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.

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

The phenomenon of "Dewetting" associated with the Vertical Bridgman (VB) crystal growth technique leads to the growth of a crystal without contact with the crucible. One dramatic consequence of this modified VB process is the reduction of structural defects within the crystal. It has been observed in several microgravity experiments for different semiconductor crystals. This work is concentrated on the growth of high resistivity (Cd,Zn)Te:ln (CZT) crystals by achieving the phenomenon of dewetting under microgravity condition and its application in the processing of CZT detectors. Two CdO.9ZnO.lTe:ln crystals were grown in space on the Russian FOTON satellite in the POLIZON-M facility in September 2007 (mission M3). At the end of the preliminary melting phase of one crystal, a Rotating Magnetic Field (RMF) was applied in order to reduce the typical tellurium clusters within the melt before the pulling. The other crystal was superheated with 20 K above the melting point before the pulling. A third reference crystal has been grown on the ground in similar thermal conditions. Profiles measurements of the space grown crystals surface gave the evidence of a successful dewetting during the crystal growth. Characterization methods such as IR microscopy and CoReMa have been performed on the three crystals. CZT detectors have been processed from the grown part of the different crystals. The influence of the dewetting on the material quality and the detector properties completes the study.

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.

The phenomenon of "dewetting" associated with the Vertical Bridgman (VB) crystal growth technique leads to the growth of a crystal without contact with the crucible. One dramatic consequence of this modified VB process is the reduction of structural defects within the crystal. It has been observed in several microgravity experiments for different semiconductor crystals. This work is concentrated on the growth of high resistivity (Cd, Zn) Te: In (CZT) crystals by achieving the phenomenon of dewetting under microgravity condition and its application in the processing of CZT detectors. Two Cd0.9Zn0.1Te In crystals were grown in space on the Russian FOTON satellite in the POLIZON-M facility in September 2007 (mission M3). At the end of the preliminary melting phase of one crystal, a Rotating Magnetic Field (RMF) was applied in order to reduce the typical tellurium clusters within the melt before the pulling. The other crystal was superheated with 20 K above the melting point before the pulling. A third reference crystal has been grown on the ground in similar thermal conditions. Profiles measurements of the space grown crystals surface gave the evidence of a successful dewetting during the crystal growth. Characterization methods such as IR microscopy and CoReMa have been performed on the three crystals. CZT detectors have been processed from the grown part of the different crystals. The influence of the dewetting on the material quality and the detector properties completes the study.

Nanostructured ZnO was obtained through two different synthetic processes: a traditional sol-gel (SG) route and a combination of vapor transport process and controlled oxidation methods. In SG synthesis, thermal decomposition of the precursor at 450 æC for 2 h in an oven led to pure zincite nanoparticles. Through the second method, instead, nanocrystalline structures in form of tetrapods (TP) were directly obtained during the synthesis process. Powder and film characterizations have been carried out by means of TG-DTA, SEM, TEM and XRD. Finally, electric measurements have been performed with the aim to compare conductive properties, surface barrier heights and gas sensing features, versus O3, NO2, CO and H2S. Despite the significant difference in morphology, it turned out that both types of sensors offered large responses to oxidizing gases at concentration suitable for environmental monitoring.

Large-scale growth capability is a general requirement for any reliable and cost-effective device application. Catalyst-free vapor-phase growth techniques generally let obtain high purity materials, but their application in large-scale growths of zinc oxide (ZnO) nanostructures is not trivial, because the lack of catalysts makes the control of these process rather difficult. Three different optimizations of the basic vapor phase growth have been studied and performed to obtain selected and reproducible growths of three different ZnO nanostructures with improved yield, i.e. nanotetrapods, nanowires and nanorods. No precursor or catalyst has been used in order to reduce contamination sources as more as possible.