Built-in elastic strain and localization effects on GaAs luminescence of MOVPE-grown GaAs-AlGaAs core-shell nanowires

The core photoluminescence emission of MOVPE-grown GaAs-Al0.33Ga0.67As core-shell nanowires is studied as function of the relevant geometrical parameter of these nanostructures, namely the shell-thickness to core-radius ratio hs/Rc. The energy of the dominant emission peak was compared with values of the GaAs heavy- and light-hole excitons redshifted by a uniaxial tensile strain, the latter calculated assuming perfect coherence at the core/shell interface and elastic energy equilibrium within the nanowires. Good agreement is obtained for hs/Rc 1 increasingly larger redshifts (up to ∼9 meV in excess of values calculated based on our elastic strain model) are observed, and tentatively ascribed to shell-dependent exciton localization effects. Experimental and calculated bound exciton peak energies for GaAs-Al0.33Ga0.67As core-shell nanowires as function of their shell-thickness to core-radius ratio hs/Rc

Development of CdTe/CZT Epitaxial Technology for Fabrication of Large Area RT 1-100 keV X-ray Photon Detectors

This paper reports on the principles and application of H2-transport vapor phase epitaxy (H2T-VPE), an innovative growth technology for the fabrication of thick (i.e., up to several hundreds micron) CdTe and CdZnTe single crystal epitaxial layers for fabrication of X-ray detector arrays. Details and advantages of the method are illustrated along with properties of materials grown using a simple proof-of-concept H2T-VPE reactor. These growth experiments, besides showing the potentials of the method, allowed also to identify critical parameters of the H2T-VPE process and its control requirements. Such knowledge has been used to design, build and test an innovative H2T-VPE reactor prototype, whose characteristics and operations are here described

La grotto di Abate Eustasio (Pu 1789) nel contest dell’area carsica di Largo Porta Grande a Castellana-Grotte (Murge, Puglia).

La recente scoperta di una nuova cavità nella zona di Largo Porta Grande a Castellana-Grotte (Murge Basse, Puglia) consente di rivisitare i caratteri carsici di quella che è la zona topografi camente più depressa del territorio castellanese, anche alla luce della storia dei rapporti tra uomo ed eventi naturali in ambiente carsico. Largo Porta Grande ha una lunga storia di eventi alluvionali, che resero necessaria, a seguito di diverse catastrofi naturali, anche con vittime, la realizzazione di opere di ingegneria idraulica, fi nalizzate alla mitigazione del rischio idraulico. Nel 2011 la scoperta della grotta di Abate Eustasio ha ulteriormente dimostrato la ricchezza carsica del sottosuolo in questa zona, per di più evidenziata dai recenti dati di esplorazione della Voragine del Canalone. L’insieme di tale materiale documentario evidenzia, da un lato, la possibilità di ulteriori esplorazioni e, dall’altro, la necessità di tenere in debito conto la fragilità del territorio carsico in qualunque azione di pianifi cazione territoriale che si progetti e/o intenda realizzare nell’area. Questi aspetti risultano però alquanto in contrasto con l’ipotesi, a nostro avviso non realizzabile, né tantomeno utile alla comunità, della proposta di turisticizzazione della grotta di Abate Eustasio

A novel CdTe/CZT epitaxial technology for large area RT 1 -100 keV X-ray photon detectors

We report on an innovative vapor phase epitaxial (VPE) technology for the growth of thick (i.e., up to several hundreds micron) CdTe and CdZnTe single crystal layers. The aim of this technology is to achieve the fabrication of large area X-ray detector arrays for operation in the 1-100 keV photon energy range. The new VPE method is a modification of the H2-transport VPE (H2T-VPE) technique previously developed in the authors laboratory for CdTe. These early growth experiments, besides showing the potentials of the method, allowed to identify critical parameters of the H2T-VPE process, and its limitations. The new VPE method proposed here is based on the combination of metalorganic-VPE and H2 reduction of solid CdTe to obtain the chemical transport of CdTe/CZT constituent elements into a hot-wall VPE reactor. Controlled and reproducible addition of dopant elements to the vapor can be similarly achieved for the insitu (i.e. during growth) intentional doping/ compensation of the epitaxial layers. Such technology is currently under testing using an ad-hoc designed and built reactor prototype, whose main characteristics are also described

Grazing incident X-ray topographs of heteroepitaxial ZnSe films on GaAs substrates

Surface reflection topographs of heteroepitaxial ZnSe films on GaAs substrates were obtained using grazing incident synchrotron X-ray radiation. The topographs indicated that diffraction occurred only in the ZnSe epilayer because no misfit dislocations within the interface were visible. Furthermore, the lattice perfection of the ZnSe epilayer was lower than that of the GaAs substrate, although strain relaxation arose due to the nucleation of misfit dislocations

Following flood dynamics by SAR/optical data fusion

Synthetic aperture radar (SAR) acquisitions are particularly useful to produce flood maps thanks to their all-weather and day-night capabilities. However, repetition intervals of radar instruments are in the order of several days for routine operations, reaching daily or higher frequencies only in tasked conditions. Therefore, to follow flood dynamics, images acquired by different sensors at different times may be beneficial. In the present work, multi-temporal SAR intensity, InSAR coherence and optical data are considered to describe a flood event occurred in the Basilicata region (southern Italy) on December 2013. In this case study, optical data have a twofold role: they allow to follow the flood dynamics (because SAR and optical data have been acquired in different dates during the inundation event), and they add information concerning the land cover of the analyzed area. The data fusion approach is based on Bayesian Networks (BNs). It is shown that the synergetic use of different information layers can help detect more precisely the areas affected by the flood, reducing false alarms and missed identifications which may affect algorithms based on data from a single source. The produced flood maps are compared to reference maps, independently obtained; the comparison indicates that the proposed methodology is able to reliably follow the temporal evolution of the phenomenon, assigning high probability to areas most likely to be flooded, reaching accuracies of up to 89%