A simple synthesis method of silver nanoparticles and its application as an active surface-enhanced Raman spectroscopy (SERS) colloid are presented in this work. The photoreduction of AgNO 3 in presence of sodium citrate (NaCit) was carried out by irradiation with different light sources (UV, white, blue, cyan, green, and orange) at room temperature. The evaluation of silver nanoparticles obtained as a function of irradiation time (1-24 h) and light source was followed by UV-visible absorption spectroscopy. This light-modification process results in a colloid with distinctive optical properties that can be related to the size and shape of the particles. The Ag colloids, as prepared, were employed as active colloids in SERS. Pyridine and caffeine were used as test molecules.

We measured the Raman spectra of ZnO nanoparticles (ZnO-NPs), as well as transition-metal-doped (5% Mn(II), Fe(II) or Co(II)) ZnO nanoparticles, with an average size of 9 nm. A typical Raman peak at 436 cm −1 is observed in the ZnO-NPs, whereas Zn 1−x Mn x O, Zn 1−x Fe x O and Zn 1−x Co x O presented characteristic peaks at 661, 665 and 675 cm −1 , respectively. These peaks can be related to the formation of Mn 3 O 4 , Fe 3 O 4 and Co 3 O 4 species in the doped ZnO-NPs. Moreover, these samples were analyzed at various laser powers. Here, we observed new vibrational modes (512, 571 and 528 cm −1 ), which are specific to Mn, Fe and Co dopants, respectively, and ZnO-NPs did not reveal any additional modes. The new peaks were interpreted either as disorder activated phonon modes or as local vibrations of Mn-, Fe-and Co-related complexes in ZnO.

Raman spectra of starting (pristine) and functionalized multiwalled carbon nanotubes (MWNTs) were analyzed by principal component analysis (PCA) because the original Raman spectra showed very little differences between them. The nanotubes were functionalized with amines: dodecylamine (MWNT1), nonylamine (MWNT2), phenylamine (MWNT3) and octadecylamine (MWNT4), and with dithiols: 1,4-butane dithiol (MWNT5), 1,6-hexane dithiol (MWNT6) and 1,8-octane dithiol (MWNT7). The D and G band intensity ratios (∼1338 and ∼1575 cm −1 ) of the functionalized MWNTs spectra were compared with those of the starting material. For the studied systems, PCA allowed the differentiation between starting and functionalized MWNTs. The present study demonstrated the potential of the application of PCA to the study of functionalized nanotubes by Raman spectroscopy.

The electrical conductance of few layer graphene during thermal evaporation of fullerene C60 as well as the conductance under illumination of this bilayer junction is reported. We obtained few layer graphene films by chemical vapor deposition technique, and then C60 was thermally evaporated on these films. We found an increase in conductance of few layer graphene during the thermal evaporation of C60 and a kind of negative photoconductivity when the bilayer junction was under illumination. We observed that at low light intensities few layer graphene is p-type doped, and we propose that its behavior changes to n-type for high light intensities.

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