Water Droplet Self-Assembly to Au Nanoporous Films with Special Light Trapping and Surface Electromagnetic Field Enhancement.

Gold nano "breath figure" films are for the first time reported and their function as ideal systems for plasmonics demonstrated. Metal nano-breath figure substrates are metal thin films containing nanohole arrays supported on a solid substrate. Au nanohole arrays are prepared from the dynamic breath figure phenomenon, in which the pore formation is controlled to provide holes smaller than 100 nm. Au layer is deposited on polymer substrates containing breath figure topology. The breath figure topology can be fully translated to the Au layer. The nanofabrication process is completed within few minutes. A simplified preparation process but very impressive light trapping and surface electromagnetic field enhancement are related to the Au breath figure films obtained in this work. The porous films demonstrated higher absorbance in the region of 500-1100 nm than nonporous Au films. In the case of 10 nm Au film, the plasmon absorbance becomes more intense than the electronic band absorbance. The electromagnetic enhancement is proved by surface enhanced Raman spectroscopy effect, which is found to be very close to the maximum possible value predicted for nonresonant species.