1,489 research outputs found
Synthesis by co-sputtering of Au-Cu alloy nanoclusters in silica
No full textIn this work we investigated the Au–Cu binary nanophase diagram by means of structural and compositional characterization of alloy nanoclusters synthesized in silica by means of rf-cosputtering technique. In order to obtain the formation of metallic nanoclusters, as deposited samples have been annealed in reducing atmosphere at 900 °C. A good agreement with the bulk alloy phase diagram has been found: in particular the fcc cubic alloy solid solution is present in all the investigated compositions from pure Au to pure Cu, with a lattice parameter following the modified Vegard’s law typical of the bulk alloy. Three ordered phases are also present corresponding to the Au:Cu atomic ratios of 3:1, 1:1 and 1:3. The linear and non-linear optical properties of the nanocomposites have been measured: the surface plasma resonance red-shifts with increasing the Cu content in the alloy and it spans the entire region from that of pure Au (530 nm) to that of pure Cu (570 nm)
RF magnetron co-sputtering deposition of Cu-based nanocomposite silica films for optical applications
No full textThe size, the size distribution, the structure and the concentration of the metallic particles embedded in a host dielectric matrix determine the linear and non-linear optical properties of this kind of composite glasses. In this work, copper-containing silica films about 0.5 um thick were prepared by radio frequency magnetron co-sputtering deposition technique, and then heat-treated in oxidizing and/or reducing atmospheres. The characterization of the samples was performed by optical absorption spectroscopy, Rutherford backscattering spectrometry and transmission electron microscopy. The investigated preparation protocols actually allow to control the final composite structure. Preliminary results indicate that some nanocomposite films have non-linear optical properties in the ps regime
Metal nanoparticles-silica composites: Z-scan determination of non-linear refractive index
No full textMetal quantum-dot composite glasses can exhibit an enhanced optical Kerr susceptibility, χ(3), whose real part is related to the n2I coefficient of the intensity-dependent refractive index. We used the Z-scan technique for measuring the n2I's of micrometric composites films formed by copper with nanometer sized particles embedded in silica glass by means of radiofrequency magnetron sputtering technique, followed by thermal annealing in reducing atmosphere, to promote cluster growth. A single 6 ps long pulse at a repetition rate of 1 Hz was used to determine the picosecond fast (noncumulative, electronic) response of the composites. We obtain n2I from (0.48 ± 0.24) × 10-11 to (2.0 ± 1.0) × 10-11 cm2/W and β of (3.1 ± 1.6) × 10-7 to (8.5 ± 4.2) × 10-7 cm/W in the explored range of Cu/SiO2 composition
Structural and optical properties of Cu:silica nanocomposite films prepared by co-sputtering deposition
No full textCopper-containing silica films were synthesized by radiofrequency (rf) co-sputtering deposition technique, and then heat-treated in different annealing atmospheres, i.e. either oxidizing or reducing, with the aim to develop suitable preparation methodologies for controlling the composite structure. Characterization of the samples along the various preparation steps was performed by Rutherford backscattering spectrometry (RBS), transmission electron microscopy and optical absorption spectroscopy. The nonlinear optical coefficient n2 of the nanocomposite films was estimated by the Z-scan technique. Experimental observations showed that copper migration and aggregation depend critically on the annealing conditions, giving rise to quite different stable structures. In particular, for samples heat-treated first in air and then in a H2–Ar gas mixture, the oxidizing atmosphere drives copper towards the surface while the reducing one promotes the subsequent clusterization in a well defined region
Fast third-order optical nonlinearities in metal alloy nanocluster composite glass: negative sign of the nonlinear refractive index
No full textThe fast component of the nonlinear refractive index, n2, of a composite film formed by alloy nanoparticles embedded in
silica was measured by Z-scan technique, in conditions free from cumulative heating effects. By using a single 6 ps long laser
pulse at 1 Hz, 527 nm of wavelength, a negative sign of n2 was evidenced. An explanation of this result is suggested, based on the dielectric confinement effect. The fast refractive index value, in modulus, is of the order of 10exp-10 cm2/W
A reciprocity formula from abelian BF and Turaev–Viro theories
No full textAbstractIn this article we show that the use of Deligne–Beilinson cohomology in the context of the U(1) BF theory on a closed 3-manifold M yields a discrete ZN BF theory whose partition function is an abelian TV invariant of M. By comparing the expectation values of the U(1) and ZN holonomies in both BF theories we obtain a reciprocity formula
The Bar BF Ranch
No full textThe area of investigation concerns the possible uses of the Bar BF Ranch in Smithville, Missouri. The business that will ultimately lead to the greatest growth potential is sought. Two possibilities are outlined. The major finding for a growth industry is that of breeding extremely rare straight Egyptian Arabian horses. They are unequaled in classic beauty and thus possess a high profit potential as a genetic pool for the Arabian market world wide. The alternate growth concept for the Bar BF Ranch would be as a quest ranch specializing in horseback riding. The site has been approved for this use by the Dude Ranchers Association of America. The author concludes that the breeding of straight Egyptian Arabian horses will be the primary objective of the Bar BF Ranch, based upon industry findings and return of investment potential
THE INFRARED SPECTRA OF BF CATION AND BFOH CATION TRAPPED IN SOLID NEON
No full textAuthor Institution: Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-8441New, more detailed studies of the photoionization and Penning ionization of BF trapped in solid neon have confirmed the earlier{} infrared spectroscopic identification of BF and BF cation and have yielded a revised assignment for the infrared absorptions of BF cation. The position of the absorption attributed to of that molecule is consistent with the distortion of the ground-state cation from D symmetry because of strong vibronic interaction between levels of the \~{B} E state and E levels of the \~{X} A ground state, as predicted by Haller and co-workers.{ppel, L.~S.~Cederbaum, W.~von~Niessen, and G.~Bieri, J.~Chem.~Phys. 78, 1359 (1983).}} The facile reaction of BF with traces of HO desorbed from the walls of the vacuum system leads to the stabilization of sufficient BFOH for the identification of two vibrational fundamentals of BFOH cation
Low Complexity BF scheme for downlink MISO-NOMA systems
No full textIn this study, the authors investigate the user selection (US), beamforming (BF) and power allocation (PA) problems for the downlink multiple-input-single-output-based non-orthogonal multiple-access system. For the US problem, they matched the BF and PA schemes with different US schemes to achieve the best spectral efficiency performance. For the BF and PA problems, they derive a non-normalised BF scheme to accomplish the BF and PA problems jointly. The non-normalised BF scheme requires much lower computational complexity than the duality BF scheme. According to their simulation results, the non-normalised BF scheme can achieve the same or better spectral efficiency performance than the duality BF scheme. When the number of users sharing the same time-frequency resource is large, both the duality BF scheme and the singular value decomposition (SVD)-based BF scheme cannot obtain spectral efficiency advantage over the OMA scheme. However, the non-normalised BF scheme can maintain the advantage over the OMA scheme.SCI(E)ARTICLE101566-15731
COHERENT RAMAN SPECTRA OF THE MODE OF BF AND BF
No full textAuthor Institution: Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, OR 97331-4003; Pacific Northwest National Laboratory, P. O. Box 999, Mail Stop K8-88, Richland, WA 99532; National Institute of Standards and Technology, Gaithersburg, MD 20899High resolution (0.001 cm) coherent anti-Stokes Raman spectroscopy (CARS) was used to directly examine the symmetric stretching mode of the D molecules BF and BF. Calculated spectra were constructed using rovibrational parameters deduced from published infrared hot band, combination band, and difference band studies, and the similarity to the experimental CARS spectra confirms the validity of the constants. No significant perturbations by Fermi resonance or Coriolis interactions with nearby states are observed, in marked contrast to the case of sulfur trioxide, a similar D molecule recently studied. Since the boron nucleus is at the center of mass, the BF and BF Q-branches are the same according to the harmonic oscillator model. Interestingly, the observed frequency of BF is 0.198 cm higher than that of BF. This result is reproduced almost exactly (0.200 cm) using {\it ab initio} calculations (B3LYP/cc-pVTZ) that included evaluation of cubic and quartic force constants and x anharmonicity constants. {\it Ab initio} methods also predict to within 1\% the B and C changes in the rotational constants in going from the ground state to the v = 1 vibrational level
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