Roland Madar

Bio: Roland Madar is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Thin film & Chemical vapor deposition. The author has an hindex of 23, co-authored 194 publications receiving 2136 citations.

Materials science: Silicon carbide in contention

Abstract: Silicon carbide is a highly desirable material for high-power electronic devices — more desirable even than silicon. And now the problem of producing large, pure wafers of the carbide could be solved.

Thermodynamic Heat Transfer and Mass Transport Modeling of the Sublimation Growth of Silicon Carbide Crystals

Abstract: The deposition of single SiC crystals has been processed inside a sealed enclosure at temperatures above 2300 K and pressures lower than 5 ⋅ 103 Pa by the modified Lely method. The purpose of this work is to examine the potentialities of different macroscopic models, thermodynamics, heat, and mass transfers on the simulation of the growth of such crystals with a special emphasis on their coupling mechanism. Thermodynamic modeling has been used to determine the most important reactive species involved in equilibrium conditions. Induction heating modeling has allowed the calculation of the actual temperatures inside the reactor which are not well known because of the difficulty associated with their measurements. Finally, mass transport modeling provided the calculated deposition rate. It was found that the calculated growth rates were close to the experimental ones which may indicate a good representation of the actual phenomena involved in the crucible. As a matter of fact each of the proposed models has contributed to a better knowledge of the process.

Nickel film on (001) SiC: Thermally induced reactions

Abstract: The reactions induced in a vacuum furnace (5×10−7 Torr) between an electron-beam-evaporated Ni film a few hundred nm thick and a (001)-oriented (i.e. Si-face-oriented) single crystalline 3C–SiC substrate are investigated by 3.2 MeV 4He2+ backscattering spectrometry, X-ray diffraction, secondary ion mass spectrometry, and scanning electron microscopy. Samples are characterized before and after annealing at temperatures of 400–700oC for 30 min. At 450oC, carbon diffuses throughout the Ni film and forms a carbon-rich layer at the Ni surface of a thickness of a few nm which remains unchanged during subsequent annealing. Some nickel silicides were detected at this initial stage but could not be clearly identified. At 450oC (after 120 min) the Ni31Si12 phase starts to form. This is the only detected phase at 500oC. The Ni2Si phase, the silicide that is thermodynamically stable with SiC and carbon, forms first at the surface and grows toward the SiC substrate. At 600oC, this reaction has consumed about half of the Ni31Si12 phase and at 700oC, Ni2Si is the only silicide in the reacted film. In all the reacted samples the carbon distribution is alike and consists of three distinct layers: a first zone with a constant carbon concentration that extends from near the SiC/silicide interface through most of the films thickness. The second zone is ∼70 nm thick and is deficient of carbon. The third zone is the thin graphite layer at the surface. There is oxygen in the film too, the distribution of which is related increasingly clearly to the carbon profile as the annealing temperature rises.

Alternative Plasmonic Materials: Beyond Gold and Silver

Abstract: 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.

Superconductivity in iron compounds

Abstract: 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.

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

Abstract: 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.

Single-crystal metallic nanowires and metal/semiconductor nanowire heterostructures

Abstract: 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.

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

Abstract: 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.