Nanoholes arrays as effective SERS substrates with multiple wavelength SERS response and large electromagnetic SERS enhancement factors

摘要

Bridged-bowtie nanohole arrays and cross bridged-bowtie nanohole arrays in a gold film are presented as surfaceenhancedRaman scattering (SERS) substrates. We employed the numerical FDTD method to calculate the maximumelectromagnetic SERS enhancement factor (EF) as a function of wavelength. It is found that the proposed nanoholearrays do not only display an extremely large enhancement factor but also have the hotspot spread over a larger areacompared to the various other nanopillar structures. The calculation of electromagnetic SERS enhancement factorreveals that the cross bridged-bowtie nanohole arrays exhibit the maximum electromagnetic SERS EF of ～ 10~9 spreadingover an area of 100 nm~2. In addition, the electromagnetic SERS EF of ～ 10~8 is spread over 500 nm~2 area which is higherthan hotspot area in case of nanopillar structures. The resonance wavelength of the nanohole array can be tuned byvarying the size of the nanoholes. These nanohole arrays can be employed both in transmission as well as in reflectionmode as effective SERS substrates. In addition, bridged-bowtie and cross bridged-bowtie nanohole arrays show thesignificantly high electromagnetic SERS EF at more than one wavelength and therefore are useful for applicationinvolving multiple wavelength SERS response. Furthermore, the cross bridged-bowtie nanohole array exhibit the spatialtunability of hotspot by rotating the direction of polarization of incident field.