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951.
Bazzicalupi C Biagini S Bencini A Faggi E Giorgi C Matera I Valtancoli B 《Chemical communications (Cambridge, England)》2006,(39):4087-4089
A new polyammonium receptor is able to selectively recognise and sense ATP among triphosphate nucleotides, thanks to ATP-induced quantitative quenching of its fluorescence emission. 相似文献
952.
Dinelli F Moulin JF Loi MA Da Como E Massi M Murgia M Muccini M Biscarini F Wie J Kingshott P 《The journal of physical chemistry. B》2006,110(1):258-263
In organic field effect transistors, charge transport is confined to a narrow region next to the organic/dielectric interface. It is thus extremely important to determine the morphology and the molecular arrangement of the organic films at their early growth stages. On a substrate of technological interest, such as thermally grown silicon oxide, it has been recently found that alpha-sexithienyl aggregates made of flat-lying molecules can simultaneously nucleate besides islands made of molecules standing vertical. In this paper, we investigate the effects due to variations in surface chemical composition on alpha-sexithienyl ultrathin film formation. Flat-lying molecules are no longer detected when Si-OH groups present at the surface are chemically removed but also when the Si-OH or Si-H group density is maximized. This gives evidence that variations in the surface chemical composition can largely affect the nucleation and growth processes of organic/dielectric interfaces. We hypothesize that isolated OH groups can interact with alpha-sexithienyl molecules and anchor them down flat with respect to the surface. 相似文献
953.
High-temperature failure of GaN LEDs related with passivation 总被引:1,自引:0,他引:1
Matteo Meneghini Lorenzo Trevisanello Gaudenzio Meneghesso Enrico Zanoni Francesca Rossi Maura Pavesi Ulrich Zehnder Uwe Strauss 《Superlattices and Microstructures》2006,40(4-6):405
This paper analyses the thermally-activated failure mechanisms of GaN LED test-structures related with the presence of a hydrogen rich SiN passivation layer, by comparing the electrical and optical behaviour of samples with and without passivation during thermal stress. The analysis was carried out by means of electroluminescence, cathodoluminescence, emission microscopy and current–voltage measurements. Thermal treatment induced degradation only on the samples with passivation: identified degradation modes were an efficiency decrease exponential in time, emission crowding, and a forward voltage increase. On the other side, thermal treatment did not change the behaviour of the LEDs without passivation. An interpretation for the degradation of the passivated samples is the following: as a consequence of passivation deposition, a considerable amount of hydrogen is incorporated in the passivation layer. Heating at 250 C allows this hydrogen to interact with the LED surface, thus worsening the transport properties of p-GaN and of the p-ohmic contact, and then the current and emission distribution, inducing the observed degradation and emission crowding. The activation energy of the degradation process was found to be equal to 1.3 eV. Comparison between spectral electroluminescence and cathodoluminescence measurements shows how the mechanism mentioned above is not the only ageing cause and the thermal worsening of QW confinement and/or the creation of nonradiative centers possibly contribute to the LED damage. 相似文献
954.
Silvia Vicini Alberto Mariani Elisabetta Princi Simone Bidali Silvia Pincin Stefano Fiori Enrico Pedemonte Antonio Brunetti 《先进技术聚合物》2005,16(4):293-298
Polymeric products are largely used for consolidation of stone in the field of cultural heritage. Nevertheless, the main problem of polymeric compounds is related to their macromolecular nature, it being difficult for a polymer to penetrate inside the pores which may have a very small diameter. These considerations are the starting points for in situ polymerization. According to this technique, not the pre‐formed polymer, but the monomer is introduced into the stone and it is polymerized in situ in a subsequent step. Frontal polymerization (FP) is a particular technique in which the heat released by the exothermal reaction of monomer to polymer conversion is exploited to promote the formation of a hot traveling front able to propagate and self‐sustain the reaction. In the present work, FP is performed inside the pores of the stone and the results lead to the conclusion that the hot front is still active in the presence of an inorganic material which dissipates partially the heat released during the polymerization. In addition some recent applications of FP are discussed in comparison with the traditional polymerization for the in situ consolidation and protection of stones. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
955.
Giacomo Parigi Enrico Ravera Marina Bennati Claudio Luchinat 《Molecular physics》2019,117(7-8):888-897
Overhauser dynamic nuclear polarisation (DNP) represents a potentially outstanding tool to increase the sensitivity of solution and solid state NMR experiments, as well as of magnetic resonance imaging. DNP signal enhancements are strongly linked to the spin relaxation properties of the system under investigation, which must contain a paramagnetic molecule used as DNP polariser. In turn, nuclear spin relaxation can be monitored through NMR relaxometry, which reports on the field dependence of the nuclear relaxation rates, opening a route to understand the physical processes at the origin of the Overhauser DNP in solution. The contributions of dipole–dipole and Fermi-contact interactions to paramagnetic relaxation are here described and shown to be responsible to both the relaxometry profiles and the DNP enhancements, so that the experimental access to the former can allow for predictions of the latter. 相似文献
956.
957.
We describe the structure of the finite groups in which the sizes of noncentral conjugacy classes have the same p-part, for some prime p. We prove that they are solvable, they have a normal p-complement and their Fitting length is at most three. 相似文献
958.
4-Trimethylstannylcoumarins 2, conveniently obtained from the corresponding 4-triflyloxycoumarins 1, undergo Pd(0)/CuI-cocatalyzed cross-coupling reactions with a variety of aryl iodides to afford 4-arylcoumarins 4 in moderate to good yields. Aryl triflates are less effective as coupling partners. 相似文献
959.
960.