Patrick Soukiassian

Hydrogen Sensor Made of Porous Silicon and Covered by TiO

Hydrogen sensor working at room and 40degC temperatures made of porous silicon covered by the TiO2-x or ZnO(Al) thin film was realized. Porous silicon layer was formed by electrochemical anodization on a p- and n-type Si surface. Thereafter, n-type TiO2-x and ZnO(Al) thin films were deposited onto the porous silicon surface by electron-beam evaporation and magnetron sputtering, respectively. Platinum catalytic layer and Au electric contacts were for further measurements deposited onto obtained structures by ion-beam sputtering. The sensitivity of manufactured structures to 1000-5000 ppm of hydrogen, propane-butane mixture, and humidity was studied. Sensitivity of obtained structures was determined as ratio of the resistivity of structures in the presence of investigated gas to that in air. Results of sensitivity measurements showed that it is possible to realize a hydrogen nanosensor, resistivity of which can be decreased up to 2.5 times at room temperature and four times at 40degC for the Pt/TiO2-x/PS structure, as well as two times for the Pt/ZnO(Al)/PS structure at 40degC at 5000 ppm hydrogen concentration, respectively. Both structures have the recovery and response time of approximately 20 s and rather high durability and selectivity to hydrogen gas.

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The liquid phase epitaxy technique is used for self-assembled InAsSbP-based strain-induced islands and quantum dots (QD) formation on InAs(1u20090u20090) substrates. The morphology, dimensions (size and shape), distribution density and composition of these objects are investigated by scanning electron and atomic force microscopies (SEM and AFM) and found to be self-organized from pyramids to globes. In addition, we perform energy dispersive x-rays analysis measurements at the top and bottom angles of the InAsSbP quaternary pyramids and lattice mismatch ratio calculations. They show that the strength at the top of the pyramids is lower than at the bottom angles, and that the island size becomes smaller when the lattice mismatch decreases. The QD average density ranges from 5 to 7 × 109u2009cm−2, with height and width dimensions from 0.7u2009nm to 25u2009nm and 20u2009nm to 80u2009nm, respectively. A critical size (~500u2009nm) for the transformation of the InAsSbP-based strain-induced pyramid shape to globe shape is determined.

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The year 2014 marks the first decade of the rise of graphene. Graphene, a single atomic layer of carbon atoms in sp2 bonding configuration having a honeycomb structure, has now become a well-known and well-established material. Among some of its many outstanding fundamental properties, one can mention a very high carrier mobility, a very large spin diffusion length, unsurpassed mechanical properties as graphene is the strongest material ever measured and an exceptional thermal conductivity scaling more than one order of magnitude above that of copper. After the first years of the graphene rush, graphene growth is now well controlled using various methods like epitaxial growth on silicon carbide substrate, chemical vapour deposition (CVD) or plasma techniques on metal, insulator or semiconductor substrates. More applied research is now taking over the initial studies on graphene production. Indeed, graphene is a promising material for many advanced applications such as, but not limited to, electronic, spintronics, sensors, photonics, micro/nano-electromechanical (MEMS/NEMS) systems, super-capacitors or touch-screen technologies. In this context, this Special Issue of the Journal of Physics D: Applied Physics on graphene reviews some of the recent achievements, progress and prospects in this field. It includes a collection of seventeen invited articles covering the current status and future prospects of some selected topics of strong current interest. This Special Issue is organized in four sections. The first section is dedicated to graphene devices, and opens with an article by de Heer et al on an investigation of integrating graphene devices with silicon complementary metal–oxide–semiconductor (CMOS) technology. Then, a study by Svintsov et al proposes a lateral all-graphene tunnel field-effect transistor (FET) with a high on/off current switching ratio. Next, Tsukagoshi et al present how a band-gap opening occurs in a graphene bilayer by using a perpendicular electric field to operate logic gates. Placais et al then show the realization of graphene microwave nano-transistors that are especially suitable for fast charge detectors. Matsumoto et al describe next some interesting graphene-based biosensor applications, while the following article by Otsuji et al shows recent advances in plasmonics in terahertz device applications. This section ends with the Dollfus et al article dealing with non-linear effects in graphene devices investigated by simulation methods. The second section concerns the electronic and transport properties and includes four articles. The first one by Gurzadyan et al provides an investigation of graphene oxide in water by femtosecond pump–probe spectroscopy to study its transient absorption properties. Jouault et al then review the quantum Hall effect of self-organized graphene monolayers epitaxially grown on the C-face of SiC. Next, Petkovic et al report on the observation of edge magneto-plasmons in graphene. Finally, Roche and Valenzuela focus on the limits of conventional views in graphene spin transport and offer novel perspectives for further progress. The third section addresses graphene tailoring and functionalization as studied by Genorio and Znidarsic for graphene nanoribbons, or by atomic intercalation as shown by the two articles from Starke and Forti, and from Bisson et al. The last section is devoted to graphene growth and morphology. Ogino et al first describe a method to grow graphene on insulating substrates using polymer films as a carbon source. Then, Suemitsu et al show the recent progresses in epitaxial graphene formation on cubic silicon carbide thin films. Finally, Norimatsu and Kusunoki investigate the structural properties and morphology of epitaxial graphene grown on hexagonal silicon carbide substrates by using a high-resolution transmission electron microscope, their article closing this Special Issue .

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One of the key steps in nanotechnology is our ability to engineer and fabricate low-dimensional nano-objects, such as quantum dots, nanowires, two-dimensional atomic layers or three-dimensional nano-porous systems. Here we report evidence of nanotunnel opening within the subsurface region of a wide band-gap semiconductor, silicon carbide. Such an effect is induced by selective hydrogen/deuterium interaction at the surface, which possesses intrinsic compressive stress. This finding is established with a combination of ab-initio computations, vibrational spectroscopy and synchrotron-radiation-based photoemission. Hydrogen/deuterium-induced puckering of the subsurface Si atoms marks the critical step in this nanotunnel opening. Depending on hydrogen/deuterium coverages, the nanotunnels are either metallic or semiconducting. Dangling bonds generated inside the nanotunnel offer a promising template to capture atoms or molecules. These features open nano-tailoring capabilities towards advanced applications in electronics, chemistry, storage, sensors or biotechnology. Understanding and controlling such a mechanism open routes towards surface/interface functionalization.

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Microwave characteristics of barrier-injected (BARITT) diodes made of silicon carbide are investigated. It is shown that the negative resistance of p/sup +/-n-p/sup +/ structure made of different polytypes of SiC is an order of magnitude higher in absolute value in comparison with the Si p/sup +/-n-/sup +/ structure, all other factors being equal, even in the absence of trap levels (TLs). It is shown also that the dynamic negative resistance, in absolute value, the power output and efficiency increase with an increase of the concentration of traps. The effects of TLs in the band gap of the semiconductor on the impedance, power output, and efficiency of SiC BARITT diodes are examined,.

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Reflectance spectrum calculations of double- and triple-layer antireflection coatings based on porous silicon layer are performed using the optical matrix approach method. Obtained results are compared with the reflectance spectrum of the SiO2/TiO2 double-layer antireflection coating. A low reflectance value of both double- and triple-layer antireflection coatings made of porous silicon is observed in comparison to that SiO2/TiO2 antireflection coating. These results are of importance for solar cells application.

Thin Film

100 years have passed since the discovery of x-ray diffraction by von Laue, Knipping and nFriedrich. nThe scientific world owes a lot to Rontgen for the discovery of x-rays in 1895 and nwith the research efforts of W L and W H Bragg in 1912, the concept of Bragg’s law and ninterpretations given by P P Ewald, saw the birth of the wonderful field of crystallography. nToday, the scientific world sees the various tools delivered by this powerful technique as nindispensible, whether it concerns the development of advanced high-tech materials or the nstructural understanding of biological molecules or drug design. Diffraction and associated nmethods for structure analysis at the atomic scale are developed into powerful fingerprint nmethods, and have become the backbone of industry for quality inspection on one hand, and non the other hand, stand at the forefront of materials characterization in research laboratory. nBeyond these characterization tools available at laboratory level, large scale facilities n(LSF) and notably the neutron and synchrotron radiation sources became increasingly nimportant during the last decades. Diffraction with neutron or synchrotron radiation is nvery complementary, as outlined below: Neutrons have the corresponding wavelengths and nenergies directly related to interatomic distances and lattice dynamics. Thus, neutron scattering nenables simultaneous access to both structure and dynamics of any type of materials. nNeutrons also have a magnetic moment allowing direct characterization of the magnetic nstructure of materials at the microscopic scale. The possibility to easily vary the contrast of na single element using its different isotopes renders the neutron to be an irreplaceable tool nin chemistry, solid state physics, biology and soft matter. Then, having no electric charge, nneutrons can easily penetrate materials without significant absorption, allowing a nondestructive ncharacterization even on large volume fractions

Strain-induced InAsSbP islands and quantum dots grown by liquid phase epitaxy on a InAs(1?0?0) substrate

Atomic (H) hydrogen interaction onto the Si‐rich β‐SiC(100) 3×2 surface reconstruction is investigated by atom‐resolved scanning tunneling microscopy and spectroscopy, and core level and valence band photoemission spectroscopies. Contrary to its well‐known role in semiconductor surface passivation, atomic H is found to metallize the β‐SiC(100) 3×2 surface, which is the first example of H‐induced semiconductor surface metallization. This unexpected behavior results from competion between H termination of top surface dangling bonds and H‐induced asymmetric attack of the Si‐dimers located below the surface (3rd plane), leading to charge transfer and to metallization. The H‐covered 3C‐SiC(100) 3×2 surface metallization is not removed by oxygen.