60 research outputs found
Defect-free ZnSe nanowire and nano-needle nanostructures
We report on the growth of ZnSe nanowires and nano-needles using molecular
beam epitaxy (MBE). Different growth regimes were found, depending on growth
temperature and the Zn--Se flux ratio. By employing a combined MBE growth of
nanowires and nano-needles without any post-processing of the sample, we
achieved an efficient suppression of stacking fault defects. This is confirmed
by transmission electron microscopy and by photoluminescence studies.Comment: 4 pages, 4 figure
Deterministic radiative coupling between plasmonic nanoantennas and semiconducting nanowire quantum dots
International audienceWe report on the deterministic coupling between single semiconducting nanowire quantum dots emitting in the visible and plasmonic Au nanoantennas. Both systems are separately carefully characterized through microphotoluminescence and cathodoluminescence. A two-step realignment process using cathodoluminescence allows for electron beam lithography of Au antennas near individual nanowire quantum dots with a precision of 50 nm. A complete set of optical properties are measured before and after antenna fabrication. They evidence both an increase of the NW absorption, and an improvement of the quantum dot emission rate up to a factor two in presence of the antenna
Photon correlation spectroscopy on a single quantum dot embedded in a nanowire
We have observed strong photoluminescence from a single CdSe quantum dot
embedded in a ZnSe nanowire. Exciton, biexciton and charged exciton lines have
been identified unambiguously using photon correlation spectroscopy. This
technique has provided a detailed picture of the dynamics of this new system.
This type of semi conducting quantum dot turns out to be a very efficient
single photon source in the visible. Its particular growth technique opens new
possibilities as compared to the usual self-asssembled quantum dots
Dark exciton optical spectroscopy of a semiconducting quantum dot embedded in a nanowire
Photoluminescence of a single CdSe quantum dot embedded in a ZnSe nanowire has been investigated. It has been found that the dark exciton has a strong influence on the optical properties. The most visible influence is the strongly reduced excitonic emission compared to the biexcitonic one. Temperature dependent lifetime measurements have allowed us to measure a large splitting of meV between the dark and the bright exciton as well as the spin flip rates between these two states
Optical properties of single ZnTe nanowires grown at low temperature
Optically active gold-catalyzed ZnTe nanowires have been grown by molecular
beam epitaxy, on a ZnTe(111) buffer layer, at low temperature 350\degree under
Te rich conditions, and at ultra-low density (from 1 to 5 nanowires per
micrometer^{2}. The crystalline structure is zinc blende as identified by
transmission electron microscopy. All nanowires are tapered and the majority of
them are oriented. Low temperature micro-photoluminescence and
cathodoluminescence experiments have been performed on single nanowires. We
observe a narrow emission line with a blue-shift of 2 or 3 meV with respect to
the exciton energy in bulk ZnTe. This shift is attributed to the strain induced
by a 5 nm-thick oxide layer covering the nanowires, and this assumption is
supported by a quantitative estimation of the strain in the nanowires
Insertion of CdSe quantum dots in ZnSe nanowires: Correlation of structural and chemical characterization with photoluminescence
International audienceZnSe nanowires with CdSe quantum dot insertions were grown by molecular beam epitaxy using gold as a catalyst. Structural, chemical, and optical properties of the wires and quantum dots were characterized using electron microscopy and photoluminescence spectroscopy. We determined the crystalline structure, the chemical composition, and the size of the quantum dot and established a correlation between quantum dot size and luminescence. As expected, a blueshift of the luminescence was observed for decreasing quantum dot size. The comparison of calculated photoluminescence energy and experimental data seems to indicate that the quantum dots consist of a ZnxCd1-xSe ternary alloy rather than pure CdSe
Insertion of CdSe quantumdots in ZnSe nanowires : MBE growth and microstructure analysis
International audienceZnSe nanowire growth has been successfully achieved on ZnSe (100) and (111)B buffer layers deposited on GaAs substrates. Cubic [100] oriented ZnSe nanowires or [0001] oriented hexagonal NWs are obtained on (100) substrates while [111] oriented cubic mixed with [0001] oriented hexagonal regions are obtained on (111)B substrates. Most of the NWs are perpendicular to the surface in the last case. CdSe quantum dots were successfully incorporated in the ZnSe NWs as demonstrated by transmission electron microscopy, energy filtered TEM and high angle annular dark field scanning TEM measurements
Extraction of the homogeneous linewidth of the spectrally diffusing line of a CdSe/ZnSe quantum dot embedded in a nanowire
International audienceWe present a simple method to extract the homogeneous linewidth of a single photon emitter line exhibiting fast (down to 1 ns) spectral diffusion (SD). It is based on a recently developed technique using photon correlation measurements on half of the line. Here we show that the SD induced bunching depends on the ratio between the width of the homogeneous line and the spectral diffusion amplitude. Using this technique on a CdSe/ZnSe quantum dot, we investigate the temperature dependence of its fast SD amplitude and its homogeneous excitonic linewidt
Exciton-phonon coupling efficiency in CdSe quantum dots embedded in ZnSe nanowires
International audienceExciton luminescence of a CdSe quantum dot (QD) inserted in a ZnSe nanowire is strongly influenced by the dark exciton states. Because of the small size of these QDs (2-5 nm), exchange interaction between hole and electron is highly enhanced and we measured large energy splitting between bright and dark exciton states (ΔE∈[4,9.2] meV) and large spin-flip rates between these states. Statistics on many QDs showed that this splitting depends on the QD size. Moreover, we measured an increase of the spin-flip rate to the dark states with increasing energy splitting. We explain this observation with a model, taking into account the fact that the exciton-phonon interaction depends on the bright to dark exciton energy splitting, as well as on the size and shape of the exciton wave function. It also has consequences on the exciton line intensity at high temperature
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