Progress in Crystal Growth and Characterization of Materials最新文献

Heusler compounds are a large group of intermetallic compounds with over 1000 members with similar crystal structures having a vast array of tunable properties. These properties depend on the number of valence electrons per formula unit allowing tuning of properties through composition and alloying. The Heusler lattice parameters span many metal oxides and semiconductors and their crystal structures are closely related. For spintronic applications, the magnetic and half-metallic properties, in particular, are of great interest. In this paper the electronic and magnetic properties of Heusler compounds are discussed as well as the importance of composition and defect control on tailoring their properties. Examples of applications include the great success of Heusler magnetic tunnel junction in metallic spintronic devices. The potential of going beyond metallic spintronics to the integration of Heusler compounds with III–V semiconductors for semiconductor spintronics device physics and technology, the tuning of magnetic properties, and the fabrication of Heusler compound heterostructures and superlattices are also discussed.

Graphene and related two-dimensional (2D) materials are attracting huge attention due to their wide-range potential applications. Because large-scale, high-quality 2D crystals are prerequisites for many of the applications, crystal growth of 2D materials has been intensively studied. We have also been conducting research to understand the growth mechanism of 2D materials and have been developing growth techniques of high-quality materials based on the understandings, in which detailed structural characterizations using low-energy electron microscopy (LEEM) have played essential roles. In this paper, we explain the principles of obtaining various structural features using LEEM, and then we review the status of our current understanding on the growth of graphene and hexagonal boron nitride.

Diamond has been used as cutting tools, and also has recently attracted extensive attention as a semiconductor. In the review, its properties and prospects of its electronic devices are shown. Then, principles of crystal growth methods, such as high-pressure, high-temperature (HPHT) and chemical vapor deposition (CVD) methods, are described. Next, current understanding of defects such as dislocations and stacking faults is described. Further, for the future electronic applications, the present status of wafer technology and impurity doping are described. Finally, the electronic devices made of diamond semiconductors are shown.

This paper presents the outline of a practical course on computer simulation that will be given at the 16th International Summer School on Crystal Growth (ISSCG-16). The aim of this course is to understand crystal growth processes from the molecular level to the macroscopic level through computer simulations. We will mainly study molecular-scale crystal growth and nucleation processes by using molecular dynamics simulations and macroscopic growth processes at crystal surfaces by using phase field simulations.

Protein crystal nucleation is a central problem in biological crystallography and other areas of science, technology, and medicine. Recent studies have demonstrated that protein crystal nuclei form within crucial precursors. Data for several proteins provided by these methods have demonstrated that the nucleation precursors are clusters consisting of protein dense liquid, which are metastable with respect to the host protein solution. The clusters are several hundred nanometers in size, they occupy from 10⁻⁷ to 10⁻³ of the solution volume, and their properties in solutions supersaturated with respect to crystals are similar to those in homogeneous, i.e., undersaturated, solutions. The clusters exist due to the conformation flexibility of the protein molecules, leading to the exposure of hydrophobic surfaces and enhanced intermolecular binding. These results indicate that protein conformational flexibility might be the mechanism behind the metastable mesoscopic clusters and crystal nucleation. The investigations of the cluster properties are still in their infancy. Results on direct imaging of cluster behaviors and characterization of cluster mechanisms with a variety of proteins will soon lead to major breakthroughs in protein biophysics.

The spatial and time resolution in the measurements of growth rates and the observation of surface morphologies and the associated transport phenomena reflecting their growth mechanism have been developed because advanced microscopes and interferometers have attained nano-scale resolution. The first part covers the historical background how in-situ observation of crystal growth at molecular-level by optical and other scanning methods had been developed for understanding of crystal growth by measuring crystal growth rates and by observing surface nano-topographies, such as growth steps and spiral hillocks, with the same vertical resolutions comparable to that of the scanning probe microscopic techniques. The potential of recently developed interferometric techniques, such as Phase-Shift Interferometry (PSI) is then reviewed with the principle of the optics. Capability of measuring growth rates of crystals as low as 10⁻⁵nm/s (1 µm/year) is introduced. Second part of the article emphasizes basic interferometric technique for the understanding of crystal growth mechanism by measuring growth rate vs supersaturation. Utilization of these techniques not only in fundamental crystal growth fields but also in environmental sciences, space sciences and crystallization in microgravity would briefly be introduced. At the end, we select a few examples how growth mechanism was analyzed based on these kinetic measurements.

In this experimental course, attendees will learn how to obtain useful information about growth processes of crystals using ordinary optical microscopes, which are usually available in laboratories. We will demonstrate how thicknesses of crystals can be estimated from interference colors. We will also show in-situ observations of spiral steps and strain distributions by differential interference contrast microscopy and polarizing microscopy, respectively.

Silicon carbide (SiC) is a wide bandgap semiconductor having high critical electric field strength, making it especially attractive for high-power and high-temperature devices. Recent development of SiC devices relies on rapid progress in bulk and epitaxial growth technology of high-quality SiC crystals. At present, the standard technique for SiC bulk growth is the seeded sublimation method. In spite of difficulties in the growth at very high temperature above 2300 °C, 150-mm-diameter SiC wafers are currently produced. Through extensive growth simulation studies and minimizing thermal stress during sublimation growth, the dislocation density of SiC wafers has been reduced to 3000–5000 cm⁻² or lower. Homoepitaxial growth of SiC by chemical vapor deposition has shown remarkable progress, with polytype replication and wide range control of doping densities (10¹⁴–10¹⁹ cm⁻³) in both n- and p-type materials, which was achieved using step-flow growth and controlling the C/Si ratio, respectively. Types and structures of major extended and point defects in SiC epitaxial layers have been investigated, and basic phenomena of defect generation and reduction during SiC epitaxy have been clarified. In this paper, the fundamental aspects and technological developments involved in SiC bulk and homoepitaxial growth are reviewed.

Microchannel epitaxy (MCE) is an outstanding technique for dislocation reduction during heteroepitaxial growth when there is a large lattice mismatch. This paper describes the MCE mechanism in detail together with experimental results. Directional growth is a principal concern of MCE, and is enabled through the assessment and control of the elementary processes of crystal growth. Vertical microchannel epitaxy (V-MCE) involves perpendicular growth relative to a substrate, from microchannels established as openings in a mask, while horizontal microchannel epitaxy (H-MCE) is growth parallel to the substrate surface. Even if many dislocations are present in the microchannels, directional growth vastly reduces their number in the grown crystal. MCE is beneficial for the fabrication of devices, as well as the quantitative study of the fundamental processes involved in crystal growth. This paper quantitatively discusses the growth mechanism involved in H-MCE of GaAs in the thickness direction. Fitting the forms of spiral steps observed on flat surfaces at an atomic level enables the accurate derivation of surface supersaturation at the time of growth. Moreover, since a simple mechanism for controlling growth in the vertical direction can be established for H-MCE with a single step source, quantitative discussion of crystal-growth mechanisms is now possible.

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.