Preferentially aligned silver nanorod arrays prepared by oblique angle vapor deposition were evaluated as substrates for surface-enhanced infrared absorption (SEIRA) spectroscopy. These nanorod arrays have an irregular surface lattice and are composed of tilted, cylindrically shaped nanorods that have an average length of 868 nm +/- 95 nm and an average diameter of 99 nm +/- 29 nm. The overall enhancement factor for chemisorbed organic films of para-nitrobenzoic acid (PNBA) deposited onto the Ag nanorod arrays analyzed by external reflection SEIRA was calculated to be 31 +/- 9 compared to infrared reflection-absorption spectroscopy (IRRAS) obtained from a 500 nm Ag film substrate. This enhancement is attributed to the unique optical properties of the nanorod arrays as well as the increased surface area provided by the nanorod substrate. SEIRA reflection-absorbance intensity was observed with both p- and s-polarized incident radiation with angles of incidence ranging from 25 degrees to 80 degrees . The largest intensity was achieved with p-polarization and incident angles larger than 75 degrees . Polarization-dependent ultraviolet/visible/near-infrared (UV/Vis/NIR) spectra of the nanorod arrays demonstrate that the red-shifted surface plasmon peaks of the elongated nanorods may be partially responsible for the observed SEIRA response. The SEIRA detection limit for the Ag nanorod arrays was estimated to be 0.08 ng/cm(2). Surface-enhanced Raman scattering (SERS) and SEIRA analysis of chemisorbed PNBA utilizing the same nanorod substrate is demonstrated.

A dual-layer, thick (∼70 nm) vapor-deposited Ag substrate has been developed that gives enhancement factors on the order of 104 for surface-enhanced Raman scattering (SERS) experiments. This substrate has a total thickness of ∼70 nm but also has an outermost surface morphology that approximates that of a thin Ag island film (AgIF) substrate. This is accomplished using a dual overlayer/underlayer structure in which a thick underlayer of 45-nm Ag is vapor-deposited onto a treated glass slide. This Ag underlayer is exposed to ambient conditions under which the surface chemisorbs oxygen, leading to the thermodynamically favorable formation of an active Ag2O interface. An overlayer of 25-nm Ag is vapor-deposited on top of this structure. The first Ag/Ag2O underlayer produces an active interface that decreases the diffusion of the Ag atoms from the second vapor-deposited overlayer, thereby forming Ag particles with shapes favorable for SERS enhancement. Atomic force microscopy results show that the Ag overlayer particles have ideal shapes for SERS enhancement with morphology comparable to thin, vapor-deposited AgIFs. X-ray photoelectron spectroscopy in the O(1s) region showed the presence of multiple forms of oxygen in the Ag/Ag2O underlayer; the main forms were identified as dissolved bulk oxygen and chemisorbed oxygen. Using self-assembled monolayers (SAMs) of 1-dodecanethiol, a SERS intensity increase of ∼400% was obtained for this new overlayer/underlayer Ag substrate when compared to SAMs formed on traditional thick Ag substrates. Enhancement factors calculated from the Raman intensity of trans-1,2-bis(4-pyridyl)ethane showed a SERS enhancement of approximately 104 for this new Ag/Ag2O/Ag substrate compared with the bulk. This compares favorably with the SERS enhancements obtained using thin AgIF substrates. The Ag/Ag2O/Ag substrates showed reproducible SERS intensities (RSD = 0.45−5%). The mechanisms responsible for the overall enhancement on this new substrate are proposed to be the ideal surface morphology of the Ag overlayer particles as well as a combined enhanced electromagnetic field produced by both the Ag/Ag2O underlayer and the Ag overlayer.

Soil contaminated with U was the focus of this study in order to develop in-situ, U bio-immobilization technology. We have demonstrated microbial production of a metal chelating biopolymer, pyomelanin, in U contaminated soil from the Tims Branch area of the Department of Energy (DOE) Savannah River Site (SRS) as a result of tyrosine amendments. Bacterial densities of pyomelanin producers were >106 cells/g wet soil.Pyomelanin demonstrated U chelating and mineral binding capacities at pH 4 and 7. In laboratory studies, in the presence of goethite or illite, pyomelanin enhanced U sequestration by these minerals. Tyrosine amended soils in field tests demonstrated increased U sequestration capacity following pyomelanin production up to 13 months after tyrosine treatments.

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