Enhanced Signal Micro-Raman Study of SiGe Nanowires and SiGe/Si Nanowire Axial Heterojuntions Grown Using Au and Ga-Au Catalysts

Producción CientíficaMicroRaman spectroscopy was used for the characterization of heterostructured SiGe/Si nanowires. The NWs were grown with alloyed AuGa catalysts droplets with different Ga compositions aiming to make more abrupt heterojunctions. The heterojunctions were first characterized by TEM; then the NWs were scanned by the laser beam in order to probe the heterojunction. The capability of the MicroRaman spectroscopy for studying the heterojunction is discussed. The results show that the use of catalysts with lower Ge and Si solubility (AuGa alloys) permits to achieve more abrupt junctions.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

UV Raman spectroscopy of group IV nanocrystals embedded in a SiO2 matrix

Nanostructures of both Ge nanocrystals formed by thermal oxidation of SiGe layers, and SiGe nanocrystals formed by crystallization of amorphous SiGe nanoparticles deposited by LPCVD have been analyzed by Raman spectroscopy. The nanostructures are formed on a silicon substrate. Raman spectra have been acquired with visible (514.5 nm) and UV (325 nm) excitation lines. When the amount of material is very small, as it has happens in these nanostructures, the visible line is not able to excite the characteristic peaks of the Ge or SiGe in the Raman spectrum; instead the Si second order spectrum of the substrate appears and it can be misinterpreted by attributing it to the Ge–Ge band associated with the nanocrystals. In this work, the use of UV excitation has been demonstrated to enhance the sensitivity respect to the conventional visible excitation, allowing the characteristic peaks of the Ge or SiGe nanocrystals to appear in the spectrum. We attributed this effect to the resonance effects

Raman Spectroscopy of group IV nanostructured semiconductors: influence of size, temperature and stress.

Group IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. However, the Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for Si nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation

Electromagnetic field enhancement effects in group IV semiconductor nanowires. A Raman spectroscopy approach

Semiconductor nanowires (NWs) are the building blocks of future nanoelectronic devices. Furthermore, their large refractive index and reduced dimension make them suitable for nanophotonics. The study of the interaction between nanowires and visible light reveals resonances that promise light absorption/scattering engineering for photonic applications. Micro-Raman spectroscopy has been used as a characterization tool for semiconductor nanowires. The light/nanowire interaction can be experimentally assessed through the micro-Raman spectra of individual nanowires. As compared to both metallic and dielectric nanowires, semiconductor nanowires add additional tools for photon engineering. In particular, one can grow heterostructured nanowires, both axial and radial, and also one could modulate the doping level and the surface condition among other factors than can affect the light/NW interaction. We present herein a study of the optical response of group IV semiconductor nanowires to visible photons. The study is experimentally carried out through micro-Raman spectroscopy of different group IV nanowires, both homogeneous and axially heterostructured (SiGe/Si). The results are analyzed in terms of the electromagnetic modelling of the light/nanowire interaction using finite element methods. The presence of axial heterostructures is shown to produce electromagnetic resonances promising new photon engineering capabilities of semiconductor nanowires.Junta de Castilla y Le on (Projects VA293U13 and VA081U16) and Spanish Government (CICYT MAT2010-20441-C02 (01 and 02) and ENE 2014-56069-C4-4-R). J. L. Pura was granted by the FPU programme (Spanish Government) (FPU14/00916)

Si and SixGe1-x NWs studied by Raman spectroscopy

Group IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. The Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for Si and SiGe nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation

Raman spectroscopy study of group IV semiconductor nanowires

Group IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. However, the Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for SiGe nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation. The interpretation of the data is supported by the calculation of the temperature inside the NWs with different diameters

Fenómenos de alteración y transformación fosgenita-cerusita.

The transformation of phosgenite into cerussite in a diffusing-reacting system has been studied. This transformation occurs in a narrow pH range. Mass-transfer and pH evolution in the system during the process was testified. The transformation development was monitored by Raman spectroscopy

Microraman analysis of corundum crystallized by cryolite flux

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

P-V-T-X-f02 evolution from wolframite to sulphide depositional stages in intragranitic W-veins. An example from the Spanish Central System

The relative P-T-X conditions of the deposition of wolframite and sulphides in quartz veins has been investigated using representative W-polymetallic sulphide veins hosted by peraluminous granites in the central domain of the Spanish Central System. Ore-bearing quartz veins fall into two groups : W-veins (wolframite-bearing quartz veins with minor amounts of sulphides) and sulphide (S) dominated veins (wolframite free). The two vein types (S and W) have similar orientation, silicate and sulphide mineralogy. A multidisciplinary approach based on a detailed fluid-inclusion analysis in relation with a paragenetic reconstruction of vein fillings suggests a similar genesis and fluid history, as follows : (i) an early fluid stage, lacking in S-veins, characterized by CO2-H20-NaCl rich vapours is at the origin of a strong K-mica alteration of the granite wall-rock, and of vein filling by milky quartz (QI) - phengite I - (wolframite), at around 130 ± 20 MPa and 525 ± 25°C ; (ii) a second stage characterized by H2O-CO2-CH4-NaCl fluids with a low volatile-phase density, at the origin of the deposition of : a) saccharoidal quartz (QII) (+ phengite II and minor amounts of scheelite in W-veins), and then, b) a chlorite-sulphide (pyrrhotite, sphalerite and galena) assemblage. A progressive decrease of the CO2 content in fluids is recorded, CH4 being the major volatile species in the latest inclusions spatially associated with sulphides. Pressure is around 130 ± 30 MPa, and temperature decreases from 380° to 330°C throughout the course of the fluid trapping. iii) later fluid inputs in the veins are shown by two types of secondary aqueous fluid inclusions in healed microfissures, which display moderate Th (160°-220°C) and salinities. The two main stages (wolframite, then sulphides) are characterized by a nearly isobaric cooling and dilution of volatile rich fluids. The X-fO2 evolution indicates that fluid chemistry was probably controlled during the first stage by graphite-fluid equilibrium, implying a fluid source external to the granite (surrounding metamorphic series). The sulphide stage, which is ubiquitous in most W deposits, appears clearly in this example as the latest stage of a primary hydrothermal cycle involving volatile bearing fluids, and is not disconnected from the W stages.Accion Integrada Francia-España PICASSOHuman Capital and MobilityDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

17th Conference on Defects (DRIP XVII)

PósterMinisterio de Economía, Industria y Competitividad (Project ENE2014-56069-C4-4-R)Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA293U13 and VA081U16