Showing papers by "C. M. Sotomayor Torres published in 2004"
TL;DR: In this article, the dependence of the Raman peak frequencies and amplitudes upon the thickness of the silicon membrane is interpreted as acoustic phonons in an acoustic cavity, and it is shown that these acoustic phonon are confined.
Abstract: Confined acoustic phonons in Silicon-on-insulator membranes have been observed by means of low frequency Raman scattering. The dependence of the Raman peak frequencies and amplitudes upon the thickness of the silicon membrane is interpreted as acoustic phonons in an acoustic cavity. The analysis confirms that these acoustic phonons are confined. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
47 citations
TL;DR: In this paper, an interface-related transmission minimum has been revealed and tentatively explained as the consequence of the distractive interference of optical modes of hetero-opal constituents, supported by the observation of the emission modification in this frequency range.
Abstract: Light-emitting hetero-opals have been synthesized by successive crystallization of one thin opal film on top of the other from beads of two different diameters and selective impregnation of one of films with luminescent CdTe nanocrystals. A strong spectral and spatial anisotropy of the reflectance and the photoluminescence spectra has been observed and attributed to the photonic bandgap mismatch in opal films. Changes of the emission anisotropy with excitation power have been associated with the stimulation of CdTe nanocrystal emission in a host opal film. An interface-related transmission minimum has been revealed and tentatively explained as the consequence of the distractive interference of optical modes of hetero-opal constituents. The idea of the interface resonance has been supported by the observation of the emission modification in this frequency range.
32 citations
TL;DR: In this article, the light reflectance in three-dimensional metallodielectric photonic crystals assembled from polyelectrolyte-coated latex spheres infiltrated with gold nanoparticles has been studied.
Abstract: The light reflectance in three-dimensional metallodielectric photonic crystals assembled from polyelectrolyte-coated latex spheres infiltrated with gold nanoparticles has been studied. Strong deviation of the optical reflectance of Au opals from bare opals has been observed, including flattening of the diffraction resonance dispersion and nondispersive surface plasmon bands.
29 citations
TL;DR: An anisotropic photonic crystal light source has been realized by impregnation of a thin film latex opal with brightly luminescent CdTe nanocrystals by exploiting the low group velocity eigenmodes to explain the resonance character of the emission with band gap frequencies.
Abstract: An anisotropic photonic crystal light source has been realized by impregnation of a thin film latex opal with brightly luminescent CdTe nanocrystals. Its photoluminescence along a given direction has been studied as a function of excitation power. An increase of the photoluminescence saturation threshold in the directional photonic band gap has been observed. This result is interpreted as a stimulation of emission coupled to specific eigenmodes of a directional band gap. A theoretical model exploiting the low group velocity eigenmodes has been elaborated to explain the resonance character of the emission with band gap frequencies.
24 citations
TL;DR: In this article, a deterministic fabrication of microscopic structures in self-assembled three-dimensional (3D) photonic crystals is reported. But the technique is highly accurate, versatile and is probably suitable to fabricate buried defects.
21 citations
TL;DR: In this paper, the authors report the fabrication of two embedded polymer single-mode waveguides, namely, polystyrene/Teflon®-AF and mr-L 6000/teflon-AF, fabricated by means of electron beam lithography and/or nano-imprint lithography.
15 citations
TL;DR: In this paper, the authors present two different approaches to nanostructured semiconducting polymer materials: (i) the generation of aqueous polyfluorene-block-polyaniline (PF-b-PANI) block copolymers composed of conjugated blocks of different redox potentials which form nanosized morphologies in the solid state.
Abstract: The paper presents two different approaches to nanostructured semiconducting polymer materials: (i) the generation of aqueous semiconducting polymer dispersions (semiconducting polymer nanospheres SPNs) and their processing into dense films and layers, and (ii) the synthesis of novel semiconducting polyfluorene-block-polyaniline (PF-b-PANI) block copolymers composed of conjugated blocks of different redox potentials which form nanosized morphologies in the solid state.
14 citations
TL;DR: In this paper, the influence of solvent effects on the electrical characteristics of solution-processed organic field effect transistors, with dihexylquaterthiophene (DH4T) as the active semiconductor material, has been investigated.
13 citations
TL;DR: Angle-resolved spectra of the light scattered in a thin opal film and the angle diagrams of the scattered light have been interpreted in terms of the weak scattering regime, when scattering serves for coupling a photon from one eigenmode of opal to another.
Abstract: Angle-resolved spectra of the light scattered in a thin opal film have been measured behind the sample in three configurations, which differ by directions of the light incidence and detection. Two minima have been observed in scattering spectra and assigned to the attenuation by the (111) Bragg photonic bandgap along directions of the incident and detected photon flux. The irrelevance of the photonic bandgap minima to the actual path of scattered photon has been demonstrated. The projection of the directional (111) photonic band gap has been allotted to the plateau observed in the angle diagrams of the scattered light intensity. The spectra and the angle diagrams of the scattered light have been interpreted in terms of the weak scattering regime, when scattering serves for coupling a photon from one eigenmode of opal to another.
13 citations
TL;DR: In this paper, it is argued that this behaviour can be explained if there is stimulated emission from photonic states in the photonic bandgap, which are strongly localized due to disorder.
Abstract: Synthetic opals filled with CdTe exhibit a pronounced decrease of the intensity of photoluminescence for photon energies within the photonic band-gap. However, the intensity of emission increases much faster with the level of pumping inside the photonic band-gap than outside. It is argued that this behaviour can be explained if there is stimulated emission from photonic states in the photonic bandgap, which are strongly localized due to disorder. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
6 citations
TL;DR: In this paper, the X-ray diffraction patterns and vibrational spectra of the pristine phase, intermediate and final products indicate a mechanism in which tubular species would be formed by the transformation under hydrothermal conditions of an intermediate state produced by a relative displacement of the laminas in the pristine α-MoO3.
Abstract: The hydrothermal treatment of molybdenum oxide in alkaline medium leads to micro and nano-fibers products among which bundles to nanofibers with dimensions in the range to 4–5 μm length and 200–700 nm wide are found. The microcrystalline product corresponds to a laminar phase with interlaminar spaces smaller than both its intermediate precursor and the pristine MoO3. Comparison of the X-ray diffraction patterns and vibrational spectra of the pristine phase, intermediate and final products indicates a mechanism in which tubular species would be formed by the transformation under hydrothermal conditions of an intermediate state produced by a relative displacement of the laminas in the pristine α-MoO3. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Proceedings Article•
16 May 2004TL;DR: In this article, the realisation of photonic crystals on silicon platforms is presented with the aim of obtaining waveguides and light emitting structures, and they report on crystallisation on patterned substrates and defect engineering by direct electronbeam writing as examples of two approaches to fabricate and structure photonic crystal.
Abstract: The realisation of photonic crystals on silicon platforms is presented with the aim to obtain waveguides and light emitting structures. We report on crystallisation on patterned substrates and defect engineering by direct electron-beam writing as examples of two approaches to fabricate and structure photonic crystals. The requirements to realise waveguides need crystallisation in confined environments.