In this work, our new experimental setup has been used to study the ionization and fragmentation of a prebiotic molecule, hydantoin, by electron impact. Scanning of the incident electron energy allows the determination of the appearance thresholds of the cations. The vertical ionization potential was found to be in good agreement with previous data. Dissociation thresholds for the main fragmentation patterns were also measured. In parallel, thanks to quantum chemical calculations, reaction schemes compatible with the experimental results are given.

Electronic emission of an isolated pyrene molecule induced by 50 to 125 keV protons has been investigated. The corresponding absolute double differential cross-sections partial derivative(2)sigma/partial derivative Omega delta E have been measured at an angle of 35 degrees with respect to the incident proton beam axis. These measurements were compared to the simulations of emitted electrons' spectra using a semi-classical trajectory Monte-Carlo (SCTMC) approach. The simulated SCTMC cross-sections show reasonably good agreement with the measured ones.

The Perseverance volcanogenic massive sulfide deposit (5.1 Mt at @ 15.8% Zn, 1.24% Cu, 29.4 g/t Ag, 0.4 g/t Au), Matagami district, Abitibi greenstone belt, consists of four pipelike orebodies discordant to local bedding in a shallow-dipping portion of the South Flank volcanic succession. Most of the ore is hosted by rhyolitic lavas of the Watson unit (2725.9 +/- 0.8 Ma) and is overlain by a thinly laminated tuffaceous unit known as the Key Tuffite, as well as by rhyodacitic lavas of the Dumagami unit (2725.4 +/- 0.7 Ma).The presence of sulfide zones predominantly hosted in the footwall rhyolite, relicts of Key Tuffite within the ore, and intricate sulfide replacement of the laminated tuff are all features consistent with the formation of most of the deposit via subseafloor replacement. The permeability of steep synvolcanic structures likely controlled the migration of metal-bearing fluids and simultaneously allowed the downward infiltration of seawater, causing mixing, cooling, and sulfide deposition in the subseafloor environment. Stratigraphic relationships suggest that massive sulfide formation was active at Perseverance while tuffaceous sedimentation was ongoing on the seafloor. Progressive growth of the massive sulfides along subvertical structures was accompanied by the development of pipelike sericite-chlorite (+/- talc) alteration halos. Both the hanging wall and the footwall units are characterized by significant MgO mass gains, K2O-Na2O mass losses, and high alteration index values (e.g., chlorite-carbonate-pyrite index, alteration index). However, these geochemical changes are less intense and widespread in the hanging wall than in the footwall. The record of a decreasing alteration above the orebodies was likely caused by the emplacement of the rhyodacite while massive sulfide deposition and hydrothermal activity were still ongoing.Primary relationships between mineralization and the host lithofacies were overprinted by intense deformation during the main event of compression induced by regional north-south shortening. Deformation is controlled by contrasting rheologies within the sulfide assemblage and between the orebodies and their host rocks. Structural modifications include the transposition of sulfide ores subparallel to the main foliation, the formation of piercement veins at the interface with the host rocks, and the generation of a series of secondary textures within the orebodies, including a vertical mineralogical banding. The distribution of Cu in the deposit is interpreted to be affected by the mechanical remobilization of chalcopyrite during deformation, whereas the zonation of Zn is likely primary. Hydrothermal alteration halos adjacent to the orebodies have accommodated significant strain, as indicated by the presence of tight folds in the Key Tuffite unit and a marked schistosity. Strain localization in the vicinity of the deposit highlights the relative ductility of the ore assemblage with respect to the host volcanic succession and resulted in a spatial association between hydrothermal alteration and deformation, despite the lack of a genetic relationship.

This study proposes an artificial neural networks-based method for predicting the unaltered (precursor) chemical compositions of hydrothermally altered volcanic rock. The method aims at predicting precursor’s major components contents (SiO2, FeOT, MgO, CaO, Na2O, and K2O). The prediction is based on ratios of elements generally immobile during alteration processes; i.e. Zr, TiO2, Al2O3, Y, Nb, Th, and Cr, which are provided as inputs to the neural networks. Multi-layer perceptron neural networks were trained on a large dataset of least-altered volcanic rock samples that document a wide range of volcanic rock types, tectonic settings and ages. The precursors thus predicted are then used to perform mass balance calculations. Various statistics were calculated to validate the predictions of precursors’ major components, which indicate that, overall, the predictions are precise and accurate. For example, rank-based correlation coefficients were calculated to compare predicted and analysed values from a least-altered test dataset that had not been used to train the networks. Coefficients over 0.87 were obtained for all components, except for Na2O (0.77), indicating that predictions for alkali might be less performant. Also, predictions are performant for most volcanic rock compositions, except for ultra-K rocks. The proposed method provides an easy and rapid solution to the often difficult task of determining appropriate volcanic precursor compositions to rocks modified by hydrothermal alteration. It is intended for large volcanic rock databases and is most useful, for example, to mineral exploration performed in complex or poorly known volcanic settings. The method is implemented as a simple C++ console program.

We present an experiment studying the interaction of a strongly focused 25 fs laser pulse with a tungsten nanotip, investigating the different regimes of laser-induced electron emission. We study the dependence of the electron yield with respect to the static electric field applied to the tip. Photoelectron spectra are recorded using a retarding field spectrometer and peaks separated by the photon energy are observed with a 45% contrast. They are a clear signature of above threshold photoemission (ATP), and are confirmed by extensive spectrally resolved studies of the laser power dependence. Understanding these mechanisms opens the route to control experiment in the strong-field regime on nanoscale objects.

An electrically pumped InAs/GaAs quantum dot laser on a Si substrate has been demonstrated. The double-hetero laser structure was grown on a GaAs substrate and layer-transferred onto a Si substrate by GaAs/Si direct wafer bonding without oxide or metal mediation. This broad-area Fabry-Perot laser operates with current injection through the GaAs/Si interface and exhibits InAs quantum dot ground state lasing at 1.31 μm at room temperature with a threshold current density of 205 A/cm2, the lowest among lasers on silicon.

We report the growth of self-assembled InAs/GaAs quantum dots (QDs) on Si, Ge/Si and germanium-on-insulator-on-silicon (GeOI) substrates by metal organic chemical vapor deposition. GaAs layers with lower surface roughness (root mean square roughness of 1 nm) and higher structural quality were obtained on Ge/Si and GeOI compared to those obtained on Si substrate. We showed that the introduction of a QD layer within the GaAs buffer layer was efficient in suppressing the propagation of anti-phase domains to the GaAs surface for both cases of Ge/Si and GeOI substrates. Coalescence-free QDs with densities above 1010 cm−2 and ground state emission in the 1.3 μm band at room temperature were obtained on all substrates. QDs grown on GeOI yield the highest photoluminescence (PL) intensity, and quite remarkably, have similar PL intensity as those grown on GaAs substrate. These results suggest the better suitability of GeOI substrate compared to Si or Ge/Si substrates for the monolithic integration of QD-based lasers on silicon (or any other III–V photonic device) for silicon photonics.

We present a promising method for the fabrication of high-quality InAs site-controlled quantum dots (QDs) by combining electron beam lithography with wet chemical etching and metalorganic chemical vapor deposition (MOCVD) in situ patterning. The (100) GaAs substrate is patterned with nanoholes by thermal etching and the dots are directly grown inside. This method should avoid the introduction of the surface defects that occurs usually with standard lithography techniques. The thermal etching time is a new growth parameter used to control the shape and size of the QDs. The optical characterization at low temperatures reveals QDs with a small linewidth down to 63 µeV.

We report on the antimony (Sb) surfactant-mediated growth of InAs quantum dots (QDs) on a germanium-on-insulator-on-silicon (GeOI) substrate. A GaAs buffer layer of high structural quality and low surface roughness was first grown on a GeOI substrate. The dependence of Sb irradiation time on the photoluminescence intensity and total density of InAs/Sb:GaAs QDs grown on a GeOI was studied. High density (above 6×1010 cm-2) QDs with ground state emission in the 1.3 µm band at room temperature and narrow linewidth (32 meV) was obtained. Together, these results are very promising for potential realization of monolithically integrated QD-based lasers on silicon.

The seismic. architecture of time average Archean-only mantle beneath exposed and subsurface Archean crust of the United States and Canada is presented here in three dimensions for the first time, using a high lateral resolution Rayleigh wave phase velocity model of the upper mantle (30- to 250-km depth). The morphology of the cratonic coherent mantle is compared with other regional and local geophysical models, geologic interpretations, and published xenolith barometric studies. In particular, the kimberlite magma source regions at the Lithosphere-Asthenosphere Boundary (LAB) inferred from xenolith data are consistent with the bottom topography of the Archean seismic mantle signature. The characteristic fast seismic response found beneath much of the exposed Archean crust is also found in Canada beneath some covered terranes, sedimentary basins, and Proterozoic mobile belts.The northeastern and northwestern parts of the Superior craton host, with the central Hearne craton, the deepest mantle roots of North America (225- to 240-km depth). However, the southern portion of the Superior craton is characterized by an cast-west channel that is 30 percent slower in seismic velocity than its northern counterpart. This contrasting seismic signature correlates with the location of the southernmost Neoarchean greenstone belts and to their plume-driven subduction zones. The scar in the mantle produced by this early tectonothermal event has been reused by widespread and sporadic carbonatite and kimberlite magmatic events spanning from the Early Proterozoic to the Cretaceous, and as a consequence, the diamond stability field has been partially to totally overprinted.Almost all diamondiferous kimberlites in Canada are located vertically over an interval of 160- to 200-km depth in areas of steep slopes surrounding deep (180-240 km), relatively small, and flat-bottomed Paleo-Mesoarchean cratonic keels.

The strong coupling regime in a ZnO microcavity is investigated through room temperature photoluminescence and reflectivity experiments. The simultaneous strong coupling of excitons to the cavity mode and the first Bragg mode is demonstrated at room temperature. The polariton relaxation is followed as a function of the excitation density. A relaxation bottleneck is evidenced in the Bragg-mode polariton branch. It is partly broken under strong excitation density, so that the emission from this branch dominates the one from cavity-mode polaritons.

We present experimental observation of the strong light-matter coupling regime in ZnO bulk microcavities grown on silicon. Angle-resolved reflectivity measurements, corroborated by transfer-matrix simulations, show that Rabi splittings in the order of 70 meV are achieved even for low finesse cavities. The impact of the large excitonic absorption, which enables a ZnO bulklike behavior to be observed even in the strong-coupling regime, is illustrated both experimentally and theoretically by considering cavities with increasing thickness.

Wide band-gap semiconductors are attractive candidates for polariton-based devices operating at room temperature. We present numerical simulations of reflectivity, transmission, and absorption spectra of bulk GaAs, GaN, and ZnO microcavities in order to compare the particularities of the strong coupling regime in each system. Indeed the intrinsic properties of the excitons in these materials result in a different hierarchy of energies among the valence-band splitting, the effective Rydberg, and the Rabi energy, defining the characteristics of the exciton-polariton states independent of the quality factor of the cavity. Knowledge of the composition of the polariton eigenstates is central to optimize such systems. We demonstrate that in ZnO bulk microcavities, only the lower polaritons are good eigenstates and all other resonances are damped, whereas upper polaritons can be properly defined in GaAs and GaN microcavities.

We report an experimental study of the excitonic properties of bulk ZnO and the strong coupling observation in hybrid ZnO-based microcavities. The strong coupling is highlighted with a Rabi splitting value of about 70meV. The influence of the excitonic and band-to-band absorptions on the observation of this strong light-matter coupling regime is analysed through the evolution of the reflectivity spectra obtained on microcavities with different active layer thicknesses.

We have investigated a series of samples embedding ZnO/(Zn,Mg)O quantum wells of different sizes, in wurtzite phase, by using timeresolved photoluminescence. The samples were grown by molecular beam epitaxy on ZnO templates, themselves deposited on sapphire substrates. The presence of large internal electric fields in these quantum wells manifests itself not only through the energies of the optical recombinations, but also through the size dependence of the recombination times. An envelope-function model that includes the variational calculation of the exciton binding energy allows us to determine a value of 0.9 MV/cm for the internal electric field.

Recently, axionlike particle search has received renewed interest, and several groups have started experiments. In this paper, we present the final results of our experiment on photon-axion oscillations in the presence of a magnetic field, which took place at the Laboratoire pour l'Utilisation des Lasers Intenses, Palaiseau, France. Our null measurement allowed us to exclude the existence of axions with inverse coupling constant M>9.x10{sup 5} GeV for low axion masses and to improve the preceding Brookhaven-Fermilab-Rochester-Trieste (BFRT) Collaboration limits by a factor of 3 or more for axion masses 1.1<m{sub a}<2.6 meV. We also show that our experimental results improve the existing limits on the parameters of a low mass hidden-sector boson usually dubbed 'paraphoton' because of its similarity with the usual photon. We detail our apparatus which is based on the 'light shining through the wall' technique. We compare our results to other existing ones.