition techniques used in epitaxial thin film growth and then discuss the classical thermodynamic approach, which led to the definition of the growth modes. These modes refer to the morphology taken on by a system grown close to thermodynamic equilibrium. Often films are grown far away from equilibrium and their morphology is determined by kinetics, that is, it is the result of the microscopic path taken by the system during growth. This path is determined by the hierarchy of rates of the single atom, cluster or molecular precursor displacements as compared to the deposition rate. Owing to the importance of kinetics, we focus in the rest of the chapter on the kinetic description of growth. In order to simplify the topic, we start with coverages below one atomic layer that is referred to as a monolayer. The first submonolayer part will be on nucleation, followed by a discussion of island shapes that, very much like snowflakes, tell us about the elementary processes that took place during their formation. We then discuss island coarsening, either by evaporation of atoms from their edges, referred to as the Ostwald ripening, or by the diffusion and subsequent coalescence of entire islands, referred to as the

Tribomechanical Behaviour of TiAlN and CrAlN Coatings Deposited onto AISI H11 with Different Pre-Treatments

“…In this sense, a high influence of the AISI H11 preparation is evidenced on the structure and crystallinity of the TiAlN coatings while it is not on the CrAlN ones, based in XRD observations. This behaviour is attributed to the differences on nucleation due to epitaxial growth influenced by the substrate structure [49]. Additionally, the crystallite size of all the coatings was measured according to the Scherrer equation in the reflections TiAlN (111) and CrAlN (111) using Fe-Kα ( The residual stresses in the coatings were measured using Cr-Kα radiation (see Figure 5).…”

Tailoring atomic layer growth at the liquid-metal interface

“…In view of the fact that the adsorbed helicene on the one hand changes the free energy of the island edge, and on the other hand contributes to the kink formation, it should be considered as a surfactant in island growth 7 , 50 . However, simply inducing and stabilizing kink sites does not suffice to control the size of islands.…”

“…The solution-to-surface and on terrace diffusion of Au atoms stops when they are bound to surface Au atoms/nucleus, and the new aggregate may remain stable, grow larger or decay again. A surfactant may affect the island coalescence via increasing the on-terrace diffusion energy of adatoms 7 . The dependence of island density on the concentration of helicenes (Fig.…”

“…When at least one dimension of a metallic structure approximates the de Broglie wavelength of electrons, energy states of the electrons become discrete and thickness-dependent 1 , 2 . In the last three decades, surface-supported nanostructures comprised of a limited number or a few layers of metal atoms, including two dimensional (2D) metallic islands and ultrathin films, have been the subject of intense study by means of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) 3 – 7 , not only for getting insight into the fundamentals of quantum mechanics 8 – 11 , but also in quest for novel electronic 12 , 13 , magnetic 14 , 15 and catalytic 16 , 17 properties to meet the demands of new and advanced materials. Varying the size and shape of such metallic nanostructures offers a feasible path to modulate their intrinsic properties 18 – 23 , but controlling the growth of metals with dimensions in the order of some angstroms to some nanometres is very challenging.…”

In Situ Observation of Epitaxial Growth during Evaporative Simultaneous Crystallization from Aqueous Electrolytes in Droplets

“…Although advances have been made, there are still several open questions regarding the epitaxial growth in eutonic systems in industrial crystallizers, such as the possible relations between epitaxy and growth conditions. Given the extensive application of epitaxial growth in conductive and semi conductive materials [8,9], the available literature focuses mainly on the growth of epitaxial monolayers or thin films. Epitaxial growth of thin layers commonly uses molecular beam epitaxy, chemical vapor 2 of 17 deposition or liquid-phase epitaxy, under high temperatures and high vacuum [10].…”