ORCID Profile
0000-0003-1048-3942
Current Organisations
Ecole Polytechnique
,
CNRS
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Publisher: American Physical Society (APS)
Date: 03-05-2001
Publisher: AIP Publishing
Date: 11-1995
DOI: 10.1063/1.168556
Abstract: Analysis of time series data using wavelets provides both scale (frequency) and position information. In contrast, the Fourier transform provides frequency information only. We discuss the Daubechies formulation of wavelets, with reference to the WaveletTransform package that calculates the filter coefficients for any Daubechies basis to arbitrary precision. Ex les of the wavelet transform applied to selected time series are presented to highlight the advantages of wavelets. We indicate an application of wavelets to s led Barkhausen noise, a nonlinear phenomenon encountered in magnetic systems. The elements of the WaveletTransform package are discussed, with the emphasis being on the calculation of filter coefficients and their application to the discrete wavelet transform (DWT) and its inverse. With the construction of quadrature mirror filters, an efficient implementation of the DWT is possible and is similar in structure to the fast Fourier transform algorithm. © 1995 American Institute of Physics.
Publisher: AIP Publishing
Date: 21-05-2014
DOI: 10.1063/1.4874875
Abstract: High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of in idual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 μm/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 × 10−9 m2/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.
Publisher: AIP Publishing
Date: 28-03-2017
DOI: 10.1063/1.4979097
Abstract: Using a microfabricated p-type GaAs Hall bar, it is shown that the combined application of co-planar electric and magnetic fields enables the observation of spatial oscillations of the photoluminescence circular polarization due to the precession of drifting spin-polarized photoelectrons. Observation of these oscillations as a function of electric field gives a direct measurement of the minority carrier drift mobility and reveals that the spin coherence length can be tuned up to more than 10μm with electric fields below 1 kV/cm.
Publisher: Wiley
Date: 09-11-2022
Abstract: Scanning tunneling luminescence microscopy (STLM) and scanning tunneling spectroscopy (STS) are used to study step‐bunched, oxidized 4H‐SiC surfaces prepared using a silicon melt process. The step‐bunched surface consists of atomically smooth terraces parallel to [0001] crystal planes, and rougher risers containing nanoscale steps formed by the termination of these planes. The striking topography of this surface is well resolved with large tip biases around −8 V and set currents less than 1 nA. Hysteresis in the STS spectra is preferentially observed on risers, suggesting that they contain a higher density of surface charge traps than the terraces where hysteresis is more frequently absent. Similarly, intense sub‐gap light emission centered around 2.4 eV is observed mainly on the risers albeit only with larger tunneling currents equal to or greater than 10 nA. The surface‐oxide‐related origin of this emission is reinforced by comparing tunneling electroluminescence spectra on the 4H‐ and 6H‐polytypes, and by the observation of a drastic reduction in emitted intensity after removal of the oxide in buffered HF. These results demonstrate the capability of STLM for the observation of surface impurities and defects responsible for sub‐gap light emission with spatial resolutions approaching the length scale of the defects themselves.
Publisher: American Physical Society (APS)
Date: 18-12-2009
Publisher: The Electrochemical Society
Date: 2011
DOI: 10.1149/1.3529936
Publisher: American Physical Society (APS)
Date: 09-12-2013
Publisher: American Physical Society (APS)
Date: 29-08-2001
Publisher: SPIE
Date: 28-08-2014
DOI: 10.1117/12.2060198
Publisher: AIP Publishing
Date: 09-04-2018
DOI: 10.1063/1.5026478
Abstract: We have combined spatially resolved steady-state micro-photoluminescence with time-resolved photoluminescence to investigate the exciton diffusion in a WSe2 monolayer encapsulated with hexagonal boron nitride. At 300 K, we extract an exciton diffusion length of LX = 0.36 ± 0.02 μm and an exciton diffusion coefficient of DX = 14.5 ± 2 cm2/s. This represents a nearly 10-fold increase in the effective mobility of excitons with respect to several previously reported values on nonencapsulated s les. At cryogenic temperatures, the high optical quality of these s les has allowed us to discriminate the diffusion of the different exciton species: bright and dark neutral excitons, as well as charged excitons. The longer lifetime of dark neutral excitons yields a larger diffusion length of LXD=1.5±0.02 μm.
Publisher: AIP Publishing
Date: 21-11-2002
DOI: 10.1063/1.1516852
Abstract: A mechanical apparatus for the application of variable uniaxial tensile stress to thin films grown on bulk material has been designed for use in measuring the electrical and/or optical properties of a thin layer over a temperature range 4.2 K& T& K, and in magnetic fields up to 7 T. The induced strain is measured with a resolution of 0.0015% by monitoring the position of a laser beam reflected off the surface of the strained s le. The use of the apparatus is demonstrated on n-type InSb layers grown on GaAs where the uniaxial tensile stress is applied in the [001] direction. At 300 K and strains of up to 0.05%, an increase in the conductivity of approximately 3.5% is observed, most of which (∼2.5%) is the result of an increase in the carrier concentration. The remaining 1% is due to an increase in the carrier mobility. Using band-structure k⋅p theory and the deformation potential parameters obtained from optical spectroscopy measurements under uniaxial compression, these observations are shown to be well described by a reduction in both the fundamental band gap and the carrier effective mass with increasing tensile strain.
Publisher: American Physical Society (APS)
Date: 18-06-2012
Publisher: Springer Berlin Heidelberg
Date: 2001
Publisher: Elsevier BV
Date: 06-2019
Publisher: AIP Publishing
Date: 11-07-2016
DOI: 10.1063/1.4955403
Abstract: A wide variety of apparently contradictory piezoresistance (PZR) behaviors have been reported in p-type silicon nanowires (SiNW), from the usual positive bulk effect to anomalous (negative) PZR and giant PZR. The origin of such a range of erse phenomena is unclear, and consequently so too is the importance of a number of parameters including SiNW type (top down or bottom up), stress concentration, electrostatic field effects, or surface chemistry. Here, we observe all these PZR behaviors in a single set of nominally p-type, 〈110〉 oriented, top-down SiNWs at uniaxial tensile stresses up to 0.5 MPa. Longitudinal π-coefficients varying from −800 × 10−11 Pa−1 to 3000 × 10−11 Pa−1 are measured. Micro-Raman spectroscopy on chemically treated nanowires reveals that stress concentration is the principal source of giant PZR. The sign and an excess PZR similar in magnitude to the bulk effect are related to the chemical treatment of the SiNW.
Publisher: IEEE
Date: 06-2009
Publisher: Wiley
Date: 13-11-2023
Publisher: IOP Publishing
Date: 18-01-2010
Publisher: AIP Publishing
Date: 20-05-2002
DOI: 10.1063/1.1481238
Abstract: A mesoscopic nonmagnetic magnetoresistive read-head sensor based on the recently reported extraordinary magnetoresistance (EMR) effect has been fabricated from a narrow-gap Si-doped InSb quantum well. The sensor has a conservatively estimated areal-density of 116 Gb/in.2 with a 300 K EMR of 6% and a current sensitivity of 147 Ω/T at a relevant field of 0.05 T and a bias of 0.27 T. Because this sensor is not subject to magnetic noise, which limits conventional sensors to areal densities of order 100 Gb/in.2, it opens a pathway to ultra-high-density recording at areal densities of order 1 Tb/in.2.
Publisher: AIP Publishing
Date: 20-02-2017
DOI: 10.1063/1.4977003
Abstract: Carrier and spin recombination are investigated in p-type GaAs of acceptor concentration NA = 1.5 × 1017 cm−3 using time-resolved photoluminescence spectroscopy at 15 K. At low photocarrier concentration, acceptors are mostly neutral and photoelectrons can either recombine with holes bound to acceptors (e-A0 line) or form excitons which are mostly trapped on neutral acceptors forming the (A0X) complex. It is found that the spin relaxation is faster for free electrons that recombine through the e-A0 transition due to exchange scattering with either trapped or free holes, whereas spin flip processes are less likely to occur once the electron forms with a free hole an exciton bound to a neutral acceptor. An increase in the photocarrier concentration induces a cross-over to a regime where the bimolecular band-to-band (b-b) emission becomes more favorable due to screening of the electron-hole Coulomb interaction and ionization of excitonic complexes and free excitons. Then, the formation of excitons is no longer possible, the carrier recombination lifetime increases and the spin lifetime is found to decrease dramatically with a concentration due to fast spin relaxation with free photoholes. In this high density regime, both the electrons that recombine through the e-A0 transition and through the b-b transition have the same spin relaxation time.
Publisher: American Physical Society (APS)
Date: 16-05-2022
Publisher: Elsevier BV
Date: 02-2009
Publisher: American Physical Society (APS)
Date: 03-04-2019
Publisher: American Physical Society (APS)
Date: 12-03-2007
Publisher: Springer Berlin Heidelberg
Date: 2001
Publisher: Springer Science and Business Media LLC
Date: 11-1993
DOI: 10.1038/366136A0
Publisher: American Physical Society (APS)
Date: 30-09-2015
Publisher: AIP Publishing
Date: 26-06-2003
DOI: 10.1063/1.1576897
Abstract: It has been proposed earlier that the extraordinary magnetoresistance (EMR) observed at room temperature in nonmagnetic semiconducting materials containing metallic inhomogeneities can be used in suitably constructed read heads for magnetic storage devices. Here, we show that such read heads are much simpler in design, and allow for higher sensitivity than is observed using magnetic layered structures that employ the phenomenon of giant magnetoresistance. We calculate, with no adjustable material parameters, the room-temperature response of an EMR read-head design, using finite element analysis, as a function of the position of the magnetic bit relative to the read head. The scaling property of the EMR bodes well for increasing the storage density to 1 Tbit/in.2 in the near future.
Publisher: AIP Publishing
Date: 05-08-2003
DOI: 10.1063/1.1600840
Abstract: Metal–semiconductor hybrids (MSHs) are found to exhibit enhanced room-temperature piezoconductance in the presence of uniaxial tensile strain. The magnitude of the enhanced piezoconductance is more than five times greater than that of the homogeneous semiconductor alone and is strongly dependent on both the location and properties of the metal–semiconductor interface. MSHs may be useful in determining the electrical properties of low-resistance metal contacts on semiconductors.
Publisher: American Vacuum Society
Date: 11-2003
DOI: 10.1116/1.1627811
Abstract: The design, fabrication, and performance of a nanoscopic magnetic field sensor based on the newly discovered phenomenon of extraordinary magnetoresistance (EMR) are reported. It is shown that a sensor with an active volume of 35 nm length×30 nm width×20 nm height yields room temperature EMR values as high as 35% at an applied field of 0.05 T. The mesoscopic physics implications of these new results are discussed.
Publisher: AIP Publishing
Date: 19-10-2015
DOI: 10.1063/1.4933189
Abstract: The electric field-induced modifications of the spatial distribution of photoelectrons, photoholes, and electronic spins in optically pumped p+ GaAs are investigated using a polarized luminescence imaging microscopy. At low pump intensity, application of an electric field reveals the tail of charge and spin density of drifting electrons. These tails disappear when the pump intensity is increased since a slight differential drift of photoelectrons and photoholes causes the buildup of a strong internal electric field. Spatial separation of photoholes and photoelectrons is very weak so that photoholes drift in the same direction as photoelectrons, thus exhibiting a negative effective mobility. In contrast, for a zero electric field, no significant ambipolar diffusive effects are found in the same s le.
Publisher: American Physical Society (APS)
Date: 17-04-2015
Publisher: American Physical Society (APS)
Date: 23-11-2010
Publisher: SPIE
Date: 08-09-2015
DOI: 10.1117/12.2188080
Publisher: AIP Publishing
Date: 15-06-2012
DOI: 10.1063/1.4730396
Abstract: Images of the steady-state luminescence of passivated GaAs self-standing films under excitation by a tightly focussed laser are analyzed as a function of light excitation power. While unipolar diffusion of photoelectrons is dominant at very low light excitation power, an increased power results in a decrease of the diffusion constant near the center of the image due to the onset of ambipolar diffusion. The results are in agreement with a numerical solution of the diffusion equations and with a physical analysis of the luminescence intensity at the centre of the image, which permits the determination of the ambipolar diffusion constant as a function of electron concentration.
Publisher: Springer Science and Business Media LLC
Date: 06-2008
Publisher: AIP Publishing
Date: 05-09-2017
DOI: 10.1063/1.4985831
Abstract: We investigate the diffusion of charge and spin at 15 K in p-type GaAs, combining transient-grating and energy-resolved microluminescence measurements to cover a broad range of photoelectron density. At very low optical power, in a unipolar nondegenerate regime, charge and spin diffuse at the same rate, implying that the spin-drag effects are negligible. Upon increasing the photoelectron concentration up to about 1016 cm–3, the charge diffusion constant decreases because of ambipolar electrostatic interactions with the slower-diffusing holes while the spin diffusion constant is reduced only weakly by the ambipolar interaction. A further increase in the excitation power causes increases in both the charge and spin diffusion constants as a consequence of the Pauli principle since the photoelectron gas becomes degenerate.
Publisher: American Physical Society (APS)
Date: 06-03-2012
Publisher: American Physical Society (APS)
Date: 08-12-2004
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6NR08918F
Abstract: Metal dielectric nanocomposites exhibit a broad range of physical properties that can be tuned by varying the metallic volume fraction (ϕ), in particular near the percolation threshold. The study and exploitation of the so-called critical properties at this threshold are currently limited by the inability to finely tune ϕ in a continuous way, for ex le in physical mixtures. Here we present a novel chemical fabrication process for metal dielectric coatings consisting of TiO
Publisher: Wiley
Date: 05-2023
Publisher: American Physical Society (APS)
Date: 23-06-2005
Publisher: AIP Publishing
Date: 14-07-2014
DOI: 10.1063/1.4889799
Abstract: A new approach is demonstrated for investigating charge and spin diffusion as well as surface and bulk recombination in unpassivated doped semiconductors. This approach consists in using two complementary, conceptually related, techniques, which are time-resolved photoluminescence (TRPL) and spatially resolved microluminescence (μPL) and is applied here to p+ GaAs. Analysis of the sole TRPL signal is limited by the finite risetime. On the other hand, it is shown that joint TRPL and μPL can be used to determine the diffusion constant, the bulk recombination time, and the spin relaxation time. As an illustration, the temperature variation of these quantities is investigated for p+ GaAs.
Publisher: American Physical Society (APS)
Date: 08-04-2008
Publisher: Elsevier BV
Date: 2010
Publisher: AIP Publishing
Date: 02-03-2015
DOI: 10.1063/1.4914357
Abstract: The charge and spin mobilities of minority photoelectrons in p+-GaAs are determined by monitoring the effect of an electric field on the spatial profiles of the luminescence and of its polarization. By using electric fields to increase the photoelectron temperature Te without significantly changing the hole or lattice temperatures, the charge and spin mobilities are shown to be principally dependent on Te. For Te & 70 K, both the charge and spin mobilities vary as Te−1.3, while at lower temperatures this changes to an even more rapid Te−4.3 law. This finding suggests that current theoretical models based on degeneracy of majority carriers cannot fully explain the observed temperature dependence of minority carrier mobility.
Publisher: Springer Science and Business Media LLC
Date: 15-09-2021
DOI: 10.1038/S41467-021-25747-5
Abstract: Monolayers of transition metal dichalcogenides are ideal materials to control both spin and valley degrees of freedom either electrically or optically. Nevertheless, optical excitation mostly generates excitons species with inherently short lifetime and spin/valley relaxation time. Here we demonstrate a very efficient spin/valley optical pumping of resident electrons in n-doped WSe 2 and WS 2 monolayers. We observe that, using a continuous wave laser and appropriate doping and excitation densities, negative trion doublet lines exhibit circular polarization of opposite sign and the photoluminescence intensity of the triplet trion is more than four times larger with circular excitation than with linear excitation. We interpret our results as a consequence of a large dynamic polarization of resident electrons using circular light.
Publisher: AIP Publishing
Date: 10-2010
DOI: 10.1063/1.3493047
Abstract: Room temperature electronic diffusion is studied in 3 μm thick epitaxial p+ GaAs lift-off films using a novel circularly polarized photoluminescence microscope. The method is equivalent to using a standard optical microscope and provides a contactless means to measure both the charge (L) and spin (Ls) diffusion lengths simultaneously. The measured values of L and Ls are in excellent agreement with the spatially averaged polarization and a sharp reduction in these two quantities (L from 21.3 to 1.2 μm and Ls from 1.3 to 0.8 μm) is found with increasing surface recombination velocity. Outward diffusion results in a factor of 10 increase in the polarization at the excitation spot. The range of materials to which the technique can be applied, as well as a comparison with other existing methods for the measurement of spin diffusion, is discussed.
Publisher: AIP Publishing
Date: 04-2017
DOI: 10.1063/1.4980038
Abstract: The ability to measure nanoradian polarization rotations, θF, in the photon shot noise limit is investigated for partially crossed polarizers (PCP), a static Sagnac interferometer, and an optical bridge, each of which can in principle be used in this limit with near equivalent figures-of-merit (FOM). In practice a bridge to PCP/Sagnac source noise rejection ratio of 1/4θF2 enables the bridge to operate in the photon shot noise limit even at high light intensities. The superior performance of the bridge is illustrated via the measurement of a 3 nrad rotation arising from an axial magnetic field of 0.9 nT applied to a terbium gallium garnet. While the Sagnac is functionally equivalent to the PCP in terms of the FOM, unlike the PCP it is able to discriminate between rotations with different time (T) and parity (P) symmetries. The Sagnac geometry implemented here is similar to that used elsewhere to detect non-reciprocal (T¯P) rotations like those due to the Faraday effect. Using a Jones’ matrix approach, novel Sagnac geometries uniquely sensitive to non-reciprocal TP¯ (e.g. magneto-electric or magneto-chiral) rotations, as well as to reciprocal rotations (e.g. due to linear birefringence, TP, or to chirality, TP¯) are proposed.
Publisher: Wiley
Date: 14-04-2014
Publisher: AIP Publishing
Date: 03-04-2000
DOI: 10.1063/1.126206
Publisher: American Physical Society (APS)
Date: 29-09-2010
Publisher: Elsevier BV
Date: 06-2012
Publisher: AIP Publishing
Date: 05-2010
DOI: 10.1063/1.3374641
Abstract: Local spin injectors using GaAs tips at the end of transparent cantilevers have been fabricated using a combination of epitaxial growth, etching processes and photolithographic techniques. The tip luminescence polarization is found to be small because of total internal light reflections of the luminescence inside the tip. However, measurements on planar films of similar doping along with a numerical solution of the spin and charge diffusion equations indicate that the injected spin polarization can be as high as 40% with corresponding electronic concentrations at the tip apex of the order of 1014 cm−3.
Publisher: American Physical Society (APS)
Date: 25-01-2021
Publisher: American Physical Society (APS)
Date: 10-03-2011
Publisher: SPIE-Intl Soc Optical Eng
Date: 29-01-2016
Publisher: American Physical Society (APS)
Date: 09-04-2008
Publisher: AIP Publishing
Date: 13-09-2013
DOI: 10.1063/1.4821139
Abstract: For n- and p-type semiconductors doped above the 1016 cm−3 range, simple analytical expressions for the surface recombination velocity S have been obtained as a function of excitation power P and surface state density NT. These predictions are in excellent agreement with measurements on p-type GaAs films, using a novel polarized microluminescence technique. The effect on S of surface passivation is a combination of the changes of three factors, each of which depends on NT: (i) a power-independent factor which is inversely proportional to NT and (ii) two factors which reveal the effect of photovoltage and the shift of the electron surface quasi Fermi level, respectively. In the whole range of accessible excitation powers, these two factors play a significant role so that S always depends on power. Three physical regimes are outlined. In the first regime, illustrated experimentally by the oxidized GaAs surface, S depends on P as a power law of exponent determined by NT. A decrease of S such as the one induced by sulfide passivation is caused by a marginal decrease of NT. In a second regime, as illustrated by GaInP-encapsulated GaAs, because of the reduced value of S, the photoelectron concentration in the subsurface depletion layer can no longer be neglected. Thus, S−1 depends logarithmically on P and very weakly on surface state density. In a third regime, expected at extremely small values of P, the photovoltage is comparable to the thermal energy, and S increases with P and decreases with increasing NT.
Publisher: IOP Publishing
Date: 29-11-2010
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2006
End Date: 2008
Funder: National Agency for Research
View Funded ActivityStart Date: 2014
End Date: 2018
Funder: National Agency for Research
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