28,917 research outputs found
Aluminum nitride insulating films for MOSFET devices
Application of aluminum nitrides as electrical insulator for electric capacitors is discussed. Electrical properties of aluminum nitrides are analyzed and specific use with field effect transistors is defined. Operational limits of field effect transistors are developed
Solid-State Chemistry with Nonmetal Nitrides
Among the nonmetal nitrides, the polymeric binary compounds BN and Si3N4are of particular interest for the development of materials for high-performance applications. The outstanding features of both substances are their thermal, mechanical, and chemical stability, coupled with their low density. Because of their extremely low reactivity, boron and silicon nitride are hardly ever used as starting materials for the preparation of ternary nitrides, but are used primarily in the manufacture of crucibles or other vessels or as insulation materials. The chemistry of ternary and higher nonmetal nitrides that contain electropositive elements and are thus analogous with the oxo compounds such as borates, silicates, phosphates, or sulfates was neglected for many years. Starting from the recent successful preparation of pure P3N5, a further binary nonmetal nitride which shows similarities with Si3N4 with regard to both its structure and properties, this review deals systematically with the solid-state chemistry of ternary and higher phosphorus(V) nitrides and the relationship between the various types of structure found in this class of substance and the resulting properties and possible applications. From the point of view of preparative solid-state chemistry the syntheses, structures, and properties of the binary nonmetal nitrides BN, Si3N4, and P3N5 will be compared and contrasted. The chemistry of the phosphorus(V) nitrides leads us to expect that other nonmetals such as boron, silicon, sulfur, and carbon will also participate in a rich nitride chemistry, as initial reports indeed indicate
Structural classification of quasi-one-dimensional ternary nitrides
This review focuses on the crystal structural features of ternary (mixed-metal) quasi-one-dimensional nitrides i.e., nitrides containing (cation-³⁻) coordination polyhedra sharing either corners, edges, or faces, arranged in linear chains, and intercalated by a counter ion. The current relevance of these nitrides, and of quasi-one-dimensional compounds in general, lies in the fact that they are closely related to the pure one-dimensional systems (i.e., nanowires), which are vastly researched for their amazing properties closely related to their low dimensionality. A number of these properties were firstly discovered in quasi-one-dimensional compounds, highlighting the importance of expanding knowledge and research in this area. Furthermore, unlike oxides, nitrides and other non-oxide compounds are less developed, hence more difficult to categorise into structural classes that can then be related to other classes of compounds, leading to a fuller picture of structure–properties relationship. Within this context, this review aims to categorise and describe a number of ternary (mixed-metal) quasi-one-dimensional nitrides according to their structural features, specifically, the polyhedra forming the one-dimensional chains
A Map of the Inorganic Ternary Metal Nitrides
Exploratory synthesis in novel chemical spaces is the essence of solid-state
chemistry. However, uncharted chemical spaces can be difficult to navigate,
especially when materials synthesis is challenging. Nitrides represent one such
space, where stringent synthesis constraints have limited the exploration of
this important class of functional materials. Here, we employ a suite of
computational materials discovery and informatics tools to construct a large
stability map of the inorganic ternary metal nitrides. Our map clusters the
ternary nitrides into chemical families with distinct stability and
metastability, and highlights hundreds of promising new ternary nitride spaces
for experimental investigation--from which we experimentally realized 7 new Zn-
and Mg-based ternary nitrides. By extracting the mixed metallicity, ionicity,
and covalency of solid-state bonding from the DFT-computed electron density, we
reveal the complex interplay between chemistry, composition, and electronic
structure in governing large-scale stability trends in ternary nitride
materials
Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging: Part I - Processing parameters, mechanical properties and microstructure
A study simulating thin slab continuous casting followed by direct charging into an equalisation furnace has been undertaken based on six low carbon (0.06wt-%) vanadium microalloyed steels. Mechanical and impact test data showed properties were similar or better than those obtained from similar microalloyed conventional thick cast as rolled slabs. The dispersion plus dislocation strengthening was estimated to be in the range 80-250MPa.A detailed TEM/EELS analysis of the dispersion sized sub-15nm particles showed that in all the steels, they were essentially nitrides with little crystalline carbon detected. In the Steels V-Nb, V-Ti and V-Nb-Ti, mixed transition metal nitrides were present. Modelling of equilibrium precipitates in these steels, based on a modified version of ChemSage, predicted that only vanadium rich nitrides would precipitate in austenite but that the C/N ratio would increase through the two phase field and in ferrite. The experimental analytical data clearly points to the thin slab direct charging process, which has substantially higher cooling rates than conventional casting, nucleating non-equilibrium particles in ferrite which are close to stoichiometric nitrides. These did not coarsen during the final stages of processing, but retained their highly stable average size of ~7nm resulting in substantial dispersion strengthening. The results are considered in conjunction with pertinent published literature
Elastic and structural instability of cubic Sn3N4 and C3N4 under pressure
We use in-situ high pressure angle dispersive x-ray diffraction measurements
to determine the equation of state of cubic tin nitride Sn3N4 under pressure up
to about 26 GPa. While we find no evidence for any structural phase transition,
our estimate of the bulk modulus (B) is 145 GPa, much lower than the earlier
theoretical estimates and that of other group IV-nitrides. We corroborate and
understand these results with complementary first-principles analysis of
structural, elastic and vibrational properties of group IV-nitrides, and
predict a structural transition of Sn3N4 at a higher pressure of 88 GPa
compared to earlier predictions of 40 GPa. Our comparative analysis of cubic
nitrides shows that bulk modulus of cubic C3N4 is the highest (379 GPa) while
it is structurally unstable and should not exist at ambient conditions.Comment: 5 pages, 4 figure
Electronic excitation of transition metal nitrides by light ions with keV energies
We investigated the specific electronic energy deposition by protons and He
ions with keV energies in different transition metal nitrides of technological
interest. Data were obtained from two different time-of-flight ion scattering
setups and show excellent agreement. For protons interacting with light
nitrides, i.e. TiN, VN and CrN, very similar stopping cross sections per atom
were found, which coincide with literature data of N2 gas for primary energies
<= 25 keV. In case of the chemically rather similar nitrides with metal
constituents from the 5th and 6th period, i.e. ZrN and HfN, the electronic
stopping cross sections were measured to exceed what has been observed for
molecular N2 gas. For He ions, electronic energy loss in all nitrides was found
to be significantly higher compared to the equivalent data of N2 gas.
Additionally, deviations from velocity proportionality of the observed specific
electronic energy loss are observed. A comparison with predictions from density
functional theory for protons and He ions yields a high apparent efficiency of
electronic excitations of the target for the latter projectile. These findings
are considered to indicate the contributions of additional mechanisms besides
electron hole pair excitations, such as electron capture and loss processes of
the projectile or promotion of target electrons in atomic collisions
Distorted wurtzite unit cells: Determination of lattice parameters of non-polar a-plane AlGaN and estimation of solid phase Al content
Unlike c-plane nitrides, ``non-polar" nitrides grown in e.g. the a-plane or
m-plane orientation encounter anisotropic in-plane strain due to the anisotropy
in the lattice and thermal mismatch with the substrate or buffer layer. Such
anisotropic strain results in a distortion of the wurtzite unit cell and
creates difficulty in accurate determination of lattice parameters and solid
phase group-III content (x_solid) in ternary alloys. In this paper we show that
the lattice distortion is orthorhombic, and outline a relatively simple
procedure for measurement of lattice parameters of non-polar group III-nitrides
epilayers from high resolution x-ray diffraction measurements. We derive an
approximate expression for x_solid taking into account the anisotropic strain.
We illustrate this using data for a-plane AlGaN, where we measure the lattice
parameters and estimate the solid phase Al content, and also show that this
method is applicable for m-plane structures as well
Effects of macroscopic polarization in III-V nitride multi-quantum-wells
Huge built-in electric fields have been predicted to exist in wurtzite III-V
nitrides thin films and multilayers. Such fields originate from heterointerface
discontinuities of the macroscopic bulk polarization of the nitrides. Here we
discuss the background theory, the role of spontaneous polarization in this
context, and the practical implications of built-in polarization fields in
nitride nanostructures. To support our arguments, we present detailed
self-consistent tight-binding simulations of typical nitride QW structures in
which polarization effects are dominant.Comment: 11 pages, 9 figures, uses revtex/epsf. submitted to PR
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