Growth Of High-quality Crystals Research Articles

Thermal Field Simulation and Optimization of PbF2 Single Crystal Growth by the Bridgman Method

PbF2 single crystals are usually grown in the temperature gradient region by the Bridgman–Stockbarger method. Temperature distribution during the growth process is particularly important for the preparation of high-quality crystals. In this study, the temperature field during the growth of the PbF2 single crystals was simulated based on the finite element method. The temperature distribution and temperature gradient changes in the crucible were investigated at different growth stages, including the seeding, shouldering, and iso-diameters stages. The calculated results show that as the crucible position continues downward during the growth process, the axial temperature gradient increases and then decreases from the bottom to the top of the crucible, with almost flat isotherms near the solid–liquid interface where the axial temperature gradient is larger. At the shoulder below the crucible, the solid–liquid interface was improved by adjusting the tilt angle. Furthermore, based on a novel design of the heat-insulating baffle, the concave solid–liquid interface in the iso-diameter stage can be effectively adjusted to realize a lower radial temperature gradient. This study provides theoretical guidance for the optimization of the growth of high-quality PbF2 crystals by the Bridgman method.

Growth of high-quality langatate crystals by the Czochralski method with elimination of Ga2O3 volatilization

This work successfully grew a high-quality langatate crystal under an air atmosphere using the Czochralski method, effectively eliminating Ga2O3 volatilization.

A flux growth technique for high quality cubic boron arsenide bulk single crystals

The growth of single crystal cubic boron arsenide (c-BAs) has attracted considerable interest due to its high room-temperature thermal conductivity and high ambipolar electrical mobility. However, currently the only growth technique reported for c-BAs crystals is the chemical vapor transport (CVT) method, which exhibits several drawbacks with regard to size scalability and crystal quality control, thereby hindering the further advancement of this semiconductor material. Herein, we report a flux growth technique using liquid arsenic (l-As) as a reaction medium at high pressures for the growth of high-quality c-BAs crystals with several millimeters size. The outstanding properties, including high uniformity, lower defect density, and lower carrier concentration of the as-grown c-BAs single crystals from flux growth, have been verified via a combination of techniques including x-ray diffraction, Raman scattering, photoluminescence spectroscopy, and electrical transport measurements, in comparison with the CVT-grown crystals.

Hexagonal Boron Nitride Seed Layer-Assisted van der Waals Growth of BaSnO3 Perovskite Films.

We have succeeded in obtaining BaSnO3 perovskite thin films with remarkable near-infrared luminescence by van der Waals growth. The films were grown on quartz glass substrates by pulsed laser deposition using hexagonal boron nitride as the seed layer, and their crystallinity was confirmed by X-ray diffraction and cross-sectional transmission electron microscopy. The near-infrared emission of the grown film exhibited a broad emission peak centered at 920 nm. The transparency of the BaSnO3 film (thickness = 1000 nm)/ hexagonal boron nitride /double-sided optically polished quartz glass substrate was approximately 90% at approximately 500 nm with or without the BaSnO3 film. Films showing remarkable near-infrared emission and high transparency obtained by van der Waals-type growth could be used in practical wavelength conversion devices that improve the efficiency of Si single-crystal solar cells. The hexagonal boron nitride seed layer supporting the van der Waals growth is an effective method for high-quality crystal growth of films. It can be used for perovskite-type oxides with many functionalities.

Promising Approach for Rapid Growth of High-Quality SiC Crystals Using Si–Nd–C Solutions

The solution growth method is a promising technology for growing high-quality silicon carbide (SiC) crystals. However, enhancing C solubility in the growth solution is a key issue in the rapid growth of SiC crystals. In this study, Nd was added to a Si–C solution to enhance the solubility of C and rapidly grow high-quality SiC crystals at low temperatures (1823–1923 K). First, high-temperature chemical equilibrium was used to investigate the temperature dependence of the C solubility in a Si–Nd–C solution. The solubility of C in the Si–Nd–C melt was the highest, compared to those of the conventional Si–Cr–C, Si–Fe–C, and Si–Ti–C melts at the same temperature. The initial Si–Nd alloys used for the solution growth of SiC crystals were determined as Si-(25–42 mol %) Nd at 1823 and 1923 K. Thereafter, a temperature difference method was used to grow SiC crystals from Si-35 mol % Nd, Si-35 mol % Cr, Si-35 mol % Ti, and Si-35 mol % Fe solutions at 1923 K with a temperature difference of 36 K. The solutions producing the largest quantity and size of precipitated SiC crystals in the descending order were Si-35 mol % Nd solution > Si-35 mol % Cr solution > Si-35 mol % Fe solution > Si-35 mol % Ti solution (no SiC crystals). After analyzing and comparing the values for the supersaturation (ΔC) and degree of supersaturation (σ), Si–Nd–C solutions show great promise for use in the rapid growth of high-quality SiC crystals at low temperatures.

General Spatial Confinement Recrystallization Method for Rapid Preparation of Thickness-Controllable and Uniform Organic Semiconductor Single Crystals.

Organic semiconductor single crystals (OSSCs) are ideal materials for studying the intrinsic properties of organic semiconductors (OSCs) and constructing high-performance organic field-effect transistors (OFETs). However, there is no general method to rapidly prepare thickness-controllable and uniform single crystals for various OSCs. Here, inspired by the recrystallization (a spontaneous morphological instability phenomenon) of polycrystalline films, a spatial confinement recrystallization (SCR) method is developed to rapidly (even at several second timescales) grow thickness-controllable and uniform OSSCs in a well-controlled way by applying longitudinal pressure to tailor the growth direction of grains in OSCs polycrystalline films. The relationship between growth parameters including the growth time, temperature, longitudinal pressure, and thickness is comprehensively investigated. Remarkably, this method is applicable for various OSCs including insoluble and soluble small molecules and polymers, and can realize the high-quality crystal array growth. The corresponding 50 dinaphtho[2,3-b:2″,3″-f]thieno[3,2-b]thiophene (DNTT) single crystals coplanar OFETs prepared by the same batch have the mobility of 4.1 ± 0.4 cm2 V-1 s-1 , showing excellent uniformity. The overall performance of the method is superior to the reported methods in term of growth rate, generality, thickness controllability, and uniformity, indicating its broad application prospects in organic electronic and optoelectronic devices.

Multi-functional buried interface engineering derived from in-situ-formed 2D perovskites using π-conjugated liquid-crystalline molecule with aggregation-induced emission for efficient and stable NiOx-based inverted perovskite solar cells

The poor and limited-functional NiOx/perovskite buried interface has hindered the development of NiOx-based perovskite solar cells (PSCs). Herein, a π-conjugated liquid-crystalline organic spacer with aggregation-induced emission (AIE), (Z)-2-([1,1′-biphenyl]-4-yl)-3-(4-(3-aminopropoxy)phenyl)acrylonitrile (BPCSA), is employed for the multi-functional NiOx/perovskite buried interface engineering. The functional groups of BPCSA spacer can coordinate with NiOx and induce the in-situ formation of 2D perovskite at the NiOx/perovskite interface. The in-situ-formed 2D perovskite interlayer can passivate interface defects, strengthen interface interconnection and optimize energy level alignment between NiOx and 3D perovskites. More markedly, the π-conjugated liquid-crystalline molecular structure and AIE property of BPCSA spacer can guide the high-quality crystal growth of upper 3D perovskite films, release interfacial strain, facilitate interfacial carrier transport and realize efficient photosensitization process concurrently. Consequently, such 3D/2D PSCs can acquire a champion power conversion efficiency (PCE) of 23.45% with improved stability. Besides, high-performance flexible 3D/2D PSCs are also successfully demonstrated.

High quality crystal growth and characterization of ferroelectric Ba0.77Ca0.23TiO3 single crystal

[Formula: see text][Formula: see text]TiO3 (BCT) single crystal has been widely studied as a promising lead-free ferroelectric material. In this work, high-quality BCT crystal was successfully grown by the Czochralski (CZ) method. The as-grown crystal is crack-free and shows black coloration. It possesses a high dielectric stability over a wide temperature range, while the dielectric loss is rather small below 90[Formula: see text]C. Furthermore, it possesses excellent ferroelectric properties with residual polarization strength ([Formula: see text]) and coercive field ([Formula: see text][Formula: see text]) of 17.93 [Formula: see text]C/cm2 and 8.47 kV/cm, respectively. Besides, BCT crystal shows large electromechanical coupling factors, with [Formula: see text][Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] of 0.535, 0.254, 0.714 and 0.721, respectively. The piezoelectric coefficients [Formula: see text], [Formula: see text] and [Formula: see text] are measured to be − 36.5, 130 and 246 pC/N, respectively.

Pseudohalide-Modulated Crystallization for Efficient Quasi-2D Tin Perovskite Solar Cells with Minimized Voltage Deficit

Regulating the crystallization dynamics and suppressing the oxidation of Sn2+ is imperative for the emerging lead-free tin perovskite solar cells (TPSCs). In this respect, quasi-2D tin perovskites exhibit relatively slow crystallization and crystal growth rate compared to the three-dimensional analogues. However, these dimensional-mixed tin perovskites suffer from random orientation, which limits the charge carrier transport for photovoltaic applications. Herein, we report a facile and feasible strategy to modulate the dimensionality and crystallization of tin perovskites with the incorporation of phenethylammonium thiocyanate (PEASCN), which is exploited to deliver a high-quality crystal growth and preferred alignment. The pseudohalide SCN– can effectively hinder Sn2+ oxidation by synergistically modulating the coordination and crystal growth of Sn perovskite films. Meanwhile, these interactions significantly suppressed the nonradiative charge recombination. Finally, a high efficiency approaching 12.88% with an open-circuit voltage (Voc) of 863 mV is achieved for the inverted TPSCs. The obtained Voc is among the highest reported values for indene-C60 (ICBA)-free TPSC devices. The PEASCN devices also exhibited high stability for over 2000 h under a N2 atmosphere.

Atomic scale insights into the epitaxial growth mechanism of 2D Cr3Te4 on mica.

Two-dimensional (2D) magnetic materials are of wide research interest owing to their promising applications in spintronic devices. Among them, chromium chalcogenide compounds are some of the limited available systems that present both high stability in air and high Curie temperatures. Epitaxial growth techniques based on chemical vapour deposition (CVD) have been demonstrated to be a robust method for growing 2D non-layered chromium chalcogenides. However, the growth mechanism is not well-understood. Here, we demonstrate the epitaxial growth of Cr3Te4 nanoplates with high quality on mica. Atomic-resolution scanning transmission electron microscopy (STEM) imaging reveals that the epitaxial growth is based on nanosized chromium oxide seed particles at the interface of Cr3Te4 and mica. The chromium oxide nanoparticle exhibits a coherent interface with both mica and Cr3Te4 with a lattice mismatch within 3%, suggesting that, as a buffer layer, chromium oxide can release the interfacial strain, and induce the growth of Cr3Te4 although there is a distinct oxygen-content difference between mica and Cr3Te4. This work provides an experimental understanding behind the epitaxial growth of 2D magnetic materials at the atomic scale and facilitates the improvement of their growth procedures for devices with high crystalline quality.

Control of growth interface shape during InGaSb growth by vertical gradient freezing under microgravity, and optimization using machine learning

The growth of high-quality InGaSb crystals by Vertical Gradient Freezing (VGF) under microgravity was numerically simulated. Machine learning tools were used to optimize the growth conditions. The study focuses on controlling growth interface shape which directly affects the quality and homogeneity of the grown crystals. Initially, Bayesian optimization was utilized to search for the most favorable growth conditions that promote a desirable flatter growth interface shape. Afterward, a reinforcement learning model was developed. The system was subjected to a lower temperature gradient near the feed crystal and to crucible rotation with a rate ranging according to the obtained optimal strategy. Results showed that the interface deformation is considerably reduced, and a flatter growth interface could be maintained. The growth rate and solute concentration uniformity were also improved. This adaptive control recipe proves to hold great potential in the continuous and rapid optimization of other crystal growth processes.

Low temperature CVD growth of WSe2 enabled by moisture-assisted defects in the precursor powder

Two-dimensional transition metal dichalcogenides (TMDs) have been proposed for a wide variety of applications, such as neuromorphic computing, flexible field effect transistors, photonics, and solar cells, among others. However, for most of these applications to be feasible, it is necessary to integrate these materials with the current existing silicon technology. Although chemical vapor deposition is a promising method for the growth of high-quality and large-area TMD crystals, the high temperatures necessary for the growth make this technique incompatible with the processes used in the semiconductor industry. Herein, we demonstrate the possibility of low-temperature growth of TMDs, using tungsten selenide (WSe2) as a model, by simply using moisture-assisted defective tungsten oxide (WO3) precursor powders during the growth of these materials. Density functional theory calculations reveal the mechanism by which moisture promotes the defect formation on the precursor crystal structure and how it dictates the reduction of the temperature of the growth. The results were compared with the standard growth at high temperatures and with a precursor mixture with alkali salts to show the high quality of the WSe2 grown at temperatures as low as 550 °C. To conclude, the work improves the understanding of nucleation and growth mechanisms of WSe2 at low temperatures and provides a useful strategy for the growth of TMDs at temperatures required for the back-end-of-line compatibility with current silicon technology.

Multiobjective Optimization of Process Parameters of Silicon Single Crystal Growth

In order to obtain higher quality silicon single crystal, a hybrid strategy for modeling of Czochralski silicon crystal growth and optimizing of process parameters is presented in the paper. The hybrid strategy includes the computational fluid dynamics (CFD) method, neural network of group method of data handing (GMDH), and improved nondominated sorting genetic algorithm II (NSGA-II). The shape variable of solid-liquid interface h and the defect evaluation criteria V / G are set to objective functions according to engineering experience and process requirement. The polynomial of the objective functions is produced by GMDH and CFD. Ultimately, an improved elitist strategy and crowding distance NSGA-II is proposed in the paper to obtain the Pareto optimum solution by the objective functions identified by the GMDH. Compared with other optimization algorithms, the improved NSGA-II can increase the lateral diversity and the uniform distribution of the nondominated solutions. Engineering validation proved that the proposed hybrid strategy can effectively solve the complex uncertain multiobjective optimization problem of system and provides a new method for obtaining high-quality crystal growth process parameters.

Existence of twisting in dislocation-free protein single crystals

The growth of high-quality protein crystals is a prerequisite for the structure analysis of proteins by X-ray diffraction. However, dislocation-free perfect crystals such as silicon and diamond have been so far limited to only two kinds of protein crystals, such as glucose isomerase and ferritin crystals. It is expected that many other high-quality or dislocation-free protein crystals still exhibit some imperfection. The clarification of the cause of imperfection is essential for the improvement of crystallinity. Here, we explore twisting as a cause of the imperfection in high-quality protein crystals of hen egg-white lysozyme crystals with polymorphisms (different crystal forms) by digital X-ray topography with synchrotron radiation. The magnitude of the observed twisting is 10−6 to 10−5°/μm which is more than two orders smaller than 10−3 to 104°/μm in other twisted crystals owing to technique limitations with optical and electron microscopy. Twisting is clearly observed in small crystals or in the initial stage of crystal growth. It is uniformly relaxed with crystal growth and becomes smaller in larger crystals. Twisting is one of main residual defects in high-quality crystals and determines the crystal perfection. Furthermore, it is presumed that the handedness of twisting can be ascribed to the anisotropic interaction of chiral protein molecules associated with asymmetric units in the crystal forms. This mechanism of twisting may correspond to the geometric frustration proposed as a primary mechanism of twisting in molecular crystals. Our finding provides insights for the understanding of growth mechanism and the growth control of high-quality crystals.

Interface stability problem towards the end of THM growth of cadmium zinc telluride crystals

Growth of CdZnTe crystals by Travelling Heater Method (THM) is widely investigated by different groups. Interface shape and stability are critical parameters for the successful growth of high-quality CZT crystals. Even though interface stability could be achieved for a significant portion of the CZT ingot, the situation towards the end of the growth is not well studied and understood. In this study, interface stability and the change of crystal quality towards the end of the growth are examined. The change of the interface shape and formation of large Te inclusions are observed. Moreover, towards the end of the growth, phase separation and formation of a new zinc-based phase are detected with a needle-like structure. The decrease of crystal quality and evolution of the CZT ingot towards the end of the growth are summarized.

High-quality optically defect-free 1D ZnS nanostructures by a modified thermal evaporation method

ZnS has great potential as a valuable material for nanoscale devices because of its rich morphologies and unique structure. Although much effort has been made, the growth of high-quality ZnS crystal is still a challenge. In this paper, high-quality optically defect-free 1D ZnS nanostructures, including nanorods, nanowires, and nanobelts, were successfully synthesized on a large scale by a modified thermal evaporation method. XRD patterns and HRTEM images indicated that the ZnS nanostructures are single phases with hexagonal structures. Under optical excitation, all the ZnS nanostructures show intense UV emissions and almost no defect emissions at room temperature. Sharp UV lasing-like peaks with the FWHM as narrow as 2–3 nm are achieved for the ZnS nanobelts and nanowires. The optical transition from free exciton A, free exciton B, and their associated LO phonon replicas were determined from the evolution of the NBE emissions. These high-quality nanostructures are envisaged to be highly promising for high-efficiency light-emitting devices and lasers in the UV region.

A facile strategy for the growth of high-quality tungsten disulfide crystals mediated by oxygen-deficient oxide precursors.

Chemical vapor deposition (CVD) has been established as a versatile route for the large-scale synthesis of transition metal dichalcogenides, such as tungsten disulfide (WS2). Yet, the precursor composition's role on the CVD process remains largely unknown and remains to be explored. Here, we employ Pulsed Laser Deposition (PLD) in a two-stage approach to tune the oxygen content in the tungsten oxide (WO3-x) precursors and demonstrate the presence of oxygen vacancies in the oxide films leads to a more facile conversion from WO3-x to WS2. Using a joint study based on ab initio density functional theory (DFT) calculations and experimental observations, we unravel that the oxygen vacancies in WO3-x can serve as niches through which sulfur atoms enter the lattice and facilitate an efficient conversion into WS2 crystals. By solely modulating the precursor stoichiometry, the photoluminescence emission of WS2 crystals can be significantly enhanced. Atomic resolution scanning transmission electron microscopy imaging (STEM) reveals that tungsten vacancies are the dominant intrinsic defects in mono- and bilayers WS2. Moreover, bi- and multilayer WS2 crystals derived from oxides with a high V0 content exhibit dominant AA'/AB or AA(A…) stacking orientations. The atomic resolution images reveal local strain buildup in bilayer WS2 due to competing effects of complex grain boundaries. Our study provides means to tune the precursor composition to control the lateral growth of TMDs while revealing insights into the different pathways for forming grain boundaries in bilayer WS2.

Impact of Dysprosium doping on the structural and electrical properties of BiSbTe3 single crystals

Breaking of time reversal symmetry in 3D topological insulators and tuning of Fermi level in the vicinity of the Dirac point is a prerequisite for unravelling various exotic physical phenomena which might be leveraged for potential technological device applications. Here we account effective single crystal growth of (BiSb)2-xDyxTe3 where x = 0, 0.005, 0.05 using modified Bridgman method. The structural, morphological, electrical and Hall measurements were performed on the synthesized single crystals. X-ray Diffraction (XRD) measurements confirmed high quality crystal growth with unidirectional orientation of the synthesized crystals. The lattice parameters were found decreasing with Dysprosium (Dy) doping thereby decreasing the lattice volume,indicating the incorporation of Dy atoms in the lattice of BiSbTe3. Scanning Electron Microscopy (SEM) confirmed the layered morphology of synthesized crystals while Energy Dispersive X-ray Spectroscopy (EDX) measurements revealed the uniform distribution of all the elements as well as stoichiometry of prepared crystals. The resistivity versus temperature (ρ-T) plot from 4 K to 300 K showed metallic behaviour of crystals with an increase in resistivity with Dy doping. The Hall resistivity (ρxy) demonstrates that holes are the predominant charge carriers. The Hall data revealed displacement of Fermi level with Dy doping. These results are indicative to the shift in the Fermi level in the vicinity of the Dirac point.

Ultrafast growth of high-quality large-sized GaSe crystals by liquid metal promoter

Ultrafast growth of high-quality large-sized GaSe crystals by liquid metal promoter

2D growth of high-quality magnetic CuCr2Se4 crystals with a high Curie temperature

Recently, two-dimensional (2D) magnetic materials have attracted broad attention due to their fascinating magnetic behavior and potential application in spintronics. However, most of exfoliated magnetic materials usually show random thickness and size, and the stability in the air is still a challenge. Hence, the controllable synthesis of 2D magnetic materials with good quality should be addressed. Here we report the controllable growth of 2D CuCr2Se4 crystals on mica substrates with large domain size. Most importantly, the as-grown CuCr2Se4 crystals demonstrate obvious ferromagnetic properties, showing a high Curie temperature of up to 436 K. Our discovery of 2D room-temperature ferromagnet CuCr2Se4 provides paves the way for the epitaxial growth of many more 2D magnets and provides a new platform for the spintronic applications.