We determine the Raman scattering efficiency of the G and 2D peaks in graphene. Three substrates are used: silicon covered with 300 or 90 nm oxide, and calcium fluoride (CaF 2). On Si/SiO x , the areas of the G and 2D peak show a strong dependence on the substrate due to interference effects, while on CaF 2 no significant dependence is detected. Unintentional doping is reduced by placing graphene on CaF 2. We determine the Raman scattering efficiency by comparison with the 322 cm −1 peak area of CaF 2. At 2.41 eV, the Raman efficiency of the G peak is ∼ 200 × 10 −5 m −1 Sr −1 , and changes with the excitation energy to the power of 4. The 2D Raman efficiency is at least one order of magnitude higher than that of the G peak, with a different excitation energy dependence.
Graphene oxide (GO) exfoliated sheets were used as two dimensional platforms to covalently tether on their surface thousands of optically active quaterthiophene molecules (T4), using an innovative microwave-assisted silanization reaction. This method allowed to perform GO functionalization in one-step, under mild conditions in a few tens of minutes rather than days. The hybrid GOT4 could be processed in either H 2 O or apolar organic solvents and deposited as single sheets, microplatelets or macroscopic membranes. Absorption/emission spectroscopy reveals that GOT4 combines limited T4-T4 interactions with strong T4-GO ones. These findings, combined with the 'user-friendly' engineering approach presented here, pave the way towards the bottom-up fabrication of new GO-based tailored materials for electronics, sensors and biological applications.
We report large-yield production of graphene flakes on glass by anodic bonding. Under optimum conditions, we counted several tens of flakes with lateral size around 20-30 μm and a few tens of flakes with larger size. About 60-70% of the flakes have a negligible D peak. We show that it is possible to easily transfer the flakes by the wedging technique. The transfer on silicon does not damage graphene and lowers the doping. The charge mobility of the transferred flakes on silicon is on the order of 6000 cm(2)/V s (at a carrier concentration of 10(12) cm(-2)), which is typical for devices prepared on this substrate with exfoliated graphene.
We present composite plasmonic nanostructures designed to achieve cascaded enhancement of electromagnetic fields at optical frequencies. Our structures were made with the help of electron-beam lithography and comprise a set of metallic nanodisks placed one above another. The optical properties of reproducible arrays of these structures were studied by using scanning confocal Raman spectroscopy. We show that our composite nanostructures robustly demonstrate dramatic enhancement of the Raman signals when compared to those measured from constituent elements. [7], and data storage [8]. Normally, optical fields are concentrated by focusing light with appropriate lenses, the minimum volume of the enhanced field ultimately being determined by the wavelength of the light used. It is well known that metal nanostructures allow one to concentrate light in smaller volumes through the excitation of localized surface plasmons, thereby enhancing the strength of the electric field over that available otherwise [9]. Individual metallic nanoparticles allow a modest field enhancement, of the order of the quality factor Q of the plasmonic resonance [10]. The field strength can be increased further in particle conglomerates [11,12] and particle pairs [13]. The gap between particles is particularly important in many systems [11][12][13][14]. Recently, it was suggested that a new class of composite metallic nanostructures might be used to provide very high and well-controlled optical-field enhancements [10].The confinement of fields using metallic nanostructures, in volumes well below the diffraction limit, down to just several tens of nanometers, involves a process mediated by the electron plasma of the metal [10]. The deeply subwavelength volumes of field confinement and strongly enhanced optical fields that are predicted for composite metallic nanostructures offer many intriguing prospects, for example, 3D optical near-field trapping [15,16]. Surface-enhanced Raman scattering (SERS) from single molecules immobilized on ''hot'' colloidal nanoparticle structures has been reported [17][18][19] with field enhancements of $100 being invoked to account for this extraordinary sensitivity [20]. These results provide an incentive to find ways to produce such high field enhancements in a controlled way, rather than relying on nondeterministic colloidal synthesis techniques.The self-similar plasmonic structure suggested by Li, Stockman, and Bergman [10] presents an appealing design for a composite nanostructure in which the near fields produced by an illuminated large metallic nanoparticle play the role of the exciting field for a smaller metallic nanoparticle, the result of which is to enhance the field further. The electromagnetic field may thus undergo a cascaded enhancement by a factor of up to g tot $ g n , where g $ Q $ Re"ð!Þ=Im"ð!Þ [10] ["ð!Þ is the metal permittivity; e.g., for gold Q $ 7 at a wavelength of 630 nm] and n is the number of cascades. Although a self-similar nanoassembly has been demonstrated [21], no experimental verif...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.