Average SEIRA Enhancements per Substrate

1. Influence of Nanostructure Design on the Structure and Spectroscopic Characterization of Self-Assembled Organic Films Deposited onto Novel Metallic Surfaces Chad L. Leverette, Dept. of Chemistry and Physics and USC NanoCenter, USC Aiken, Aiken, SC 29801 Understanding the organization and structure of nanofilms on planar metallic surfaces is an important area of research that has led to many practical uses of thin film technology. The incorporation and use of novel nanostructures as substrates for these thin film systems represents a new advancement in this technology. However, the organization and structure of organic films on these nanostructures is not known. The primary goals of this project are 1) to fundamentally understand nanofilm organization and structure onto non-planar metallic surfaces and 2) to understand the influence of nanostructure design on the surface-enhanced infrared absorption (SEIRA) enhancement phenomena. SEIRA is used as the molecularly specific instrumental technique that measures the structural properties of the monolayer system. Notable outcomes to date include: 1) glancing angle vapor deposition (GLAD) fabrication of various shaped Ag nanostructured films onto six different infrared substrates, 2) determined and optimized the SEIRA activity of these substrates and obtained data correlating metallic nanoparticle shape to observed SEIRA activity, 3) investigated spectroscopically the nanofilm organization of monolayers of para-nitrobenzoic acid (PNBA) onto these non-planar metallic surfaces. Based on our work, when comparing six different infrared substrates, the best SEIRA active substrate appears to be a 10 nm Ag film deposited at a slow rate of deposition in a stepwise fashion onto a CaF2 substrate. This SEIRA substrate produces signal for the adsorbed monolayer that is 160x greater than the same monolayer unenhanced. The signal produced from this optimized SEIRA substrate is attributed to specific particle shapes and spacing in the Ag film. Spectroscopic comparison of monolayers of para-nitrobenzoic acid (p-NBA) formed onto six different IR windows, each coated simultaneoulsy with a 10 nm SEIRA active Ag film, showed that the monolayer organization is quite different for each substrate. The varying morphologies of the Ag film on each substrate is believed to be responsible for the different surface organization of the PNBA monolayers. Therefore, it appears that monolayer organization is greatly affected by the shape and spacing of the nanoparticles in the non-planar substrate. PNBA Monolayer Organization on Six Different Metallic Substrates Average SEIRA Enhancements per Substrate