1,721,084 research outputs found
Properties and applications of graphene membranes grown on Co
No full textGraphene grows on cobalt by means of diffusion of carbon atoms during the isothermal stage of exposure to hydrocarbon precursor, followed by precipitation during cooling. This method, largely applied with the nickel catalyst, is known to produce continuous, but not uniform, layers with the concurrent presence of mono- and poly-graphene areas. Many distortions of the Raman signatures can, however, be interpreted as related to strain. A detailed investigation of this effect is provided. The material has better mechanical stability with respect to the Cu-grown graphene and can be easily transferred without the aid of any polymeric support. This makes our graphene particularly suited for the realization of suspended membranes. One possible application of such membranes is the realization of suspended lithographic masks for shadow evaporation. 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 those made with graphene. Advantages and differences with respect to the polymers commonly employed are presented and discussed
In situ control of dewetting of Cu thin films in graphene chemical vapor deposition.
No full textChemical vapor deposition (CVD) on Cu thin films is a promising approach for the large area formation of graphene on dielectric substrates, but a fine control of the deposition parameters is required to avoid dewetting of the Cu catalyst. In this paper we report on the study of the Cu dewetting phenomena by monitoring the intensity of the infra-red emission from the film surface during rapid thermal CVD of graphene. The reduction of Cu film coverage consequent to dewetting is detected as a variation of sample's emissivity. Results indicate three time constants of dewetting, describing three typical stages, hole formation, propagation and ligament breakup. Slowing the first incubation stage by tuning pressure in the chamber allows for an effective surface activation resulting in the deposition of graphene at temperatures lower than those in the case of Cu foils
Procedimento per formare materiali semiconduttori porosi mediante attacco elettrochimico e corrispondente dispositivo moltiplicatore di elettroni a microcanali
No full textProcedimento per formare materiali semiconduttori porosi mediante attacco elettrochimico e corrispondente dispositivo moltiplicatore di elettroni a microcanali
Procedimento per formare materiali semiconduttori porosi, del tipo che comprende le operazioni di:
- eseguire un passo di attacco elettrochimico su una fetta di materiale semiconduttore, ponendo detta fetta di materiale semiconduttore a contatto con un elettrolita e imponendo il passaggio in detta fetta di materiale semiconduttore di una corrente elettrica, per ottenere dei pori passanti a posizioni preselezionate su detta fetta di materiale semiconduttore, caratterizzato dal fatto che detta operazione di imporre il passaggio di una corrente elettrica comprende un passo di modulazione nel tempo di detta corrente elettrica al fine di modulare un diametro (d) di detti pori
A New Approach in the Optical Characterization of Amorphous Hydrogenated Silicon Carbon Alloys
No full text
Optical and Morphological Properties of Light-Emitting Porous Silicon Prepared by Chemical Dissolution of Silicon-Wafers
No full textHigh Temperature Growth of Graphene from Cobalt Volume: Effect on Structural Properties
Full text linkSeveral transition metals other than the largely used Cu and Ni can be, in principle, employed to catalyze carbon precursors for the chemical vapor deposition of graphene, because the thermodynamics of their alloying with carbon is well known. For example, the wealth of information in the Co-C phase diagram can be used to predict the properties of graphene grown in this way. It is, in fact, expected that growth occurs at a temperature higher than in Ni, with beneficial consequences to the mechanical and electronic properties of the final product. In this work, the growth of graphene onto Co film is presented together with an extensive Raman characterization of the structural properties of the material so far obtained. Previous results reporting the full coverage with negligible defective areas, in spite of discontinuities in the underlying metal, are confirmed, together with the occurrence of strain in the graphene sheet. Strain is deeply investigated in this work, in view of possible employment in engineering the material properties. The observed strain is ascribed to the high thermal mismatch with the substrate, even if an effect of the crystallographic transition of Co cannot be excluded
Gap-States Distribution in Amorphous-Silicon Films as Obtained by Photothermal Deflection Spectroscopy
No full text- …
