Plasma modified MoS(2) nanoflakes for surface enhanced raman scattering.

Though the SERS effect based on pristine MoS2 is hardly observed, however, the plasma treated MoS2 nanoflakes can be used as an ideal substrate for surface enhanced Raman scattering. It is proved that the structural disorder induced generation of local dipoles and adsorption of oxygen on the plasma treated MoS2 nanosheets are the two basic and important driven forces for the enhancement of Raman signals of surface adsorbed R6G molecules.

Other origins for the fluorescence modulation of single dye molecules in open-circuit and short-circuit devices.

Fluorescence intensity modulation of single Atto647N dye molecules in a short-circuit device and a defective device, caused by damaging an open-circuit device, is due to a variation in the excitation light focus as a result of the formation of an alternating electric current.

Surface-enhanced Raman scattering (SERS) of nitrothiophenol isomers chemisorbed on TiO2.

Surface-enhanced Raman scattering (SERS) spectroscopy and density functional theory (DFT) calculations were used to investigate the nature of the charge-transfer (CT) process between nitrothiophenol (NTP) isomers and the n-type semiconductor, TiO(2). The Raman signals of p-NTP and m-NTP that were chemisorbed onto TiO(2) were significantly enhanced with respect to their corresponding neat compounds. In particular, an enhancement factor (EF) of 10(2)-10(3) was observed for both p-NTP and m-NTP, with m-NTP displaying a larger EF compared to p-NTP. The Raman signal of o-NTP on TiO(2) was not detectable, owing to interference from fluorescence emissions. A molecule-to-TiO(2) charge-transfer mechanism was responsible for the enhanced Raman signals observed in p-NTP and m-NTP. This transfer was due to a strong coupling between the adsorbate and the metal oxide, which led to an optically driven CT transition from the HOMO of NTP into the conduction band of TiO(2). Based on the mesomeric effect, the NO(2) group para to the thiol had a stronger electron-withdrawing ability than the NO(2) group at the meta position. A less-efficient CT transition from p-NTP to TiO(2) in the surface complex resulted in a weaker Raman-signal enhancement for p-NTP compared to m-NTP. The DFT calculation determined that the HOMO and the LUMO of NTP bound to TiO(2) were located entirely on the adsorbate and the semiconductor, respectively, thereby supporting the experimental findings that a molecule-to-TiO(2) mechanism was the driving force behind the observed SERS effect.

Visualizing polymer crystallization in ultrathin layers using a single-macromolecule tracking method.

Single-(macro) molecule tracking is used for the first time here to study the crystallization process in ultrathin layers of single poly(ethylene oxide) (PEO) chains. Diffusion trajectories of macromolecules diffusing toward the crystal followed by deposition onto the crystal-growth front display different types of motion, such as Brownian and directed motions, prior to crystallization. We show that PEO chains in the amorphous layer and in the less concentrated or depleted zone exhibit Brownian motion of different diffusion rates as a result of heterogeneities in the environment.