Villeneuve-la-Rivière, France
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Zhang W.,IEMN | Zhang W.,CAS Institute of Physics | Delerue C.,IEMN | Niquet Y.-M.,CEA Grenoble | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Using a sp3d5s* tight-binding model for electrons and a valence force-field model for phonons, we study the transport properties of [110]-oriented silicon nanowires including all electron-phonon interactions. Using a full resolution of the Boltzmann transport equation, the low-field mobility is calculated and its dependence on the temperature, density of electrons, and size of the nanowires is investigated. We predict that, as a result of strong quantum confinement, (1) electrons couple to a wide and complex distribution of phonon modes and (2) the mobility has a nonmonotonic variation with wire diameter and is strongly reduced with respect to the bulk. © 2010 The American Physical Society.

Groeneveld E.,University Utrecht | Delerue C.,IEMN | Allan G.,IEMN | Niquet Y.-M.,Laboratoire Of Simulation Atomistique L Sim | De Mello Donega C.,University Utrecht
Journal of Physical Chemistry C | Year: 2012

In this paper, we present a detailed investigation of the size dependence of the optical transitions of colloidal CdTe QDs ranging in diameter from 2.9 to 14.8 nm. The energy integrated absorption cross section per CdTe unit is investigated in detail for the lowest two exciton transitions (1S 3/2(h)-1S (e) and 2S 3/2(h)-1S (e)) and shown to increase with decreasing size, although the size dependence of the 2S 3/2(h)-1S (e) is less pronounced. The experimental absorption spectra are compared to spectra calculated by using a tight-binding approach. The calculations were carried out with electron-hole configuration interaction (CI) and without (single-particle, SP). The optical absorption spectra calculated by using the CI approach are in excellent agreement with the experiment, as well as the evolution of the optical gap and the optical transitions with nanocrystal size. © 2012 American Chemical Society.

Lapierre F.,IEMN | Piret G.,University of Lille Nord de France | Drobecq H.,Institute Of Biologie Of Lille | Melnyk O.,Institute Of Biologie Of Lille | And 3 more authors.
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2011

We present for the first time an electrowetting on dielectric (EWOD) microfluidic system coupled to a surface-assisted laser desorption-ionization (SALDI) silicon nanowire-based interface for mass spectrometry (MS) analysis of small biomolecules. Here, the transfer of analytes has been achieved on specific locations on the SALDI interface followed by their subsequent mass spectrometry analysis without the use of an organic matrix. To achieve this purpose, a device comprising a digital microfluidic system and a patterned superhydrophobic/superhydrophilic silicon nanowire interface was developed. The digital microfluidic system serves for the displacement of the droplets containing analytes, via an electrowetting actuation, inside the superhydrophilic patterns. The nanostructured silicon interface acts as an inorganic target for matrix-free laser desorption-ionization mass spectrometry analysis of the dried analytes. The proposed device can be easily used to realize several basic operations of a Lab-on-Chip such as analyte displacement and rinsing prior to MS analysis. We have demonstrated that the analysis of low molecular weight compounds (700 m/z) can be achieved with a very high sensitivity (down to 10 fmol μL-1). © 2011 The Royal Society of Chemistry.

Al Hadi R.,University of Wuppertal | Sherry H.,University of Wuppertal | Sherry H.,STMicroelectronics | Grzyb J.,University of Wuppertal | And 6 more authors.
IEEE Journal of Solid-State Circuits | Year: 2012

A 1 k-pixel camera chip for active terahertz video recording at room-temperature has been fully integrated in a 65-nm CMOS bulk process technology. The 32x32 pixel array consists of 1024 differential on-chip ring antennas coupled to NMOS direct detectors operated well-beyond their cutoff frequency based on the principle of distributed resistive self-mixing. It includes row and column select and integrate-and-dump circuitry capable of capturing terahertz videos up to 500 fps. The camera chip has been packaged together with a 41.7-dBi silicon lens (measured at 856 GHz) in a 5x5x3 cm 3 camera module. It is designed for continuous-wave illumination (no lock-in technique required). In this video-mode the camera operates up to 500 fps. At 856 GHz it achieves a responsivity Rv of about 115 kV/W (incl. a 5-dB VGA gain) and a total noise equivalent power (NEPtotal) of about 12 nW integrated over its 500-kHz video bandwidth. At a 5-kHz chopping frequency (non-video mode) a single pixel can provide a maximum responsivity Rv of 140 kV/W (incl. a 5-dB VGA gain) and a minimum noise equivalent power (NEP) of 100 pW/√Hz at 856 GHz. The wide-band antenna and pixel design achieves a 3-dB bandwidth of at least 790-960 GHz. © 2012 IEEE.

Lampin E.,IEMN | Krzeminski C.,IEMN
Journal of Applied Physics | Year: 2011

Classical molecular dynamics simulations are applied to the study of amorphous silicon regrowth in a nanodevice. A simplified atomistic amorphous nanostructure presenting the main features of a FinFET device is designed. A thermal treatment is used to simulate the annealing of the atomic model. The structure after annealing is very close to what observed experimentally, with perfect crystal near the silicon seed, an intermediate crystalline layer presenting [111] twins, and an upper terminal region of polysilicon. The comparison with 2D system suggests surface proximity effects that impact the probability to form grains and twins. As a consequence, it seems like the solid phase epitaxy was arrested in the nanostructure. © 2011 American Institute of Physics.

Houfaf F.,STMicroelectronics | Houfaf F.,University of Twente | Egot M.,STMicroelectronics | Kaiser A.,IEMN | And 2 more authors.
Digest of Technical Papers - IEEE International Solid-State Circuits Conference | Year: 2012

As of today, the highest cut-off frequency low-pass continuous-time analog filters are in the frequency band of 1 to 3GHz [2,4-6], targeting applications like UWB communications or hard disk drives. Nevertheless, bands much higher, of about 10GHz, are to be addressed in the near future. This paper demonstrates an active low-pass filter tunable from 1 to 10GHz in 65nm CMOS, which is to our knowledge the highest ever cutoff frequency reported. © 2012 IEEE.

We present calculations of impact ionization rates, carrier multiplication yields, and solar-power conversion efficiencies in solar cells based on quantum dots (QDs) of a semimetal, β-Sn. Using these results and previous ones on PbSe and PbS QDs, we discuss a strategy to select QDs with the highest carrier multiplication rate for more efficient solar cells. We suggest using QDs of materials with a close to zero band gap and a high multiplicity of the bands in order to favor the relaxation of photoexcited carriers by impact ionization. Even in that case, the improvement of the maximum solar-power conversion efficiency appears to be a challenging task. © 2011 American Chemical Society.

Keuleyan S.E.,James Franck Institute | Guyot-Sionnest P.,James Franck Institute | Delerue C.,IEMN | Allan G.,IEMN
ACS Nano | Year: 2014

HgTe colloidal quantum dots are synthesized with high monodispersivity with sizes up to ∼15 nm corresponding to a room temperature absorption edge at ∼5 μm. The shape is tetrahedral for larger sizes and up to five peaks are seen in the absorption spectra with a clear size dependence. The size range of the HgTe quantum dots is extended to ∼20 nm using regrowth. The corresponding room temperature photoluminescence and absorption edge reach into the long-wave infrared, past 8 μm. Upon cooling to liquid nitrogen temperature, a photoconductive response is obtained in the long-wave infrared region up to 12 μm. Configuration-interaction tight-binding calculations successfully explain the spectra and the size dependence. The five optical features can be assigned to sets of single hole to single electron transitions whose strengths are strongly influenced by the multiband/multiorbital character of the quantum-dot electronic states. © 2014 American Chemical Society.

Hackens B.,Catholic University of Louvain | Martins F.,Catholic University of Louvain | Faniel S.,Catholic University of Louvain | Dutu C.A.,Catholic University of Louvain | And 7 more authors.
Nature Communications | Year: 2010

In the quantum Hall regime, near integer filling factors, electrons should only be transmitted through spatially separated edge states. However, in mesoscopic systems, electronic transmission turns out to be more complex, giving rise to a large spectrum of magnetoresistance oscillations. To explain these observations, recent models put forward the theory that, as edge states come close to each other, electrons can hop between counterpropagating edge channels, or tunnel through Coulomb islands. Here, we use scanning gate microscopy to demonstrate the presence of QH Coulomb islands, and reveal the spatial structure of transport inside a QH interferometer. Locations of electron islands are found by modulating the tunnelling between edge states and confined electron orbits. Tuning the magnetic field, we unveil a continuous evolution of active electron islands. This allows to decrypt the complexity of high-magnetic-field magnetoresistance oscillations, and opens the way to further local-scale manipulations of QH localized states. © 2010 Macmillan Publishers Limited. All rights reserved.

Delerue C.,IEMN | Vanmaekelbergh D.,University Utrecht
2D Materials | Year: 2015

Wereport on the electronic band structure of 2D CdSe and PbSe semiconductors that have a silicenetype honeycomb geometry. Atomistic tight-binding calculations are performed on several model systems that bear a strong resemblance to the silicene-type honeycomb structures that were recently obtained by nanocrystal self-assembly. The calculated band structures are compared both to those of 2D quantum wells and graphene-type honeycomb structures. It is found that in silicene type CdSe honeycomb structures, the lowest electron conduction bands (derived from S-type nanocrystal wave functions) form a Dirac-type dispersion, very similar as in graphene. The P-type bands are usually more complex. However, when the hybridization between S- and P-type bands increases, a second Dirac cone and a genuine non-trivial flat band is observed, similar as in the case of graphene-type honeycomb structures of CdSe. There is a strong non-trivial gap between the first and second valence band, hosting the quantum spin Hall effect. Silicene-type PbSe structures show Dirac features in their bands, which however can be clouded due to the multi-valley character of PbSe. ©2015 IOP Publishing Ltd.

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