1,721,255 research outputs found
Alice (and Bob) in Flatland
No full text2D quantum materials have opened infinite doors, hosting intriguing phenomena and featuring incredible engineering potential. Whether these qualities can boost the use of 2D crystals for quantum applications remains an open field with yet unexplored paths
Exploring information achieved from Automatic Information Systems to assess time of ships in port
No full textThe time of ships in ports affects not only the performance of the ships, but also the entire supply chain. It represents a competitive indicator for the challenges of international trade. This work highlights the possibility of using Automatic Information System (AIS) devices to evaluate the ship turnaround time. The paper moves from a review of the most used approaches and critical variables identified in the literature to assess terminal productivity and then evaluates the opportunity offered by AIS devices in analyzing the activities of ships in a container port. The procedure aims to highlight how simply operating over AIS raw data can assist analysts in capturing ship navigation status (anchoring and berthing operations) and analyzing the terminal traffic conditions. As a practical example, statistical information is resumed on the average berthing service time and occupation ratio for the Port of Melbourne; the traffic conditions and the berth occupancy ratio are investigated. The result was how the AIS data provide fundamental information on berth calls and their distribution over time, the average occupation time for handling operations, and the residual capacity to accept further incoming ships. Although such data can provide a snapshot of the port’s performance by providing information on spatial-temporal phenomena, AIS data cannot be considered fully explanatory of the activities within the terminal. Nevertheless, operating on these, it is possible to move a step forward to more traditional statistical analyses that do not directly consider spatial and temporal events within the terminal areas. The availability of historical records also allows analysts to test different scenarios through simulations. Similarly, having a rich database of real-time data can help analysts and port managers detect incoming events. For such reasons, further studies should focus on provisional models and the combined use of AIS data and other databases to provide information on terminal equipment and workloads
Role of Hydrogen in Dilute Nitrides
No full textVol. 21 della serie "Optoelectronic properties of semiconductors and superlattices" edita da M.O. Manasre
Hydrogen-induced defect engineering in dilute nitride semiconductors
No full textIn dilute nitrides, such as GaAsN, hydrogen-induced passivation of the electronic activity of N atoms offers an unprecedented opportunity to tune the electronic and structural properties of those materials. By deposition of hydrogen-opaque metallic masks on GaAsN and subsequent hydrogen irradiation, it is possible to alternate in the growth plane regions having the physical properties of GaAsN with those of N-passivated GaAsN. After reporting the main characteristics of deuterium diffusion in GaAsN as derived by secondary ion mass spectrometry, we present two examples of hydrogen-induced defect engineering. In the first case, we show that anisotropic strain fields can be created by selective H incorporation. The resulting in-plane symmetry breaking determines an in-plane polarization dependence of the light emitted along the crystal growth, otherwise unattainable in bulk GaAsN. Secondly, we report evidence of quantum confinement effects in dot-like structures obtained by in-plane patterning of the crystal band gap energy. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA
Carrier masses and band-gap temperature sensitivity in Ga(AsBi) alloys
No full textThe effects of external perturbations-such as temperature, photo-excited carrier density, and magnetic field-on the electronic properties of Ga(AsBi) alloys are investigated in a large range of Bi-concentration (x up to similar to 11%). These studies allow us to disclose the existence of Bi-induced localized states that largely contribute to the recombination spectra up to relatively-high temperature (T similar to 150 K). The sensitivity of the band-gap energy to temperature variation is found to diminish strongly with Bi-concentration and to result in a reduction of about a factor of two at the highest concentrations. Magneto-photoluminescence studies have also revealed the role exerted by the Bi-induced levels on the host band states and have disclosed an unexpectedly strong carrier-carrier scattering, which hampers the observation of Landau-level quantization at low magnetic fields. An unusual compositional dependence of the exciton reduced mass, as well as an unexpected increase of the electron effective mass at relatively-low Bi-concentration (x < 6%), are reported and related to the presence of Bi-induced states
Hydrogen, the modern philosopher’s stone
No full textEditori G. Guizzetti, L.C. Andreani, F. Marabelli, M. Patrin
Electronic properties of wurtzite-phase InP nanowires determined by optical and magneto-optical spectroscopy
No full textThanks to their peculiar shape and dimensions, semiconductor nanowires (NWs) are emerging asbuilding components of novel devices. The presence of wurtzite (WZ) phase in the lattice structure ofnon-nitride III-V NWs is one of the most surprising findings in these nanostructures: this phase,indeed, cannot be found in the same materials in the bulk form, where the zincblende (ZB) structure isubiquitous, and therefore the WZ properties are poorly known. This review focuses on WZ InP NWs,because growth techniques have reached a high degree of control on the structural properties of thismaterial, and optical studies performed on high-quality samples have allowed determining the mostuseful electronic properties, which are reviewed here. After an introduction summarizing the reasonsfor the interest in WZ InP nanowires (Sec.I), we give an overview on growth process and structuraland optical properties of WZ InP NWs (Sec.II). In Sec.III, a complete picture of the energy and sym-metry of the lowest-energy conduction and valence bands, as assessed by polarization-resolved photo-luminescence (PL) and photoluminescence-excitation (PLE) studies is drawn and compared to all theavailable theoretical information. The elastic properties of WZ InP (determined by PL under hydro-static pressure) and the radiative recombination dynamics of spatially direct and indirect (namely,occurring across the WZ/ZB interfaces) transitions are also discussed. SectionIV, focuses on themagneto-optical studies of WZ InP NWs. The diagram of the energy levels of excitons in WZ materi-als—with and without magnetic field—is first provided. Then, all theoretical and experimental infor-mation available about the changes in the transport properties (i.e., carrier effective mass) caused bythe ZB!WZ phase variation are reviewed. Different NW/magnetic field geometrical configurations,sensitive to polarization selection rules, highlight anisotropies in the diamagnetic shifts, Zeeman split-ting, and field-induced circular dichroism of the emitted light. These characteristics are indeed inherentto the NW crystal symmetry. Such an exhaustive summary of the electronic properties of WZ InPNWs (energy, symmetry, thermal-, and pressure-induced shift of near band gap electronic bands,impurities binding energy, WZ and ZB band-offset values, exciton lifetime, exciton, electron, and holeeffective masses) is valuable in the prediction of fundamental device parameters or as a reference fordetailed band-structure calculations, as summarized in the last section (Sec.V), where also the openissues are critically discussed.Published by AIP Publishing
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