115 research outputs found
L'artista satirico nell'epos: Giandomenico Tiepolo e il cavallo di Troia
No full textThe Artist Satirist and the Classical Epos: Giandomenico Tiepolo and the Trojan Horse
This study reconsiders a remarkable but overlooked work by Giandomenico Tiepolo–the so-called Building of the Trojan Horse in the collections of the Wadsworth Atheneum Museum of Art at Hartford. Starting from a fresh look to the content, the author identifies a slightly different iconography, as well as the presence of an enigmatic self-portrait of the painter seen from the back. The possible precedents in the tradition of the artists' self-portraits in Venice are investigated, and an interpretation is offered in connection with the peculiar satirical themes of Gian Domenico's art
Direct evidence of the dependence of surface state density on the size of SnO2 nanoparticles observed by scanning tunneling spectroscopy
No full textIn this work, we report a scanning tunnelling spectroscopy (STS) study of 30 and 10 nm tin dioxide nanoparticles.
The STS spectra give a surface band gap of 2.5 eV for both samples and show that the density of surface states in the
band gap is around 6 times higher for the 30 nm particles than for the 10 nm particles. This provides direct experimental
evidence for our theoretical model, which predicts a decrease in the surface state density as the particle size decreases,
and partly accounts for the improved sensitivity of gas sensing devices fabricated with nanoparticles
Highly Sensitive Hydrogen Gas Sensors Based on Gold Nanoparticle Decorated Zinc Oxide Nanosheets
No full textHighly sensitive gold nanoparticle decorated zinc oxide nanosheet gas sensors have been fabricated using simple and rapid chemical methods capable of producing a normalised current gain of 2.54 (at 10V) in dry air containing 2.5ppm of hydrogen gas at 200C and a current gain of 382.53 under 125ppm. Compared to undecorated sheet based sensors where a response of 1.24 was observed under 125ppm at 200C a massive relative increase in signal is observed. The zinc oxide nanosheets are produced via a previously reported simple microwave assisted hydrothermal growth method and gold nanoparticles with mean diameter of 5nm synthesized via a simple sodium borohydride reduction of hydrogen tetrachloroaurate in the presence of polyvinylpyrrolidone (PVP) followed by drop casting onto a pre-patterned aluminium oxide substrate
XANES-Based Determination of Redox Potentials Imposed by Steel Corrosion Products in Cement-Based Media
No full textThe redox potential (Eh) in a cementitious nuclear waste repository is critical to the retardation behavior of redox-sensitive radionuclides (RNs), and largely controlled by embedded steel corrosion but hard to be determined experimentally. Here, we propose an innovative Eh determination method based on chemical/spectroscopic measurements. Oxidized nuclides (UVI, SeIV, MoVI, and SbV) were employed as species probes to detect the Eh values imposed by steel (Fe0) and steel corrosion products (magnetite/hematite, and magnetite/goethite couples) in cement pore water. Nuclides showed good sorption affinity, especially toward Fe0, in decreasing Kd order for U > Sb > Se > Mo under both N2 and H2 atmospheres. The reduced nuclide species were identified as UO2, U4O9, FeSe, FeSe2, Se0, Sb0, and Sb2O3, but no redox transformation occurred for Mo. Eh values were obtained by using the Nernst equation. Remarkably, their values fell in a small range centered around −456 mV at pH ∼ 13.5 for both Fe0 and Fe-oxyhydroxides couples. This Eh value appears to be controlled by the nanocrystalline Fe(OH)2/Fe(OH)3 or (Fe1–x,Cax)(OH)2/Fe(OH)3 couple, whose presence was confirmed by pair distribution function analyses. This approach could pave the way for describing the Eh gradient in reinforced concrete where traditional Eh measurements are not feasible
Analysis of the kinetics of surface reactions on a zinc oxide nanosheet-based carbon monoxide sensor using an Eley–Rideal model
No full textHerein, we experimentally test a mathematical model of the reactions on the surface of a zinc oxide nanosheet-based carbon monoxide sensor. The carbon monoxide is assumed to react with surface oxygen via an Eley–Rideal mechanism, considering only the direct reaction between the two species. We demonstrate that the measured resistance responses of the system are well described by the model, facilitating further analysis of the physical rate constants in the system. By initially considering the system in the absence of any reducing gas, it is shown that various reaction parameters may be precisely estimated. For instance, fitting the model to response curves obtained at different temperatures shows the activation energy of the reaction between oxygen ions and carbon monoxide to be 54 ± 9 kJ mol−1, whereas the recovery curves yield an estimate of 42 ± 7 kJ mol−1. Similarly, the energy barrier for the formation of oxygen ions is found to equal 72 ± 9 kJ mol−1 from the sensor response and 63 ± 10 kJ mol−1 from the recovery. These estimates are in agreement with values quoted elsewhere in the literature, corroborating the validity of the model. In the absence of surface ions, the energy difference between the Fermi level and the conduction band minimum at the surface is estimated as 590 ± 90 meV
Evidence of band bending flattening of 10 nm polycrystalline SnO2
No full textWe developed a model for n-type metal-oxide semiconductors, which allows one to calculate the density of charged surface states on
nanostructured grains, once the Schottky barrier height is known.We characterised structurally and electrically two sets of polycrystalline
SnO2 films with average grain radius of 30 and 10 nm. The purpose of this experiment was to observe the flattening of the bandbending
and the corresponding decrease in the density of charged surface states which are, in turn, responsible for the pinning of the Fermi level.
Finally, we highlighted how this phenomenon affects the characteristics of the films as gas sensors
The effect of metal layers on the morphology and optical properties of hydrothermally grown zinc oxide nanowires
No full textNano-crystalline SnO2 gas sensor response to O2 and CH4 at elevated temperature investigated by XPS
No full textSynthesis of nanocrystalline ZnO nanobelts via pyrolytic decomposition of zinc acetate nanobelts and their gas sensing behavior
No full textThe effects of surface stripping ZnO nanorods with argon bombardment
No full textZnO nanorods are used in devices including field effects transistors, piezoelectric transducers, optoelectronics and gas sensors. However, for efficient and reproducible device operation and contact behaviour, surface contaminants must be removed or controlled. Here we use low doses of argon bombardment to remove surface contamination and make reproducible lower resistance contacts. Higher doses strip the surface of the nanorods allowing intrinsic surface measurements through a cross section of the material. Photoluminescence finds that the defect distribution is higher at the near-surface, falling away in to the bulk. Contacts to the n-type defect-rich surface are near-Ohmic, whereas stripping away the surface layers allows more rectifying Schottky contacts to be formed. The ability to select the contact type to ZnO nanorods offers a new way to customize device behaviour
- …
