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In this comprehensive yet compact monograph, Michel W.Barsoum, one of the pioneers in the field and the leading figure in MAX phase research, summarizes and explains, from both an experimental and a theoretical viewpoint, all the features that are necessary to understand and apply these new materials.

A study is presented on the synthesis of reaction-mixed nitride nanopowders in the reference system of aluminium nitride AlN, gallium nitride GaN, and titanium nitride TiN (Al:Ga:Ti = 1:1:1) followed by their high-pressure and high-temperature sintering towards novel multi-nitride composite nanoceramics. The synthesis starts with a 4 h reflux in hexane of the mixture of the respective metal dimethylamides, which is followed by hexane evacuation, and reactions of the residue in liquid ammonia at −33 °C to afford a mixed metal amide/imide precursor. Plausible equilibration towards a bimetallic Al/Ga-dimethylamide compound upon mixing of the solutions of the individual metal-dimethylamide precursors containing dimeric Al[N(CH3)2]32 and dimeric Ga[N(CH3)2]32 is confirmed by 1H- and 13CH-NMR spectroscopy in C6D6 solution. The precursor is pyrolyzed under ammonia at 800 and 950 °C yielding, respectively, two different reaction-mixed composite nitride nanopowders. The latter are subjected to no-additive high-pressure and high-temperature sintering under conditions either conservative for the initial powder nanocrystallinity (650 °C, 7.7 GPa) or promoting crystal growth/recrystallization and, possibly, solid solution formation via reactions of AlN and GaN towards Al0.5Ga0.5N (1000 and 1100 °C, 7.7 GPa). The sintered composite pellets show moderately high mechanical hardness as determined by the Vicker’s method. The starting nanopowders and resulting nanoceramics are characterized by powder XRD, Raman spectroscopy, and SEM/EDX. It is demonstrated that, in addition to the multi-nitride composite nanoceramics of hexagonal AlN/hexagonal GaN/cubic TiN, under specific conditions the novel composite nanoceramics made of hexagonal Al0.5Ga0.5N and cubic TiN can be prepared.

In this study we perform a comparison of the reaction mechanism and the activation barrier for the rate-determining step in various metal nitrides (Ta3N5, Mn6N5, Fe3Mo3N, Co3Mo3N) for the ammonia synthesis reaction. The reactions are explained with simplified schematics and the energy profiles for the various reaction mechanisms are given in order to screen the catalytic activity of the catalysts for the ammonia synthesis reaction. We find that the catalytic activity ranks in the following order: Co3Mo3N > Fe3Mo3N > Ta3N5 > Mn6N5. We also find that the reaction mechanism proceeds either by a Langmuir–Hinshelwood and an Eley–Rideal/Mars–van Krevelen mechanism. This is an overview of about 10 years of computational research conducted to provide an overview of the progress established in this field of study.

Introducing an extremely thin layer of boron nitride between a sapphire substrate and the gallium nitride semiconductor grown on it is shown to facilitate the transfer of the resulting nitride structures to more flexible and affordable substrates. Lift-off for nitride semiconductors Nitride semiconductors are renowned for their excellent electronic and optical properties and are the materials of choice for many optical devices, including BluRay players. But they have an important practical drawback: they are very particular about the substrates (typically sapphire) on which they can be grown. This has stimulated the search for new ways of transferring such materials from one substrate to another. Here Kobayashi et al . demonstrate, using a gallium nitride-based device, that the addition of an extremely thin layer of hexagonal boron nitride to the initial growth surface facilitates the straightforward mechanical release of the resulting nitride structures, as well as subsequent transfer to any suitable substrate, including metals, glass and transparent plastics. Nitride semiconductors are the materials of choice for a variety of device applications, notably optoelectronics 1 , 2 and high-frequency/high-power electronics 3 . One important practical goal is to realize such devices on large, flexible and affordable substrates, on which direct growth of nitride semiconductors of sufficient quality is problematic. Several techniques—such as laser lift-off 4 , 5 —have been investigated to enable the transfer of nitride devices from one substrate to another, but existing methods still have some important disadvantages. Here we demonstrate that hexagonal boron nitride (h-BN) can form a release layer that enables the mechanical transfer of gallium nitride (GaN)-based device structures onto foreign substrates. The h-BN layer serves two purposes: it acts as a buffer layer for the growth of high-quality GaN-based semiconductors, and provides a shear plane that makes it straightforward to release the resulting devices. We illustrate the potential versatility of this approach by using h-BN-buffered sapphire substrates to grow an AlGaN/GaN heterostructure with electron mobility of 1,100 cm 2  V −1  s −1 , an InGaN/GaN multiple-quantum-well structure, and a multiple-quantum-well light-emitting diode. These device structures, ranging in area from five millimetres square to two centimetres square, are then mechanically released from the sapphire substrates and successfully transferred onto other substrates.

Recent measurements of the band properties of AlN and GaN by fluorescence yield absorption and soft X-ray emission spectroscopies revealed that their valence band (VB) is composed of two separate subbands. The upper VB subband of GaN is composed of gallium sp and nitrogen p orbitals; the lower subband consists of metal d and nitrogen s orbitals. These findings were confirmed by extensive ab initio simulations. These results are not consistent with the standard tetrahedrally coordinated semiconductors, which are bonded by sp3-hybridized orbitals of metal and nonmetal atoms. The new analysis techniques and ab initio simulations create a new picture, allowing the calculation of overlap integrals to determine the bond order in these crystals. According to these results, bonding occurs between resonant p-states of nitrogen and sp3-hybridized metal orbitals in tetrahedral nitrides, allowing tetrahedral symmetry to be maintained. A similar resonant bonding mechanism is observed in hexagonal BN, where the p orbitals of nitrogen create three resonant states necessary for maintaining the planar symmetry of the lattice. In addition, nonresonant π-type bonds in BN are created by the overlap of pz orbitals of boron and nitrogen. BN bonding differs from that in graphene, where carbon states are fully sp2-hybridized. Additionally, π-type bonds in graphene have no ionic contributions, which leads to the formation of Dirac states with linear dispersion close to the K point, closing the band gap.

This paper proposes a mathematical description of nitriding atmospheres obtained from a one-component ammonia ingoing atmosphere and a two-component ammonia inlet nitrogen-diluted atmosphere. The Fe-N phase equilibrium diagrams of the nitriding atmosphere in the hydrogen content-temperature (Q-T) system for selected NH[sub.3]/N[sub.2] atmosphere compositions are presented. The nitriding atmosphere obtained with different degrees of nitrogen dilution of the ingoing atmosphere was characterized. It has been shown that in processes carried out in nitriding atmospheres obtained from a two-component atmosphere with nitrogen, there is no direct relationship between the value of the nitrogen potential and the degree of dilution of the ingoing atmosphere with nitrogen. It has been shown analytically and confirmed experimentally that with changes in the degree of dilution of ammonia with nitrogen, the hydrogen content of the nitriding atmosphere and, consequently, the nitrogen availability of the nitriding atmosphere change. Using the example of nitriding AISI 52100 steel, it has been experimentally demonstrated that the change in nitrogen availability, caused by a change in the degree of dilution of the ingoing atmosphere with nitrogen, is not accompanied by a change in the value of the nitrogen potential. It has also been shown that the change in the nitrogen availability of the nitriding atmosphere, induced by the change in the composition of the aNH[sub.3]/bN[sub.2] ingoing atmosphere, affects the kinetics of nitrogen mass gain in the nitrided layer and the distribution of nitrogen mass between the iron nitride layer and the solution zone. It has also been shown that with the change in nitrogen availability, what changes in addition to the thickness of the iron nitride layer is also the phase composition of the layer. Using gravimetric tests, the mass of nitrogen in the iron nitride layer and the solution zone has been determined. To describe the equilibrium between the NH[sub.3]/H[sub.2] atmosphere and nitrogen in the different iron phases, a modified Lehrer diagram in the coordinate system of temperature and hydrogen content in the nitriding atmospheres (T-Q) has been proposed.

Two-dimensional film materials with unique atomic structures and electronic operation modes have demonstrated amazing application potential and value in the field of high technology. Among the various methods for preparing 2D film materials, PLD technology has become the preferred technology for rapid and green preparation of high-quality, complex structured 2D film materials due to its features such as maintaining the excellent stoichiometric ratio of the target, strong process flexibility, and non-polluting environment. Therefore, this paper discusses the exciting topic of PLD technology in the preparation and application of 2D film materials. Based on a systematic exposition of its basic principles and influencing factors, it provides a detailed overview of the current application status of PLD technology in the preparation of various 2D film materials such as carbides, sulfides, oxides, nitrides, and perovskites. Meanwhile, the advantages and disadvantages of PLD technology in the preparation of 2D film materials were also positively summarized, and the challenges and emerging strategies it faces in the future preparation of 2D film materials were cautiously discussed. This provides practical suggestions and reflections for the sustainable development of PLD technology in the fields of basic research, performance regulation, device development, and application of 2D film materials preparation.

Today, the introduction of wide band gap (WBG) semiconductors in power electronics has become mandatory to improve the energy efficiency of devices and modules and to reduce the overall electric power consumption in the world. Due to its excellent properties, gallium nitride (GaN) and related alloys (e.g., AlxGa1−xN) are promising semiconductors for the next generation of high-power and high-frequency devices. However, there are still several technological concerns hindering the complete exploitation of these materials. As an example, high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures are inherently normally-on devices. However, normally-off operation is often desired in many power electronics applications. This review paper will give a brief overview on some scientific and technological aspects related to the current normally-off GaN HEMTs technology. A special focus will be put on the p-GaN gate and on the recessed gate hybrid metal insulator semiconductor high electron mobility transistor (MISHEMT), discussing the role of the metal on the p-GaN gate and of the insulator in the recessed MISHEMT region. Finally, the advantages and disadvantages in the processing and performances of the most common technological solutions for normally-off GaN transistors will be summarized.

Graphitic carbon nitride (g-C[sub.3]N[sub.4]), recognized for its considerable potential as a heterogeneous photocatalyst in water splitting, has attracted extensive research interest. By using density functional theory (DFT) calculations, the regulatory role of p-block metal (PM) single atoms on the photocatalytic activity of g-C[sub.3]N[sub.4] in overall water splitting was systematically explored. The incorporation of PM atoms (Ge, Sn and Pb) led to a reduction in the overpotentials required for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Combined with the electronic structures analysis via hybrid functional, it was found that the introduction of Ge, Sn or Pb optimizes the positions of the valence band maximum (VBM) and the conduction band minimum (CBM), providing a robust driving force for HER and ensuring substantial driving force for OER. Meanwhile, the presence of these three PMs induces the spatial separation of VBM and CBM, inhibiting the recombination of carriers. These findings have significant implications for the design and preparation of efficient photocatalysts.