Preface

This book is intended to provide information on advances of new knowledge in the different technologies of growing single-crystalline materials to physicists, researchers, and engineers working in the field of crystal growing or applications.

Chapter 1 is an introductory chapter and is devoted to growing and testing W single crystals, which are oriented for single slip and have been tested in dynamical tensile tests at temperatures between 26 and 800 K. Critical shear stress τc at 800 K was not high (τ ≈ 13 MPa), which was consistent with both the high purity and structural quality of tested W specimens. The value of τ down to low T increased very quickly and parabolically. Qualitatively, these results agreed well with type A and type B tests of high-purity Mo single crystals. The measurements also confirmed the existence of three regimes for the dependence of flow stress on temperature for W single crystals.

In Chapter 2 the doping of SiC crystals during sublimation growth and diffusion is presented. The preparation of SiC crystals doped with various impurities introduced during the process of sublimation growth and diffusion is described. Crystals of n- and p-type conductivity with maximum content of electrically active impurities (of the order of 1021 cm−3) are obtained. The solubility values of more than 15 impurities are determined. Special tantalum containers with several temperature zones, allowing the introduction of any impurity into SiC, are developed. The dependence of impurities concentration on temperature, growth rate, and seed orientation are found. Diffusion of impurities of boron, aluminum, gallium, beryllium, lithium, nitrogen, and phosphorus in silicon carbide polytypes is studied. Diffusion coefficients of these impurities in a wide temperature range are determined. Fast-diffusing states are atoms located in interstices, as well as centers, including the impurity atom and point defect. The extremely low diffusion mobility of lattice point atoms in the SiC lattice is noted.

Chapter 3 is devoted to the analysis of the behavior of the profile curves of the melt menisci for sapphire crystal growth by the edge-defined film-fed growth (EFG) technique. The menisci of the shaped crystals with capillary channels, fibers, and tubes (including cases of outer and inner circular menisci) are considered. Also, we investigate the profile curves of menisci in the cases of both positive and negative angles between profile curve and the working edge of the die. The cases of outer and inner circular menisci of the tubular crystals and menisci at capillaries and fibers are considered.

Chapter 4 describes growth of single-crystalline LiNbO3 particles by the aerosolassisted chemical vapor deposition method. Adjusting nucleation conditions, the effective shape and size control in the preparation of single-crystal lithium niobate nanoparticles by the aerosol-assisted chemical vapor deposition method is demonstrated. The effect of the most relevant parameters leading to nanocrystals taking a specific shape or size once they are synthesized is analyzed. This allows us to demonstrate that it is possible to control the size and morphology of particles prepared by adjusting the nucleation conditions. The synthesized nanocrystals

show different morphologies, including quasi-cubic, tetrahedral, polyhedral, and hexagonal shapes, with characteristic sizes ranging from a few tens to a few hundred nanometers. However, rod-like structures with characteristic lengths ranging from 3 to 5 μm are also obtained. Electron microscopy techniques reveal the singlecrystal nature of the synthesized particles.

Chapter 5 presents epitaxial thin film heterostructures, which are critical for integrating multifunctionality on a chip and creating smart structures for next-generation solid-state devices. Here, we discuss the traditional lattice matching epitaxy for small lattice misfit and domain matching epitaxy, which handles epitaxial growth across the misfit scale, where lattice misfit strain is predominant and can be relaxed completely, meaning that only thermal and defect strains remain upon cooling. In low misfit systems, all three sources contribute to the residual strain upon cooling, a result of incomplete lattice relaxation. In the second part of the chapter, we discuss the two critical contributors to the stress of epitaxial film: the thermal coefficient of expansion mismatch and the lattice plane misfit. In the last part of the chapter, the authors focus on unique cases where room temperature epitaxial growth is possible in nitride and oxide thin films.

Chapter 6 discusses the crystallization behavior of fats and oils, which is essential to ensure certain desirable characteristics in a specific industrial application. In recent years, some advances in the structuring of lipid phases have enabled direct influence on food properties. The structuring mechanisms of lipid bases can be classified as either conventional or unconventional. Conventional crystallization mechanisms consist of nucleation, growth, and maturation of the crystals, thus resulting in a crystalline lattice. Co-crystallization or seeding agents and emerging technologies such as ultrasound can be used to aid in crystallization and improve the physical properties of fats and oils. Unconventional mechanisms bring organogel technology as a trend, which consists in the use of self-assembly agents to entrap the liquid oil, resulting in a structured gel network. In this chapter, the formation process of crystalline networks and gel networks is presented in stages, highlighting the main differences related to the mechanisms of formation and stabilization of both types of network.

> **Vadim Glebovsky** Professor, Institute of Solid State Physics, Russian Academy of Sciences, Russia

Section 1

Introduction

1

Section 1 Introduction

Chapter 1

Vadim Glebovsky

integration (VLSI) metallization [2, 3].

1. Introduction

3

Introductory Chapter: Growing

Studying Mechanical Behavior

W Single Crystals by EBFZM for

Tungsten (W) is one of the most perspective metals for different applications of its physical and chemical properties [1]. An incredible complex of diversified natural properties, such as mechanical properties, wear, and radiation resistance, stimulates a wide use of high-purity W single crystals in many modern applications, sometimes like quite unexpected ones, that is, W single crystals as high-resolution STM tips or elements of sputter composite magnetron targets for very-large-scale

Electron-beam floating zone melting technique (EBFZM) is a unique technique

. In

contraindicated to have any contact with any refractory materials. This method is practically indispensable for the melting, refining, and growing of tungsten single crystals. As a result of numerous studies, it was established that the structure of tungsten crystals under the influence of large temperature gradients can differ from ideal. The author and his colleagues dealt with this structural problem for a long time. Single crystals of BCC refractory metals grown from the melt contain a lot of dislocations, so their density in regular samples can be up to 10<sup>5</sup> to 10<sup>7</sup> cm<sup>2</sup>

many studies, it is shown that most of these dislocations aggregate into walls and grids, thus forming a characteristic dislocation substructure [4–6]. This chapter presents the results of the complex studies of the growth and mechanical properties of W single crystal by EBFZM depending on the growth rate, seed perfection, and axial temperature gradients. It seems that single crystals of W are the optimal objects for studying both growth processes and plastic deformation processes. I am confident that the studies presented in this chapter will contribute to further progress in this area. For several years, studies have been conducted in which attempts have been made to find out what prevents the growth of more or less perfect single crystals of W, on the one hand, and, on the other hand, attempts have been made to understand the patterns of plastic deformation of W over a wide temperature range. Because single crystals of high-purity metals like W, Mo, Ta, and Nb, grown from the melt have the dislocation structure, characterized by blocks and boundaries thus, in our opinion, it is more correct to use such words as substructure, subblocks, or sub-boundaries. Several mechanisms for the appearance of dislocations and, accordingly, a characteristic substructure in the process of growing crystals are experimentally investigated before studying the mechanical behavior of W single crystals: under the action of the thermal gradients and mechanical stresses developed at the crystal growth, other factors have no such pronounced influence. An investigation of the impact of a number of technological parameters of EBFZM on the substructure of grown single crystals has been carried out on the newly created growth equipment using fundamentally new electron guns allowing

for the crucibleless melting of such refractory metals as W, when it is

#### Chapter 1
