Search results for "Mesoscopic System"
showing 10 items of 587 documents
Si nanocrystals embedded in $SiO_2$: Optical studies in the vacuum ultraviolet range
2011
Photoluminescence excitation and transmission spectra of Si nanocrystals of different diameters embeddedin a SiO2 matrix have been investigated in the broad visible-vacuum ultraviolet spectral range usingsynchrotron radiation. The dependence of the photoluminescence excitation spectra on the nanocrystals sizewas experimentally established. It is shown that the photoluminescence excitation and absorption spectra aresignificantly blueshifted with decreasing Si nanocrystal size. A detailed comparison of photoluminescenceexcitation and absorption spectra with data from theoretical modeling has been done. It is demonstrated thatthe experimentally determined blueshift of the photoluminescence exc…
Temperature dependent optical properties of stacked InGaAs/GaAs quantum rings
2008
4 páginas, 3 figuras, 2 tablas.-- MADICA 2006 Conference, Fifth Maghreb-Europe Meeting on Materials and their Applicatons for Devices and Physical, Chemical and Biological Sensors
Size-filtering effects by stacking InAs/InP (001) self-assembled quantum wires into multilayers
2002
Multilayer structure containing vertically stacked InAs/InP self-assembled quantum wires have been successfully grown by molecular-beam epitaxy. The influence of the InP spacer layer thickness on the structural and optical properties of the wire superlattice has been studied by means of transmission electron microscopy and photoluminescence. The coherent propagation of the strain field in the sample with a 5-nm-thick spacer determines by a size filtering effect a good homogeneity and uniformity of the wire stacks, and hence a good optical quality. The exciton recombination dynamics in the wire superlattice cannot be related to thermal escape of carriers out to the barriers, as occurs in sin…
Size self-filtering effect in vertical stacks of InAs/InP self-assembled quantum wires
2003
3 páginas, 2 figuras.-- PACS: 73.21.Hb; 78.55.Cr; 78.67.Lt.-- Proceedings of the International Conference on Superlattices, Nano-structures and Nano-devices ICSNN 2002.
Photoluminescence study of excitons in homoepitaxial GaN
2001
High-resolution photoluminescence spectra have been measured in high-quality homoepitaxial GaN grown on a free-standing GaN substrate with lower residual strain than in previous work. Unusually strong and well-resolved excitonic lines were observed. Based on free- and bound exciton transitions some important GaN parameters are derived. The Arrhenius plot of the free A exciton recombination yields a binding energy of 24.7 meV. Based on this datum, an accurate value for the band-gap energy, EG(4.3 K) = 3.506 eV, can be given. From the donor bound excitons and their “two-electron” satellites, the exciton localization energy and donor ionization energy are deduced. Finally, estimates of the ele…
Non-resonant Raman spectroscopy of individual ZnO nanowires via Au nanorod surface plasmons
2016
We present a non-resonant Raman spectroscopy study of individual ZnO nanowires mediated by Au nanorod surface plasmons. In this approach, selective excitation of the plasmonic oscillations with radiation energy below the semiconductor bandgap was used to probe surface optical modes of individual ZnO nanowires without simultaneous excitation of bulk phonons modes or band-edge photoluminescence. The development of a reproducible method for decoration of nanowires with colloidal Au nanorods allowed performing an extensive statistical analysis addressing the variability and reproducibility of the Raman features found in the hybrid nanostructures. An estimated field enhancement factor of 103 was…
Temperature Sensor Based on Colloidal Quantum Dots PMMA Nanocomposite Waveguides
2012
In this paper, integrated temperature sensors based on active nanocomposite planar waveguides are presented. The nanocomposites consist of cadmium selenide (CdSe) and cadmium telluride (CdTe) quantum dots (QDs) embedded in a polymethylmethacrylate (PMMA) matrix. When the samples are heated in a temperature range from 25$^{circ}{rm C}$ to 50 $^{circ}{rm C}$, the waveguided photoluminescence of QDs suffers from a strong intensity decrease, which is approximately quadratic dependent on temperature. Moreover, the wavelength peak of the waveguided emission spectrum of CdTe-PMMA shows a blue shift of 0.25 ${rm nm}/^{circ}{rm C}$, whereas it remains constant in the case of CdSe-PMMA. A temperature…
<title>New aspect of light emission from silicon nanocrystals</title>
2003
Intensive light emission (photoluminescence) from silicon nanocrystals has been interpreted in literature as recombinative emission. It has been supposed that the band structure is "pseidodirect." The literature analysis presented in our paper shows that the band structure is indirect and therefore intensive recombinative emission is not possible. According to new aspect, a part of electrons reaches the second conduction subband due to Auger recombination. Then the intensive visible radiation could be caused by transitions of these electrons from the second to the first conduction subband. We have constructed continuity equations for the electron concentration in the first and the second co…
Optical properties of wurtzite GaN/AlN quantum dots grown on non-polar planes: the effect of stacking faults in the reduction of the internal electri…
2016
The optical emission of non-polar GaN/AlN quantum dots has been investigated. The presence of stacking faults inside these quantum dots is evidenced in the dependence of the photoluminescence with temperature and excitation power. A theoretical model for the electronic structure and optical properties of non-polar quantum dots, taking into account their realistic shapes, is presented which predicts a substantial reduction of the internal electric field but a persisting quantum confined Stark effect, comparable to that of polar GaN/AlN quantum dots. Modeling the effect of a 3 monolayer stacking fault inside the quantum dot, which acts as zinc-blende inclusion into the wurtzite matrix, result…
A Composite Phononic Crystal Design for Quasiparticle Lifetime Enhancement in Kinetic Inductance Detectors
2019
A nanoscale phononic crystal filter (reflector) is designed for a kinetic inductance detector where the reflection band is matched to the quasiparticle recombination phonons with the aim to increase quasiparticle lifetime in the superconducting resonator. The inductor is enclosed by a 1 um wide phononic crystal membrane section with two simple hole patterns that each contain a partial spectral gap for various high frequency phonon modes. The phononic crystal is narrow enough for low frequency thermal phonons to propagate unimpeded. With 3D phonon scattering simulations over a 40 dB attenuation in transmitted power is found for the crystal, which was previously estimated to give a lifetime e…