64 research outputs found
Coherent Diffraction Imaging of Single 95nm Nanowires
Photonic or electronic confinement effects in nanostructures become
significant when one of their dimension is in the 5-300 nm range. Improving
their development requires the ability to study their structure - shape, strain
field, interdiffusion maps - using novel techniques. We have used coherent
diffraction imaging to record the 3-dimensionnal scattered intensity of single
silicon nanowires with a lateral size smaller than 100 nm. We show that this
intensity can be used to recover the hexagonal shape of the nanowire with a
28nm resolution. The article also discusses limits of the method in terms of
radiation damage.Comment: 5 pages, 5 figure
Self-Powered Conformable Deformation Sensor Exploiting the Collective Piezoelectric Effect of Self-Organised GaN Nanowires
International audienceWe present a novel integration-driven approach to the design of multi-scale multi-physics sensors and systems. We implement this method to model, design, fabricate and characterize a thin, conformable low-cost impact detection sensor based on assemblies of piezoelectric GaN nanowires. When suitably assembled, the latter demonstrate a macroscale additivity of their nanoscale intrinsic properties, which enables to appeal to classical fabrication techniques and exploitable electronic readouts at the system level. We also exploit multi-level simulations to provide useful insights of adapted application-driven integration solutions for these new forms of sensors. We demonstrate the potential of such application-targeted, fully-integrated and modular systems to accommodate to the stringent requirements of structural health monitoring (SHM)
Quantum Communication with Quantum Dot Spins
Single electron spins in quantum dots are attractive for quantum
communication because of their expected long coherence times. We propose a
method to create entanglement between two remote spins based on the coincident
detection of two photons emitted by the dots. Local nodes of several qubits can
be realized using the dipole-dipole interaction between trions in neighboring
dots and spectral addressing, allowing the realization of quantum repeater
protocols. We have performed a detailed feasibility study of our proposal based
on tight-binding calculations of quantum dot properties.Comment: 4 pages, 2 figures, new and improved version, explicit performance
estimate
Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates
3 pagesInternational audienceThe shape of c-oriented GaN nanostructures is found to be directly related to the crystal polarity. As evidenced by convergent beam electron diffraction applied to GaN nanostructures grown by metal-organic vapor phase epitaxy on c-sapphire substrates: wires grown on nitridated sapphire have the N-polarity ([000math]) whereas pyramidal crystals have Ga-polarity ([0001]). In the case of homoepitaxy, the GaN wires can be directly selected using N-polar GaN freestanding substrates and exhibit good optical properties. A schematic representation of the kinetic Wulff's plot points out the effect of surface polarity
InGaN/GaN core/shell nanowires for visible to ultraviolet range photodetection
International audienceWe report on the fabrication and characterization of single nitride nanowire visible-to-ultraviolet p-n photodetec-tors. Nitride nanowires containing 30 InGaN/GaN radial quantum wells with 18% indium fraction were grown by catalyst-free metal-organic vapour phase epitaxy. Single nanowires were contacted using optical lithography. As expected for a radial p-n junction, the current-voltage (I-V) curves of single wire detectors show a rectifying behavior in the dark and a photocurrent under illumination. The detectors present a response in the visible to UV spectral range starting from 2.8 eV. The peak responsivity is 0.17 A/W at 3.36 eV. The on-off switching time under square light pulses is found to be below 0.1 sec
Flexible White Light Emitting Diodes Based on Nitride Nanowires and Nanophosphors
International audienceWe report the first demonstration of a flexible white phosphor-converted light emitting diodes (LEDs) based on p-n junction core/shell nitride nanowires. GaN nanowires containing 7 radial In 0.2 Ga 0.8 N/GaN quantum wells were grown by metal-organic chemical vapor deposition on a sapphire substrate by a catalyst-free approach. To fabricate the flexible LED, the nanowires are embedded into a phosphor-doped polymer matrix, peeled off from the growth substrate and contacted using flexible and transparent silver nanowire mesh. The electroluminescence of a flexible device presents a cool-white color with a spectral distribution covering a broad spectral range from 400 to 700 nm. Mechanical bending stress down to a curvature radius of 5 mm doesnot yieldany degradation of the LED performance. The maximal measured external quantum efficiency (EQE) of the white LED is 9.3% and the wall plug efficiency is 2.4%
Flexible Photodiodes Based on Nitride Core/Shell p-n Junction Nanowires
International audienceA flexible nitride p-n photodiode is demonstrated. The device consists of a composite nanowire/polymer membrane trans- ferred onto a flexible substrate. The active element for light sensing is a vertical array of core/shell p−n junction nanowires containing InGaN/ GaN quantum wells grown by MOVPE. Electron/hole generation and transport in core/shell nanowires are modeled within nonequilibrium Green function formalism showing a good agreement with experimental results. Fully flexible transparent contacts based on a silver nanowire network are used for device fabrication, which allows bending the detector to a few millimeter curvature radius without damage. The detector shows a photoresponse at wavelengths shorter than 430 nm with a peak responsivity of 0.096 A/W at 370 nm under zero bias. The operation speed for a 0.3 × 0.3 cm2 detector patch was tested between 4 Hz and 2 kHz. The −3 dB cutoff was found to be ∼35 Hz, which is faster than the operation speed for typical photoconductive detectors and which is compatible with UV monitoring applications
- …