Materials research plays a vital role in transforming breakthrough scientific ideas into next-generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions.

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Alternative Plasmonic Materials: Beyond Gold and Silver

Kamihara and coworkers' report of superconductivity at ${T}_{c}=26\text{ }\text{ }\mathrm{K}$ in fluorine-doped LaFeAsO inspired a worldwide effort to understand the nature of the superconductivity in this new class of compounds. These iron pnictide and chalcogenide (FePn/Ch) superconductors have Fe electrons at the Fermi surface, plus an unusual Fermiology that can change rapidly with doping, which lead to normal and superconducting state properties very different from those in standard electron-phonon coupled ``conventional'' superconductors. Clearly, superconductivity and magnetism or magnetic fluctuations are intimately related in the FePn/Ch, and even coexist in some. Open questions, including the superconducting nodal structure in a number of compounds, abound and are often dependent on improved sample quality for their solution. With ${T}_{c}$ values up to 56 K, the six distinct Fe-containing superconducting structures exhibit complex but often comparable behaviors. The search for correlations and explanations in this fascinating field of research would benefit from an organization of the large, seemingly disparate data set. This review provides an overview, using numerous references, with a focus on the materials and their superconductivity.

Superconductivity in iron compounds

Silicon carbide (SiC), a material long known with potential for high-temperature, high-power, high-frequency, and radiation hardened applications, has emerged as the most mature of the wide-bandgap (2.0 eV ≲ Eg ≲ 7.0 eV) semiconductors since the release of commercial 6HSiC bulk substrates in 1991 and 4HSiC substrates in 1994. Following a brief introduction to SiC material properties, the status of SiC in terms of bulk crystal growth, unit device fabrication processes, device performance, circuits and sensors is discussed. Emphasis is placed upon demonstrated high-temperature applications, such as power transistors and rectifiers, turbine engine combustion monitoring, temperature sensors, analog and digital circuitry, flame detectors, and accelerometers. While individual device performances have been impressive (e.g. 4HSiC MESFETs with fmax of 42 GHz and over 2.8 W mm−1 power density; 4HSiC static induction transistors with 225 W power output at 600 MHz, 47% power added efficiency (PAE), and 200 V forward blocking voltage), material defects in SiC, in particular micropipe defects, remain the primary impediment to wide-spread application in commercial markets. Micropipe defect densities have been reduced from near the 1000 cm−2 order of magnitude in 1992 to 3.5 cm−2 at the research level in 1995.

Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: A review

Substantial effort has been placed on developing semiconducting carbon nanotubes and nanowires as building blocks for electronic devices--such as field-effect transistors--that could replace conventional silicon transistors in hybrid electronics or lead to stand-alone nanosystems. Attaching electric contacts to individual devices is a first step towards integration, and this step has been addressed using lithographically defined metal electrodes. Yet, these metal contacts define a size scale that is much larger than the nanometre-scale building blocks, thus limiting many potential advantages. Here we report an integrated contact and interconnection solution that overcomes this size constraint through selective transformation of silicon nanowires into metallic nickel silicide (NiSi) nanowires. Electrical measurements show that the single crystal nickel silicide nanowires have ideal resistivities of about 10 microOmega cm and remarkably high failure-current densities, >10(8) A cm(-2). In addition, we demonstrate the fabrication of nickel silicide/silicon (NiSi/Si) nanowire heterostructures with atomically sharp metal-semiconductor interfaces. We produce field-effect transistors based on those heterostructures in which the source-drain contacts are defined by the metallic NiSi nanowire regions. Our approach is fully compatible with conventional planar silicon electronics and extendable to the 10-nm scale using a crossed-nanowire architecture.

Single-crystal metallic nanowires and metal/semiconductor nanowire heterostructures

This review highlights the use and great potential of liquid metals as exotic and powerful solvents (i.e. fluxes) for the synthesis of intermetallic phases. The results presented demonstrate that considerable advances in the discovery of novel and complex phases are achievable utilizing molten metals as solvents. A wide cross-section of examples of flux-grown intermetallic phases and related solids are discussed and a brief history of the origins of flux chemistry is given. The most commonly used metal fluxes are surveyed and where possible, the underlying principal reasons that make the flux reaction work are discussed.

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The metal flux: a preparative tool for the exploration of intermetallic compounds.

A device for feeding precursors of one or more elements to be deposited on a hot substrate into a chemical vapour deposition chamber (1). The device includes at least one container (10) for the liquid or dissolved precursor(s) (11), a system (12) for maintaining a higher pressure in the container than in the chamber, at least one injector combined with each container and provided with a control unit for periodically injecting precursor droplets of a given volume into the deposition chamber, and a system (3) for delivering the vaporised injected materials to a substrate located in the deposition chamber.

Method and device for feeding precursors into a chemical vapour deposition chamber

Refractory metal silicides can be used as protective coatings for high temperature applications as well as interconnectors in silicon integrated circuits. A good understanding of their properties as thin films, however, requires a careful determination of their intrinsic physical and mechanical characteristics. We report resistivity and magnetoresistance measurements (4.2⩽ T ⩽300 K, H ⩽7.6 T) of monocrystalline VSi 2 (RRR ≈ 20) and TaSi 2 (RRR ⩾ 400) (RRR is the residual resistance ratio ρ(293 K)/ρ(4.2 K)). Single crystals have been obtained by Czochralski pulling from a levitated melt. Both materials crystallize in the hexagonal C40 structure (space group P 6222). The two metallic compounds have about the same anisotropic behaviour in resistivity. The measurements show a linear behaviour of resistivity at high temperatures (150 ⩽ T ⩽ 300 K) for the directions [0001] for both materials, whereas a negative deviation from the linearity is found at high temperatures ( T ⩾ 200 K) with the current parallel to the [1010] axis. For TaSi 2 a strong magnetoresistance effect has been observed, which is about 600 times stronger than the effect for VSi 2 .

Resistivity and magnetoresistance of monocrystalline TaSi2 and VSi2

Structural chemistry of a new ternary uranium rhodium phosphide - U6 Rh20 P13

Thermodynamic and experimental studies of the CVD of A-15 superconductors I. Nb3Ga

We have studied the direct bonding of platinum to silicon for applications where an electrical conduction through the bonding interface is desired. Platinum has been deposited on silicon wafers by mean of physical vapor deposition. Levels of surface roughness compatible with direct bonding have been achieved for the deposited Pt thin films. The surface preparation of the Pt films was performed using a diluted HF or H 2 SO 4 based chemistry. The sequence used allowed achieving the direct bonding of Pt to Si. The post bonding thermal treatments have been investigated. Such thermal treatments lead to the silicidation of the platinum layer. Adhesion between the wafers after the thermal treatments has been strengthened as measured by Maszara's blade technique (440 mJ/cm 2 were achieved after a 300°C thermal treatment). The morphological evolution of the buried silicide layer has been followed for different thermal budget by scanning electron microscopy. The higher thermal budgets probed (i.e., 700°C, 1 h) resulted in the agglomeration of the buried silicide layer, but without observing debonding of the two silicon wafers. The vertical electrical conduction has been measured for the final sample annealed at 300°C. Schottky type contacts have been obtained between the semiconductor and the silicide.

http://jes.ecsdl.org/content/158/3/H255.full.pdf

Roland Madar

Papers

Method and device for feeding precursors into a chemical vapour deposition chamber

Resistivity and magnetoresistance of monocrystalline TaSi2 and VSi2

Structural chemistry of a new ternary uranium rhodium phosphide - U6 Rh20 P13

Thermodynamic and experimental studies of the CVD of A-15 superconductors I. Nb3Ga

Direct Bonding of Silicon to Platinum