Plasmonic nano apertures for molecular sensing and colour displays

The discovery of extraordinary optical transmissions through metallic periodical subwavelength apertures has seen promising applications in filtering and sensing. Such a unique optical property is due to the excitation of surface plasmon resonance. Through accurate control of the aperture’s geometrical shape and dimension, the optical resonance of such nanostructure can be tuned in a wide range from the visible to near infrared. In addition, the highly confined resonant electromagnetic field supported by such a nanostructure can be utilised in surface enhanced Raman spectroscopy. This thesis studied metallic nano aperture arrays for the application of molecular sensing and colour displays. The development of nanofabrication processes for making complex metallic nano apertures was the foundation of this research. Gold was chosen as the appropriate material for sensing mainly due to its stable chemical and physical properties. Aluminium was selected for making colour pixels because its optical resonant frequency can be tuned over the whole visible range. One aspect of this research relating to surface enhanced Raman spectroscopy considered symmetrical gold nano apertures: annular aperture arrays and circular aperture arrays. Comparisons between two annular aperture arrays and between one annular aperture array and one circular aperture array were carried out. The asymmetrical gold nanostructures studied were split-ring shaped aperture arrays. One structure can be used to generate two polarisation dependent resonances in which one of them was able to match the laser in the Raman spectrometer for molecular interrogation and the other was not. The other aspect related to dual-colour pixels. Aluminium cross-shaped aperture arrays were fabricated. By varying the structural dimensions and incident polarisation, colours could be tuned over the whole visible range. Polarisation controlled chromatic displays were demonstrated by employing these pixels