Keywords: surface plasmons, extraordinary transmission, nanoholes, sub-wavelength apertures, metal films, surface-enhanced Raman scattering, surface plasmon resonance, sensors, nonlinear optics, spectroscopy, enhanced fluorescence, nanotechnology, quantum dots, microfluidics
Nanoholes in metals with applications to sensors and spectroscopy
In this paper, we review our experimental and theoretical investigations of nano-holes in metal films. Our first contribution to this field was to demonstrate experimentally that the shape of the holes in arrays could be used to influence the optical properties; in particular, we showed how to control the polarisation with elliptical nano-holes. A theory explaining this shape-effect was presented for a single rectangular hole. This theory agreed well with experimental findings. Furthermore, the separate contributions of the isolated hole and the lattice were shown experimentally and theoretically by varying the orientation and shape of the isolated holes. A new double-hole structure was presented to enable significantly enhanced local fields in the nano-holes, which has applications in non-linear optics and spectroscopy. Theory and experiments are presented for this double-hole structure, showing enhanced second-harmonic generation. We have used nano-hole arrays in surface plasmon resonance spectroscopy, surface-enhanced Raman spectroscopy and enhanced fluorescence. Along with those works, we present studies on the coupling between surface plasmons and quantum dots in nano-hole array samples. Finally, our work on integrating nano-hole samples into microfluidic devices for sensing applications is presented.