CdZnTe crystals for the preparation of X-ray imaging detectors have been grown by the boron oxide encapsulated vertical Bridgman method. The homogeneity of the crystals has been studied by photoluminescence mapping, energy dispersion X-ray analysis, and resistivity mapping. The zinc distribution follows an anomalous behavior that deviates from the normal freezing equation. The wafers cut perpendicular to the growth direction show an homogeneous resistivity distribution, suggesting the possible exploitation of these crystals for the production of large volume imaging detectors.

Large-yield zinc oxide (ZnO) nanosized tetrapods have been obtained by a standard vapour-phase growth technique to which a few modifications have been added, such as the separation of the Zn source evaporation region from the Zn oxidation region inside the reactor setup. This modification allows to keep the growth conditions constant and continuous for a long time, thus favouring the obtainment of large amounts of ZnO tetrapod nanostructures. As some contaminations usually occur due to metallic Zn particles and/or different ZnO nanostructures, including not completely reacted ZnO1-x solid phases, they can be removed by a three-step "purification" procedure as described in the article. Further to that, a deposition method from suitable liquid suspensions is also reported, which allows to produce homogeneous distributions of ZnO tetrapods on large substrate areas. The proposed procedures are expected to be particularly appropriate for a large production of samples for device use.

Standard vapour phase growth process for ZnO tetrapods has been optimized in order to reach a very large yield, a good reproducibility and a single morphology (tetrapods are separated from the other possible ZnO nanostructures). The large yield of the growth and the simple deposition of these nanostructures on an alumina substrate with contacts and heater, allowed us to realize gas sensor prototypes with a relatively low-cost procedure. The obtained ZnO tetrapods-based gas sensors have been tested with different gases (CH3CH2OH, NO2, CO and H2S) and, especially, response values S = 25 and S = 100 have been measured towards 1 ppm and 5 ppm of hydrogen sulphide, respectively.

Cadmium Zinc Telluride (CZT) is one of the most exploited materials for x-ray and gamma ray radiation detection. Nevertheless CZT ingots are still affected by many defects, the most common features are Te inclusions, dislocations and grain boundaries. In this work the results of many investigation techniques are put together and compared in order to have a better understanding of the role of each defect in the degradation of the detector performances. A CZT ingot grown by low pressure Bridgman technique in IMEM Institute, Parma, was analyzed. The material was studied by means of the IR microscopy, for the identification of Te inclusions and then studied with the use of the synchrotron light source (NSLS National Synchrotron Light Source) for the analysis of the crystalline structure and uniformity of the x-ray response.

Rutherford Backscattering Spectrometry (RBS) using 6 MeV alpha particles and X-Ray Fluorescence (XRF) using a Pdanode X-Ray generator were performed to characterize Au and Pt contacts deposited by electroless technique and thermal evaporation on differently treated surfaces of CdZnTe and CdTe crystals. The aim of this study is to understand and improve the structure of the material-electrode interface. The thickness, the stoichiometry and the concentration profiles of platinum, gold, cadmium, zinc, tellurium and oxygen present at the surface layers were determined. The distribution of Cd deficiency at the interface layers was profiled using simulations and showed complex profiles in the samples, which can greatly affect the electrical quality of the detectors.

Tin oxide (SnO2) and zinc oxide (ZnO) nanostructures are widely studied because of their peculiar physical and chemical properties and the large number of possible application fields. Among these application, nanostructure-based chemoresistive gas sensing devices are very promising because they are considered faster and more stable than traditional thin or thick film sensors. Metallic oxide gas sensors are usually very sensitive towards a large number of gases and volatile organic compounds (VOCs), but unfortunately their response is characterized by very low selectivity (the capability to distinguish among different gases). Selectivity enhancements by adding palladium/palladium oxide (Pd/PdO) nanoparticles to traditional film-based gas sensors are widely reported in literature and they are generally obtained by co-deposition or co-synthesis techniques (in sputtering, sol-gel, etc). SnO2 nanowires and ZnO nanotetrapods have been grown on large areas by a combination of metal evaporation and controlled oxidation. Unfortunately Pd and PdO nanoparticles cannot be directly obtained in the same growth process used for the synthesis of SnO2 or ZnO nanostructures, because the large difference in evaporation rates of these different metals and oxides excludes the chance of preforming a co-evaporation process. So, a MOCVD (Metal Organic Chemical Vapour Deposition) process has been chosen in order to deposit Pd/PdO nanoparticles on the surface of oxide nanostructures. Palladium acetylacetonate, Pd(acac)2, has been evaporated and thermally decomposed, in presence of a co-reagent gas, on the substrates with SnO2 and ZnO nanostructures in different experimental conditions and, then, the obtained samples has been annealed in air and/or hydrogen in order to remove carbon residual and/or change the oxidation state of palladium nanoparticles. Samples morphology, structure and composition have been studied by means of SEM and TEM microscopy, EDS microanalysis and X-Ray diffraction. T

Two-inch-diameter CdZnTe crystals doped with indium were grown by the boron oxide encapsulated vertical Bridgman technique. The crystals showed large single crystalline yield and low etch pit density. The background impurity content was dominated by boron in concentration lower than 1 ppm. High resistivity was obtained and a procedure for contact preparation was developed. The mobility-lifetime product of the material was determined by both X-ray irradiation and photocurrent spectroscopy. The X-ray detector prepared with this material showed good spectroscopic performance.

Tailoring the structural and electronic properties of 3D nanostructures via bottom-up techniques would pave the way for novel low-cost applications. One of such possibilities is offered by ZnO branched nanostructures like tetrapods, that have recently attracted attention for nanodevice applications from nanoelectronics to drug delivery. The conventional picture is that ZnO arms are thermodynamically stable only in the wurtzite phase. Here, we provide the first experimental evidence of unpredicted extended zinc blend phases (50-60 nm long) embedded in the arms of ZnO wurtzite tetrapods. In particular, decisive evidence is obtained from the one-to-one correlation between high lateral resolution cathodoluminescence spectroscopy, monochromatic contrast maps, and atomic resolution transmission electron microscopy images of ZnO single TIPS. This observation is not specific to ZnO and can have a general validity for the understanding of the nucleation mechanisms in semiconducting 3D nanostructures for device applications.