Growth Of Large Crystals Research Articles

Growth of large size diamond single crystals by plasma assisted chemical vapour deposition: Recent achievements and remaining challenges

Abstract Diamond is a material with outstanding properties making it particularly suited for high added-value applications such as optical windows, power electronics, radiation detection, quantum information, bio-sensing and many others. Tremendous progresses in its synthesis by microwave plasma assisted chemical vapour deposition have allowed obtaining single crystal optical-grade material with thicknesses of up to a few millimetres. However the requirements in terms of size, purity and crystalline quality are getting more and more difficult to achieve with respect to the forecasted applications, thus pushing the synthesis method to its scientific and technological limits. In this paper, after a short description of the operating principles of the growth technique, the challenges of increasing crystal dimensions both laterally and vertically, decreasing and controlling point and extended defects as well as modulating crystal conductivity by an efficient doping will be detailed before offering some insights into ways to overcome them.

Single-crystal growth of organic semiconductors

Abstract

FEM simulations and experimental studies of the temperature field in a large diamond crystal growth cell

We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method (TGM) at high pressure and high temperature (HPHT). We employ both the finite element method (FEM) and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.

The enhanced photocatalytic and bactericidal activities of carbon microsphere-assisted solvothermally synthesized cocoon-shaped Sn4+-doped ZnO nanoparticles

Cocoon-shaped Sn(4+)-doped ZnO nanoparticles have been synthesized by a solvothermal method using carbon microspheres as a template. The optimum doping level for photocatalysis is 3% (g. atom). Powder X-ray diffractograms show that the ZnO has a primitive hexagonal crystal structure and that doping ZnO with Sn(4+) increases the unit cell lengths and the Zn-O bond lengths. Larger crystal growth along the c-axis is also observed. The measured size of the cocoon-shaped Sn(4+)-doped ZnO nanoparticles is larger than the mean crystallite size. Solid state impedance spectroscopy studies reveal that Sn(4+)-doping increases the charge transfer resistance. Doping does not significantly modify the optical band gap, but does suppress green emission. A decrease in the number of crystal defects due to oxygen vacancies is likely to be a reason for the enhanced photocatalytic properties of the cocoon-shaped Sn(4+)-doped ZnO nanoparticles. Doping ZnO with Sn(4+) enhances the bactericidal activity as well.

Large CuI crystal growth by evaporation technique and its growth mechanism

Based on the negative temperature dependence of CuI solubility in acetonitrile solvent, a novel evaporation technique combined with increasing temperature programming was used to grow CuI crystals. It was found that the nucleation and growth of the CuI crystals can be adjusted by changing the temperature in the evaporation technique and a large transparent CuI single crystal of nearly 1 cm was first grown under a suitable temperature gradient. The growth process of the large CuI crystal in solution was then studied by measuring the evolution of the solute concentration with a spectrophotometer. The suitable temperature and solute concentration for the growth of large CuI crystals were in the range of 50–51.9 °C and 0.050–0.058 mol L−1, respectively. The variation of the CuI crystal growth mechanism at different stages was also discussed. These results could provide a useful clue to further optimize the experimental scheme to grow larger CuI crystals.

Nucleation kinetics, growth, mechanical, thermal and optical characterization of sulphamic acid single crystal

Sulphamic acid (HSO3NH2) is a potential material that exhibits excellent piezoelectric and non-linear optical properties. Nucleation and growth kinetics give valuable information about the crystal growth process, which can be employed in the growth of large size crystals. Thus we have studied its nucleation parameters such as solubility, metastable zone width, induction period, interfacial tension, critical free energy, volume free energy change, critical nucleus and found that good quality sulphamic acid crystal can be grown at low temperature. Growth of good quality crystal was done by adopting slow evaporation solution growth technique at room temperature and as a result, good quality single crystal was grown. The grown bulk single crystal of the title compound was subjected to various characterization analyses. Its unit cell dimensions were confirmed using powder X-ray diffraction. Further its crystalline perfection was assessed using high resolution X-ray diffraction and X-ray topography techniques and it was found that it is reasonably good. Its various functional groups were identified from the Fourier transform-Raman method. Nanoindentation was performed to identify the load dependence and independence of hardness (H) and Young's modulus (E) using the Oliver–Pharr method and it was found that both H and E exhibit peak load dependence. Photopyroelectric study was performed to identify its thermal properties such as thermal diffusivity (α), thermal conductivity (k), thermal effusivity (e), and heat capacity (cp). These studies reveal that it has high thermal stability compared to other single crystals. The optical homogeneity of the grown crystal was assessed using a birefringence interferometer and it was found to be reasonably good.

Growth of large single MOF crystals and effective separation of organic dyes

Through the optimization of synthesis conditions, we obtained large Cu3(BTC)2 crystals with a diameter of 2–4 mm. Such large crystals could be utilized as “chromatographic columns” for effective separation of organic dyes such as thionine (TH) and pyronin B (PB). It was found that the concentration of hydron was the key factor to obtain the large pure crystals. This strategy could be used to grow other hydrophilic MOFs.

Topological semimetal in a Bi-Bi2Se3infinitely adaptive superlattice phase

We report spin- and angle-resolved photoemission studies of a topological semimetal from the infinitely adaptive series between elemental Bi and Bi${}_{2}$Se${}_{3}$. The compound, based on Bi${}_{4}$Se${}_{3}$, is a 1:1 natural superlattice of alternating Bi${}_{2}$ layers and Bi${}_{2}$Se${}_{3}$ layers; the inclusion of S allows the growth of large crystals, with the formula Bi${}_{4}$Se${}_{2.6}$S${}_{0.4}$. The crystals cleave along the interfaces between the Bi${}_{2}$ and Bi${}_{2}$Se${}_{3}$ layers, with the surfaces obtained having alternating Bi or Se termination. The resulting terraces, observed by photoemission electron microscopy, create avenues suitable for the study of one-dimensional topological physics. The electronic structure, determined by spin- and angle-resolved photoemission spectroscopy, shows the existence of a surface state that forms a large, hexagonally shaped Fermi surface around the $\ensuremath{\Gamma}$ point of the surface Brillouin zone, with the spin structure indicating that this material is a topological semimetal.

Successive Electronic Transitions and Anisotropic Properties in a Double-Perovskite SmBaMn2O6Single Crystal

We have succeeded in growth of large high-quality single crystals of SmBaMn 2 O 6 and measured their magnetism and electrical transport properties. The temperature dependence of the magnetization and resistivity exhibits anomalies at ∼375 and ∼200 K. The anomalies accompany hystereses and can be assigned to ordering and rearrangement transitions of charge and orbital of Mn ions, respectively. A broad peak in magnetic susceptibility at 250 K observed for pulverized samples is strongly suppressed in the case of single crystal. Magnetic susceptibility for a magnetic field parallel to the a -axis shows a kink at 175 K, below which a magnetic anisotropy emerges. The result indicates an antiferromagnetic transition of the Mn spin moments below the charge and orbital rearrangement transition, disagreeing with previous studies of polycrystalline samples.

Effect of precursor calcination temperature on the microstructure and thermoelectric properties of Ca3Co4O9 ceramics

Ca3Co4O9 (CCO) powder precursors were prepared by the chemical sol–gel route and calcined at various temperatures between 923 K (CCO-923 K) and 1,073 K (CCO-1,073 K). The calcination temperature was found to be a critical factor affecting the microstructure and thermoelectric properties of CCO ceramic bulk samples. The grain size increases with calcination temperature. The nano-crystals with size about 100 nm in the powders calcined at 923 K promote large crystal growth and texture development during sintering. Bulk pellets made from CCO-923 K powder have large crystal grains, uniform grain size distribution, and a high degree of crystal alignment. By contrast, pellets made from CCO powders at higher calcination temperatures have a bimodal distribution of large and small grains and a large amount of randomly oriented grains. Transmission electron microscopy analysis shows that each crystal grain (identified in SEM images) consists of bundles of CCO nano-lamellas. The nano-lamellas within one bundle share the same c-axis orientation and have fiber texture. The electrical resistivity of CCO-923 K is weakly dependent on operating temperature. Compared to the CCO-1,073 K sample, the CCO-923 K sample has the highest power factor, a lower thermal conductivity, and higher electrical conductivity.

Floating zone growth of large single crystals of [formula omitted

The Fe4+-containing cubic perovskite phase SrFeO3−δ is of interest both for its high-temperature, oxygen-conducting properties as a solid oxide fuel cell component, and at low temperatures, where it exhibits a plethora of helical magnetic phases and a candidate Skyrmion lattice. However, a sequence of structural phase transitions encountered on cooling to room temperature has limited the size of single crystals. We report the floating-zone growth and oxygen-annealing of multiple-cubic-centimetre-sized single crystals of SrFeO3−δ, suitable for inelastic neutron scattering and other measurement techniques requiring large sample volumes.

Two-Step Growth of Large Pentacene Single Crystals Based on Crystallization of Pentacene Monolayer Film

A two-step growth method, namely, initial crystallization from pentacene monolayer grains to nanosized single crystals (nanocrystals) and subsequent physical vapor transport (PVT) growth on the nanocrystals as seeds, is demonstrated to fabricate larger microsized pentacene single crystals. The pentacene monolayer film deposited on a bare SiO2 substrate was found to self-assemble to nanoparticles during a post-annealing process. Selected area electron difffraction demonstrates unambiguously the nanoparticles and the microsized particles grown by the following PVT are both single crystals but with different crystal phases. Such a two-step growth technology maintains the intrinsic interface states between the SiO2 dielectric and the pentacene active layer and provides a more flexible way to in-situ prepare oraganic single crystals for device fabrication. The detailed investigation of morphology evolution and the discussion of formation mechanism of nanocrystal seeds indicate that the pentacene molecular tran...

Vibrational properties of the nonlinear optical crystal β-BaTeMo2O9

We report growth of large single crystals of β-BaTeMo2O9, and single crystal infrared (IR) reflectance spectra as well as polarized Raman spectra for these crystals. Based on these results, the symmetry and LO–TO splitting have been established for the observed modes. We also propose assignment of the observed modes to the respective vibrations of structural units.

Speleothem microstructure/speleothem ontogeny: a review of Western contributions

Mineral ontogeny is the study of the growth and development of mineral deposits in general and, in the present context, speleothems in particular. Previous researchers, mainly in Russia, have developed a nomenclatural hierarchy based on the forms and habits of individual crystals and the assembly of individual crystals into both monomineralic and polymineralic aggregates (i.e. speleothems). Although investigations of the growth processes of speleothems are sparse, there is a large literature on growth processes of speleothem minerals and related crystals in the geochemical and materials science literature. The purpose of the present paper is to sort through the various concepts of crystal growth and attempt to relate these to observations on speleothems and to the Russian conceptual framework of mineral ontogeny. For calcite, the most common mineral in speleothems, the activation energy for two-dimensional nucleation (required for the growth of large single crystals) is almost the same as the activation energy for three-dimensional nucleation (which would result in the growth of many small crystals) Calcite growth is highly sensitive to minor impurities that may poison growth in certain crystallographic directions or may poison growth altogether. Extensive recent research using the atomic force microscope (AFM) provides many details of calcite growth including the transition from growth on screw dislocations to growth by two-dimensional nucleation. The deposition of aragonite speleothems requires additional supersaturation which is usually ascribed to the impurities Mg2+ and Sr2+. AFM studies reveal that Mg2+ poisons calcite growth by blocking deposition sites on dislocations, thus allowing supersaturation to build up past the aragonite solubility curve. Sr2+ precipitates as a Sr-rich nucleus with the aragonite structure which acts as a template for aragonite growth. The different morphology of gypsum speleothems can be explained by the different growth habit of gypsum. Examples of twinned growth, dendrite growth, and spherulitic growth are common in the crystal growth literature and can be used to interpret the corresponding cave forms. Interpretation of monomineralic aggregate growth follows from individual crystal mechanisms. Interpretation of polymineralic aggregate growth requires knowing the evolving chemistry which in turn requires new methods for the sampling and analysis of microliter or nanoliter quantities of fluid.

Process and Crucible Modification for Growth of High Doped 4H-SiC Crystal with Larger Diameter

The present research was focused to investigate various process parameters influenced on the large 4H-SiC crystal growth on a 6H-SiC seed by PVT method. The crucible diameter along horizontal axial direction and inserted graphite ring was modified to change the growth parameter like the temperature gradient. In the initial stage of growth, foreign polytypes such as 6H/4H were observed on 6H-SiC seed, indicating the growth temperature to be unstable on crystal surface. However, from the middle of growth step, 4H-SiC was successfully formed in the ingot with the modification of growth pressure and a SIMS analysis confirmed the high doping concentration in grown 4H-SiC crystal.

Electrocrystallisation of (perylene)2[M(mnt)2] salts

AbstractThe study of the family of compounds α‐(Per)2[M(mnt)2], (M = Cu, Au, Ni, Pd, Pt, Co, Fe) has started more than 30 years ago with the report of first members, but has been always limited by difficulties in the growth of high quality and large single crystals. These compounds can be obtained by oxidation of perylene in the presence of anion salts, either with iodine or electrochemically. The electrocrystallisation, which usually yields better quality crystals than the chemical oxidation route, has however several limitations and it is significantly more difficult to apply to these perylene compounds, which may present different stoichiometries and polymorphs, than to charge transfer salts of many other donors. These difficulties are associated with the low solubility of perylene and the instability of its radical cation in solution. The results of a systematic study to optimise the growth conditions of these compounds by electrocrystallisation and to identify key factors governing the formation of their different phases are presented. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Single crystal Ce doped scintillator material with garnet structure sensitive to gamma ray and neutron radiation

A mixed garnet scintillator host material is obtained from the melt—Yttrium Gadolinium Gallium Aluminum Garnet (YGGAG). In addition to the high thermal and chemical stability and radiation hardness found in garnet crystals, it offers sensitivity to neutrons due to the presence of Gd atoms, has lower melting temperature than yttrium aluminum garnet, and similar crystallization behavior suitable for growth of large volume crystals. Crystals of YGGAG doped with Ce of 10×10×10mm3 have already demonstrated energy resolution of 10% at 662keV.

Development of large size high-purity germanium crystal growth

Growing large diameter (∼15cm) dislocation-free crystals for the GEODM experiment at DUSEL is a challenging task. A crystal of such high purity and large size has never been grown before and the process will require much research and development. In pursuing this goal, we are growing high-purity germanium crystals by the Czochralski method in our laboratory at USD in order to understand the details of the growing process, especially for large diameter crystals. Using a radio frequency (RF) heating method, germanium crystals with two different orientations (along 〈100〉 and 〈111〉) have been grown. The growth characteristics of 〈100〉 crystals have been investigated to understand the impact of the thermal field on the size of the grown crystals. In order to establish the optimal thermal field for growing large high-purity germanium crystals, three different radial thermal fields have been studied. Furthermore, the dislocation density in the grown crystals was measured using an optical microscope and was determined to be about 1×103–4×103/cm2, which falls in the required range for a high-purity germanium detector. X-ray diffraction tests on the surfaces of (100) indicate the grown crystals are of high quality.

Featured issue: zinc oxide

In the first two issues of 2013 we are highlighting fields which are topics of particular current interest in our discipline, as we did in the first two issues of 2012. The February featured papers will be devoted to electronic materials related to Solar Energy Generation and Energy Storage, but in this (January) issue we again highlight the material featured in the February 2012 issue—Zinc Oxide. Reasons for the high interest in this material was outlined in my editorial in the February 2012 issues as follows. While this II–VI semiconductor has been known for many years, the modern appreciation of its potential began in the 1950s, utilising properties such as piezoelectric, luminescent, and UV absorption characteristics, as well as its semiconductor features. The growth of single crystals facilitated the development of devices such as piezoelectric transducers, strain gauges, and pressure sensors, in addition to earlier devices such as varistors. Further work on the growth of large single crystals was stimulated by the potential for lattice matched epitaxial growth of optoelectronic III–V nitrides, but more recently it has become apparent that ZnO might be a good optoelectronic material on its own account, owing to similarities with GaN. Having a similarly wide band-gap, and similar lattice dimensions, the key advantageous feature of ZnO is that it has a free exciton binding energy of 60 meV, more than twice that of GaN. This combination offers the possibility of UV laser action at room temperature, and has given rise to much research to address outstanding problems, including that on doping and thin film growth by several different growth techniques. Further work is also pursuing the potential of ZnO-based dilute magnetic semiconductors in spintronics’. Continued interest in this subject has led to this second Featured issue from papers submitted as regular submissions, and updates the position last year. We hope you will find this issue of interest, and that it will help to guide further work on this important topic.

Physical modeling of heat and mass transfer in large crystal growth by high-temperature horizontal directional crystallization

The conditions of heat and mass transfer in a growth container in horizontally oriented crystallization of refractory oxides are studied by means of physical modeling. It is found that increasing the thickness of the fluid layer has no significant impact on the character and intensity of mass transfer in the near-surface and near-bottom areas, but it contributes to an increase in the width of the central zone, in which the convective mass transfer is substantially limited.