Hybrid observation of crystal growth using laser confocal microscope with atomic force microscope

We built up a hybrid microscope system that consists of an atomic force microscope (AFM) and a laser confocal microscope with differential interference contrast microscope (LCM-DIM) and investigated the combined imaging of a potassium dihydrogen phosphate (KDP) crystal surface and its growth. Using this integrated setup, we were able to approach a AFM cantilever tip to several-ten μm$\mathrm{\mu }\mathrm{m}$ crystals using an optical microscope with AFM and to observe steps with measuring the height using LCM-DIM/AFM. Evaluation of the accuracy of the setup was studied and resulted in less than 100 nm of the AFM tip accuracy using LCM-DIM/AFM. We also demonstrated an in-situ observation of a KDP crystal growth using LCM-DIM/AFM. The interference fringes at the cantilever and the movements of steps were simultaneously observed.     

In‐situ observation of InGaN quantum well decomposition during growth of laser diodes

The deterioration of the InGaN active region of laser diode structures emitting around 440 nm is observed in‐situ during epitaxial growth and analyzed ex‐situ by cathodoluminescence spectroscopy and transmission electron microscopy. The growth conditions of the p‐layers on top of the InGaN active region are found to affect the homogeneity of the InGaN material properties which can be monitored by the in‐situ reflectance signal at 950 nm. The deposition of the p‐layers at 950 °C results in the formation of metallic indium platelets as well as voids changing the refractive index of the active region and thus the reflectance. A reduction of the p‐layer deposition temperature by 30 °C prevents this undesirable decomposition.     

In-situ observation of crystal growth and the mechanism

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 10⁻⁵ nm/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.     

Purification and crystal growth of TlBr for application as a radiation detector

Thallium bromide is a semiconductor compound with high atomic number and density. It has a CsCl‐type simple cubic crystal structure and it is non‐hygroscopics. The TlBr crystals are relatively soft with a knoop hardness number of 12. In this work, the TlBr commercial powder was purified by zone refining and the purest material section was used for crystal growth by Bridgman method. Efforts have been concentrated on the purification of the TlBr. The purification efficiency has been evaluated (NAA and ICP‐MS) by impurities reduction results after zone refining passes. The crystalline quality was evaluated by X‐ray diffraction. The characterized TlBr crystal as a detector has shown good response to gamma radiation. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nondestructive three-dimensional observation of defects in semi-insulating 6H-SiC single-crystal wafers using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST)

Peripheral and central areas of a semi-insulating 6H-SiC single-crystal wafer were examined using a scanning laser microscope (SLM) and infrared light-scattering tomography (IR-LST). The form and density of the defects in each area were observed by SLM. We reconstructed three-dimensional (3D) IR-LST images of scatterers by stacking 2D layer-by-layer IR-LST images on different planes. Using these 3D IR-LST images, variations in the defect distribution with depth were observed for the first time. To study the defect distribution and defect form in detail, we observed the defect configuration in the same volume as for 3D IR-LST images by magnified SLM and merged the images from the two techniques. Information on defects obtained using this approach will be very important in the development of high-quality semi-insulating silicon carbide (SiC) substrates.     

In situ atomic force microscopy of layer-by-layer crystal growth and key growth concepts

Contradictions that have been found recently between the representations of classical theory and experiments on crystal growth from solutions are considered. Experimental data show that the density of kinks is low in many cases as a result of the low rate of their fluctuation generation, the Gibbs-Thomson law is not always applicable in these cases, and there is inconsistency with the Cabrera-Vermilyea model. The theory of growth of non-Kossel crystals, which is to be developed, is illustrated by the analysis of the experimental dependence of the growth rate on the solution stoichiometry.     

Ultra-high-vacuum in situ electron microscopy of growth processes of epitaxial thin films

Extracts from recent results of ultra-high-vacuum in-situ electron microscopy of growth processes of epitaxial thin films are given. As a modified monolayer-by-monolayer mode, the growth process in Fe/(111)Au of the initial Frank-van der Merwe type, followed by the intrinsic γ → α transformation of Fe is mentioned. For the nucleation and growth mode, a systematic selection of epitaxial orientation according to interfacial lattice fitting, nucleation and coalescence features, the validity of Cabrera's suggestion extending Frank and van der Merwe's idea, the cluster mobility and effects of grown-in dislocations in substrate crystals are discussed on the basis of the observations.     

Some features of two commercial softwares for the modeling of bulk crystal growth processes

Two commercial codes, FIDAP and MARC, have been used to model a number of crystal growth processes in collaboration with industrial and research teams. Examples of global and local simulations in the field of heat transfer, hydrodynamics, chemistry and mechanics are given and the results are compared to experimental measurements, with good agreement as a rule. This establishes that such codes can be used to help improve crystal growth processes, while full global transient models still belong to software specifically written in order to model crystal growth. Emphasis is put on the necessity to validate the numerical results by comparison with experiments and to have a clear understanding of the physical laws hidden behind the software.     

Rotating magnetic fields as a means to control the hydrodynamics and heat transfer in single crystal growth processes

The paper discusses a possibility to use different types of rotating magnetic fields (RMF) and combinations of these to control the hydrodynamics and heat/mass transfer in the processes of bulk semiconductor single crystal growth. Some factors contributing to the efficiency of RMF and their influence on different technologies are analyzed. Their specific practical application is illustrated by some examples.     

Numerical simulation of MHD rotator action on hydrodynamics and heat transfer in single crystal growth processes

The article presents the results of the mathematical and physical simulations of the influence of a rotating magnetic field (RMF) on the hydrodynamics and heat transfer in processes of large semiconductor single crystal growth in ampoules. Different versions of the RMF are considered, in particular, for symmetric and asymmetric positions of a RMF inductor with regard to the melt in the ampoule, for two counter-rotating magnetic fields, for different geometrical ratios in the “RMF inductor - liquid melt” system, and for different electrical conductivities of the hard walls at their contact with the melt. The interconnection between the distribution of the electromagnetic forces in the liquid volume and the formed velocity patterns, temperature distribution and shape of the solidification front is studied. An original method for the definition of the electromagnetic forces, which considers finite dimensions of the RMF inductor and melt, was used to calculate real conditions of the RMF influence on growth processes. The numerical results obtained are compared to the data of model experiments. Their satisfactory agreement permits us to propose this calculation method for the definition of the optimal parameters of a growth process under specific conditions and to select the most rational type of RMF influence.     

In‐situ measurements of mass transport rate in vapour growth of hexamethylenetetramine crystal layers

This paper refers to the implementation of a remote optical imaging system suitable for in‐situ mass transport rate measurements in the growth of crystalline layers when grown in closed cylindrical ampoules by a physical vapour transport (PVT) technique. By means of this system, the measurements are carried out by taking photographs, at regular time intervals, of the source material volume as it reduces itself because of mass transfer. After storing the photographs, in real time, in a PC, a suitable software allows to estimate the mass transport rate during the growth process. The authors report here on the detailed setting up of such system when aimed at measuring the growth rate, as it varies with time, of hexamethylenetetramine (HMT, urotropine) crystal layers. A presentation and discussion of the results of these measurements have previously been reported. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The application of scanning microscopy in the study of brittleness in copper and its alloys

Among others the following results were attained: the transcrystalline ductile fracture of copper and some of its alloys resulting from a considerable plastic deformation, with numerous dimples, in the middle of which there usually appear second phase inclusions. — Intercrystalline fracture due to cracks along the grain boundaries may be different, sometimes scarecely to be disguished from the transcrystalline cleavable fracture. It should rank among brittle fracture as its appearance is always characterized by considerable brittleness of the material. Brittleness of copper and its alloys result from precipitations of these phases on the grain boundaries.     

In situ study of the growth and degradation processes in tetragonal lysozyme crystals on a silicon substrate by high-resolution X-ray diffractometry

The results of an in situ study of the growth of tetragonal lysozyme crystals by high-resolution X-ray diffractometry are considered. The crystals are grown by the sitting-drop method on crystalline silicon substrates of different types: both on smooth substrates and substrates with artificial surface-relief structures using graphoepitaxy. The crystals are grown in a special hermetically closed crystallization cell, which enables one to obtain images with an optical microscope and perform in situ X-ray diffraction studies in the course of crystal growth. Measurements for lysozyme crystals were carried out in different stages of the crystallization process, including crystal nucleation and growth, developed crystals, the degradation of the crystal structure, and complete destruction.     

New empirical kinetic equation of size dependent crystal growth and its use

Size dependent crystal growth kinetic can be measured indirectly in Mixed Suspension Mixed Product Removal Crystallizer by means of differential number balance of crystal product population. Some simple formula relating growth rate G and crystal size L is needed for statistical processing of scattered experimental crystal size distribution data. The new exponential formula has been proposed which provides physically realizable values of G at extreme size values. The formula is simple enough to yield analytic solution of the number balance. Methods of estimation of three formula parameters and nucleation rate and examples of experimental data fitting have been presented as well.     

A novel method of temperature control for a crystal growth puller

A facile method to control the contracting rate of the thermal expansible bars for pulling crystal is first suggested. The thermal expansible bars, set in a modified Dewar flask whose vacuum degree is controlled, are heated to designed temperature and then switch off the power to let it cool down at a desired rate, which depends largely on the changeable vacuum degree. This new approach is expected to completely eliminate the effects, which possibly reduces the smooth extent of thermal expansion, caused by the minor temperature fluctuations during crystal growth process and to realize the utmost smooth and slow pulling rate. It is expected to install this apparatus in optical floating zone furnace, instead of traditional motor, to grow peritectic crystal, such as crystal Bi‐2223, since for the peritectic reaction, in principle, the extremely slow growing rate is considerably essential.     

Synthesis, growth and characterization of a new laser upconversion crystal Ba2ErCl7

A modified method to synthesize the new laser upconversion material Ba₂ErCl₇ using Er₂O₃, BaCl₂ 2H₂O and NH₄CI is reported for the first time in this paper. Single crystals up to 5–8mm in diameter and 10–20 mm in length have been grown by Czochralski method. The transmittance spectra of Ba₂ErCl₇ single crystal has first been measured by using an HITACHI U-3500 spectrophotometer. There are three intense absorption peaks ⁴I_9/2⁴I_11/2 and ⁴I_13/2 in the infrared range which can be excited by 803nm, 980nm and 1.5μm laser diodes (LDs), respectively. The cut-off wavelength of the crystal is 230mn. Intense green luminescence can be observed when the crystal is pumped by a ED at 803nm. The formation of the defects is also discussed.     

The precipitation of alkaline-earth metal polymetaphosphate hydrate powders from aqueous solution. Nucleation and crystal growth processes,final precipitate compositions and crystal sizes

The precipitation of barium, strontium, calcium and magnesium polymetaphosphate hydrates was studied from aqueous solutions of initial metal salt concentrations from 0.001 to 3 M at 20 °C; equivalent sodium polymetaphosphate solutions were added to the alkaline-earth metal chloride solutions. Precipitate compositions were determined by chemical analysis, paper chromatography, potentiometric analysis, thermogravimetric and differential thermal analysis and infra-red spectrophotometry; final crystallite morphologies and sizes were studied by scanning electron microscopy and X-ray powder diffraction. Nucleation rates and nucleus numbers (at the end of the induction periods) were very high; crystal numbers varied from 10¹⁴ to 10¹⁵ at the critical concentrations to above 10¹⁷ per 1. solution. Crystal growth rates were also very high and varied as the fourth power of the initial metal salt concentration. High molecular-weight metal polymetaphosphate hydrates were precipitated from the more dilute solutions (0.001 to 0.025 M) while increasing amounts of the more soluble intermediate and low molecular-weight products were precipitated from the more concentrated solutions. Washing with cold water removed the tri- and tetralinear and cyclic phosphate products. The magnesium salts were not precipitated even from 3 M aqueous solutions. The precipitates from aqueous (NaPO₃(I))_n (n = 12) solutions had the compositions (BaP₂O₆ · 2.5 H₂O)₆, (SrP₂O₆ · 3 H₂O)_n and (CaP₂O₆ · 4 H₂O)_n while the magnesium salt precipitate from 20 percent aqueous acetone solution had the composition (MgP₂O₆ · 4 H₂O)_n, the precipitate n values varied from 19 to 13. The precipitates from aqueous (NaPO₃(II))_n (n = 20) solutions contained 0.5n to n additional adsorbed water molecules; these precipitate n values varied in turn from 40 to 26. The final precipitate powders consisted of ‘spherules’ of highly microcrystalline or amorphous polymer glass; the spherule diameters were about 0.2 μm at the critical concentrations and decreased to below 0.05 μm with increasing solution concentrations.     

Computer analysis of regularities of nucleation and crystal growth in a solid

An interplay between the homogeneous nucleation and growth processes during recrystallization and phase first-kind transformation was investigated. Computer simulation taking account of unsteadility of nucleation process and possibility of elimination of potential nucleation sites at a constant growth rate allowed to obtain the time dependence of nucleation rate of the new phase, Ṅ, in the total bulk of a sample. The various kinds of the dependence Ṅ including an increase, a constancy and a decrease are obtained.     

Bulk crystal growth of congruent MgO-doped LiNbO3 crystal with stoichiometric structure and its second-harmonic-generation properties

A new LiNbO₃ bulk crystal has been grown by doping with MgO (cs-MgO:LN; Li₂O:Nb₂O₅:MgO=45.30:50.00:4.70, (Li_0.906Mg_0.047V^Li_0.047)NbO₃), which successfully has the congruent point coinciding with the stoichiometric point. Its second-harmonic-generation (SHG) properties were evaluated. It was found that cs-MgO:LN has a much more homogeneous composition leading to uniform in-plane distribution of the non-critical phase-matching wavelength than the conventional LiNbO₃ crystals such as congruent LiNbO₃ (c-LN), stoichiometric LiNbO₃ (s-LN), and MgO-doped congruent LiNbO₃ (5MgO:LN). This homogeneity arose from the observation that none of the solute components including ionic species were segregated at the interface during growth. The SHG conversion efficiency of cs-MgO:LN is comparable to those of s-LN and 5MgO:LN.     

Computational analysis of three-dimensional flow and mass transfer in a non-standard configuration for growth of a KDP crystal

Computational analysis of three-dimensional flow and mass transfer in a non-standard configuration for growth of a KDP crystal was conducted. The results show that the surface shear stress is mainly affected by the inlet velocity, and the distribution of the surface supersaturation is determined by the bulk supersaturation and the inlet velocity. By adjusting the inlet velocity, the homogeneity of surface supersaturation can be improved, which is helpful for reducing the occurrence of inclusions and enhancing the crystal quality. The thickness of solute boundary layer is closely related to the flow intensity, but it is almost free from the impact of the bulk supersaturation.