Conductive oxide thin films: Model systems for understanding and controlling surface plasmon resonance Attenuated-total-reflection predictions to surface-plasmon resonance in a layered structure J. Appl. Phys. 98, 053708 (2005); 10.1063/1.1991977 High resolution surface plasmon resonance spectroscopy Rev. Sci. Instrum. 70, 4656 (1999); 10.1063/1.1150128Detection of surface-plasmon evanescent fields using a metallic probe tip covered with fluorescence Rev.

Surface plasmon resonance (SPR) measurements provide a highly sensitive means for detecting biomolecular interactions in a label-free manner. Numerous studies of biomolecular interactions have been performed with fixed-angle SPR imaging (SPRi) on surfaces patterned with a variety of biomolecules such as DNA, RNA, proteins, and peptides. 1 Arrays increase the information obtainable in a single experiment as multiple reactions can be monitored in parallel.A current and significant limitation of SPR is that the substrate must be a metal thin film. A number of metal thin films are capable of supporting surface plasmons in the near-infrared and visible regions of the electromagnetic spectrum. 2,3 Gold surfaces have been the substrate of choice for SPR measurements for two reasons: gold is relatively stable in the aqueous environments needed for monitoring biomolecular interactions and a versatile chemistry based on the attachment of sulfur-containing ligands to the gold surface has been developed and wellcharacterized. The readily formed gold-sulfur bond enables the direct attachment of ligands to the gold surface 4 as well as attachment via an intermediate self-assembled monolayer (SAM). 5-7 This gold-thiol chemistry has made possible the routine analysis of aqueous binding processes to immobilized molecules at near-neutral pH values and moderate temperatures. The susceptibility of the gold-sulfur bond to oxidation and photodecomposition has prevented SPR sensing from finding utility in areas such as on-surface combinatorial chemistry (due to the harsh chemical conditions employed) and photolithography (due to the adverse effects of ultraviolet radiation on the gold-sulfur bond). 8Here we describe the development of a lamellar structure in which a thin layer of amorphous carbon is deposited onto a surface plasmon-active gold thin film (Figure 1a). Carbon-based surfaces are readily modified with biomolecules of interest using a well-developed and robust chemistry, based upon the attachment of alkene-containing molecules to the substrate through the UV light-mediated formation of carbon-carbon bonds. 9 Recently, a similar lamellar structure utilizing a thin silicate overlayer was used to fabricate and monitor supported bilayer membranes with SPR. 10 E-mail: smith@chem.wisc.edu. Arrays prepared on functionalized carbon-based substrates such as diamond thin films, 11,12 glassy carbon, 12 and amorphous carbon thin films 13 have superior stability to analogous arrays prepared on functionalized glass, silicon, and gold substrates. Amorphous carbon is of particular interest as it can be deposited at room temperature, allowing it to be integrated with other materials 14 such as quartz crystal microbalances, 13 electrodes, 15 and metal thin films without perturbing their structure. The utility of a multilayered substrate containing a metal thin film and an amorphous carbon overlayer is shown here by their use for in situ synthesis of oligonucleotide arrays, which are then employed in the analysis of biomolecule binding proces...

The sections in this article are Introduction to Polarization‐Modulation Reflection–Absorption Spectroscopy Experimental Considerations for the PM ‐ IRRAS Measurement Experimental Setup The PEM The PM ‐ IRRAS Measurement PM ‐ IRRAS Spectral Normalization Examples and Applications of PM ‐ IRRAS Measurement Metal Surfaces – Ex Situ Self‐Assembled Monolayers in the CH Stretching Region SAMs in the Fingerprint Region Metal Surfaces – Liquid Phase In Situ Structural Studies of SAMs Electrochemical Studies Metal Surfaces – Gas Phase In Situ Corrosion Studies on Copper Carbon Monoxide on Co (0001) Organic Vapors on Silicon Dioxide Nanoparticle Thin Films on Gold Air/Water Interface Summary

The gold-sulfur (Au-S) and silver-sulfur (Ag-S) bonds are integral to the surface modification of metal films with alkanethiol monolayers. Although the metal-sulfur bond can be characterized with surface-enhanced Raman spectroscopy (SERS) at roughened metal films, some applications require or perform better when using a smooth metal surface, which is not suitable for SERS signal enhancement. Directional-surface-plasmon-coupled Raman scattering (directional Raman scattering) is an approach to measure metal-sulfur bonds on smooth metal films with sub-monolayer sensitivity. The metal-sulfur bonds formed from a benzenethiol monolayer on smooth planar gold or silver films are observed in the directional Raman scattering spectra between 240 and 270 cm À1 ; the signal-to-noise ratio of the Au-S Raman peak is 60. Importantly, the directional Raman scattering signal measured with smooth metal surfaces can be simply modeled and easily compared across many samples. Directional Raman scattering can also be measured at roughened metal films, which makes it applicable for many analyses.

We report the development of a polarization-division interferometer (PDI) for the mid-infrared region. This interferometer uses a self-designed beamsplitter constructed in-house from a BaF2 polarizer and a matching substrate. In conjunction with a linear polarizer in front of the source and two roof-top mirrors, one in each arm of the interferometer, the PDI divides the input beam into two orthogonal linear polarization components, recombines them for interference at the beamsplitter, and directs the output beam at 90° to the direction of the input beam. Light exiting the interferometer is manipulated entirely with lenses, to avoid polarization distortions that are inherent to the reflecting surfaces of the mirrors. Details of the instrumental design for this mid-infrared PDI are presented. The performance of the PDI is evaluated by measuring the circular dichroism of α-pinene and camphor and the linear dichroism of oriented polypropylene and polystyrene. These measurements establish the utility of the PDI to measure transmission, circular dichroism, and linear dichroism spectra simultaneously without need for any additional components. The dichroic multiplex advantage (ability to measure dichroism in the entire mid-infrared region from a single measurement) and throughput advantage are demonstrated.

No abstract

Directional-surface-plasmon-coupled Raman scattering (directional RS) has the combined benefits of surface plasmon resonance and Raman spectroscopy, and provides the ability to measure adsorption and monolayer-sensitive chemical information. Directional RS is performed by optically coupling a 50 nm gold film to a Weierstrass prism in the Kretschmann configuration and scanning the angle of the incident laser under total internal reflection. The collected parameters on the prism side of the interface include a full surface-plasmon-polariton cone and the full Raman signal radiating from the cone as a function of incident angle. An instrument for performing directional RS and a quantitative study of the instrumental parameters are herein reported. To test the sensitivity and quantify the instrument parameters, self-assembled monolayers and 10 to 100 nm polymer films are studied. The signals are found to be well-modeled by two calculated angle-dependent parameters: three-dimensional finite-difference time-domain calculations of the electric field generated in the sample layer and projected to the far-field, and Fresnel calculations of the reflected light intensity. This is the first report of the quantitative study of the full surface-plasmon-polariton cone intensity, cone diameter, and directional Raman signal as a function of incident angle. We propose that directional RS is a viable alternative to surface plasmon resonance when added chemical information is beneficial.

A new methodology for the real-time in situ monitoring of atmospheric corrosion processes is presented. The mid-infrared spectra of surface films formed on polished copper substrates exposed to humid air containing sub-ppm levels of sulfur dioxide, nitric oxide, and hydrogen chloride were obtained by using a novel surface-sensitive infrared technique: real-time polarization modulation grazing angle reflection-absorption spectroscopy. The new methodology demonstrated improved signal-to-noise ratios, by a factor of 2.5, as compared to conventional Fourier transform infrared reflection absorption spectroscopy. Molecular spectroscopic data for water- and hydroxyl-containing species present at the metal surface were obtained with no interference from water vapor. Over the spectral region 4000–800 cm−1, bands were identified and assigned to nitro and nitrito adsorbates, to sulfite ions, and to bound water on the copper surface. Analysis of the time evolution and the profile composition of these bands is possible because of the sensitivity of this new optical sampling technique.