Ammonothermal Synthesis and Crystal Growth of Nitrides
Chemistry and Technology
- 2021
- Book
- Editors
- Dr. Elke Meissner
- Prof. Dr. Rainer Niewa
- Book Series
- Springer Series in Materials Science
- Publisher
- Springer International Publishing
About this book
This book provides a collection of contributed chapters, delivering a comprehensive overview of topics related to the synthesis and crystal growth of nitride compounds under supercritical ammonia conditions. Focusing on key chemical and technological aspects of ammonothermal synthesis and growth of functional nitride compounds, the book also describes many innovative techniques for in-situ observation and presents new data fundamental for materials synthesis under ammonothermal conditions. With its detailed coverage of many thermodynamic and kinetics aspects, which are necessary for understanding and controlling crystal growth, this contributed volume is the ideal companion to materials chemists and engineers at any point in their journey in this rich and exciting field.
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Table of Contents
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Frontmatter
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General Importance for the Synthesis and Crystal Growth of Nitrides
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Frontmatter
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Chapter 1. Significance of Ammonothermal Synthesis for Nitride Materials
Rainer NiewaThe chapter delves into the importance of ammonothermal synthesis for nitride materials, a class of materials less stable than oxides and requiring specialized handling. It compares ammonothermal synthesis with traditional methods, emphasizing its potential for crystal growth and materials synthesis. The chapter also discusses the advantages of ammonia as a solvent, its unique properties, and the challenges associated with its use. It highlights the successful synthesis of various binary and ternary nitrides under ammonothermal conditions and the future potential of this technique in the field of nitride-based materials.AI Generated
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AbstractThis chapter is intended to introduce the ammonothermal synthesis as an alternative technique to other methods for nitride materials production. Properties of liquid and supercritical ammonia with focus on use as a solvent for nitride synthesis and crystal growth are discussed and compared to those of water. Finally, inherent drawbacks of the use of fluidic ammonia arising from its chemical properties are considered. -
Chapter 2. The Potential of Nitride Materials
Mathias Mallmann, Niklas Cordes, Wolfgang SchnickNitride materials, such as silicon nitride, exhibit exceptional chemical, thermal, and mechanical stability due to their covalent bonding. This chapter delves into their diverse applications, including high-performance ceramics for aerospace engineering, thermally conductive materials like AlN for electronics, and semiconductors like GaN for optoelectronics and solid-state lighting. Additionally, it explores nitrides' potential in energy storage solutions, such as solid electrolytes for lithium-ion batteries, and their role in superconductors and carbon nitrides. The chapter also highlights the growing research interest in nitride materials, evidenced by the rapid increase in publications since 1950.AI Generated
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AbstractThe following chapter provides an overview of the most important application fields of nitride and oxonitride materials and outlines briefly their structural features as well as their materials properties. (Oxo)nitrides are employed in a variety of important technological areas such as structural ceramics, heat conductors, semiconductor technology, solid-state lighting, water splitting and solid-state battery materials. Their significance for daily life as well as possible advancement of (oxo)nitride materials with respect to these applications is examined. -
Chapter 3. Technological Challenges of Autoclave Design for Ammonothermal Syntheses
Eberhard Schlücker, Anna-Carina Luise KimmelThe chapter delves into the intricate challenges of designing high-pressure autoclaves for ammonothermal syntheses, emphasizing the critical role of high-performance materials with exceptional strength, ductility, and corrosion resistance. It explores the selection of alloys such as duplex steel, Ni-base superalloys, and Co-base superalloys, each with unique properties suited for high-temperature and high-pressure environments. The text also highlights the importance of meticulous design considerations, including wall thickness calculations, stress distribution analysis, and the mitigation of notch effects. Additionally, it underscores the necessity of robust sealing mechanisms and safety measures to prevent failures and ensure the safe operation of these specialized vessels.AI Generated
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AbstractThe challenges of ammonothermal reactor design are manifold. High-pressure and temperature require the use of high-performance alloys with sufficient strength at elevated temperature and excellent creep resistance: highly alloyed Ni-base and Co-base alloys and a Mo-base alloy have been in use in ammonothermal reactor design. Furthermore, the dimensioning rules have to be strictly followed to minimize stress concentration. Repeated loading cycles and degradation over time have to be considered. Finally yet importantly, good handling of the equipment not only minimizes the workload but also reduces the risk of crucial operating errors. The chapter Technological challenges of autoclave design discusses design options for high-pressure at high-temperature equipment with regard to their mechanic and thermal stability. Materials suitable for ammonothermal pressure vessels will be reviewed and some basic safety advice is given at the end of this chapter.
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Technology of Ammonothermal Synthesis
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Frontmatter
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Chapter 4. Technical Solutions for In Situ Monitoring of Ammonothermal Processes
Eberhard SchlückerThe chapter explores the critical aspects of designing and manufacturing high-pressure sight glasses for ammonothermal processes. It delves into the selection of materials based on spectral transmission, mechanical strength, and chemical resistance, with a focus on borosilicate, quartz, and sapphire glasses. The design process includes calculations for window thickness and outer diameter, considering factors such as bending strength, compressive strength, and Poisson’s ratio. The chapter also discusses the importance of manufacturing tolerances, surface quality, and the use of sealing materials like copper, silver, or gold to achieve optimal sealing. Additionally, it highlights the practical applications of these sight glasses in monitoring ammonothermal processes, including UV-VIS spectroscopy, Raman spectroscopy, and X-ray monitoring, providing a comprehensive overview of in situ monitoring techniques.AI Generated
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AbstractDue to the thick-walled autoclaves, the ammonothermal system has long been regarded as a black box and the crystal quality was only improved through systematic, time-consuming experiments [1]. One of the main goals therefore was to bring “light into the dark” with new window design for the extreme process parameters of larger than 650 °C and simultaneously 300 MPa. -
Chapter 5. Innovative Techniques for Fast Growth and Fabrication of High Purity GaN Single Crystals
Daisuke Tomida, Makoto Saito, Quanxi Bao, Tohru Ishiguro, Shigefusa F. ChichibuThe chapter delves into the ammonothermal method for GaN single crystal growth, emphasizing the acidic ammonothermal method's potential for industrialization due to its lower pressure requirements and better corrosion resistance. It explores the crucial parameters affecting crystal growth, such as temperature, pressure, and mineralizer concentration, and introduces advanced techniques to enhance crystal growth rates and purity. Notably, the use of ammonium iodide as a mineralizer and the mineralizer gas phase synthesis method are highlighted for their significant impact on crystal growth rate and purity, respectively. The chapter also discusses the importance of seed crystals and oxygen contamination prevention methods, making it a comprehensive resource for professionals interested in the latest advancements in GaN crystal growth technology.AI Generated
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AbstractThe ammonothermal method involves an upper and lower temperature difference that is provided in an autoclave by a baffle plate, and GaN, which is dissolved in supercritical ammonia in the raw material dissolution region and deposited on a seed crystal in the crystal growth region. Because dissolution and deposition can be continuously performed in an autoclave, this is a suitable method for producing large crystals. The growth of bulk GaN single crystals by the ammonothermal method is currently under development and there remain many indeterminate factors. This chapter describes the technological developments to achieve a high-speed growth and high quality of grown crystals. -
Chapter 6. A New Perspective on Growth of GaN from the Basic Ammonothermal Regime
Elke Meissner, Dietmar Jockel, Martina Koch, Rainer NiewaThe chapter delves into the ammonothermal growth of GaN, particularly focusing on the basic ammonobasic regime. It introduces a new chemical model that considers the transport of intermediate species and the role of mineralizers. The authors discuss the potential existence of a liquid phase during the growth process, which could significantly impact the growth rates and quality of GaN crystals. The chapter also highlights the challenges and opportunities in controlling the growth process, suggesting new avenues for research and development in the field of semiconductor crystal growth.AI Generated
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AbstractAlthough the crystal growth of GaN under ammonothermal conditions is being performed for quite some years now, the physical processes going on in the autoclave are still debated. Insight in the autoclave by in situ techniques is difficult and numerical simulations are based on physical models where the experimental prove is eventually vague. This chapter reports a period of experimental work leading to a new vision of the basic ammonothermal process. We shortly summarize the 3D thermal- and transport model and a first chemical model. Subsequently, we propose an alternative picture for the ammonobasic crystal growth of GaN, which not only leads to consequences with regard to required pressures and temperatures but also to a potential new growth process. The proposed hypothesis and empirical model involves the presence of a liquid phase in the autoclave in form of an amidogallate complex. -
Chapter 7. Ultrasound Measurement as a Tool for in Situ Determination of Filling Degree Under Extreme Conditions
Wilhelm Schwieger, Hasan BaserThe chapter delves into the critical role of ammonia in ammonothermal syntheses and the necessity for precise control of its filling level in autoclaves. It highlights the limitations of conventional level sensors in high-pressure environments and introduces ultrasound measurement as a viable alternative. The text discusses the historical methods of ammonia filling, such as condensation and high-pressure pumps, and presents a novel approach using ultrasound for in situ determination of the filling degree. The chapter emphasizes the safety implications and the need for reproducible and exact adjustment of ammonia concentrations, making it a crucial read for professionals in the field.AI Generated
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AbstractAmmonothermal syntheses require high pressures and temperatures to realize the supercritical conditions. For this a special autoclave technology is required, which places special demands on both the material and the geometrical design. Characteristics are thick walls, high weight, opaque, narrow interior. Therefore the exact determination of initial weights and in particular filling degrees of liquids, which are liquid only under pressure, becomes difficult. In this section, we are going to compare three methods (i) pumping time measurement, (ii) determination by weighing and (iii) ultrasound for adjusting and/or determining the ammonia filling degree of ammonia in an autoclave are presented and the advantages and disadvantages of the individual methods are compared. In addition it is important to have the Ammonia amount very precise to describe the all the concentrations in the autoclave, even under the ammothermal conditions. -
Chapter 8. Direct Determination of Viscosity of Supercritical Solutions
Thomas G. Steigerwald, Eberhard SchlückerThe chapter delves into the critical role of viscosity in ammonothermal processes, emphasizing the need for accurate viscosity measurements to optimize crystallization processes. It discusses the development of various viscometers, such as ultrasonic and rolling ball viscometers, tailored to withstand high temperatures and pressures. The chapter also explores the influence of temperature, pressure, and dissolved substances on the viscosity of ammonia, highlighting the complexities and the innovative solutions required to measure and control this parameter effectively. The development of a rolling ball viscometer specifically designed for ammonothermal conditions is a notable highlight, showcasing the advancements in the field.AI Generated
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AbstractThe following chapter is mainly aimed at simulators and crystal growers, as viscosity has an influence on the flow behaviour in the reactor and the diffusion coefficient in the crystal’s vicinity. So, the chapter gives an overview of influencing factors to viscosity in ammonothermal media, which are the pressure and temperature as well as the concentration of used mineralizers. Therefore, different possible viscometers are described and discussed in detail for its potential use in ammonothermal media. Hereby two promising options are presented in detail: a modified rolling ball viscometer as well as an adaptation of the ultrasonic pulse-echo method for viscosity measurement for ammonothermal systems. While the last is mostly based on literature research and only some general prove of principle are carried out, the first one is fully described and analysed during operation. This means for the adaptation of this principle four critical aspects have to be overcome. As a result, the viscosity of ammonia in the range above 400 °C up to 600 °C at maximum pressure of 252 MPa is shown. Additionally, some measurements of ammonia-ammonium-fluoride-mixtures are compared with pure ammonia, whereas the viscosity is about 1.4 times lager with ammonium fluoride then without. -
Chapter 9. Determination of Solubility of GaN in Ammonobasic Systems
Wilhelm Schwieger, Hasan BaserThe chapter delves into the ammonothermal method for growing GaN crystals, focusing on the solubility of GaN in ammonobasic systems. It discusses the role of mineralizers such as KNH2 and NaNH2 in enhancing solubility and the impact of temperature and pressure on the crystallization process. The chapter presents experimental data and comparisons with literature values, highlighting the differences in solubility behavior between KNH2 and NaNH2. It also explores the kinetics of solubility and the optimization of process conditions for efficient crystal growth. The findings are crucial for advancing the understanding and application of the ammonothermal method in semiconductor manufacturing.AI Generated
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AbstractIn this study, the solubility of GaN in the ammonobasic MNH2–GaN–NH3 (M = Na, K) systems in the temperature range of 350–550 °C was studied. The target value for the ammonia filling degree was 45% and 55% for mineralizers NaNH2 and KNH2, respectively. The mineralizer concentration was varied at all temperatures from 1 M to 3 M, in respect to the liquid ammonia. It has been found that the solubility of GaN with NaNH2 as a mineralizer increases slightly with increasing temperature in the range 400–600 °C, but is generally very low. A dependence of solubility on mineralizer concentration was not observed. An increase in the ammonia filling degree from 45% to 55% only slightly increased the solubility of GaN. The use of KNH2 as a mineralizer brought an enormous increase in the solubility of GaN. Here, 7 times higher solubilities than those for NaNH2 were observed. A retrograde solubility behavior of GaN in the temperature range 400–550 °C was determined for KNH2 as a mineralizer. In the range of 350–400 °C the solubility showed a positive temperature dependence. The maximum solubility was reached at 400 °C. The solubility of GaN at 400 °C was found three times higher than at 550 °C. -
Chapter 10. In Situ Visualization of the Ammonothermal Crystallization Process by X-ray Technology
Saskia Schimmel, Peter WellmannThis chapter delves into the application of X-ray technology for in situ visualization of ammonothermal crystallization processes. It covers two primary X-ray methods: projection imaging and diffraction signals. The text emphasizes the importance of X-ray energy for achieving optimal contrast and transmittance through autoclave materials. It also discusses the development of X-ray transparent autoclave windows, which has enabled significant advancements in the field. The chapter provides detailed insights into the experimental setup, data evaluation, and the unique advantages of in situ X-ray imaging for studying dissolution kinetics, solubility, and mass transport in ammonothermal reactions. Additionally, it highlights the challenges and solutions related to the chemical stability and mechanical properties of potential window materials, making it a valuable resource for specialists in the field.AI Generated
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AbstractX-ray based in situ monitoring techniques for ammonothermal processes are reviewed. Technological aspects are discussed, including general aspects of in situ X-ray visualization technology as well as the corrosion resistance of prospective materials for X-ray transparent windows under ammonothermal conditions (for more comprehensive information on corrosion resistance see Chap. 11). In situ X-ray visualization methods have proven to be extremely useful for gaining insights that are inaccessible through other methods to date. Results obtained by in situ X-ray imaging comprise information on solubility and dissolution kinetics as well as insights into the transport of solutes and local concentration changes of solutes. Moreover, phase changes of the fluid can be monitored and the technique has been adapted for solubility studies of novel materials that are unavailable as bulk materials to date. Findings of particular interest include a revision of solubility data for GaN, insights into face-selective and mineralizer-selective dissolution kinetics of GaN, and the visualization of Ga transport within the fluid upon dissolution of GaN. The observed extremely slow motion of Ga-containing species suggests a pronounced influence of solutes on the viscosity of the fluid, which has largely been treated as negligible due to the lack of data for the respective mixtures so far. -
Chapter 11. Corrosive Degeneration of Process Equipment and Technical Solutions for Corrosion Protection Under Ammonothermal Conditions
Anna-Carina Luise Kimmel, Eberhard SchlückerThe chapter delves into the critical issue of corrosion in ammonothermal research, highlighting the severe degradation of autoclaves and internal setups due to ammonothermal conditions. It discusses the corrosive attack on Ni-base and Co-base alloys, particularly in acidic environments, and presents detailed studies on the stability of various alloys, including TZM and Mo. The chapter also explores protective systems such as noble metal liners and coatings, as well as ceramic and semi-hermetic capsule systems, offering insights into their effectiveness and potential for reducing corrosion and contamination. The comprehensive analysis of different materials and protective measures under various ammonothermal conditions makes this chapter a valuable resource for researchers and engineers seeking to optimize ammonothermal processes.AI Generated
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AbstractIn addition to the high pressure and temperature, process equipment for ammonothermal syntheses has to withstand ammonothermal reaction media: an aggressive mixture of supercritical ammonia with basic or acidic additives. Severe corrosive attack of process equipment can occur under ammonothermal conditions but needs to be minimized for two reasons. Firstly, corrosive attack can lead to safety issues that must not be neglected. Secondly, corrosion products represent a major source of impurities, which represents a critical issue especially for the synthesis of semiconductors. Consequently, measures for minimizing corrosion are of utmost importance for the adequate design of ammonothermal equipment. In this chapter, materials suitable for ammonothermal applications, for pressure bearing parts as well as for internal setups and corrosion protection, and recent investigations on their corrosion behavior will be reviewed with suggestions for suitable applications and protection systems.
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Chemistry of Ammonothermal Synthesis
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Frontmatter
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Chapter 12. Explorative Synthesis of Novel Nitride Compounds by Ammonothermal Synthesis
Mathias Mallmann, Niklas Cordes, Wolfgang SchnickThe chapter delves into the ammonothermal method for synthesizing nitride compounds, emphasizing its advantages over conventional solid-state reactions. It covers the synthesis of binary, ternary, and multinary nitrides, as well as oxonitrides, and discusses their properties and potential applications. Notably, the method has been successfully used to grow large single crystals of GaN, a key semiconductor material in laser diodes and LEDs. The chapter also highlights recent advancements in synthesizing ternary and quaternary nitrides, which hold promise as next-generation semiconductors. Additionally, it explores the synthesis of oxonitride perovskites, which have applications in water splitting materials and other technologies.AI Generated
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AbstractThis chapter provides a brief overview of the synthesis of nitrides and oxonitrides by the ammonothermal method. Numerous binary, ternary and multinary nitrides as well as oxonitrides are discussed. The synthesis conditions with regard to the temperatures, pressures, precursors and mineralizers are mentioned. In addition, the crystal structure of the respective compounds will be briefly described. Since most of these compounds possess interesting electronic and optical properties, the bandgaps of the compounds are discussed in more detail and are summarized at the end. -
Chapter 13. Intermediates in Ammonothermal Synthesis and Crystal Growth
Rainer NiewaThe chapter 'Intermediates in Ammonothermal Synthesis and Crystal Growth' delves into the complex processes of ammonothermal synthesis, a method used to produce a variety of inorganic compounds under high-pressure ammonia conditions. It begins with a historical overview of the pioneering work in this field and discusses the range of materials that have been synthesized using this method, including metal amides, nitrides, and other compounds. The chapter highlights the crucial role of mineralizers in enhancing the solubility of source materials and facilitating crystal growth. It also explores the different types of mineralizers, such as ammonobasic and ammonoacidic, and their impact on the synthesis process. Additionally, the chapter provides insights into the mechanisms of dissolution and crystal formation, emphasizing the importance of understanding these processes for optimizing the production of high-quality crystals. The discussion on the specific case of gallium nitride (GaN) crystal growth under both ammonobasic and ammonoacidic conditions offers a detailed example of how mineralizers influence the outcome of the synthesis. The chapter concludes by emphasizing the need for further research to fully understand the complex interplay between mineralizers, solubility, and crystal growth in ammonothermal synthesis.AI Generated
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AbstractMineralizers possess a central relevance in ammonothermal synthesis and formation of soluble species for material transport and crystal growth in particular, governing the solubility, transport direction and deposition processes. In this chapter we review the knowledge on solubilities and chemical behavior of common mineralizers for ammonothermal synthesis. Additionally, we present the current knowledge on intermediates during ammonothermal gallium nitride crystal growth, depending on the nature of the applied mineralizer, as well as during a conceivable ammonothermal synthesis of zinc nitride. Additionally, crystal growth of indium nitride is discussed with focus on chemical processes within the ammonia medium. -
Chapter 14. Equation of States and Ammonia Decomposition in Ammonothermal Systems
Siddha PimputkarThis chapter delves into the ammonothermal method for growing nitride crystals, highlighting the challenges and importance of understanding the chemical composition of supercritical ammonia mixtures. It introduces a newly developed equation of state (EOS) for these mixtures, which significantly improves the accuracy of modeling ammonothermal systems. The chapter reviews the theoretical background of equations of state for pure gases and discusses the extension of the Beattie-Bridgeman EOS for ammonia mixtures. It also presents experimental data validating the new EOS and its application in predicting the pressure trace and chemical make-up of ammonothermal systems. The chapter concludes by emphasizing the potential of this new EOS in advancing the understanding and control of ammonothermal growth processes.AI Generated
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AbstractThermodynamic modeling of the ammonia decomposition under ammonothermal conditions (T > 600 K, P > 100 MPa) is presented given recent advances in developing a new, simple equation of state (EOS) describing ammonia, hydrogen, nitrogen and their mixtures under these conditions. The simplified EOS is based on the traditional form of the Beattie-Bridgeman (BB) EOS and expands relevant parameters to second order in density. As a consequence, a seven-parameter EOS is presented and compared to experimental data for ammonia up to 250 MPa and 810 K. Experimental data for ammonia, hydrogen and nitrogen are simulated using the reference multiparameter EOS for each individual gas. Gas mixtures are formed by applying mixing rules with separated contributions for polar and non-polar interactions. The accuracy of the expanded BB EOS is suggested to be 1–2% in pressure for temperatures greater than 700 K for ammonia, hydrogen, nitrogen and NH3–N2–H2 mixtures. Additionally, a general thermodynamic expression for the equilibrium constant is presented and applied to the ammonia decomposition reaction by using non-ideal mixing contributions from the second virial coefficient using the expanded BB EOS. Comparison with experimental data (P <210 MPa, T <810 K) suggests an accuracy of ~2% in pressure. -
Chapter 15. Molecular Simulations as Guides to Ammonothermal Syntheses of Nitrides—State of the Art and Perspectives
Tanakorn Wonglakhon, Dirk ZahnThe chapter delves into the intricate processes of ammonothermal syntheses, focusing on the production of amide semiconductors like AlN and GaN. It discusses the challenges posed by the complex reactions involving ammonia as both a reactant and a solvent. The authors present an in-depth exploration of quantum mechanical calculations and molecular mechanics simulations, highlighting their roles in understanding and predicting these syntheses. The text also covers the historical development of these simulation methods, from early studies on ammonia clusters to recent advancements in dynamics simulations. By combining these approaches, the chapter offers a unique perspective on the state-of-the-art and future directions in ammonothermal syntheses of nitrides.AI Generated
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AbstractMolecular Simulations are increasingly entering the realm of materials syntheses. While pioneering studies were bound to simple models which could only address selected aspects of ‘real chemistry’ in the lab, recent advances in simulation methodology and computing hardware indeed paved the way to also modelling complex systems. Yet, we are hardly more than at the beginning of establishing molecular simulations as a routine tool for guiding syntheses. In the present contribution, we discuss the progress that has been made to understand ammonothermal syntheses of nitrides. This encompasses molecular dynamics simulations based on non-reactive force-fields—such as studies of liquid ammonia as a solvent, and its supercritical nature at high temperature and pressure. Moreover, we report on recent work on quantum and hybrid quantum/classical approaches for modelling the auto-protolysis of ammonia and ammonia protolyses in the course of metal ion solvation. This forms a basis for rationalizing the association of ion aggregates, size-induced proton transfer and the self-organization of amides, imides and nitrides from molecular simulations. -
Chapter 16. Properties of Ammonothermal Crystals
Jaime A. Freitas Jr., Marcin ZającThe chapter delves into the properties of ammonothermal crystals, highlighting the importance of GaN for various optical, optoelectronic, and electronic devices. It discusses the ammonothermal growth method, which is superior for producing high-quality GaN substrates. The structural properties of GaN, including its lattice parameters and defects, are examined in detail. The chapter also explores the challenges in reducing oxygen concentration and the implications for device performance. Additionally, it covers the thermal properties of GaN and the successful deposition of high-quality epitaxial films on ammonothermal substrates. The chapter concludes with a discussion on the potential applications of ammonothermal GaN in high-power and high-frequency devices, emphasizing the need for further improvement in substrate quality.AI Generated
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AbstractThis chapter summarizes the present status of bulk GaN crystals grown by ammonothermal basic and acidic methods, and reviews their intrinsic physical properties. Crystals with low dislocation densities, typically well below 105 cm−2, high crystal lattice flatness, and sharp X-ray rocking curves (typically below 20 arcsec) are reproducibly grown by both methods. High quality strain-free homoepitaxial films have been successfully deposited on both polar and non-polar ammonothermal substrates. Characteristics of testing devices produced using these epitaxial templates confirm the potential of ammonothermal substrates for fabrication of high performance and high yield devices.
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Future Aspects and Challenges
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Frontmatter
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Chapter 17. Special Equipment for Ammonothermal Processes
Eberhard Schlücker, Benjamin Hertweck, Saskia Schimmel, Peter WellmannThis chapter delves into the intricate design and construction of specialized equipment for ammonothermal processes, focusing on optical cells for in situ monitoring. It highlights the development of uniaxial and biaxial optical cells, each tailored for specific monitoring techniques such as UV-VIS spectroscopy, Raman spectroscopy, and X-ray diffraction. The challenges of material selection, notch factors, and stress management are meticulously addressed, with solutions like boron carbide windows and advanced sealing mechanisms. The chapter also introduces a rotatable feedthrough for in situ X-ray diffraction experiments, enabling precise alignment and rotation under extreme conditions. Additionally, it explores innovative liner concepts based on ceramic crucibles, offering enhanced corrosion protection and improved thermal gradient control. The chapter concludes by summarizing the significance of these advanced technologies in providing a comprehensive understanding of ammonothermal processes, setting the stage for further research and development in the field.AI Generated
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AbstractAs the ammonothermal method often requires technically challenging conditions such as high temperature, high pressure and reaction media that are rather corrosive towards most metals (see Chap. 11), the further development of ammonothermal process equipment is of vital importance for tapping the full potential of the ammonothermal method. Suitable high-pressure/high-temperature autoclaves are therefore the basic requirement for a successful process. Ammonothermal syntheses are conventionally carried out in autoclaves, which do not allow monitoring of the physical and chemical processes during the experiments. Therefore, in situ measurement techniques at process conditions are crucial for obtaining a holistic understanding of ammonothermal processes. The following chapter presents optical cells for in situ monitoring enabling UV/Vis and Raman spectroscopy, X-ray imaging and X-ray diffraction as well as ultrasonic measurements. Additionally, special equipment like a rotatable feedthrough and a ceramic-crucible-based systems for minimization of corrosion and contamination are described. -
Chapter 18. Ammonothermal Materials
Wolfgang Schnick, Niklas Cordes, Mathias Mallmann, Rainer Niewa, Elke MeissnerAmmonothermal synthesis is a versatile method for crystallizing materials, particularly GaN, at lower temperatures compared to other techniques. This chapter delves into the advantages of this method, such as the ability to synthesize bulk materials and the potential for commercial large-scale production. It also addresses the complex chemistry and technical challenges involved in controlling the crystal growth process. The chapter highlights the need for further research to improve our understanding of the physical and chemical processes within the autoclave, which could lead to the synthesis of new materials and improved crystal growth. Additionally, it explores the potential of ammonothermal synthesis for producing a wide range of nitrides and oxide nitride perovskites, opening up new avenues for research and application in fields such as optoelectronics, thermoelectrics, and photocatalysis.AI Generated
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AbstractEven more than fifty years after the first ammonothermal syntheses, the synthetic potential of this technique is still far from established. Even in the already commercialized crystal growth of GaN substrates, various technical obstacles remain, partly because of lack of materials for high pressure equipment sufficiently resistant against the aggressive medium and at the same time persistent at the process conditions, but clearly because of insufficient understanding of the chemical and physical processes in supercritical ammonia. Still, many novel nitrides already emerge from ammonothermal synthesis. This technique has already proven to hold great prospects in crystal growth of the other group III nitrides, AlN and InN, relevant from a technical point of view, and substitution variant among those nitrides with further trivalent ions. Huge potential was also demonstrated for synthesis of further hard to produce nitrides as nitridosilicates, nitridophosphates and similar compounds, or oxide nitride perovskites. With increasing understanding of the physiochemical background and concomitant extension of the accessible process parameters we definitely will see great advances in the ammonothermal synthesis of novel materials for future applications.
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Backmatter
- Title
- Ammonothermal Synthesis and Crystal Growth of Nitrides
- Editors
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Dr. Elke Meissner
Prof. Dr. Rainer Niewa
- Copyright Year
- 2021
- Publisher
- Springer International Publishing
- Electronic ISBN
- 978-3-030-56305-9
- Print ISBN
- 978-3-030-56304-2
- DOI
- https://doi.org/10.1007/978-3-030-56305-9
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