Morphological and Near-Field Properties of Silver Columnar Thin Film for Surface-Enhanced Raman Scattering.

Noble metal sculptured thin films have attracted great research interest last decade as competitive surface-enhanced Raman scattering (SERS) substrates. However, the influences of the deposition conditions and the morphology on the plasmonic properties and SERS performance of the metal sculptured thin films have not been well understood due to the complexities of the morphology. In this work, the influences of the deposition angle and the height are investigated in both experiment and numerical simulation. A more accurate geometrical model based on the binarized scanning electron microscope images has been utilized to study the near-field plasmonic properties of Ag column thin films by taking account of the geometry irregularities, size distributions and random arrangement of the columns. It's found that the cross-sectional electric field enhancement is mainly dominated by the column density. When the deposition angle increases from 68 degrees to 82 degrees the SERS enhancement factors increases monotonously due to the increase of the self-shadow effect. While with the increase of height the SERS enhancement factors firstly increase to the largest value of 3.05x108 at the thickness of 694 nm then decrease because of competitive growth mechanism during the deposition. The detection limit of the optimized sample is found to be lower than 10(-1)2 M. Our work could be helpful in understanding the SERS mechanism and useful to the optimization of metal sculptured thin films as SERS substrates.