Although generally ascribed to the presence of defects, an ultimate assignment of the different contributions to the emission spectrum in terms of surface states and deep levels in ZnO nanostructures ...is still lacking. In this work we unambiguously give first evidence that zinc vacancies at the (1010) nonpolar surfaces are responsible for the green luminescence of ZnO nanostructures. The result is obtained by performing an exhaustive comparison between spatially resolved cathodoluminescence spectroscopy and imaging and ab initio simulations. Our findings are crucial to control undesired recombinations in nanostructured devices.
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
°C 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 O
3, NO
2, CO and H
2S. 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.
The laser-induced current technique has been successful used to reconstruct the spatial profile of the electric field along the thickness of a set of CdZnTe spectroscopic X-ray detectors. Current ...transient profiles for electrons at different applied voltages have been analyzed by means of a minimization procedure demonstrating its applicability to samples with thickness ranging from 250 μm to 4 mm. Mobility and lifetime of electrons have also been deduced and compared with the mobility-lifetime products, as evaluated by fitting the charge collection efficiency curves under a suitable electric field profile model. Comparison between results from both techniques gives a good agreement and confirms the validity of the procedure. This method results applicable each time that carrier transit times can be evaluated from the laser-induced current transients. It could be suitable for many other devices provided that they are made of materials with sufficiently high resistivity, i.e., with a sufficiently low density of free carriers in dark conditions.
A long-standing goal of neuroscience is a theory that explains the formation of the minicolumns in the cerebral cortex. Minicolumns are the elementary computational units of the mature neocortex. ...Here, we use zinc oxide nanowires with controlled topography as substrates for neural-cell growth. We observe that neuronal cells form networks where the networks characteristics exhibit a high sensitivity to the topography of the nanowires. For certain values of nanowires density and fractal dimension, neuronal networks express small world attributes, with enhanced information flows. We observe that neurons in these networks congregate in superclusters of approximately 200 neurons. We demonstrate that this number is not coincidental: the maximum number of cells in a supercluster is limited by the competition between the binding energy between cells, adhesion to the substrate, and the kinetic energy of the system. Since cortical minicolumns have similar size, similar anatomical and topological characteristics of neuronal superclusters on nanowires surfaces, we conjecture that the formation of cortical minicolumns is likewise guided by the interplay between energy minimization, information optimization and topology. For the first time, we provide a clear account of the mechanisms of formation of the minicolumns in the brain.
The use of cadmium sulphide quantum dots (CdS QDs) is increasing, particularly in the electronics industry. Their size (1-10 nm in diameter) is, however, such that they can be taken up by living ...cells. Here, a bakers' yeast (Saccharomyces cerevisiae) deletion mutant collection has been exploited to provide a high-throughput means of revealing the genetic basis for tolerance/susceptibility to CdS QD exposure. The deletion of 112 genes, some associated with the abiotic stress response, some with various metabolic processes, some with mitochondrial organization, some with transport and some with DNA repair, reduced the level of tolerance to CdS QDs. A gene ontology analysis highlighted the role of oxidative stress in determining the cellular response. The transformation of sensitive mutants with centromeric plasmids harbouring DNA from a wild type strain restored the wild type growth phenotype when the complemented genes encoded either HSC82, DSK2 or ALD3. The use of these simple eukaryote knock-out mutants for functional toxicogenomic analysis will inform studies focusing on higher organisms.
KAMEO (Kaonic Atoms Measuring Nuclear Resonance Effects Ob-servables) is a proposal for an experiment aiming to perform the first consistent measurement of the E2 nuclear resonance effects in kaonic ...molybdenum A=94,96,98,100 isotopes. The E2 nuclear resonance mixes atomic states, due to the electrical quadrupole excitation of nuclear rotational states. It occurs in atoms having the energy of a nuclear excitation state closely matching an atomic de-excitation state energy, and affects the rates of X-ray atomic transitions matching the energy of the resonance. The measurement E2 nuclear resonance effect in KMO isotopes allows the study of the strong kaon-nucleus interaction in a rotational excited nuclear state. Moreover, the effect enables the K - to access an inner atomic level not easily reachable by the kaon normal cascade, due to the nuclear absorption. The KAMEO proposed apparatus consists of 4 enriched Mo A=94,96,98,100 isotope strips, exposed to the kaons produced by the DAφNE collider, for kaonic atoms formation, with a high-purity germanium detector, cooled with liquid nitrogen, used to measure the X-ray atomic transitions. The DAφNE collider is located at the National Laboratories of Frascati (LNF-INFN), in Italy. It is already suited for kaonic atoms measurement by the SIDDHARTA-2 collaboration.
We present the tests performed by the SIDDHARTA-2 collaboration at the
DA
Φ
NE
collider with a quasi-hemispherical CdZnTe detector. The very good room-temperature energy resolution and efficiency in ...a wide energy range show that this detector technology is ideal for studying radiative transitions in intermediate and heavy mass kaonic atoms. The CdZnTe detector was installed for the first time in an accelerator environment to perform tests on the background rejection capabilities, which were achieved by exploiting the SIDDHARTA-2 Luminosity Monitor. A spectrum with an
241
Am
source has been acquired, with beams circulating in the main rings, and peak resolutions of 6% at 60 keV and of 2.2% at 511 keV have been achieved. The background suppression factor, which turned out to be of the order of
≃
10
5
-
6
, opens the possibility to plan for future kaonic atom measurements with CdZnTe detectors.
Metal oxide nanocrystals for gas sensing Baratto, C.; Comini, E.; Faglia, G. ...
Sensors and actuators. B, Chemical,
08/2005, Volume:
109, Issue:
1
Journal Article
Peer reviewed
Quasi-one-dimensional nanostructures (so-called nanobelts or nanowires) of tin dioxide, obtained by vapour phase deposition, have been investigated for gas sensing. The physical quantity for signal ...transduction could be either electrical conductance or photoluminescence. Tin dioxide nanobelts/nanowires could be used as conductometric gas sensors for oxygen and environmental polluting species like CO and NO
2 as well as ethanol.
The visible photoluminescence is quenched by nitrogen dioxide at hundreds of ppb in a fast (time scale order of seconds) and reversible way. The response is highly selective towards humidity and other polluting species like CO and NH
3. The differences between conductometric and optical sensor are discussed.
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