Progress in Crystal Growth and Characterization of Materials最新文献

The aim of this lecture is to provide an overview on solid-state wetting, starting from basic concepts, and introducing the useful mathematical paraphernalia. We review and discuss the similarities and the differences between liquid-state and solid-state wetting. Then, we show how wetting concepts provide tools to understand the morphology and stability of solid-state thin films and nano-islands.

In this review article, we address key material parameters as well as the fabrication and application of crystalline GeSn binary and SiGeSn ternary alloys. Here, the transition from an indirect to a fundamental direct bandgap material will be discussed. The main emphasis, however, is put on the Si–Ge–Sn epitaxy. The low solid solubility of α-Sn in Ge and Si of below 1 at.% along with the large lattice mismatch between α-Sn (6.489 Å) and Ge (5.646 Å) or Si (5.431 Å) of about 15% and 20%, respectively, requires non-equilibrium growth processes. The most commonly used approaches, i.e. molecular beam epitaxy (MBE) and chemical vapor deposition (CVD), will be reviewed in terms of crucial process parameters, structural as well as optical quality and employed precursor combinations including Germanium hydrides, Silicon hydrides and a variety of Sn compounds like SnD₄, SnCl₄ or C₆H₅SnD₃. Special attention is devoted to the growth temperature window and growth rates being the most important growth parameters concerning the substitutional incorporation of Sn atoms into the Ge diamond lattice. Furthermore, the mainly CVD-driven epitaxy of high quality SiGeSn ternary alloys, allowing the decoupling of band engineering and lattice constant, is presented. Since achieving fundamental direct bandgap Sn-based materials strongly depends on the applied strain within the epilayers, ways to control and modify the strain are shown, especially the plastic strain relaxation of (Si)GeSn layers grown on Ge.

Based on recently achieved improvements of the crystalline quality, novel low power and high mobility GeSn electronic and photonic devices have been developed and are reviewed in this paper. The use of GeSn as optically active gain or channel material with its lower and potentially direct bandgap compared to fundamentally indirect Ge (0.66 eV) and Si (1.12 eV) provides a viable solution to overcome the obstacles in both fields photonics and electronics. Moreover, the epitaxial growth of Sn-based semiconductors using CMOS compatible substrates on the road toward a monolithically integrated and efficient group IV light emitter is presented.

III/V semiconductors with cubic zinc-blende crystal structure, for example GaAs, GaP or InP, become metastable if atoms with significantly smaller or larger covalent radius than the matrix atoms are alloyed. Examples are the incorporation of Boron, Nitrogen and Bismuth in the above-mentioned materials. The resulting multinary compound semiconductors, like for example (Ga,In)(N,As), Ga(N,As,P) and Ga(As,Bi), are extremely interesting for several novel applications. The growth conditions, however, have to be adopted to the metastability of the material systems. In addition, structure formation can occur which is different from stable materials. This paper summarizes our current knowledge on growth characteristics of several metastable materials. Mainly examples for Metal Organic Vapor Phase Epitaxy (MOVPE) are given. The MOVPE growth characteristics are compared to selected examples using Molecular Beam Epitaxy growth to highlight that the observed growth characteristics are intrinsic for the studied metastable material systems. Furthermore, structural peculiarities of dilute borides, nitrides and bismides occurring during growth as well as in growth interruptions are summarized and correlated to the growth conditions.

This report centers on different modern chemical synthesis methods suitable for production with which low-dimensional crystalline structures are attainable in the Ge–Sb–Te material system. The general characteristics of the methods are described first. The special challenges are discussed for the Ge–Sb–Te material system. Growth optimization is studied, and the resulting nanostructures are presented. At last a comparison of the methods is given with respect to research scale vapor transport approach on the one hand and the potential described for future application in technology on the other hand.

The rapid advance in superconducting magnet technology enables more and more applications for the use of high magnetic fields in scientific researches and industrial manufacturing. These applications include material processing, separation, chemical reaction, nuclear fusion, high energy physics, and many more. Generally, a superconducting magnet provides both homogeneous and inhomogeneous magnetic fields simultaneously, and both can affect the samples in the field so that the magnetic field can be utilized for various purposes. A homogeneous or inhomogeneous magnetic field will exert a torque on suspending particles in a solution if the particles have anisotropic magnetic susceptibility, which will further influence the properties of the solution; in an inhomogeneous magnetic field, a repulsive force will act on a diamagnetic solution so that the levels of apparent or effective gravity of the solution can be tuned in a vertical magnetic field. These effects can be utilized to govern the physical and chemical processes in solution like crystallization. In recent years, high magnetic fields have been applied in protein crystallization. It was found that a magnetic field can align the crystals along the field direction, decrease the diffusivity of macromolecules in the solution, and increase the viscosity of the solution; a suitable inhomogeneous magnetic field can damp the natural convection substantially, which resembles the case in a space environment. Both homogeneous and inhomogeneous magnetic fields have been found to improve the quality of some protein crystals. These discoveries showed that the researches on protein crystallization in high magnetic field is potentially valuable, because obtaining high quality protein crystals is important for 3-dimensional structure determination of proteins using X ray crystallography. This paper will review the background and more recent progress and discuss the future perspectives in this research field.

A powder-bed 3D printer (3DP) is investigated to fabricate porous titanium components. The titanium material was 3D printed and subsequently post-processed by thermal debinding and sintering. Characterization work was carried out to investigate the effects of sintering temperature on the internal porosity profile and shrinkage of 3D printed titanium components, the effects of different binder content on the overall shape of the pre-designed porous components and the effects of post-processing debinding profiles on the titanium components.