Individualization and Electrical Characterization of SiGe Nanowires

SiGe nanowires of different Ge atomic fractions up to 15% were grown and ex-situ n-type doped by diffusion from a solid source in contact with the sample. The phenomenon of dielectrophoresis was used to locate single nanowires between pairs of electrodes in order to carry out electrical measurements. The measured resistance of the as-grown nanowires is very high, but it decreases more than three orders of magnitude upon doping, indicating that the doping procedure used has been effectiv

SiGe nanowires grown by LPCVD using Ga-Au catalysts

The use of Ga-Au alloys as metal catalysts for the growth of SiGe nanowires has been investigated. The grown nanowires are cylindrical and straight, with a defect-free crystalline structure, sharp nanowire-droplet interfaces and an almost constant Ge atomic fraction throughout all their length. These features represent significant improvements over the results obtained using pure A

SiGe/Si nanowire axial heterostructures grown by LPCVD using Ga-Au

The use of Ga-Au alloys of different compositions as metal catalysts for the growth of abrupt SiGe/Si nanowire axial heterostructures has been investigated. The heterostructures grown in a continuous process by just switching the gas precursors, show uniform nanowire diameters, almost abrupt compositional changes and no defects between the different sections. These features represent significant improvements over the results obtained using pure Au

Hierarchically organized micellization of thermoresponsive rod-coil copolymers based on poly[oligo(ethylene glycol) methacrylate] and poly(ε-caprolactone)

A series of amphiphilic triblock copolymers, poly[oligo(ethylene glycol) methacrylate]x-block-poly(ε-caprolactone)-block-poly[oligo(ethylene glycol) methacrylate]x, POEGMACo(x), were synthesized. Formation of hydrophobic domains as cores of the micelles was studied by fluorescence spectroscopy. The critical micelle concentrations in aqueous solution were found to be in the range of circa 10⁻⁶ M. A novel methodology by modulated temperature differential scanning calorimetry was developed to determine critical micelle temperature. A significant concentration dependence of cmt was found. Dynamic light scattering measurements showed a bidispersed size distribution. The micelles showed reversible dispersion/aggregation in response to temperature cycles with lower critical solution temperature between 75 and 85 °C. The interplay of the two hydrophobic and one thermoresponsive macromolecular chains offers the chance to more complex morphologies.The authors are indebted to Francesç Catala, from Mettler-Toledo, for valuable discussions. The authors are grateful to LABMET, TEM Laboratory associated to the Comunidad Autónoma de Madrid network and Mr. J. González-Casablanca for his cooperation with the TEM images. The authors would like to thank the Plan Nacional IþDþI (Ministerio de Ciencia e Innovación) for financial support (MAT2009-09671) as well as the Comunidad Autónoma de Madrid for the funding through IþD Program (S0505/MAT-0227)

Raman spectroscopy in Group IV nanowires and nanowire axial heterostructures

The control of the SiGe NW composition is fundamental for the fabrication of high quality heterostructures. Raman spectroscopy has been used to analyse the composition of SiGe alloys. We present a study of the Raman spectrum of SiGe nanowires and SiGe/Si heterostructures. The inhomogeneity of the Ge composition deduced from the Raman spectrum is explained by the existence of a Ge-rich outer shell and by the interaction of the NW with the electromagnetic field associated with the laser beam

PVDF based nanocomposites produced by solution blow spinning, structure and morphology induced by the presence of MWCNT and their consequences on some properties

Nanocomposites based on poly(vinylidene fluoride), PVDF, filled with multiwalled carbon nanotubes, MWCNT, were prepared by solution blow spinning, SBS. PVDF was modified with MWCNT with the aim of changing final properties inducing structural and morphological variations in the polymer by the simple presence of conductive particles. Different compositions were considered (0%, 1%, 2%, 3%, and 5% by weight of MWCNT) to understand the influence of the presence of MWCNT on the polymer structure, morphology, and consequently other properties. Morphology was inspected by optical and electron (SEM and TEM) microscopies, while structure was studied by Fourier transformed infrared spectroscopy, FTIR. Thermal behavior was monitored by differential scanning calorimetry, DSC, while the surface and electrical properties were studied by contact angle and capacitance measurements, respectively. SBS allowed obtaining mats of nanocomposites constituted by submicrometric fibers where the MWCNT are uniformly dispersed and well aligned along the PVDF fibers. In this study, several aspects about structure and thermal behavior of PVDF were clarified in relation to other researches carried out up to the moment. Although MWCNT concentration did not seem to affect much the fibrous morphology of the SBS materials, the PVDF crystalline structure and surface properties of the materials were slightly modified. Dielectric behavior of PVDF was highly affected by the presence of MWCNT leading to a particular change in the permittivity and being possible to obtain a value of 0.023 for the percolation fraction.The authors appreciate the financial support received from the Ministerio de Economía y Competitividad [MAT2014-59116-C2]; the Universidad Carlos III de Madrid due to Fondos de Investigación de Fco. Javier González Benito [2012/00130/004] and the strategic Action in Composites materials and interphases [2011/00287/002]. TEM characterization was made at LABMET, associated to the Red de Laboratorios de la Comunidad de Madrid.Publicad

Nanopatterning of silicon surfaces by low-energy ion-beam sputtering: dependence on the angle of ion incidence

5 pages, 3 figures.-- PACS nrs.: 81.16.Rf, 81.65.Cf, 68.35.B-, 68.37.Lp, 68.37.Ps, 68.47.Fg.We report on the production of nanoscale patterning on Si substrates by low-energy ion-beam sputtering. The surface morphology and structure of the irradiated surface were studied by atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). Under ion irradiation at off-normal incidence angle (~50°), AFM images show the formation of both nanoripple and sawtooth-like structures for sputtering times longer than 20 min. The latter feature coarsens appreciably after 60 min of sputtering, inducing a large increase in the surface roughness. This behaviour is attributed to the preferential direction determined on the substrate by the ion beam for this incidence angle, leading to shadowing effects among surface features in the sputtering process. Under irradiation at normal incidence, the formation of an hexagonal array of nanodots is induced for irradiation times longer than 2 min. The shape and crystallinity of the nanodots were determined by HRTEM. At this incidence angle, the surface roughness is very low and remains largely unchanged even after 16 h of sputtering. For the two angle conditions studied, the formation of the corresponding surface structures can be understood as the interplay between an instability due to the sputtering yield dependence on the local surface curvature and surface smoothing processes such as surface diffusion.Publicad

Structural stability of SiGe nanoparticles under "in situ" electron beam irradiation in TEM

The structure of amorphous and crystalline SiGe nanoparticles, embedded in a dielectric medium, SiO2, and its stability under “in situ” electron beam irradiation is reported. High-resolution transmission electron microscopy and electron-diffraction pattern simulation by fast Fourier transform was used to analyze the crystal structure of the SiGe nanoparticles. Electron beam irradiation induces structural alternate order-disorder transitions in the nanoparticles for irradiation effects are mainly associated to the density of current. For irradiation with current densities < 7 A·cm-2 no effects are observed in the as-deposited amorphous samples, whereas in the crystallized samples, SiGe nanocrystals show higher stability and no effects are observed for irradiation densities of current < 50 A·cm-2. Irradiation with densities of current greater than these thresholds cause consecutive amorphous-crystalline or crystalline-amorphous structure transitions respectively for both amorphous and crystallized nanoparticles. A hexagonal structure is proposed for those nanocrystals obtained after irradiation in the as deposited amorphous samples

Anisotropy of uni-axial and bi-axial deformation behavior of pure Titanium after hydrostatic extrusion

Coarse-grained commercially pure (CP) Titanium is subjected to hydrostatic extrusion resulting in the formation of ultrafine lamellar-type microstructure having very strong fiber texture. Uni-axial tensile tests of longitudinal and transverse specimens are carried out to study anisotropy of uni-axial deformation behavior of hydrostatically extruded CP Titanium. Small punch testing of longitudinal and transverse specimens is performed to study the anisotropy of its bi-axial deformation behavior. It is demonstrated that there is significant anisotropy of both uni-axial and bi-axial deformation of CP Titanium after hydrostatic extrusion which is related to the specific microstructure and texture developed in the material during hydrostatic extrusion.This work was carried out in frames of the European project LIMEDU (FP7 ERA-NET MATERA+2009, Project No MATERA/ESM- 1889) funded by Fundacion MADRI+D and by the National Centre for Research and Development (Project NCBiR/ERA-NET MATERA+/03/ 2011)

Fabrication and characterization of Y₂O₃ dispersion strengthened copper alloys

Part of special issue: Proceedings of the 16th International Conference on Fusion Reactor Materials (ICFRM-16).Three copper base materials were fabricated following different routes: cast Cu–1 wt.%Y (C-Cu1Y) produced by vacuum induction melting, and Cu–1 wt.%Y (PM-Cu1Y) and Cu–1 wt.%Y2O3 (PM-Cu1Y2O3) both processed by a powder metallurgy route and sintering by hot isostatic pressing. PM-Cu1Y alloy was prepared by cryomilling and PM-Cu1Y2O3 by conventional milling at room temperature. The materials were characterized by X-ray diffraction, optical and electron microscopy and microhardness measurements. C-Cu1Y presents a characteristic eutectic microstructure while PM-Cu1Y2O3 exhibits a composite like microstructure. Electron microscopy analyses of as-HIP PM-Cu1Y revealed irregular decoration of yttrium-rich oxides at the grain boundaries and an inhomogeneous dispersion of polygonal shaped yttrium-rich oxides dispersed in the Cu matrix. Tensile tests performed on PM-Cu–1Y on the temperature range of 293–773 K have showed a decrease of the yield strength at temperatures higher than 473 K, and monotonically decrease of the ultimate tensile strength and maximum plastic strain on increasing temperature.This research has been supported by Ministerio de Economía y Competitividad of Spain (ENE2012-39787-C06-05). The financial support from the Comunidad de Madrid, through the programs TECHNOFUSION (S2009/ENE-1679) and ESTRUMAT (CM S2009MAT-1585), and the additional subvention from EURATOM/CIEMAT association through contract EFDA (WP12-MAT-HHFMAM-02) are also gratefully acknowledged.Publicad