Fano resonances in the symmetry-broken gold-SiO2-gold(BGSG)nanotubes and the associated dimers have been investigated based on the finite element method.In the BGSG nanotube,the symmetry breaking induced the interactions of the inner gold core and outer gold nanoshell plasmons of all multipolar orders and hence the red-shifts of the plasmon resonance modes and the enhanced quadrupole mode peaks were observed.The interference of the quadrupole mode peak with the subradiant dipole mode caused a Fano-dip in the scattering spectrum.By increasing the core offset-value in the BGSG nanotube,the Fano dip with low energy showed a red-shift and became deeper.Unexpectedly the plasmon coupling between a GSG nanotube and a BGSG nanotube can lead to two strong Fano dips in the scattering spectra of the dimer.It was further noted that the thin side of the BGSG nanotube located at two sides of the dimer gap can lead to the strong near-field coupling between two BGSG nanotubes and hence a deeper and broader Fano dip.
In order to design a sonochemical reactor with high reaction efficiency, it is important to clarify the size and intensity of the sonochemical reaction field. In this study, the reaction field in a sonochemical reactor is estimated from the distribution of pressure above the threshold for cavitation. The quantitation of hydroxide radical in a sonochemical reactor is obtained from the calculation of bubble dynamics and reaction equations. The distribution of the reaction field of the numerical simulation is consistent with that of the sonochemical luminescence. The sound absorption coefficient of liquid in the sonochemical reactor is much larger than that attributed to classical contributions which are heat conduction and shear viscosity. Under the dual irradiation, the reaction field becomes extensive and intensive because the acoustic pressure amplitude is intensified by the interference of two ultrasonic waves.
The electric field enhancement properties of an active gold nanoshell with gain material inside have been investigated by using Mie theory. As the gain coefficient of the inner core increases to a critical value, a super-resonance appears in the active gold nanoshell, and enormous enhancements of the electric fields can be found near the surface of the particle. With increasing shell thickness, the critical value of the gain coefficient for the super-resonance of the active gold nanoshell first decreases and then increases, and the corresponding surface enhanced Raman scattering(SERS) enhancement factor(G factor) also first increases and then decreases. The optimized active gold nanoshell can be obtained with an extremely high SERS G factor of the order of 1019–1020. Such an optimized active gold nanoshell possesses a high-efficiency SERS effect and may be useful for single-molecule detection.
