Activity Report 2010 - CNRS

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HIGHLIGHT : NANOPHOTONICS CONTACTS julien.claudon@cea.fr FURTHER READING J. Claudon et al. Nature Photonics, 4, p174, (<strong>2010</strong>) J. Bleuse et al, Phys. Rev. Lett, 106, 103601 (2011) 5 A BRIGHT SINGLE- PHOTON SOURCE BASED ON A PHOTONIC NANOWIRE The realization of an efficient, on-demand single-photon source (SPS) is an important goal for the development of quantum cryptography and photonic quantum information processing. In this context, semiconductor quantum dots (QD) are very attractive: at low temperature, they offer a stable singlephoton emission with a nearly perfect radiative yield. However, they are generally embedded in a high index semiconductor matrix that prevents the efficient collection of light in the far field. Within the “Strongchip” young scientist project supported by the Nanoscience Foundation, we have overcome this limitation and demonstrated a very bright SPS by inserting the QD inside a novel, well controlled electromagnetic environment: a photonic nanowire. A photonic wire is a monomode optical waveguide that is made of a high index dielectric material. Specifically, we consider here a structure defined in III- As semiconductors and shown in Fig. 1: the wire is made of GaAs (n=3.5) and is surrounded by air (n=1). It contains an InAs QD whose fundamental optical transition emits single photons at a free space wavelength around 920 nm. The high refractive index contrast between the wire and the air cladding has two important consequences. First, the guided mode is confined very tightly inside a wire having a 200 nm diameter, which guarantees a good coupling to the emitter. In addition, the coupling to the continuum of non-guided modes is strongly inhibited, thanks to a pronounced dielectric screening effect. As a consequence, the spontaneous emission of the QD is nearly completely funneled into the guided mode. Next, one has to collect efficiently the guided photons with a microscope objective located above the wire. For this goal, the two ends of the wire are carefully engineered. The photons emitted downward are reflected back into the guided mode with an integrated mirror, made of gold and silica. The upper wire end features a conical tip, designed to deconfine progressively the guided mode into the air cladding, in order to obtain a more directive far-field emission pattern. The fabrication process of such devices starts from a planar structure grown by molecular beam epitaxy. After deposition of the SiO 2 -Au mirror and a flip-chip step, the photonic nanowires are obtained with a dry plasma etching. Because it defines the nanowire geometry, this last step is critical and was carefully optimized. The sample was then mounted in a micro-photoluminescence setup and cooled down to liquid helium temperature. The injection of electronhole pairs to excite the QD luminescence was provided by a pulsed laser. The source efficiency, defined as the probability to emit a photon into the collecting cone of the microscope objective after an excitation pulse, reaches a maximum when the emitter is saturated. In these conditions, a record value of 0.72 photon per pulse was obtained. Simultaneously, intensity correlation measurements have provided the unambiguous signature of a very pure single-photon emission (g (2)
QUANTUM HETEROSTRUCTURES IN II-VI NANOWIRES Semiconductor nanowires (NWs) have attracted much attention in recent years because of their unique properties and potential use in a variety of technological applications. The flexibility of the NW growth allows designing quantum structures with unprecedented freedom. With narrow NW, quantum dot structures can be formed by inserting a low gap semiconductor along the NW axis (without the necessity of self-assembly), at defined position and size. On the other hand, core-shell heterostructures can be grown where the nanowires are surrounded by a radial shell which enables passivation of interfaces, and allows efficient charge separation in type II heterostructures for photovoltaic application. We have developed the growth of ZnSe/CdSe nanowire heterostructures by molecular beam epitaxy, using gold droplets as catalysts. Narrow wires with typical diameter of 10 nm have been obtained so that carriers in the CdSe QD are in the strong confinement regime (bulk exciton Bohr diameter is 11 nm for CdSe). These NW-QD show intense photoluminescence (PL) thank to the efficient light extraction from such structures as well as high linear polarization (linear polarization rate is about 90%) induced by the wire geometry. The strong Coulomb interaction in CdSe/ZnSe QDs (excitonbiexciton separation is 20meV in fig 1) makes this system particularly suitable for an application as high temperature (non cryogenic) single photon source. for non-classical light emission from a non-blinking semiconductor QD system. The intense PL emission of such QDs enables to carry out fine optical studies on the dynamics of elementary QD excitations (exciton, biexciton and trion). Moreover, we have introduced a novel technique to probe the dynamics of the microscopic events responsible for the spectral diffusion and broadening of QD lines. It relies on the measurement of the temporal correlations between photons emitted in the low-energy or high-energy parts of the QD exciton line; its resolution (90ps) represents an improvement by four orders of magnitude with respect to previous work. However pretty little control could be obtained with the growth on oxidized silicon: no epitaxial relation between the substrate, random orientation, quality hard to be reproduced. In order to gain control over the NW crystal structure and growth direction, we have investigated the epitaxial growth on a ZnSe buffer layer. The epitaxial growth has allowed us to obtain vertical and uniform NW (fig. 2b) and a better reproducibility. With CdSe QD inserted in these ZnSe NW, we have managed very recently to demonstrate single photon emission up to room temperature, within the project of Miryam ELOUNEG, a PhD student funded by the Foundation. Fig. 2 (a) HRTEM image of two ZnSe NW embbeding a CdSe QD (gold catalyst is on top). (b) Low density of ZnSe NWs of uniform 10nm diameter. HIGHLIGHT : NANOPHOTONICS Fig. 1: Very pure emission spectrum showing exciton (X) and biexciton (XX) from a single ZnSe/CdSe NW-QD With a first generation of NWs grown on an oxidized Si (001) wafer, we have demonstrated in 2008 single photon emission up to 220 K, which was at that time the highest reported temperature This expertise of CdSe axial heterostructures into II-VI nanowires is extended nowadays to lateral growth: a conformal layer of CdSe over a template of ZnO nanowires is an optimized geometry configuration for photovoltaic cells. In such core-shell semiconductor wires, the electron and the hole wavefunctions are naturally confined in the core and the shell region respectively. Such “quantum coaxial cables” open a promising route towards high efficiency solar cells which is explored within Yong ZHANG’s Chair of Excellence project entitled “II-VI photovoltaics”. CONTACTS kuntheak.kheng@cea.fr jean-philippe.poizat@grenoble.cnrs.fr henri.mariette@grenoble.cnrs.fr FURTHER READING A. Tribu et al. Nano Lett 8, 4326 (2008) G. Sallen et al, Phys. Rev. B 80, 085310 (2009) G. Sallen et al, Nature Photonics 4, 696 (<strong>2010</strong>) 6
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Date of publication: May 2011 We wo
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Nanosciences Foundation Activity Re
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Part I: ACHIEVEMENTS & PROSPECTS Th
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THE NANOSCIENCES FOUNDATION AT THE
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OUTSTANDING BENEFITS CATALYZED BY T
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The laureates of the 2010 Chairs of
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‘Mobilité d’Excellence’: a n
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INTEGRATION ON SITE BETWEEN BASIC R
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OVERVIEW Fig.3: LANEF framework. Ba
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The Nanosciences Foundation budget
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The evolution of the funding progra
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OVERVIEW Fig. 6: Total number of vi
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ACKNOWLEDGEMENTS One couldn’t fin
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Part II: SCIENTIFIC REPORT 1 - QUAN
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1 - QUANTUM NANOELECTRONICS Moore
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Core/shell nanowires: conductance C
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2 - NANOMAGNETISM AND SPINTRONICS B
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than 10 8 V/m and to compare this t
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sites. The calculations indicate th
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3 - NANOPHOTONICS The optical prope
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Cavity-feeding : decoherence as a r
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4 - MOLECULAR ELECTRONICS Molecular
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5 - NANOMATERIALS, NANOASSEMBLY AND
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Phase-change memory RTRA Project 20
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6 - NANO- CHARACTERISATION AND NANO
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when compared, for example, to the
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7 - NANO APPROACHES TO LIFE SCIENCE
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Innovative biochips to detect and s
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Implantable brain computer interfac
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8 - NANOMODELING, THEORY & SIMULATI
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Growth, patterning, defects & struc
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9 - TECHNOLOGICAL FACILITIES Create
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CRG: The French Cooperative Researc
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The Numerical Simulation Facility T
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10 - EDUCATION AND SCIENTIFIC ANIMA
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Q-NET: a new European Initial Train
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Thesis Prize Award Ceremonies 2009
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2010 Speaker From Date Title Resear
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Workshop “Super Resolution Optica
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Workshop “Electronic Noise and Re
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Workshop « New trends in Electrica
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List of the Quantum Nanoelectronics
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Hélène LE SUEUR Laboratoire de Ph
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Quantum Nanoelectronics Seminars in
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Invitations to talk at seminars: "
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- Anton ANDREEV (University of Wash
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Cellulose Hybrid block copolymers /
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PART 3 S. J. C. Yates, J. J. A. Bas
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D. A. Stewart, I. Savic, and N. Min
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DISPOGRAPH / RTRA project Post-doct
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2009 Call for Proposals MUSCADE Cha
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Piotr Laczkowski, Danny Hykel, Serg
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Part IV: SUPPLEMENTS Appendix 1: th
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Appendix 2: the Foundation’s boar
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Page 130 and 131: PhD students supported in 2010 Name
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Page 150 and 151: SUPPLEMENTS 5 : Très nombreuses vi
Page 152 and 153: Nom du laboratoire Laboratoire Inte
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Page 158 and 159: SUPPLEMENTS 48
Page 160: HIGHLIGHTS QUANTUM NANOELECTRONICS:
Page 163 and 164: FIB NANO- TOMOGRAPHY OF DEFECTS IN
Page 165: DETECTING SINGLE NANOPARTICLE MAGNE
Page 169 and 170: ELECMOL’10 CONFERENCE An importan
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Page 173 and 174: SCANNING GATE NANOELECTRONICS In th
Page 175 and 176: CONTROL OF THERMAL CONDUCTIVITY AT
Page 178 and 179: Roland HERINO (past Director) Jean-
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