Light can be used to excite plasmon resonance in gold nanoparticles. Plasmon resonance occurs on the nanoscale as the particles become excited and plasmon oscillations arise in each particle of a pair of metal nanoparticles. There is plasmon coupling between the neighboring particles as the individual oscillations affect each other due to their close proximity. The coupling of plasmons between nanoparticles is the basis for the development of the nanoplasmonic ruler, which is used to measure nanoscaled molecular distances. In our specific sample, the gold nanoparticles occur in a ‘checkered board’ pattern 150nm by 150nm in size across the quartz substrate. The particles of the array in the sample that was investigated have a radius of between 170 and 180nm and a gap of 40nm – 50 nm between the paired particles. An electric field is enhanced in the area between the particles as plasmon resonance and coupling occur and each particle acts as a pole antenna of a dipole. A fairly new method of microscopy, Near-Field Scanning Optical Microscopy (NSOM), along with far field spectroscopy, is used to investigate and characterize the plasmon resonance and the electric field enhancement that occurs. Electron beam lithography is used to produce samples with a high control over the particle geometry allowing for detailed feedback and device applications.
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