A high-sensitivity in situ optical diagnostic technique for laser cleaning of transparent substrates

A differential optical transmission technique has been used to monitor in situ the efficiency of laser cleaning for the removal of sub-micrometer-sized particles on substrates transparent at the monitoring wavelength. This technique has been applied to the removal of sub-micrometer polystyrene particles on polyimide substrates using laser pulses of 30 ps duration at 292 nm while probing the material transmission at 633 nm. The sensitivity achieved -1/10⁴ for the transmission changes induced upon single-pulse laser exposure – allows us to monitor the removal of just a few sub-micron-sized particles from the probed region inside the irradiated area. Received: 2 October 2002 / Accepted: 7 October 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +33-3/87844082, E-mail: nchaoui@iut.univ-metz.fr RID="**" ID="**"Present address: Laboratoire de Chimie et Applications, Institut Universitaire de Technologie de Metz, Département Chimie, Rue Victor Demange, 57500 Saint-Avold, France     

Towards controllable optical response of GaN quantum dots in alumina

GaN nanocrystals (in the wurtzite phase) have been synthesized by thermal annealing in reducing atmosphere of Ga⁺+N⁺ sequentially implanted alumina. We show that the reduction of Ga local concentration (by lowering the implantation dose) yields to an overall increase in the intensity of the GaN photoluminescence signal, to a decrease of the PL bandwidth and to the shift of its onset towards higher energies, due to quantum confinement effects in GaN nanocrystals with a narrow size distribution. The interpretation of the optical results is supported by structural analyses. Moreover, by investigating different forming treatments for GaN synthesis, the key role of hydrogen in the annealing atmosphere is evidenced.Received: 20 February 2003, Published online: 24 April 2003PACS: 61.46.+w Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals - 81.05.Ea III-V semiconductors - 78.67.Hc Quantum dots - 85.40.Ry Impurity doping, diffusion and ion implantation technologyC. Maurizio: Present address: INFM, GILDA-CRG ESRF, B.P. 220, 38043 Grenoble, France.E. Borsella: Permanent address: ENEA-UTS FIS, Via E. Fermi 45, 00044 Frascati (Rome), Italy.     

Landau-Zener interferometry for qubits

One may probe coherence of a qubit by periodically sweeping its control parameter. The qubit is then excited by the Landau-Zener (LZ) mechanism. The interference between multiple LZ transitions leads to an oscillatory dependence of the energy absorption rate on the sweeping amplitude and on the period. This interference pattern allows to determine the decoherence time of the qubit. We introduce a simple phenomenological model describing this interferometer, and find the form of the interference pattern.Received: 21 October 2003, Published online: 8 December 2003PACS: 03.67.-a Quantum information - 85.25.Dq Superconducting quantum interference devicesD.A. Ivanov: Present address: Paul Scherrer Institute, 5232 Villigen PSI, Switzerland     

Fluctuation conductivity in layered d-wave superconductors near critical disorder

We consider the fluctuation conductivity in the critical region of a disorder induced quantum phase transition in layered d-wave superconductors. We specifically address the fluctuation contribution to the systems conductivity in the limit of large (quasi-two-dimensional system) and small (quasi-three-dimensional system) separation between adjacent layers of the system. Both in-plane and c-axis conductivities were discussed near the point of insulator-superconductor phase transition. The value of the dynamical critical exponent, z = 2, permits a perturbative treatment of this quantum phase transition under the renormalization group approach. We discuss our results for the system conductivities in the critical region as function of temperature and disorder.Received: 10 October 2003, Published online: 23 December 2003PACS: 74.40. + k Fluctuations (noise, chaos, nonequilibrium superconductivity, localization, etc.) - 73.43.Nq Quantum phase transitions     

Electromagnetic form factors of bound nucleons revisited

We investigate the possible modifications of the nucleons' electromagnetic form factors in the framework of a modified Skyrme model allowing for nucleon deformation and using realistic nuclear mass distributions. We show that such effects are small in light nuclei Received: 19 November 2002 / Accepted: 3 December 2002 / Published online: 18 March 2003 RID="a" ID="a"Address after January 1st, 2003: Helmholtz Institut für Strahlen- und Kernphysik (Theorie), Universit?t Bonn, Nu?allee 14-16, D-53115 Bonn, Germany; e-mail: meissner@itkp.uni-bonn.de RID="b" ID="b"Present address: Helmholtz Institut für Strahlen- und Kernphysik (Theorie), Universit?t Bonn, D-53115 Bonn, Germany. Communicated by V. Vento     

Confinement of molecular liquids: Consequences on thermodynamic,static and dynamical properties of benzene and toluene

We relate the dynamical behavior of molecular liquids confined in mesoscopic cylindrical pores to the thermodynamic properties, heat capacity and density and to the static structure by combining different experimental methods (H-NMR, calorimetry, elastic and inelastic neutron scattering, numerical simulations). The crystallization process is greatly reduced or avoided by confinement under standard cooling conditions, instead a glass transition temperature T _g at the 1000s time scale can be observed. The pore averaged local structure of the confined liquid is not noticeably affected when excluded-volume corrections are carefully applied, but follows the density changes reflected by the Bragg peak intensities of the porous matrices. The pore size dependence of T _g is dominated by two factors, surface interaction and finite-size effect. For the smallest pores ( , being the van der Waals radius of a molecule), one observes an increase of T _g and a broadening of the transition region, related to the interaction with the surface that induces a slowing-down of the molecules close to the wall. This is confirmed by neutron scattering experiments and molecular-dynamics simulations at shorter time scales and higher temperatures, which indicate a remaining fraction of frozen molecules. For larger pore sizes, taking the decrease of density under confinement conditions into account, a decrease of T _g is observed. This could be related to finite-size effects onto the putative cooperativity length that is often invoked to explain glass formation. However, no quantitative determination of this length (not to mention its T-dependence) can be extracted, since the interaction with the wall itself introduces an additional length that adds to the complexity of the problem.Received: 1 January 2003, Published online: 30 October 2003PACS: 64.70.Pf Glass transitions - 65.20. + w Thermal properties of liquids: heat capacity, thermal expansion, etc. - 61.12.-q Neutron diffraction and scatteringD. Morineau: Present address: Groupe Matiére Condensée et Matériaux, CNRS-UMR 6626, Bâtiment 11A, Université de Rennes 1, F-35042 Rennes, France.V. Teboul: Present address: Laboratoire des Propriétés Optiques des Matériaux et Applications, CNRS-UMR 6136, Université dAngers, F-49045 Angers, France.Y. Xia: Present address: School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom.     

Infrared photodetection with semiconductor self-assembled quantum dots

Semiconductor self-assembled quantum dots are potential candidates to develop a new class of midinfrared quantum photodetectors and focal plane arrays. In this article, we present the specific midinfrared properties of InAs/GaAs quantum dots associated with the intersublevel transitions. The electronic structure, which accounts for the strain field in the islands, is obtained within the framework of a three-dimensional 8 band k.p formalism. The midinfrared intersublevel absorption in n-doped quantum dots is described. We show that the carrier dynamics can be understood in terms of polarons which result from the strong coupling regime for the electron–phonon interaction in the dots. The principle of operation of vertical and lateral quantum dot infrared photodetectors is described and discussed by comparison with quantum well infrared photodetectors. We review the performances of different type of detectors developed to date and finally give some orientation to realize high performance quantum dot infrared photodetectors. To cite this article: P. Boucaud, S. Sauvage, C. R. Physique 4 (2003).     

Electronic structure of three-dimensional quantum dots

We study the electronic structure of three-dimensional quantum dots using the Hartree-Fock approximation. The confining potential of the electrons in the quantum dot is assumed to be spatially isotropic and harmonic. For up to 40 interacting electrons the ground-state energies and ground-state wavefunctions are calculated at various interaction strengths. The quadrupole moments and electron densities in the quantum dot are computed. Hund's rule is confirmed and a shell structure is identified via the addition energies and the quadrupole moments. While most of the shell structure can be understood on the basis of the unperturbed non-interacting problem, the interplay of an avoided crossing and the Coulomb interaction results in an unexpected closed shell for 19 electrons. Received 5 November 2001 / Received in final form 12 November 2002 Published online 1st April 2003 RID="a" ID="a"e-mail: vorrath@physnet.uni-hamburg.de     

Elasticity and plasticity of two-dimensional amorphous solid layers of β-lactoglobulin

We investigate the mechanical properties of a two-dimensional amorphous solid. It is formed spontaneously by the adsorption of a protein (the β-lactoglobulin) at the surface of water. We measure its mechanical response in both elastic and plastic regimes by applying a point-like force (using a glass fiber). We compare our results with previous measurements of shear moduli using a floating torsion device. Received: 10 February 2003 / Accepted: 23 April 2003 / Published online: 27 May 2003 RID="a" ID="a"Present address: Cavendish Laboratory, Madingley Road, Cambridge, CB3 0HE, UK; e-mail: sc374@phy.cam.ac.uk RID="b" ID="b"e-mail: graner@ujf-grenoble.fr     

Quantum cascade transitions in nanostructures

In this article we review the physical characteristics of quantum cascade transitions (QCTs) in various nanoscopic systems. The quantum cascade laser which utilizes such transitions in quantum wells is a brilliant outcome of quantum engineering that has already demonstrated its usefulness in various real-world applications. After a brief introduction to the background of this transition process, we discuss the physics behind these transitions in an externally applied magnetic field. This has unravelled many intricate phenomena related to intersubband resonance and electron relaxation modes in these systems. We then discuss QCTs in a situation where the quantum wells in the active regions of a quantum cascade structure are replaced by quantum dots. The physics of quantum dots is a rapidly developing field with its roots in fundamental quantum mechanics, but at the same time, quantum dots have tremendous potential applications. We first present a brief review of those aspects of quantum dots that are likely to be reflected in a quantum-dot cascade structure. We then go on to demonstrate how the calculated emission peaks of a quantum-dot cascade structure with or without an external magnetic field are correlated with the properties of quantum dots, such as the choice of confinement potentials, shape, size and the low-lying energy spectra of the dots. Contents PAGE 1 Introduction 456 2 Intersubband transitions in quantum wells 458 3 Quantum cascade transitions 462 3.1. Basic principles 462 3.1.1. Minibands and minigaps 464 3.1.2. Vertical transitions 464 3.1.3. GaAs/AlGaAs quantum cascade lasers 464 3.1.4. QCLs based on superlattice structures 465 3.1.5. Type-II quantum cascade lasers 466 3.1.6. Recent developments 466 3.2. Applications: sense-ability and other qualities 466 4 Quantum cascade transitions in novel situations 467 4.1. External magnetic field 467 4.1.1. Parallel magnetic field 468 4.1.2. Many-body effects: depolarization shift 470 4.1.3. The role of disorder 471 4.1.4. Tilted magnetic field 475 4.2. Magneto-transport experiments and phonon relaxation 479 4.3. Magneto-optics experiment and phonon relaxation 484 5 A brief review of quantum dots 485 5.1. From three- to zero-dimensional systems 485 5.2. Making the dots 487 5.2.1. Lithographic patterning 487 5.2.2. Self-assembled quantum dots 488 5.3. Shell filling in quantum dots 489 5.4. Electron correlations: spin states 490 5.5. Anisotropic dots 491 5.6. Influence of an external magnetic field 491 5.6.1. The Fock diagram 491 5.6.2. The no-correlation theorem 492 5.6.3. Correlation effects and magic numbers 492 5.6.4. Spin transitions 493 5.7. Quantum dots in novel systems 494 5.8. Potential applications of quantum dots 494 5.8.1. Single-electron transistors (SETs) 494 5.8.2. Single-photon detectors 494 5.8.3. Single-photon emitters 495 5.8.4. Quantum-dot lasers 495 6 Quantum cascade transitions in quantum-dot structures 496 6.1. Quantum dots versus quantum wells 496 6.2. QCT with rectangular dots 497 6.2.1. Vertical transitions 500 6.2.2. Diagonal transitions 501 6.3. QCT in a parabolic dot 504 6.4. Magnetic field effects on intersubband transitions 506 6.5. Mid-IR luminescence from a QD cascade device 512 7 Summary and open questions 513 Acknowledgements 515 References 515     

Lifetime of a new high-spin isomer in 150 Dy

A new high-spin isomer in ¹⁵⁰Dy has been observed at an excitation energy of 10.3 MeV by combining the inverse-kinematic reaction induced by a pulsed beam of ¹³²Xe and the -ray recoil-shadow technique. The half-life of this isomeric state has been determined to be ns using the conventional centroid-shift method with the ¹⁴¹Pr(¹⁶O, p6n)¹⁵⁰Dy reaction at 165 MeV. The mechanism producing high-spin isomers in N = 83,84 isotones is qualitatively discussed in terms of the difference of the neutron particle-hole configuration between the high-spin isomer and the lower-lying state.Received: 3 September 2003, Revised: 8 October 2003, Published online: 5 January 2004PACS: 21.10.Tg Lifetimes - 23.20.Lv transitions and level energies - 27.70. + q T. Fukuchi: Present address: Center for Nuclear Study (CNS), University of Tokyo, RIKEN campus, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.W. Sato: Present address: Graduate School of Science, Osaka University, 1-1 Machikaneyamacho, Toyonaka, Osaka 560-0043, Japan.     

High-spin states in the <Superscript>97</Superscript>Tc nucleus

High-spin states in the ⁹⁷Tc nucleus have been studied by in-beam γ-ray spectroscopy with the reaction ⁸²Se(¹⁹F,4nγ) at 68 MeV incident energy. Excited states have been observed up to about 8 MeV excitation and spin 43/2. The observed level scheme is compared with results of shell model calculations. Received: 22 November 2002 / Accepted: 23 December 2002 / Published online: 18 March 2003 RID="a" ID="a"e-mail: bucurescu@tandem.nipne.ro RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="b" ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy. RID="c" ID="c"Present address: Università di Padova, Padova, Italy. Communicated by C. Signorini     

Integrable scattering theories with unstable particles

We formulate a new bootstrap principle which allows for the construction of particle spectra involving unstable as well as stable particles. We comment on the general Lie algebraic structure which underlies theories with unstable particles and propose several new scattering matrices. We find a new Lie algebraic decoupling rule, which predicts the renormalization group flow in dependence of the relative ordering of the resonance parameters. The proposals are exemplified for some concrete theories which involve unstable particles, such as the homogeneous sine-Gordon models and their generalizations. The new decoupling rule can be validated by means of our new bootstrap principle and also via the renormalization group flow, which we obtain from a thermodynamic Bethe ansatz analysis.O.A. Castro-Alvaredo: Present addressLaboratoire de Physique, Ecole Normale Supérieure de Lyon, Allée dItalie, 69364 Lyon Cedex, FranceJ. Dreißig: Present address Universität Potsdam, Institut für Physik, Am Neuen Palais 10, 14469 Potsdam, GermanyA. Fring: Present address Centre for Mathematical Science, City University, Northampton Square, London EC1V 0HB, UK     

Gamma-ray feeding and decay of superdeformed states

We report on four recent results concerning the population and the decay of superdeformed states, namely the structure of excited superdeformed states in ¹⁹⁴Hg, the search for fine structure of the last superdeformed transitions in ¹⁹⁴Pb, the primary decay-out strength analysis in ¹⁹⁴Hg and, as a consequence of this, the possibility of using the decay-out as a tool to study order-to-chaos properties of normally deformed states.Received: 3 December 2002, Published online: 17 February 2004PACS: 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 24.60.-k Statistical theory and fluctuations - 24.60.Lz Chaos in nuclear systems - 27.80. + w F. Hannachi: Present address: CENBG/IN2P3, Gradignan, France.H. Amro: Present address: WNSL, Yale, USA.K. Hauschild: Present address: CSNSM/IN2P3, Orsay, France.T. Kröll: Present address: TU, Munich, Germany.M. Rejmund: Present address: GANIL, Caen, France.     

Ion irradiation of exchange bias systems for magnetic sensor applications

It has been demonstrated that He⁺ ion irradiation is an excellent tool for modifying magnetic properties, like the magnetic anisotropy, the interlayer exchange coupling strength and the exchange bias field of ultra-thin magnetic layered systems. This paper summarizes the effects of ion irradiation on exchange bias systems. As a first example, for possible applications of the ion induced magnetic effects, the realization of an angle sensing device is described. Received: 11 November 2002 / Accepted: 12 November 2002 / Published online: 4 April 2003 RID="*" ID="*"Corresponding author. Fax: +49-631-205-4095, E-mail: fassbend@physik.uni-kl.de RID="**" ID="**"Present address: Université de Rouen, Rouen, France     

Intersublevel transitions in self-assembled quantum dots

Intersublevel transitions in semiconductor quantum dots are transitions of a charge carrier between quantum dot confined states. In InAs/GaAs self-assembled quantum dots, optically active intersublevel transitions occur in the mid-infrared spectral range. These transitions can provide a new insight on the physics of semiconductor quantum dots and offer new opportunities to develop mid-infrared devices. A key feature characterizing intersublevel transitions is the coupling of the confined carriers to phonons. We show that the effect of the strong coupling regime for the electron–optical phonon interaction and the formation of mixed electron–phonon quasi-particles called polarons drastically affect and control the dynamical properties of quantum dots. The engineering of quantum dot relaxation rates through phonon coupling opens the route to the realization of new devices like mid-infrared polaron lasers. We finally show that the measurement of intersublevel absorption is not limited to quantum dot ensembles and that the intersublevel ultrasmall absorption of a single quantum dot can be measured with a nanometer scale resolution by using phonon emission as a signature of the absorption. To cite this article: P. Boucaud et al., C. R. Physique 9 (2008).     

Mixing length scales: step meandering and island nucleation on vicinal surfaces

Simultaneous island nucleation and step flow growth on vicinal surfaces are studied by Monte Carlo simulations. Step edges experience meandering instability under growth conditions if there is a kink barrier suppressing adatom jumps around kink sites. This instability has a characteristic length scale, with different scaling properties from the island separation scale. We show that there is a coupling between island nucleation and step edge instability. The length scale associated with nucleation begins to couple with the wavelength of the step edge patterns when islands and steps coalesce. Only in the submonolayer regime step meandering is independent of island formation. In this regime the island separation has a cross-over scaling behaviour as terrace width is varied.Received: 9 April 2003, Published online: 19 November 2003PACS: 81.15.Aa Theory and models of film growth - 68.55.Ac Nucleation and growth: microscopic aspects - 81.16.Rf Nanoscale pattern formationM. Rusanen: Present address: Institut Français du Pétrole, Groupe de Modélisation Moléculaire, BP 311, 92852 Rueil-Malmaison, FranceJ. Kallunki: Present address: Laboratory of Physics, PO Box 1100, FIN-02015 HUT, Espoo, Finland     

Coherent coupling of a single <Superscript>40</Superscript>Ca<Superscript>+</Superscript> ion to a high-finesse optical cavity

We demonstrate coherent coupling of the quadrupole S_1/2D_5/2 optical transition of a single trapped ⁴⁰Ca⁺ ion to the standing wave field of a high-finesse cavity. The dependence of the coupling on temporal dynamics and spatial variations of the intracavity field is investigated in detail. By precisely controlling the position of the ion in the cavity standing wave field and by selectively exciting vibrational state-changing transitions the ion’s quantized vibration in the trap is deterministically coupled to the cavity mode. We confirm coherent interaction of ion and cavity field by exciting Rabi oscillations with short resonant laser pulses injected into the cavity, which is frequency-stabilized to the atomic transition. Received: 23 August 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. E-mail: christoph.becher@uibk.ac.at RID="**" ID="**"Present address: Time and Frequency Division, National Institute of Standards and Technology, Boulder, CO 80305, USA