Investigation of <i>n</i>-Layer Graphenes as Substrates for Raman Enhancement of Crystal Violet

In this work, Raman signals from crystal violet (CV) molecules on n-layer graphenes are clearly observed while these signals are invisible on SiO2/Si substrate under the same deposition condition with the same concentration of CV solution. This indicates that n-layer graphenes can be used as substrates for enhancing Raman signals of adsorbed CV molecules. The enhanced efficiency is found to be closely related to the layer number n. These conclusions can be further confirmed by Raman spectra of CV molecules on gold-decorated n-layer graphenes. The Raman enhancement effect of n-layer graphenes is attributed to chemical mechanism (CM) while electromagnetic mechanism (EM) dominates the enhancement effect of gold. Thus, graphene provides a convenient way to study CM exclusively. The morphology and density of gold nanostructures on n-layer graphenes play a significant role in the EM related Raman enhancement effect

Thickness-Dependent Morphologies and Surface-Enhanced Raman Scattering of Ag Deposited on <i>n</i>-Layer Graphenes

After thermal deposition of silver films onto n-layer graphenes, the following results have been obtained. First, the dependence of silver morphologies on the layer number is studied via controlling the sample temperature at 298, 333, and 373 K. This can be attributed to the changes in surface properties and/or surface diffusion coefficient of n-layer graphenes at different temperatures. Second, Raman scattering of n-layer graphenes is greatly enhanced after Ag deposition and the enhancement factors depend on the layer number of n-layer graphenes. Monolayer graphene has the largest enhancement factors, and the enhancement factors decrease with layer number increasing. For graphite, almost no enhancement effect has been detected. Third, the dependences of the enhancement factors on laser wavelength, thickness, and morphologies (nanoparticle size and spacing) of silver film are also studied. The Raman enhancement observed here is mainly attributed to the coupled surface plasmon resonance (SPR) absorption of silver nanoparticles

Modification on Single-Layer Graphene Induced by Low-Energy Electron-Beam Irradiation

In this work, we present studies of the effects of electron-beam irradiation on the modification of single-layer graphene. Micro-Raman spectra show that the D, D′, and D + G Raman bands, which are invisible for pristine graphene, appear after the graphenes are irradiated by low-energy electron-beam irradiation (10 keV), and the intensities of these peaks increase with increasing irradiation time, indicating disorder in graphene. The characteristics of G and 2D bands of graphene are also studied before and after irradiation. In the meantime, the height of graphene is studied by atomic force microscopy and found to increase for increasing irradiation time due to the contaminant deposition on graphene. The effects introduced by irradiation can be recovered partly by vacuum annealing. These results provide important information about the modification of graphene under electron-beam irradiation

Thickness-Dependent Morphologies of Gold on <i>N</i>-Layer Graphenes

Thickness-Dependent Morphologies of Gold on N-Layer Graphene

Experimental Evidence of Local Magnetic Moments at Edges of <i>n</i>-Layer Graphenes and Graphite

Ferromagnetism in graphite/graphenes is attractive for fundamental science and potential applications in carbon-based magnetism and spintronics. In this work, we show that magnetic particle inspection can be miniaturized to detect local magnetic moments with a high spatial resolution of ∼1.0 nm using scanning electron microscopy. A metal nanowire and adjacent nanogap can be found at the edges of graphenes and graphite for atoms with magnetic moments (Fe, Co, Ni, Mn, Pd, Al), whereas no similar characteristics are found for diamagnetic metals (Au, Ag). By investigating these features under an external magnetic field and at different temperatures, we discuss possible mechanisms and propose that intrinsic ferromagnets exist and form a one-dimensional array at the edges of graphenes and graphite. Meanwhile, the size of individual magnets (B per carbon edge atom) of magnetic moments, and their Curie temperature (>95 °C) are obtained, which are novel and interesting