1,721,106 research outputs found
Scanning LLL x-ray interferometry .1. Theory
No full textA new formalism is presented for the theory of scanning LLL x-ray interferometry, which takes account also of the amount of x-ray absorption and of crystal yawing. It is based on the Takagi approach to the dynamical theory of x-ray diffraction and uses, to a great extent, the formalism of quantum mechanics, in order to reduce the algebraic complexity of the Ewald-von Laue approach. The formalism presented here is an easy-to-handle tool for the study of x-ray propagation in multicrystal systems and for the investigation into deviations of the travelling-fringe period from the spacing of diffracting planes, as it explains how interference features change when moving in paramater space
Scanning LLL x-ray interferometry .2. Aberration analysis
No full textBy using the formalism developed in Part I, we investigated errors in the measurement of the silicon lattice parameter by scanning LLL x-ray interferometry. We show that lattice spacing does not determine uniquely the period of travelling fringes unless crystal motion and form are free from geometrical aberrations. Owing to limited accuracy in manufacturing and operation, crystal movement may change interferometer geometry which, in turn, causes period deviations from the spacing of diffracting planes. We review the special cases of the so-called weak and strong absorptions and, additionally, consider the case of medium absorption, which is of great experimental interest. Finally, we examine how the phase of travelling fringes depends on interferometer design and point out non-linear effects and resonances, so far overlooked, which are related to the oscillatory structure of x-ray diffraction
Bernardo Vittone e la Disputa fra Classicismo e Barocco nel Settecento, 1972
No full textSouchal François. Bernardo Vittone e la Disputa fra Classicismo e Barocco nel Settecento, 1972. In: Dix-huitième Siècle, n°8, 1976. Les Jésuites. pp. 513-514
Graphene membrane as suspended mask for lithography
Full text linkThanks to its excellent mechanical properties, graphene is particularly suited for the realization of suspended membranes. The present paper deals with one possible application of such membranes that is the realization of suspended lithographic masks for shadow evaporation onto a substrate. This technique, which is largely used for realizing mesoscopic devices, where the quality requirements for the junctions prevent the exposure to ambient air and the occurrence of quantum phenomena requires highly defined structures, can be improved by the use of pure 2-dimensional masks, like graphene ones. Advantages and differences of this material with respect to commonly employed polymers are presented and discussed
Studio strutturale di un popolamento artificiale di pino nero (Pinus nigra Arnold) localizzato in Val Messa (TO).
No full textThe study has been carried out in an 250 ha wide area, between 600 and 1300 m asl. The reforestation, realized in the time period between the two world wars, is one of the most successful examples of watershed management in Piedmont (North-western Italy). The forest has a tipical even aged dense structure with new clearings due to windfalls. The protection funcion of the pine in ending but natural regeneration of autochtonous broadleaved tre species is already present
Kinetics of defect formation in chemically vapor deposited (CVD) graphene during laser irradiation: The case of Raman investigation
Full text linkThe effect of laser irradiation on chemically vapor deposited (CVD) graphene was studied by analyzing the temporal evolution of Raman spectra acquired under various illumination conditions. The spectra showed that the normalized intensity of the defect-related peak increases with the square root of the exposure time and varies almost linearly with the laser power density. Furthermore, the hardness of graphene to radiation damage depends on its intrinsic structural quality. The results suggest that, contrary to the common belief, micro-Raman spectroscopy cannot be considered a noninvasive tool for the characterization of graphene. The experimental observations are compatible with a model that we derived from the interpretative approach of the Staebler–Wronski effect in hydrogenated amorphous silicon; this approach assumes that the recombination of photoexcited carriers induces the breaking of weak C–C bonds
SVILUPPO DI UN SISTEMA INTEGRATO SiC/GaN RIVELATORE/FRONT-END PER SPETTROMETRIA DI RADIAZIONI IONIZZANTI A TEMPERATURA AMBIENTE E AD ALTE TEMPERATURE
No full textL’ attività è stata dedicata dapprima allo studio dei campioni di 4H SI- SiC samples di differente provenienza (CREE Research Inc. and Okmetic) e quindi a quello di una serie di campioni di 4H-SiC epitassiale irraggiati con neutroni e protoni.
La caratterizzazione è stata condotta con misure di fotocorrente per determinare i valori di lunghezza di diffusione, Ld, usando il set-up descritto in bibliografia (1) e con misure di fotoluminescenza a bassa temperatura. Inoltre sono state compiute analisi di spettroscopia a giunzione (Deep Level Transient Spectroscopy, DLTS, per i campioni semiconduttori e Photo-Induced Current Transient Spectroscopy (PICTS)fino a 650 K per i campioni con alta resistività , per individuare i livelli elettronici che controllano le proprietà di trasporto e quindi l'efficienza di raccolta dei rivelatori
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