Linker-Molecule-Free Gold Nanorod Films: Effect of Nanorod Size on Surface Enhanced Raman Scattering

A methodology for synthesizing different sized gold nanorods and ordering them into a two-dimensional array at a water/hexane interface without a linker-molecule is reported. The resulting nanorod film was transferred to a solid substrate repeatedly, allowing for systematic control of the nanorod film thickness. An investigation into the thickness-dependent surface enhanced Raman scattering (SERS) of adsorbed molecules revealed different SERS enhancement as a function of the size of gold nanorods under similar experimental conditions. The SERS enhancement factor per layer of each nanorod size was obtained from a plot of the peak intensity versus the number of layers. The comparison of such values enables a systematic evaluation of the SERS enhancement of the resulting nanorod films. Theoretical consideration by discrete dipole approximation calculation and finite different time domain method was also performed and the local surface plasmon coupling was believed to induce such differences in the SERS enhancement.