RESUMEN
Raman spectra of large graphene bubbles showed size-dependent oscillations in spectral intensity and frequency, which originate from optical standing waves formed in the vicinity of the graphene surface. At a high laser power, local heating can lead to oscillations in the Raman frequency and also create a temperature gradient in the bubble. Based on Raman data, the temperature distribution within the graphene bubble was calculated, and it is shown that the heating effect of the laser is reduced when moving from the center of a bubble to its edge. By studying graphene bubbles, both the thermal conductivity and chemical reactivity of graphene were assessed. When exposed to hydrogen plasma, areas with bubbles are found to be more reactive than flat graphene.
RESUMEN
The covalent functionalization of single and bilayer graphene on SiO2 (300 nm)/Si was effected through sequential treatment with the alkalide reductant [K(15-crown-5)2]Na and electrophilic aryl or alkyl halides, of which the iodides proved to be the most reactive. The condensation reactions proceeded at room temperature and afforded the corresponding aryl- or alkyl-appended graphenes. For each sample, Raman and X-ray photoelectron spectroscopies were used to evaluate the degrees and uniformities of functionalization. Statistical analyses of the Raman data revealed that the introduction of the organic moieties was accompanied by sp3-rehybridization of the basal plane atoms. When bilayers consisting of 13C and 12C layers were treated, both the top and bottom sheets were decorated with organic groups. The reaction was followed using Raman spectroscopy, and the mechanism was studied by theoretical calculations. Indicative of its structure and reactivity, 4-pyridyl-decorated single-layer graphene was readily benzylated and appears to be an ideal platform to develop functional materials.
RESUMEN
Few-layer graphenes, supported on Si with a superficial oxide layer, were subjected to a Birch-type reduction using Li and H2O as the electron and proton donors, respectively. The extent of hydrogenation for bilayer graphene was estimated at 1.6-24.1% according to Raman and X-ray photoelectron spectroscopic data. While single-layer graphene reacts uniformly, few-layer graphenes were hydrogenated inward from the edges and/or defects. The role of these reactive sites was reflected in the inertness of pristine few-layer graphenes whose edges were sealed. Hydrogenation of labeled bilayer (12C/13C) and trilayer (12C/13C/12C) graphenes afforded products whose sheets were hydrogenated to the same extent, implicating passage of reagents between the graphene layers and equal decoration of each graphene face. The reduction of few-layer graphenes introduces strain, allows tuning of optical transmission and fluorescence, and opens synthetic routes to long sought-after films containing sp3-hybridized carbon.