Hot-wire photonics: materials, science, and technology

The prospect of an integrated photonic technology has fueled an effort to understand the optical properties and to gauge the photonic engineering potential of hydrogenated amorphous silicon-based materials. Of particular interest for photonic engineering is the tunable range of the refractive index in amorphous silicon and the fast and slow light induced optical changes. The advance of photonic-engineered amorphous silicon technology requires an investigation into the relationships among fabrication processes, material properties, and the interrelations among the various optically important parameters. Here, the experimental investigation into H-implant refractive engineered amorphous silicon materials is detailed. Interestingly, the H-implant can interact with the amorphous structure to produce compacting of the structure, which may indicate refractive index increase. In addition, the evolving prospects for an amorphous silicon-based photonic technology will be up-dated. Waveguide-based light valve structures for the further scientific investigation of light induced refractive index change in amorphous silicon and technological applications are described.     

Phase formation under non-equilibrium processing conditions: rapid solidification processing and mechanical alloying

Rapid solidification processing (RSP) of metallic alloys, involving solidification of liquid metals at very high rates, results in the formation of a variety of metastable phases such as supersaturated solid solutions, crystalline intermetallic compounds, quasicrystalline phases, and metallic glasses. Additionally, significant refinement of the grain sizes and segregation patterns also occurs. Mechanical alloying (MA), another powerful non-equilibrium processing technique, utilizes repeated cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill. MA also results in the formation of metastable phases and microstructural refinement similar to what happens during RSP. Consequently, comparisons are frequently made between the phases produced by RSP and MA and the general understanding is that they both result in similar metastable effects. A detailed analysis of the metastable phases produced by RSP and MA is made in the present work, and it is shown that even though the effects may appear similar, the mechanisms of formation and the composition ranges in which particular phases form are quite different. These two methods also have some unique features and produce different phases. The differences have been ascribed to the fact that RSP involves solidification from the melt while MA is a completely solid-state process that is not restricted by the phase diagram.     

Recent advances in computational materials design: methods,applications, algorithms,and informatics

Journal of Materials Science -     

The solidification characteristics of near rapid and supercooling directional solidification

In the comparison of the solidification characteristics of supercooling directional solidification (SDS) with constrained directional solidification (DS) and with the consideration of the inheritance of supercooled melt, the SDS technique established with the combination of melt supercooling and traditional DS was proposed. An exploring study on SDS techniques was also conducted using appropriate facilities, designed and manufactured by the authors’ laboratory and the deep supercooling of Cu–5.0%Ni alloy, and its DSs were implemented.     

The solidification characteristics of near rapid and supercooling directional solidification

In the comparison of the solidification characteristics of supercooling directional solidification (SDS) with constrained directional solidification (DS) and with the consideration of the inheritance of supercooled melt, the SDS technique established with the combination of melt supercooling and traditional DS was proposed. An exploring study on SDS techniques was also conducted using appropriate facilities, designed and manufactured by the authors’ laboratory and the deep supercooling of Cu–5.0%Ni alloy, and its DSs were implemented.     

Functional gradients and heterogeneities in biological materials: Design principles,functions, and bioinspired applications

Living organisms have ingeniously evolved functional gradients and heterogeneities to create high-performance biological materials from a fairly limited choice of elements and compounds during long-term evolution and selection. The translation of such design motifs into synthetic materials offers a spectrum of feasible pathways towards unprecedented properties and functionalities that are favorable for practical uses in a variety of engineering and medical fields. Here, we review the basic design forms and principles of naturally-occurring gradients in biological materials and discuss the functions and benefits that they confer to organisms. These gradients are fundamentally associated with the variations in local chemical compositions/constituents and structural characteristics involved in the arrangement, distribution, dimensions and orientations of the building units. The associated interfaces in biological materials invariably demonstrate localized gradients and a variety of gradients are generally integrated over multiple length-scales within the same material. The bioinspired design and applications of synthetic functionally graded materials that mimic their natural paradigms are revisited and the emerging processing techniques needed to replicate the biological gradients are described. It is expected that in the future bioinspired gradients and heterogeneities will play an increasingly important role in the development of high-performance materials for more challenging applications.     

Effect of rapid solidification processing on corrosion resistance of Cu-Ni-Cr alloys

Cu-Ni-Cr ribbons produced by rapid solidification were studied for their corrosion resistance and compared with their counterparts produced by conventional metallurgy. The corrosion rate of the rapidly solidified Cu-Ni-Cr ribbons varies with composition and is many times lower than that of conventional alloy ingots for some compositions.     

Combinatorial solid state materials science and technology

Conventional ‘one by one’ synthesis approach has been a major rate limiting step in the systematic exploration of increasingly complex materials for the demanding new technologies. New concepts of ‘combinatorial chemistry’ are presented for the substantially efficient and cost-effective parallel synthesis and optimization of variety of multicomponent compounds as well as artificially designed lattices and devices. Effectiveness of variety of application areas developed by us is discussed with typical examples and brief review of the merits, challenges, current status and the future directions.     

Recent advances in anisotropic two-dimensional materials and device applications

Two-dimensional(2D)materials,such as transition metal dichalcogenides(TMDs),black phosphorus(BP),MXene and borophene,have aroused extensive attention since the discovery of graphene in 2004.They have wide range of applications in many research fields,such as optoelectronic devices,energy storage,catalysis,owing to their striking physical and chemical properties.Among them,anisotropic 2D material is one kind of 2D materials that possess different properties along different directions caused by the intrinsic anisotropic atoms5 arrangement of the 2D materials,mainly including BP,borophene,low-symmetry TMDs(ReSe2 and ReSa)and group IV monochalcogenides(SnS,SnSe,GeS,and GeSe).Recently,a series of new devices has been fabricated based on these anisotropic 2D materials.In this review,we start from a brief introduction of the classifications,crystal structures,preparation techniques,stability,as well as the strategy to discriminate the anisotropic characteristics of 2D materials.Then,the recent advanced applications including electronic devices,optoelectronic devices,thermoelectric devices and nanomechanical devices based on the anisotropic 2D materials both in experiment and theory have been summarized.Finally,the current challenges and prospects in device designs,integration,mechanical analysis,and micro-/nano-fabrication techniques related to anisotropic 2D materials have been discussed.This review is aimed to give a generalized knowledge of anisotropic 2D materials and their current devices applications,and thus inspiring the exploration and development of other kinds of new anisotropic 2D materials and various novel device applications.     

The Young's moduli of in situ Ti/TiB composites obtained by rapid solidification processing

In situ Ti/TiB composites (Ti-6Al-4V matrix reinforced with TiB phase) with different volume fractions of the TiB phase, have been produced by consolidation of rapidly solidified Ti-6Al-4V alloys with different levels of boron addition. The microstructural examination of such composites shows that the reinforcing phase has a fine grain size and a uniform distribution throughout the matrix. The Young's moduli of the in situ composites have been determined experimentally to study the strengthening effect of the TiB phase. It was found that the Young's modulus of an in situ composite with 10 vol % TiB phase can be increased to 140 GPa, compared to 116.7 GPa for the matrix alloy. The theoretical predictions are in good agreement with the present experimental results and other results of similar composites obtained by the reactive sintering technique.     

Design and processing of porous materials for electronic applications

The use of porosity, either unintentionally or intentionally, in the fabrication of materials for electronic and optoelectronic applications is introduced. Unintentional uses include the fabrication of ceramic magnets, where high electrical resistivities are required to reduce eddy currents at high frequency, and the powder technology, often used, inevitably results in porosity. The generation of light from porous silicon created a huge impact in the early 1990s, followed by extensive work on the mechanism responsible, and has now been followed by a more balanced evaluation of its potential. Porous ferroelectrics have shown significant advantages over dense materials for positive temperature coefficient of resistance applications, and for sensors such as hydrophones, and these will be discussed. Low dielectric constant materials are required for the next generation of silicon integrated circuits, where a reduction compared with silicon dioxide is required, and here porosity is a convenient strategy. Finally, the use of deliberately engineered porous nanostructures, with dimensions in the range of the wavelength of light, are discussed for applications in optical processing.     

Sol-gel processing of materials for electronic and related applications

Various techniques of sol-gel processing for the preparation of electronic and related materials are described and reviewed. Typical examples are chosen from thin films and coatings of gels, crystalline materials and glasses as also bulk glasses to illustrate the variations in processing parameters and material properties.     

Structure of nanocomposites of Al-Fe alloys prepared by mechanical alloying and rapid solidification processing

Structures of Al-based nanocomposites of Al-Fe alloys prepared by mechanical alloying (MA) and subsequent annealing are compared with those obtained by rapid solidification processing (RSP). MA produced only supersaturated solid solution of Fe in Al up to 10 at.% Fe, while for higher Fe content up to 20 at.% the nonequilibrium intermetallic Al₅Fe₂ appeared. Subsequent annealing at 673 K resulted in more Al₅Fe₂ formation with very little coarsening. The equilibrium intermetallics, Al₃Fe (Al₁₃Fe₄), was not observed even at this temperature. In contrast, ribbons of similar composition produced by RSP formed fine cellular or dendritic structure with nanosized dispersoids of possibly a nano-quasicrystalline phase and amorphous phase along with α-Al depending on the Fe content in the alloys. This difference in the product structure can be attributed to the difference in alloying mechanisms in MA and RSP.     

Advances in science and technology of modern energetic materials: an overview

Energetic materials such as explosives, propellants and pyrotechnics are widely used for both civilian and military explosives applications. The present review focuses briefly on the synthesis aspects and some of the physico-chemical properties of energetic materials of the class: (a) aminopyridine-N-oxides, (b) energetic azides, (c) high nitrogen content energetic materials, (d) imidazoles, (e) insensitive energetic materials, (f) oxidizers, (g) nitramines, (h) nitrate esters and (i) thermally stable explosives. A brief comment is also made on the emerging nitration concepts. This paper also reviews work done on primary explosives of current and futuristic interest based on energetic co-ordination compounds. Lead-free co-ordination compounds are the candidates of tomorrow's choice in view of their additional advantage of being eco-friendly. Another desirable attribute of lead free class of energetic compounds is the presence of almost equivalent quantity of fuel and oxidizer moieties. These compounds may find wide spectrum of futuristic applications in the area of energetic materials. The over all aim of the high energy materials research community is to develop the more powerful energetic materials/explosive formulations/propellant formulations in comparison to currently known benchmark materials/compositions. Therefore, an attempt is also made to highlight the important contributions made by the various researchers in the frontier areas energetic ballistic modifiers, energetic binders and energetic plasticizers.