RESUMO
Continuous-variable (CV) entanglement frequency comb can be produced by enhanced Raman scattering in an above-threshold optical oscillator cavity in which a hexagonally-poled LiTaO3 crystal resides as a Raman gain medium. The Stokes and anti-Stokes Raman signals are enhanced by a coupled quasi-phase-matching optical parametric process and the entanglement natures among these Raman signals and pump are demonstrated by applying a sufficient inseparability criterion for CV entanglement. Such entanglement frequency comb source with different frequencies and continuously tunable frequency interval may be very significant for the applications in quantum communication and networks.
RESUMO
Poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer templates which present in-plane cylinders of polystyrene (PS) aligned parallel to the plane of the substrate have been prepared by a solvent-induced order-disorder phase transition method. Silver nanoclusters have been obliquely deposited onto the SBS copolymer templates at low coverage, utilizing the directed low-energy cluster beam deposition (LECBD) method. The morphology of the samples has been characterized by a tapping-mode AFM. It is shown that the silver nanoclusters form ordered linear arrays and the intercluster distance within each individual linear array is comparable to the cluster size. Optical absorption spectra indicate that the surface plasmon resonance (SPR) of the silver nanocluster linear arrays occurs at about 444.5 nm, manifesting a red shift of approximately 21.4 nm compared to the SPR absorption of silver nanoclusters deposited on a fused quartz substrate. This is attributed mainly to the near-field electrodynamic interactions between the silver nanoclusters. This hierarchical approach to create ordered nanostructures transcends the spatial limits of lithography and provides a promising route to achieve well-ordered cluster-based nanostructures.
RESUMO
Anatase Co-doped TiO2 nanoparticles capped by oleic acid with a wide range of dopant concentrations (0-23.27%) were synthesized. The surface chemistry of the doped nanoparticles was probed by Fourier transform infrared spectroscopy and thermogravimetric analyses. An interesting effect of doping was discovered: doping with Co2+ at the nanocrystal surface significantly improves the solubility and dispersibility of the nanocrystals in apolar solvents, which can originate in the change in the self-assembled structure of the surface ligand from the weakly hydrophobic quasibilayer in undoped TiO2 nanorods to the strongly hydrophobic monolayer in Co-doped TiO2 nanocrystals.
