Progress in Crystal Growth and Characterization of Materials最新文献

Nucleation and growth of crystals is a pervasive phenomenon in the synthesis of man-made materials, as well as mineral formation within geochemical and biological environments. Over the past two decades, numerous ex situ studies of crystallization have concluded that nucleation and growth pathways are more complex than envisioned within classical models. The recent development of in situ liquid phase TEM (LP-TEM) has led to new insights into such pathways by enabling direct, real-time observations of nucleation and growth events. Here we report results from LP-TEM studies of Au nanoparticle, CaCO₃ and iron oxide formation. We show how these in situ data can be used to obtain direct evidence for the mechanisms underlying crystallization, as well as dynamic information that provides constraints on important kinetic and thermodynamic parameters not available through ex situ methods.

An overview of the important defect types, their origins and interactions during the bulk crystal growth from the melt and selected epitaxial processes is given. The equilibrium and nonequilibrium thermodynamics, kinetics and interaction principles are considered as driving forces of defect generation, incorporation and assembling. Results of modeling and practical in situ control are presented. Strong emphasis is given to semiconductor crystal growth since it is from this class of materials that most has been first learned, the resulting knowledge then having been applied to other classes of material. The treatment starts with melt-structure considerations and zero-dimensional defect types, i.e. native and extrinsic point defects. Their generation and incorporation mechanisms are discussed. Micro- and macro-segregation phenomena – striations and the effect of constitutional supercooling – are added. Dislocations and their patterning are discussed next. The role of high-temperature dislocation dynamics for collective interactions, like cell structuring and bunching, is specified. Additionally, some features of epitaxial dislocation kinetics and engineering are illustrated. Next the grain boundary formation mechanisms, such as dynamic polygonization and interface instabilities, are discussed. The interplay between facets, inhomogeneous dopant incorporations and twinning is shown. Finally, second phase precipitation and inclusion trapping are discussed. The importance of in situ stoichiometry control is underlined. Generally, selected measures of defect engineering are given at the end of each sub-chapter.

The semiconductors formed from group 13 metals and from group 15 anions, referred to as the III-V semiconductors, have found use in a broad range of technologies. Their versatility arises from the wide range of optical and electronic properties accessed through the formation of multi-component alloys. These alloys can be synthesized using the epitaxial growth techniques for devices consisting of several-to-hundreds of highly controlled individual layers monolithically formed into a nearly defect-free structure. This ability to design and fabricate such detailed structures, whose dimensions can be at the nanometer scale, has been driven by an understanding of the crystal growth and materials technology. The paper introduces key features of these materials, their materials science and crystal growth.

The course focuses on the polymorphism and polymorphic transformation of edible fat crystals, such as chocolate. The morphology, crystallization behavior and polymorphic transformation will be observed under optical microscopy, and melting point of each polymorph will be determined.

This paper focuses on the recent developments in Czochralski (CZ) crystal growth of silicon for large-scale integrated circuits (LSIs) and multi-crystalline silicon growth using a directional solidification method for solar cells. Growth of silicon crystals by the CZ method currently allows the growth of high-quality crystals that satisfy the device requirements of LSIs or power devices for electric cars. This paper covers how to obtain high-quality crystals with low impurity content and few point defects. It also covers the directional solidification method, which yields crystals with medium conversion efficiency for photovoltaic applications. We discuss the defects and impurities that degrade the efficiency and the steps to overcome these problems.

To understand what entropy is, thermodynamical entropy was derived from Boltzmann's entropy formula. After defining the Helmholtz and the Gibbs free energies, we calculated the formation Gibbs free energies of an equilibrium and a non-equilibrium nucleus following Toschev's approach taking a water droplet as an example. It is demonstrated that the Gibbs free energy for the formation of a cluster takes the maximum as the cluster radius is increased. The cluster at this maximum is called critical nucleus.

Thermodynamics is also a useful tool to obtain the rate of crystal growth in a vapor phase. The partial pressures of all gaseous species are calculated by solving equations given by the law of mass action and the initial conditions. The mathematical formulas to give the growth rates in a closed tube and in a gas flow system are derived.

Beyond fundamental aspects of crystal growth and morphology, the growth of minerals is a challenging subject because in most cases we face a problem with unknown growth conditions. Actually, in the field of geological studies, we have to decipher the growth conditions of a crystal using the information contained in the very crystal. One of these characteristics of crystals that contain information about their growth is their morphology and time evolution. In this article, we introduce the subject of crystal morphology by using three important minerals, calcite, halite and gypsum, as three didactic case studies to illustrate the application of the current knowledge in the field.

Nucleation is an important step in crystallization, and many self-organized patterns are determined in this process. In this study, after briefly reviewing the fundamentals of nucleation theory, we take a few examples to show the significance of concave-corner-mediated nucleation in both self-organized formation of long-range-ordered patterns and in self-assembly of metallic nano wire array. We show that successive concave-corner-mediated nucleation on the growth front is an important mechanism leading to many long-range ordering effects in crystallization. This mechanism can also be applied in fabricating metallic nano wires with specific geometry, including straight metallic wire array with tunable line width and nanowires with periodic structures.

Fluid dynamics are important in processes that grow large crystals from a liquid phase. This paper presents a primer on fluid mechanics and convection, followed by a discussion of the physics and scaling of flows in such processes. Specific examples of fluid flows in crystal growth systems are presented and classified according to their impact on outcomes, good or bad. Turbulence in crystal growth is discussed within the limited extent of our understanding, which is incomplete, or ugly.

Crystal growth occurs at the interface of a crystal and its growth medium. Due to the abrupt termination at the surface, at the interface the properties of the crystal will typically deviate from the bulk and this can affect the growth behaviour. Also the properties of the growth medium at the interface will typically differ from the bulk. In growth from solution, for example, the liquid will show ordering induced by the crystal surface or have a different composition. Here techniques to study such growth interfaces will be discussed together with examples of the effect that the properties of the interface can have on the growth.