173 research outputs found
Transport properties of mid-infrared colloidal quantum dot films
The transport and thermal properties of HgTe colloidal quantum dot films with
cut-off wavelengths in the mid-IR are investigated. The cut-off wavelength of
this material can be tuned over the 3-5 \mu m range, which makes it a promising
alternative to existing high cost detectors. Post deposition processes such as
ligand exchange and atomic layer deposition are investigated as a way to
increase the carrier mobility.Comment: 7 pages, 7 figure
Highly photo-stable Perovskite nanocubes: towards integrated single photon sources based on tapered nanofibers
The interest in perovskite nanocrystals (NCs) such as CsPbBr for quantum
applications is rapidly raising, as it has been demonstrated that they can
behave as very efficient single photon emitters. The main problem to tackle in
this context is their photo-stability under optical excitation. In this
article, we present a full analysis of the optical and quantum properties of
highly efficient perovskite nanocubes synthesized with an established method,
which is used for the first time to produce quantum emitters, and is shown to
ensure an increased photostability. These emitters exhibit reduced blinking
together with a strong photon antibunching. Remarkably these features are
hardly affected by the increase of the excitation intensity well above the
emission saturation levels. Finally, we achieve for the first time the coupling
of a single perovskite nanocube with a tapered optical nanofiber in order to
aim for a compact integrated single photon source for future applications
15{\mu}m Quantum well infrared photodetector for thermometric imagery in cryogenic windtunnel
Quantum Well Infrared Photodetector (QWIP) usually suffer from a too moderate
quantum efficiency and too large dark current which is often announced as
crippling for low flux applications. Despite this reputation we demonstrate the
ability of QWIP for the low infrared photon flux detection. We present the
characterization of a state of the art 14.5\mu m QWIP from Alcatel-Thales 3-5
Lab. We developed a predictive model of the performance of an infrared
instrument for a given application. The considered scene is a Cryogenic Wind
Tunnel (ETW), where a specific Si:Ga camera is currently used. Using this
simulation tool we demonstrate the QWIP ability to image a low temperature
scene in this scenario. QWIP detector is able to operate at 30K with a NETD as
low as 130mK. In comparison to the current detector, the temperature of use is
three times higher and the use of a QWIP based camera would allow a huge
simplification of the optical part
Interface roughness transport in THz quantum cascade detectors
Infrared Detectors based on a Quantum Cascade have been proposed to suppress
the dark current which is identified as a limiting factor in Quantum Well
Infrared Photodetectors. Those detectors have been mostly designed for the
3-5um and 8-12um range of wavelength. For detector operating in the THz range a
complete change of regime of transport is expected since the photon energy is
lower than the Longitudinal Optical (LO) phonon energy. Using a two dimensional
code of transport we have identified Interface Roughness (IR) as the key
interaction in such a structure. We have used scanning transmission electron
microscopy (STEM) to evaluate the IR parameters (magnitude of the roughness and
mean distance between defects) instead of the classical mobility measurements.
Finally, we used these parameters to study their influence on the resistance of
the device
Visual analytics for the interpretation of fluency tests during Alzheimer evaluation
International audienceA possible way to evaluate the progress of Alzheimer disease is to conduct the Isaac set test [13, 14]. In this activity, patients are asked to cite the largest possible number of city names within a minute. Since the city names are handwritten very quickly by a medical practitioner some cities are abbreviated or poorly written. In order to analyze such data, medical practitioners need to digitize the notes first and clean the dataset. Because these tasks are intricate and error prone we propose a novel set of tools, involving interactive visualization techniques, to help medical practitioners in the digitization and data-cleaning process. This system will be tested as part of an ongoing longitudinal study involving 9500 patients
Quantum well infrared photodetectors hardiness to the non ideality of the energy band profile
We report results on the effect of a non-sharp and disordered potential in
Quantum Well Infrared Photodetectors (QWIP). Scanning electronic transmission
microscopy is used to measure the alloy profile of the structure which is shown
to present a gradient of composition along the growth axis. Those measurements
are used as inputs to quantify the effect on the detector performance (peak
wavelength, spectral broadening and dark current). The influence of the random
positioning of the doping is also studied. Finally we demonstrate that QWIP
properties are quite robust with regard to the non ideality of the energy band
profile
Halide Ligands to Release Strain in Cadmium Chalcogenide Nanoplatelets and Achieve High Brightness
International audienceZinc blende II-VI semiconductor nanoplatelets (NPLs) are defined at the atomic scale along the thickness of the nanoparticle and are initially capped with carboxylates on the top and bottom [001] facets. These ligands are exchanged on CdSe NPLs with halides that act as X-L-type ligands. These CdSe NPLs are costabilized by amines to provide colloidal stability in nonpolar solvents. The hydrogen from the amine can participate in a hydrogen bond with the lone pair electrons of surface halides. After ligand exchange, the optical features are redshifted. Thus, ligand tuning is another way, in addition to confinement, to tune the optical features of NPLs. The improved surface passivation leads to an increase in the fluorescence quantum efficiency of up to 70% in the case of bromide. However, for chloride and iodide, the surface coverage is incomplete, and thus, the fluorescence quantum efficiency is lower. This ligand exchange is associated with a decrease in stress that leads to unfolding of the NPLs, which is particularly noticeable for iodide-capped NPLs
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