Enormous enhancement of electric field in active gold nanoshells

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. (condensed matter: electronic structure, electrical, magnetic, and optical properties)