Search results for "Ciència"
showing 10 items of 602 documents
Polarized and resonant Raman spectroscopy on single InAs nanowires
2011
We report polarized Raman scattering and resonant Raman scattering studies on single InAs nanowires. Polarized Raman experiments show that the highest scattering intensity is obtained when both the incident and analyzed light polarizations are perpendicular to the nanowire axis. InAs wurtzite optical modes are observed. The obtained wurtzite modes are consistent with the selection rules and also with the results of calculations using an extended rigid-ion model. Additional resonant Raman scattering experiments reveal a redshifted E1 transition for InAs nanowires compared to the bulk zinc-blende InAs transition due to the dominance of the wurtzite phase in the nanowires. Ab initio calculatio…
Phonon-plasmon coupling in Si doped GaN nanowires
2016
Abstract The vibrational properties of silicon doped GaN nanowires with diameters comprised between 40 and 100 nm are studied by Raman spectroscopy through excitation with two different wavelengths: 532 and 405 nm. Excitation at 532 nm does not allow the observation of the coupled phonon–plasmon upper mode for the intentionally doped samples. Yet, excitation at 405 nm results in the appearance of a narrow peak at frequencies close to that of the uncoupled A 1 (LO) mode for all samples. This behavior points to phonon–plasmon scattering mediated by large phonon wave-vector in these thin and highly doped nanowires.
Polylactide-based self-reinforced composites biodegradation: Individual and combined influence of temperature, water and compost
2018
[EN] Self-reinforced polymer composites (SRCs) are proposed as a suitable alternative for composite development, based in the combination of a polymeric matrix and a polymeric fibre made of the same polymer. SRCs based in polylactide (PLA) could be fully biodegradable and their valorisation routes could presumably be assimilated to those for neat PEA. In this sense, the aim of this study was to develop new self-reinforced PLA-based composites and ascertain their biodegradability. For this purpose, PLA-based SRCs were obtained through a thermo-compression procedure and their biodegradability corroborated under standard conditions (ISO 20200). Moreover, a deep study of the effect of the diffe…
Poly(3,4-Ethylenedioxythiophene) nanoparticles as building blocks for hybrid thermoelectric flexible films
2019
Hybrid thermoelectric flexible films based on poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles and carbon nanotubes were prepared by using layer-by-layer (LbL) assembly. The employed PEDOT nanoparticles were synthesized by oxidative miniemulsion polymerization by using iron(III) p-toluenesulfonate hexahydrate (FeTos) as an oxidant and poly(diallyldimethylammonium chloride) (PDADMAC) as stabilizer. Sodium deoxycholate (DOC) was used as a stabilizer to prepare the aqueous dispersions of the carbon nanotubes. Hybrid thermoelectric films were finally prepared with different monomer/oxidant molar ratios and different types of carbon nanotubes, aiming to maximize the power factor (PF). The …
Design of Bistable Gold@Spin‐Crossover Core–Shell Nanoparticles Showing Large Electrical Responses for the Spin Switching
2019
<p>A simple protocol to prepare core-shell gold@spin-crossover (Au@SCO) nanoparticles (NPs) based on the 1D spin-crossover [Fe(Htrz)<sub>2</sub>(trz)](BF<sub>4</sub>) coordination polymer is reported. The synthesis relies on a two-step approach consisting on a partial surface ligand substitution of the citrate-stabilized Au NPs followed by the controlled growth of a very thin layer of the SCO polymer. As a result, colloidally stable core@shell spherical NPs of 19 nm in size exhibiting a narrow distribution in sizes have been obtained, revealing a switchable SCOshell of <i>ca.</i>4 nm. Temperature-dependent charge transport measurements of an electri…
Coefficient of thermal expansion and elastic modulus of thin films
1999
The coefficient of thermal expansion (CTE), biaxial modulus, and stress of some amorphous semiconductors (a-Si:H, a-C:H, a-Ge:H, and a-GeCx:H) and metallic (Ag and Al) thin films were studied. The thermal expansion and the biaxial modulus were measured by the thermally induced bending technique. The stress of the metallic films, deposited by thermal evaporation (Ag and Al), is tensile, while that of the amorphous films deposited by sputtering (a-Si:H, a-Ge:H, and a-GeCx:H) and by glow discharge (a-C:H) is compressive. We observed that the coefficient of thermal expansion of the tetrahedral amorphous thin films prepared in this work, as well as that of the films reported in literature, depen…
Erratum: Polarized and resonant Raman spectroscopy on single InAs nanowires (vol 84, 085318, 2011)
2012
We found out that the polar pattern for the zinc-blende InAs LO mode displayed in Fig. 2(b) of our original paper represents the backscattering Raman intensities from a (11¯2) top surface and not as stated in the original manuscript from a (110) top surface.In the latter the LO mode is forbidden for all configurations.
Focusing of surface-acoustic-wave fields on (100) GaAs surfaces
2003
Focused surface-acoustic waves (SAWs) provide a way to reach intense acoustic fields for electro- and optoacoustic applications on semiconductors. We have investigated the focusing of SAWs by interdigital transducers (IDTs) deposited on (100)-oriented GaAs substrates. The focusing IDTs have curved fingers designed to account for the acoustic anisotropy of the substrate. Different factors that affect focusing, such as the aperture angle and the configuration of the IDT fingers, were systematically addressed. We show that the focusing performance can be considerably improved by appropriate choice of the IDT metal pads, which, under appropriate conditions, create an acoustic waveguide within t…
Surface properties of AlInGaN/GaN heterostructure
2016
Abstract Surface structural, electronic and electrical properties of the quaternary alloy AlInGaN/GaN heterostructures are investigated. Surface termination, atomic arrangement, electronic and electrical properties of the (0001) surface and (10–11) V-defect facets have been experimentally analyzed using various surface sensitive techniques including spectroscopy and microscopy. Moreover, the effect of sub-band gap (of the barrier layer) illumination on contact potential difference (VCPD) and the role of oxygen chemisorption have been studied.
The effects of modifying contact, duration, and teaching strategies in awareness interventions on attitudes towards inclusion in physical education
2020
This quasi-experimental study analyses the effects of an awareness intervention programme with five different branches designed to improve the attitudes of physical education (PE) students towards the inclusion of classmates with disabilities. The contact (yes/no) and its frequency (×1 vs. ×3) with para-athletes, the duration of the programme (1 vs. 6/7 sessions), and the provision of teaching strategies and materials (yes/no) were manipulated. The study involved 603 students aged 14‒19 from five public educational centres in southern Spain. Attitudes were assessed pre- and post-intervention with the Spanish version of the Children's Attitude towards Integrated Physical Education (general a…