Plasmonic refractive index sensitivity of ellipsoidal Al nanoshell: Tuning the wavelength position and width of spectral dip

The absorption spectra of ellipsoidal Al nanoshell show a distinct dip due to the two adjacent localized surface plasmon resonance (LSPR) peaks corresponding to the longitudinal resonance from the inner and outer surfaces of the Al shell. Both the dip position and its linewidth are sensitive to the refractive index of the outer surrounding. And the sensitivity could be well tuned by the shell thickness, aspect ratio, shell nonuniformity and the dielectric environment. By comparing with the dip wavelength, the dip width is more sensitive to the geometry of the Al nanoshell. It has been found that the widening speed of the spectrum dip as a function of environmental dielectric could be greatly enlarged by increasing the aspect ratio and longitudinal shell thickness. It has also been interesting to note that the dip width changes non-monotonously when the Al nanoshell has a large dielectric constant of the inner core and a thick transverse shell thickness. The physical mechanism has been attributed to the different shift speeds between symmetric and antisymmetric LSPR along the longitudinal direction. This dielectric environment dependent-spectrum dip presents a new sensing picture based on tuning the dip width and position.