Fabrication and Optical Properties of Gold Semishells

Gold (Au) nanoshells are known to exhibit many attractive optical properties caused by the excitation of localized surface plasmon resonances (LSPRs). Reducing the symmetry of these nanoshells has a number of interesting consequences, such as exciting different plasmon modes, making the optical response angle-dependent, and enhancing the local electric field intensity. In this paper, a versatile procedure involving ion milling has been developed to fabricate reduced-symmetrical Au semishells. This allows us to precisely control the reduced-symmetrical geometry and, particularly, the upward orientation of the created nanoaperture. These features, along with a combination of finite different time domain (FDTD) calculations, suggest Au semishell monolayer structures for a potential application in surface-enhanced Raman spectroscopy (SERS)-based biomolecule detection. Au semishells, additionally, exhibit advantageous features over Au nanoshells, for example, a more pronounced red shift of LSPR bands by tuning the aspect ratio, a larger tuning range of optical properties, increased optical absorption at higher wavelengths, and an enhanced local electromagnetic field.