Defects in epitaxial multilayers: I. Misfit dislocations*
IBM1
TL;DR: In this paper, it was shown that the interfaces between layers were made up of large coherent areas separated by long straight misfit dislocations and the Burgers vectors were inclined at 45° to (001) and were of type 1/2a.
About: This article is published in Journal of Crystal Growth.The article was published on 1974-12-01. It has received 3179 citations till now. The article focuses on the topics: Partial dislocations & Dislocation.
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TL;DR: In this paper, it is shown that very large stresses may be present in the thin films that comprise integrated circuits and magnetic disks and that these stresses can cause deformation and fracture to occur.
Abstract: The mechanical properties of thin films on substrates are described and studied. It is shown that very large stresses may be present in the thin films that comprise integrated circuits and magnetic disks and that these stresses can cause deformation and fracture to occur. It is argued that the approaches that have proven useful in the study of bulk structural materials can be used to understand the mechanical behavior of thin film materials. Understanding the mechanical properties of thin films on substrates requires an understanding of the stresses in thin film structures as well as a knowledge of the mechanisms by which thin films deform. The fundamentals of these processes are reviewed. For a crystalline film on a nondeformable substrate, a key problem involves the movement of dislocations in the film. An analysis of this problem provides insight into both the formation of misfit dislocations in epitaxial thin films and the high strengths of thin metal films on substrates. It is demonstrated that the kinetics of dislocation motion at high temperatures are expecially important to the understanding of the formation of misfit dislocations in heteroepitaxial structures. The experimental study of mechanical properties of thin films requires the development and use of nontraditional mechanical testing techniques. Some of the techniques that have been developed recently are described. The measurement of substrate curvature by laser scanning is shown to be an effective way of measuring the biaxial stresses in thin films and studying the biaxial deformation properties at elevated temperatures. Submicron indentation testing techniques, which make use of the Nanoindenter, are also reviewed. The mechanical properties that can be studied using this instrument are described, including hardness, elastic modulus, and time-dependent deformation properties. Finally, a new testing technique involving the deflection of microbeam samples of thin film materials made by integrated circuit manufacturing methods is described. It is shown that both elastic and plastic properties of thin film materials can be measured using this technique.
2,347 citations
TL;DR: In this article, the authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices.
Abstract: This review covers important advances in recent years in the physics of thin-film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin-film form. The authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this the review covers the enormous progress that has been made in the first-principles computational approach to understanding ferroelectrics. The authors then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, this review ends with a look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in nonconventional nanoscale geometries.
1,908 citations
TL;DR: This paper is a review of recent progress made in organic thin films grown in ultrahigh vacuum or using other vapor-phase deposition methods and describes the most important work which has been published in this field since the emergence of OMBD in the mid-1980s.
Abstract: During the past decade, enormous progress has been made in growing ultrathin organic films and multilayer structures with a wide range of exciting optoelectronic properties. This progress has been made possible by several important advances in our understanding of organic films and their modes of growth. Perhaps the single most important advance has been the use of ultrahigh vacuum (UHV) as a means to achieve, for the first time, monolayer control over the growth of organic thin films with extremely high chemical purity and structural precision.1-3 Such monolayer control has been possible for many years using well-known techniques such as Langmuir-Blodgett film deposition,4 and more recently, self-assembled monolayers from solution have also been achieved.5 However, ultrahighvacuum growth, sometimes referred to as organic molecular beam deposition (OMBD) or organic molecular beam epitaxy (OMBE), has the advantage of providing both layer thickness control and an atomically clean environment and substrate. When combined with the ability to perform in situ highresolution structural diagnostics of the films as they are being deposited, techniques such as OMBD have provided an entirely new prospect for understanding many of the fundamental structural and optoelectronic properties of ultrathin organic film systems. Since such systems are both of intrinsic as well as practical interest, substantial effort worldwide has been invested in attempting to grow and investigate the properties of such thin-film systems. This paper is a review of recent progress made in organic thin films grown in ultrahigh vacuum or using other vapor-phase deposition methods. We will describe the most important work which has been published in this field since the emergence of OMBD in the mid-1980s. Both the nature of thin-film growth and structural ordering will be discussed, as well as some of the more interesting consequences to the physical properties of such organic thin-film systems will be considered both from a theoretical as well as an experimental viewpoint. Indeed, it will 1793 Chem. Rev. 1997, 97, 1793−1896
1,809 citations
TL;DR: This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.
Abstract: Biaxial compressive strain has been used to markedly enhance the ferroelectric properties of BaTiO 3 thin films. This strain, imposed by coherent epitaxy, can result in a ferroelectric transition temperature nearly 500°C higher and a remanent polarization at least 250% higher than bulk BaTiO 3 single crystals. This work demonstrates a route to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.
1,672 citations
TL;DR: An overview of the state of the art in ferroelectric thin films is presented in this paper, where the authors review applications: micro-systems' applications, applications in high frequency electronics, and memories based on Ferroelectric materials.
Abstract: An overview of the state of art in ferroelectric thin films is presented. First, we review applications: microsystems' applications, applications in high frequency electronics, and memories based on ferroelectric materials. The second section deals with materials, structure (domains, in particular), and size effects. Properties of thin films that are important for applications are then addressed: polarization reversal and properties related to the reliability of ferroelectric memories, piezoelectric nonlinearity of ferroelectric films which is relevant to microsystems' applications, and permittivity and loss in ferroelectric films-important in all applications and essential in high frequency devices. In the context of properties we also discuss nanoscale probing of ferroelectrics. Finally, we comment on two important emerging topics: multiferroic materials and ferroelectric one-dimensional nanostructures. (c) 2006 American Institute of Physics.
1,632 citations
References
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IBM1
TL;DR: The study of superlattices and observations of quantum mechanical effects on a new physical scale may provide a valuable area of investigation in the fieId of semiconductors.
Abstract: We consider a one-dimensional periodic potential, or "superlattice," in monocrystalline semiconductors formbeyd a periodic variation of alloy composition or of impurity density introduced during epitaxial growth. If the period of a superlattice, of the order of 100A, is shorter than the electron mean free path, a series of narrow allowed and forbidden bands is expected duet o the subdivision of the Brillouin zone into a series of minizones. If the scattering time of electrons meets a threshold condition, the combined effect of the narrow energy band and the narrow wave-vector zone makes it possible for electrons to be excited with moderate electric fields to an energy and momentum beyond an inflection point in the E-k relation; this results ina negative differential conductance in the direction of the superlattice. The study of superlattices and observations of quantum mechanical effects on a new physical scale may provide a valuable area of investigation in the fieId of semiconductors.
2,569 citations
TL;DR: In this article, the authors present a calculation of the stresses and energies for interfaces between different crystals, where the difference between the two crystals is expressed in terms of different elastic constants and variable interfacial bondings, and the contribution of the normal forces to the interfacial energies is negligible for the approximation used.
Abstract: This paper presents a calculation of the stresses and energies for interfaces between different crystals. Only simple cases corresponding to interfacial dislocations of pure screw or edge type are treated. The difference between the two crystals is expressed in terms of different elastic constants and variable interfacial bondings. Two kinds of interfacial forces appear: tangential forces with a periodic character and normal forces. The latter are induced by different normal displacements of the two contact surfaces of the crystals due to the equal and opposite tangential interfacial forces and are accounted for by assuming a linear relation between force and relative displacement. By using a periodic parabolic model to represent the periodic potential associated with the tangential forces, it is shown that the contribution of the normal force to the interfacial energies is negligible for the approximation used. When these normal forces are neglected, the Peierls‐Nabarro representation of the interfacial ...
629 citations
TL;DR: In this paper, the Peierls stress is used to explain the elastic strains present in films of germanium on gallium asrenide and explain the reduction of these strains by a high temperature anneal.
Abstract: Misfit dislocations are often transported to the interface between crystals by glide. In materials with the diamond or sphalerite structures, glide is inhibited by the Peierls stress. The aim of this paper is to present a theory for misfit accommodation which includes the effect of the Peierls stress. It is used to explain the elastic strains present in films of germanium on gallium asrenide and to explain the reduction of these strains by a high‐temperature anneal. The strains in germanium on gallium arsenide, and the effect of temperature upon them, are not explained by earlier theories for the accommodation of misfit between one crystal and another.
563 citations
TL;DR: In this article, a shutter was moved between source and substrate so that iron deposits in which there were thickness gradients were obtained, and diffraction patterns from the thin (less than about 20 A) parts of the iron deposits showed that they were face-centred cubic and were strained to exactly match the copper substrates.
Abstract: Iron was deposited at room temperature in ultra-high vacuum (5 × 10−8 Torr) onto single-crystal films of copper oriented with (001) parallel to their plane. A shutter was moved between source and substrate so that iron deposits in which there were thickness gradients were obtained. Transmission electron micrographs and diffraction patterns from the thin (less than about 20 A) parts of the iron deposits showed that they were face-centred cubic and were strained to exactly match the copper substrates. The thicker parts of the deposits contained dislocations to accommodate part of the misfit between face-centred cubic iron and copper. They also contained small nuclei of body-centred cubic iron.
223 citations
TL;DR: In this paper, a pair of single-crystal films in contact and in parallel orientation were prepared by successive evaporation of the film materials in ultra-high vacuum onto the (001) surfaces of hot sodium chloride crystals.
Abstract: Specimens consisting of a pair of single-crystal films in contact and in parallel orientation were prepared by successive evaporation of the film materials in ultra-high vacuum onto the (001) surfaces of hot sodium chloride crystals The combinations of film materials used were gold-palladium, gold-silver and platinum-gold Examination of the specimens by transmission electron microscopy revealed that the difference between the lattice parameters of the pairs of metals was divided between elastic strain and misfit dislocations in approximately the manner predicted by van der Merwe (1963) Most of the 4·6% misfit between a 100 A gold film and its 400 A palladium substrate was accommodated by misfit dislocations The 0·19% misfit between a gold film and its 1500 A silver substrate was entirely taken up by elastic strain until the thickness of the gold reached between 250 A and 300 A When the thickness of the gold film exceeded 250 to 300 A some misfit was accommodated by dislocations that moved by
212 citations