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51.
The growth of pentacene on suitable metallic templates is studied by means of low-energy electron diffraction and ultraviolet photoelectron spectroscopy. Highly ordered pentacene single layers can be prepared by deposition on filled d-band metal templates kept at 370 K. The presence of the steps for the Cu(119) vicinal surface and of the Au troughs for the Au(110)-(1 x 2) surface allows the formation of commensurate long-range ordered structures with (3 x 7) and (3 x 6) periodicities, respectively. A detailed analysis of the molecular induced electronic states evolution is performed for different growth morphologies. The adsorption energy of the ordered molecular single layers on the Au(110) surface is lower (1.90 eV) than on the Cu vicinal surface (2.36 eV), where the steps enhance the molecule adsorption energy. 相似文献
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53.
Secondary ion mass spectrometry (SIMS) was optimised for characterisation of uranium- and plutonium-containing particles
in soils, swipes and forensic samples. This was done by analysing in-house produced spherical UO2-particles. Screening techniques as α-autoradiography together with SIMS analysis were employed to detect UO2-particles in a soil sample from Chernobyl.
The use of SIMS was exploited for the identification of uranium- and plutonium-containing particles and for the determination
of their isotopic composition. The particles collected on swipe samples were transferred to a special adhesive support for
the analysis by SIMS. Particles containing highly enriched uranium with diameters up to 10 μm were also detected in a forensic
sample. For the measurements of the isotopic ratios a mass resolution of 1000 was used. At this resolution flat-top peaks
were obtained which greatly improve the accuracy of the measurement. The isotopic composition of the particles was measured
with a typical accuracy and precision of 0.5%. Statistically meaningful results can be obtained, for instance, from a specimen
containing as few as 1010 atoms/μm3 of uranium in particles of UO2 weighing a few picograms. 相似文献
54.
Solatie D Carbol P Betti M Bocci F Hiernaut T Rondinella VV Cobos J 《Fresenius' Journal of Analytical Chemistry》2000,368(1):88-94
The choice of the analytical method for the determination of actinide isotopes in leachate solutions has to be made considering several parameters: detection limit for each isotope, sample preparation procedure in terms of duration and complexity, counting time and interferences. A leachate solution obtained by keeping a pellet of UO2 doped with 238Pu in contact with distilled water was investigated for the content of U and Pu isotopes by radiometric methods (alpha-, gamma-spectrometry and liquid scintillation counting). The results of the radiometric methods were compared with those obtained from the analysis performed by inductively coupled plasma mass spectrometry on-line to a system for chromatographic separation (IC-ICP-MS). The comparison confirmed that IC-ICP-MS is a powerful method for the detection of long-lived radionuclides. The radiometric methods have a detection limit two orders of magnitude lower than IC-ICP-MS in the case of short-lived radioisotopes mostly due to the low background in the detector. On the other hand, the sample preparation and the analysis duration are more time-consuming compared to IC-ICP-MS; moreover, not all isotopes can be determined by using only one radiometric technique. 相似文献
55.
Mattia Scardamaglia Giuseppe Forte Silvano Lizzit Alessandro Baraldi Paolo Lacovig Rosanna Larciprete Carlo Mariani Maria Grazia Betti 《Journal of nanoparticle research》2011,13(11):6013-6020
Iron-phthalocyanine (FePc) molecules have been adsorbed on a graphene sheet prepared on the Ir(111) surface. The FePc molecules
are flat-lying on graphene, as determined by near-edge X-ray absorption fine-structure, constituting a sub-nanometer thick
molecular array at the single-layer coverage. The flat FePc single-layer presents a weak interaction of the organic macrocycle
with the graphene surface and Ir subsurface substrate. Further FePc deposition on top of the first flat single-layer determines
a three-dimensional island growth with varying molecular orientation. 相似文献
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In recent decades, in addition to long-haul, high-capacity links, research activity in optical fiber communication systems has addressed possible advantageous applications in distribution networks, local and metropolitan area networks, CATV backbones and distribution, and high-speed computer networks. As a consequence, new possibilities in optical transmission systems have been explored to face the new requirements in terms of capacity, spectral efficiency, and receiver sensitivity. Among the possible solutions capable to exploit effectively the potentials offered by the optical channel, novel multilevel modulation formats have been proposed for future communication environment. This paper reviews multilevel modulation techniques for optical transmission: a comparative analysis is performed between conventional modulations, such as N-PSK and N-QAM, and new modulation/demodulation techniques, such as N-4QSK, N-SPSK, and PM-DD, taking into account both system performance and technological constraints. 相似文献
60.
Dichiarante V Betti C Fagnoni M Maia A Landini D Albini A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(6):1834-1841
The triplet N,N-dimethylaminophenyl cation, a highly reactive but chemospecific electrophile, has been used as a probe for characterizing the properties of reaction media for a series of imidazolium ILs. With the N-hexyl-N-methyl imidazolium derivatives (not with the N-butyl analogues), hydrogen transfer leading to the aniline was the main process. Trapping by iodide occurred with an inverse dependence on viscosity. Trapping by pi nucleophiles exhibited a more complex behavior. This was explained by the effect of both the bulk viscosity and the structure of the IL cation on both steps of the reaction, namely, initial electrophilic attack and ensuing cation elimination or nucleophile addition. However, with an excellent nucleophile, such as thiophene, or when the latter step was intramolecular, as with 4-pentenol, the difference was obliterated and trapping became uniform. Incorporation of the probe into the IL cation (through insertion into the C--H bond alpha to the imidazolium ring) was demonstrated, while no addition to the anion tested (including bis(trifluoromethanesulfonimide)) took place. 相似文献