Graphene is a monolayer of carbon atoms packed into a two-dimensional (2D) honeycomb crystal structure, which is a special material with many excellent properties. In the present study, we will discuss the possibility that graphene can be used as a substrate for enhancing Raman signals of adsorbed molecules. Here, phthalocyanine (Pc), rhodamine 6G (R6G), protoporphyin IX (PPP), and crystal violet (CV), which are popular molecules widely used as a Raman probe, are deposited equally on graphene and a SiO(2)/Si substrate using vacuum evaporation or solution soaking. By comparing the Raman signals of molecules on monolayer graphene and on a SiO(2)/Si substrate, we observed that the intensities of the Raman signals on monolayer graphene are much stronger than on a SiO(2)/Si substrate, indicating a clear Raman enhancement effect on the surface of monolayer graphene. For solution soaking, the Raman signals of the molecules are visible even though the concentration is low to 10(-8) mol/L or less. What's more interesting, the enhanced efficiencies are quite different on monolayer, few-layer, multilayer graphene, graphite, and highly ordered pyrolytic graphite (HOPG). The Raman signals of molecules on multilayer graphene are even weaker than on a SiO(2)/Si substrate, and the signals are even invisible on graphite and HOPG. Taking the Raman signals on the SiO(2)/Si substrate as a reference, Raman enhancement factors on the surface of monolayer graphene can be obtained using Raman intensity ratios. The Raman enhancement factors are quite different for different peaks, changing from 2 to 17. Furthermore, we found that the Raman enhancement factors can be distinguished through three classes that correspond to the symmetry of vibrations of the molecule. We attribute this enhancement to the charge transfer between graphene and the molecules, which result in a chemical enhancement. This is a new phenomenon for graphene that will expand the application of graphene to microanalysis and is good for studying the basic properties of both graphene and SERS.

Polycrystalline BiFeO3 nanoparticles (size 80–120 nm) are prepared by a simple sol–gel technique. Such nanoparticles are very efficient for photocatalytic decomposition of organic contaminants under irradiation from ultraviolet to visible frequencies. The BiFeO3 nanoparticles also demonstrate weak ferromagnetism of about 0.06 μB/Fe at room temperature, in good agreement with theoretical calculations.

We have measured resonance Raman spectra with greatly suppressed fluorescence (FL) background from rhodamine 6G (R6G) and protoporphyrin IX (PPP) adsorbed on graphene. The FL suppression is estimated to be approximately 10(3) times for R6G. The successful observation of resonance Raman peaks demonstrates that graphene can be used as a substrate to suppress FL in resonance Raman spectroscopy (RRS), which has potential applications in low-concentration detection and RRS study of fluorescent molecules.