Gallium oxide is one of the most promising ultra-wide bandgap materials among the contemporary semiconductors. Fabrication of its conductive layers with superb crystal perfection is a great challenge for high power electronics. The present review analyzes the papers on homoepitaxial growth of thick monoclinic gallium oxide layers using MOCVD, HVPE and mist CVD. It has been shown that, by providing high growth rates and flexible doping control, each of them can ensure high structural quality combined with advanced electronic characteristics while being inexpensive.
As a prominent wide-bandgap semiconductor material, silicon carbide (SiC) is highly suitable for high-temperature, high-frequency, and high-power applications due to its excellent physical and electrical properties. In particular, for ultra-high-voltage power electronics, bipolar devices such as insulated-gate bipolar transistors and gate-turn-off thyristors, benefiting from conductivity modulation, demonstrate significantly superior performance compared to conventional silicon-based devices. However, the fabrication of these devices relies heavily on the availability of high-quality p-type SiC substrates. Currently, the performance of p-type SiC is limited by two major challenges: high resistivity and high defect density, which collectively hinder the development of ultra-high-voltage SiC power devices. Achieving p-type SiC single crystals with both low resistivity and high crystalline quality is therefore crucial to overcoming these challenges. This review focuses on three mainstream growth methods for p-type SiC single crystals: chemical vapor deposition (CVD), solution growth (SG), and physical vapor transport (PVT). It systematically summarizes recent advances in p-type doping technologies, addressing critical issues such as the high ionization energy of acceptor impurities, doping-induced lattice stress and defects formation, and low doping efficiency on the C-face. By analyzing the interplay between growth techniques and the resulting crystal characteristics, this work aims to shed light on the pathways toward achieving high-quality, low-resistivity p-type SiC single crystals and to stimulate further research in the crystal engineering of advanced semiconductor materials.
Magnetite (Fe3O4) nanoparticles have garnered significant attention due to their small size and high surface area, biocompatibility, and magnetic properties. This review offers an insightful and comprehensive discussion of recent advances in synthesis techniques and their impact on nanoparticle formation and characteristics. The diverse applications of Fe3O4 nanoparticles in medicine, modern photonics, energy storage, biosensing, catalysis, and environmental remediation are examined. Additionally, surface functionalization strategies designed to enhance stability, biocompatibility, and application-specific reactivity are outlined. Finally, current limitations are discussed with an outline for future research directions along with concluding perspectives on the continued development of Fe3O4 nanoparticle technologies.
Machine learning (ML) has become an increasingly powerful tool in crystal growth research, enabling new ways to model processes, optimize growth conditions, and automate characterization of crystalline materials. This review provides a comprehensive overview of ML applications in the growth of semiconductors and electronic materials, covering both bulk crystal growth techniques (Czochralski, Floating Zone, Directional Solidification, Top Seed Solution Growth, etc.) and epitaxial growth methods (MOCVD, MOVPE, etc.), along with related characterization methods (photoluminescence imaging, X-ray diffraction, microscopy, etc.). We trace the historical development of ML in crystal growth and highlight recent advances such as deep learning for defect detection, surrogate modeling for process optimization, and reinforcement learning for autonomous control. Key ML methodologies (e.g., decision trees, neural networks, Gaussian processes, and generative models) are discussed in the context of crystal growth tasks like property prediction, defect classification, clustering of microstructural features, process optimization, and more. We also detail how various data sources, from in situ sensor readings and furnace design parameters (e.g., geometry and materials), to process simulations and ex situ characterization data, can be integrated into ML frameworks for prediction, optimization, and control. Challenges specific to crystal growth (limited data, data heterogeneity, integration with physical models, and others) are examined, and we outline emerging trends and future outlook, including physics-informed ML and digital twin approaches for crystal growth. Overall, this work aims to demonstrate the significant progress achieved at the intersection of ML and crystal growth, while providing guidance for future research in this rapidly evolving interdisciplinary field.
Doped sapphire crystals (e.g., Ti: Al₂O₃, Cr: Al₂O₃, C: Al₂O₃, etc.), with their excellent physicochemical properties and tunable optoelectronic properties, are of great value for applications in the fields of laser devices, radiation detectors, and pyroelectric devices. In this paper, we systematically review the defect structures, preparation methods, and the modulation of the properties of different doped sapphire crystals, focus on the modulation mechanisms of different doping elements on the optical, mechanical, and laser properties of sapphire, and also details their optoelectronic applications in devices such as lasers, radiation detectors, and pyroelectric components. In addition, based on the current research progress, this paper also looks forward to the future development direction of doped sapphire crystals, including the optimization of the preparation technology for large-size and high-concentration uniformly doped crystals, as well as the potential for applications in emerging fields such as photonic chips and high-energy physics detectors, in anticipation of growing higher-quality doped sapphire crystals through the comprehensive improvement of the preparation technology and other aspects of the laser devices (e.g. photonic computing, LIDAR and other key hardware for artificial intelligence) and other applications.
A targeted survey of structural databases, particularly focusing on salts of organic perrhenates, pertechnetates, and permanganates reveals that these tetrahedral anions (MO₄) form a variety of notable supramolecular synthons. These anions can assume diverse roles within the crystal structures. This review provides a detailed analysis of known organic and some selected inorganic salts and complexes containing such tetrahedral anions, identifying several previously overlooked subtypes of suprastructures. These suprastructures are classified into four categories based on their non-covalent contacts: clusters, polymers, networks, and framework. Our analysis demonstrates that tetrahedral anions are capable of forming 55 distinct structural motifs through non-covalent interactions in both organic and inorganic crystals, which can be categorized into 24 types of bonding interactions. We introduce the concept of denticity of the tetrahedron and its central atom within superstructures. Additionally, a brief statistical analysis of anion–anion non-covalent interactions in compounds of the manganese subgroup is presented.
Gallium Nitride (GaN) materials have unique electronic, optical, and mechanical properties that make them useful for various applications. However, these materials have complex structures and behavior, making it challenging to characterize them. Micro-Raman spectroscopy (MRS) is an appreciatively effective and adaptable method for analyzing the different properties of GaN materials, such as stress, strain, carrier concentration, and phonon lifetime. This review article provides an overview of the principles of MRS and its applications in GaN material characterization. The behavior of E2H vibration modes of GaN material depends on the defects in the epilayer which alters the materials physical properties, such as stress and strain. The A1(LO) vibration mode of longitudinal optical phonons provides information on electrical properties, such as carrier concentration and phonon lifetime. This review explains the MRS use in quantifying the physical and electrical properties of GaN materials over other characterization.
The main application of Ti doped sapphire (Ti:sapphire) lies in the field of lasers, thanks to its outstanding production of ultra-short pulses due to the presence of doping Ti3+ ions. The absorption and emission mechanisms of this crystal are intricate, necessitating consideration of point defects existing in the grown crystal. A plethora of liquid-phase growth methods yield crystals of diverse sizes and quality. This paper gives a comprehensive review of the literature on managing dopants during the growth of Ti doped bulk sapphire crystals.Substantial research has indicated that the presence of detrimental Ti4+ ions diminishes the crystal laser efficiency due to their residual absorption. Although annealing under reducing atmosphere is an efficient way to increase the Ti3+/Ti4+ ratio, this process becomes increasingly time-consuming as the demand for larger optical components increases. Consequently, it would be more practical and convenient to control this ratio directly during the growth processes. However, the conversion mechanisms between the two Ti ions valences during crystal growth and annealing remain largely unexplored.A study of the thermodynamics of the Al2O3/TiO2 and Al2O3/Ti2O3 solid and liquid solutions as a function of the partial pressure (pO2) and oxygen activity is crucial for understanding these mechanisms. This paper presents corrected, reliable phase diagrams that enable quantitative prediction of the effect of pO2 on the melt concentrations of the two ions. Consequently, a novel value of the absorption coefficient constant, pertinent to Ti4+ concentration measurement, is proposed. Equilibrium with the solid solution yields segregation coefficients that appear distinct for the two ions. Given their influence on oxygen activity during growth, the effect of surrounding furnace parts, such as graphite casing or Mo crucible, is also important.Understanding the behavior of Ti3+and Ti4+ ions in the grown crystal as a function of pulling time and considering the pO2 levels in the furnace atmosphere, requires the knowledge of solid-state electrochemistry, including the charge carriers and the Al and O vacancies. This foundation allows the development of a physico-chemical model illustrating the evolution of ion valence during growth. Analysis of experimental results from existing literature gives the necessary diffusion coefficients and reaction rate constants. Investigating crystal-atmosphere interaction provides the required boundary condition for solving the problem. The findings exhibit qualitative agreement with experimental measurements of Ti3+ and Ti4+ concentrations in grown Ti:sapphire crystals.
X-ray crystallography remains the gold standard for resolving high-resolution atomic structures of biomolecules. Its unparalleled precision continues to provide critical structural insights that drive advances in drug discovery, enzyme mechanism elucidation, and molecular engineering across biotechnology, materials science, and nanomedicine. Despite its strengths, its success is fundamentally limited by the requirement for high-quality, well-ordered crystals, a persistent bottleneck in structural biology. Crystallization begins with nucleation, the critical step where solute molecules organize into a stable nucleus capable of initiating crystal growth. Controlling nucleation is essential for improving crystal reproducibility, size, and diffraction quality. To overcome this challenge, various interfaces, including liquid/liquid, air/water, and solid/liquid, have been explored, with the solid/liquid interface gaining increasing attention due to its ability to promote and modulate nucleation events. This review systematically discusses strategies utilizing solid/liquid interfaces to enhance protein crystallization efficiency and quality. It emphasizes the roles of diverse surfaces, including porous, hydrophobic, charged, rough, and functionalized substrates, and additive-assisted nucleation using micro-/macroparticles, nanoparticles, and DNA. Both electrostatic and non-electrostatic surface-induced mechanisms are critically analysed, with mechanistic insights into how these surfaces influence nucleation kinetics and crystal growth mechanisms. Comparative evaluations of different surface and additive systems are presented to identify effective nucleation enhancers and promote rational crystallization design. By deepening our understanding of interface-mediated nucleation and growth, this review provides a comprehensive knowledge base to support the rational development of reproducible, high-throughput crystallization strategies and outlines future directions for innovation in structural biology and crystallization science.
We investigate the defect structure of gallium nitride (GaN) substrates grown by hydride vapor phase epitaxy (HVPE) and ammonothermal method, with emphasis on the seeding approach (“foreign seed” or “native seed”). X-ray Bragg diffraction imaging techniques (laboratory X-ray Lang topography (L-XRT) and synchrotron monochromatic rocking curve imaging (RCI)) were used to study the defects of the GaN substrates. The efficiency of the in-process L-XRT method, whereas being strongly dependent on the structural perfection of the crystals, is important because it provides a good overview of the defect structure for entire substrates. But it remains qualitative, or semi-quantitative. RCI, on the other hand, allows obtaining complete quantitative information about lattice misorientation and distortion with sub-µm resolution. The contrast of the diffraction images of defects such as grain boundaries, dislocations, dislocation bundles, planar defects and others, is discussed, with emphasis on the influence of threading dislocation density on the contrast of the Bragg diffraction imaging. We complemented the diffraction studies with defect selective etching analyses and, to determine the level of impurities in the GaN substrates, by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The main finding of this study is that a native seed approach is essential for crystallizing GaN with high structural perfection and low threading dislocation density. This is true whether the GaN crystals are grown by HVPE or ammonothermal methods. A potential route to low-defect, low-impurity GaN substrates is outlined as a fundamental element for realizing GaN-based devices with high performance, life-time, and reliability.
High-quality crystals commonly exhibit regular morphology features and symmetries related to their crystal structures. The recognition of morphology features, especially on the shoulder morphology, will provide crucial guidance for the crystal growth and quality control. Here, the morphology features of β-Ga2O3 bulk crystals were discussed from three aspects of growth technology, orientation of seed crystal as well as pulling and rotation rates. Combined with the theoretical morphology of β-Ga2O3 crystal, the morphology features of β-Ga2O3 bulk crystals under different growth conditions were illuminated and summarized. The hexagonal seed crystal was also demonstrated, and more suitable for the growth of β-Ga2O3 bulk crystals with different principle surfaces by EFG method. The first review in the morphology features will become an important reference for future research on the growth of β-Ga2O3 bulk crystals.
Experimental observations of metastable zone width (MSZW) of various solute−solvent systems obtained by cooling crystallization at controlled rates RL are reviewed and interpreted from the standpoint of deterministic theoretical models based on the classical three-dimensional (3D) nucleation theory containing two nucleation parameters: effective solid−solvent interfacial energy γeff and preexponential factor A for nucleation. After a brief introduction to the parameters F and F1 of the models in terms of nucleation parameters of the classical nucleation theory and the effects of additives contained in the solution on the nucleation parameters A and γeff, typical experimental data of MSZW for selected solute−solvent systems are described and discussed according to the models to observe general trends of variations of γeff and A as functions of solution saturation temperature T0 and concentration ci of additives contained in the saturated solutions of different systems. Thereafter the observed general trends of variations of γeff and A as functions of solution saturation temperature T0, solvent and concentration ci of additives contained in the saturated solutions of different systems are discussed. The dimensions of 3D nuclei formed during MSZW of different systems and the limitations and applicability of deterministic models in crystallization processes are then presented and discussed. Finally, a summary of the contents of the review is given.
This work provides a review of crystal growth, crystal structure, compositional details, magnetism, thermodynamic, and transport behavior in the family of the trigonal intermetallic systems EuT2Pn2 (T= Cd, Zn; Pn= P, As, Sb; space group P3¯m1, No. 164). The physical properties observed in these materials, and how these change depending on the growth conditions are discussed. In particular, the case of EuCd2As2 is considered where data from many sources are available. The possible small contamination of the material during crystal growth experiments is hard to verify as it is often below the detection limit of the standard characterization techniques. It turns out that samples from different sources exhibit variations in the lattice parameters exceeding the experimental errors. The review of these parameters reveals that they are very similar for antiferromagnetic samples grown from Sn flux in Al2O3 crucibles, while there is a wider spread for samples grown from salt flux grown in SiO2 ampules, which are mostly ferromagnetic. The influence of the different experimental setups with regard to possible impurities in the samples is discussed.
Hydroxyapatite (HAp), ideal formula Ca10(PO4)6(OH)2, has unique physicochemical properties, including an excellent adsorption ability for functional biomolecules (e.g. nucleic acids, proteins) thanks to its specific large crystal surface. This property can be further improved with cationic and anionic replacements within the HAp framework. The adsorption of such biomolecules, indeed, can cause changes in the electric properties of the HAp surface in terms of resistivity and capacitance, generating the conditions for an improvement of the materials targeted for sensor applications. This work relates to the multiple routes for the synthesis of HAp materials, their electrochemical and structural investigations, and a short overview on the most well-known applications in sensor design. Moreover, with the aim of finding new promising HAp-based materials tailored for bioreceptor immobilization in biosensing, we underwent some doped-hydroxyapatite materials, specifically Sr-HAp, Gd-HAp, and Er-HAp, to a complete characterization. Electrochemical analyses, based on differential pulse voltammetry and cyclic voltammetry, evidenced improved analytical performances of HAp in terms of signal enhancement, repeatability, reproducibility, and reusability, in particular concerning the Er-HAp phase. A multi-methodological structural study, based on powder X-ray diffraction analysis, microscopy techniques (optical, electron, and fluorescence), energy dispersive X-ray spectroscopy (for chemical analyses), Fourier transform infrared spectroscopy, and absorption/fluorescence spectroscopies, showed the mechanism of doping replacement in HAp crystallographic sites, owing to the results of the Rietveld refinement from powder X-ray data, and a strong fluorescence for Sr-HAp.
This review presents a comprehensive discussion of the electrospray crystallization process, which represents a combination of electrospraying and crystallization through solvent evaporation, offering an efficient and cost-effective approach for the synthesis of submicrometric and nanosized crystals. Electrospray crystallization has demonstrated a multitude of advantages, including the generation of smaller crystals, enhanced dispersion, and the creation of diverse product morphologies, such as planar and cubic tetragonal structures. These benefits surpass those of conventional electrospraying methods and traditional crystallization mechanisms. This review also provides a historical context of works and highlights the wide array of potential applications. It explores the mechanisms and fundamental concepts related to both electrospraying and crystallization processes. Moreover, it presents an experimental process development proposal, with the aim of charting a course for future applications of advanced crystals, including drug delivery, catalysis, and energy storage.
With the emergence and popularity of high-performance computers, advances in materials informatics, and improvements in computing architectures and algorithms, the application of modeling in the field of materials science has become increasingly common and affordable. The ability to compute has benefited materials discovery in the last decade alone with many breakthroughs: improved photovoltaics, new functional nanomaterials, more efficient rechargeable batteries, and tailorable catalytic surfaces to name a few. Among various computing tools, first -principles calculations based on density functional theory (DFT) have been widely applied to high throughput computational analysis to better understand the formation, properties, and stability of new and existing materials. The advantages of DFT methods are that they are inexpensive, fast, and are capable of capturing nuances at the atomistic scale. Since DFT calculations are performed at 0 K and in vacuum, thermodynamic corrections need to be taken into account to match real world operating conditions in the laboratory and during use. These thermodynamic corrections have been applied for over twenty years and provided valuable guidance to the analysis of surface structure, vacancy formation, and stability across varying gaseous environments. The combination of DFT with experimental corrections significantly expands its flexibility as it can be used to generate stability conditions for specific elements and multi -component solids in water. This literature review will provide a thorough survey of first -principles DFT calculations combined with thermodynamics, as well as their application and research in the design, predicted stability, and characterization of 2D materials, their surfaces, and interfacial surface reactivity. A particular emphasis will be placed on the behavior of 2D materials in aqueous environments, comparing their surface transformation thermodynamics via processes such as ion release and adsorption using the newly created DFT + Solvent Ion Model (DSIM).
Structural transformations in the solid state dictate operating regimes of materials for engineering applications. Advanced structural characterisation facilitated by electron microscopy has resulted in significant progress in our understanding of structural transformations across resolvable length scales. We shall confine this communication to one of the metallic systems. This refers to titanium (Ti) alloys. They exhibit formation of a variety of solid solution phases, intermetallic phases, quasicrystals, incommensurate structures, and metallic glasses under different processing conditions. Additionally, newer phase formation at nanometer length scales has also been observed in Ti alloys. The exploration of properties in presence of structures at nanoscale in these alloys have not been discussed in literature extensively. Such an approach will open an avenue for nano-engineered alloys. An attempt will be made to indicate the direction of investigation in this connection succinctly. Understanding the nature and pathways of solid state structural transformations in Ti alloys seem to be important in view of the wide variety of engineering applications. Nanostructured materials have shown formation of newer phases not included in equilibrium phase diagrams. This review shall dwell on this aspect by drawing parallelism from many other alloy systems at nanoscale. In particular, Au−Cu nanostructures will be discussed as an example. It will be argued that size of the system will have influence on the formation of structures that are normally not observed at microscopic length scales in Ti alloys. In view of the complexities involved in phase transformations in Ti alloys, it is important to evolve or look for a model that will help us understand structural transformations by minimum geometrical distortion from a parent phase. Such an approach will offer one of the ways of comprehending formation of phases at nanoscale. In addition to this, it will also help us to consider group-subgroup relationship. It will be shown that unified structural description towards this will be helpful. A brief summary of higher dimensional structural modelling will be presented here with particular reference to phases formed in Ti alloys.
The origin of life has been marked by existing chemical, physical and atmospheric conditions in the primeval era of Earth. In this sense, experiments have been carried out that emulate the conditions of the Precambrian era, where organic blocks such as amino acids, sugars, organic compounds and O2 have been synthesized from the elements of this condition. Nevertheless, even while these results have been disruptive, allowing a significant advance in the origin of life, no functional biomolecules have been synthesized. Considering the work done previously, as a starting point and the evidences of the synthesis of biomorphs in the presence of biomolecules, the objective of this study was the synthesis of barium silico-carbonate biomorphs, based on biomolecules in Precambrian conditions. The purpose of this is to identify if it is possible to obtain functional biomolecules. The results showed that the barium biomorphs synthesized in conditions that emulate the primitive era present spherical or circular morphology, with a chemical composition that corresponds to the polymorphs of witherite, goethite and carbonaceous material (CM) such as protein, carbohydrate and phosphate group bonds. However, the synthesis of an active or functional biomolecule was not possible. The results therefore show that to be able to obtain a functional biomolecule that could be considered a sign of life springing from organic and inorganic compounds, it is necessary to involve other factors heretofore not considered. This is due to the fact that chemical elements per se, together with some atmospheric factors that have been described which apparently permitted the formation of the protocell in the primitive era of Earth, are not sufficient to obtain functional biomolecules. In this way, the origin of life may be understood from the equation of life (L = amc2), considering all involved factors and not only the chemical composition of elements that make up various organisms in combination with only some atmospheric factors.
Silicon carbide (SiC) is a promising semiconductor material which attracts huge attention due to its wide bandgap, high thermal conductivity and great potential for electronic applications. Residual stress causes defects in crystals that can noticeably decrease the performance of SiC devices. This paper reviews the origins of residual stress and different methods for stress characterization. To begin with, the origins of residual stress during crystal growth and post-processing is introduced. Then, the development of wafer size and quality over the last decade is demonstrated. Identification and characterization of residual stress using different techniques are discussed in detail. Optimizing temperature distribution and post-processing parameters is critical for reducing stress in SiC crystals.
