SERS Not To Be Taken for Granted in the Presence of Oxygen

Department of Chemistry, Chemical Biology and Biomedical Engineering, Stevens Institute of Technology, Castle Point on Hudson, Hoboken, New Jersey 07030, USA.
Journal of the American Chemical Society (Impact Factor: 12.11). 06/2009; 131(22):7480-7481. DOI: 10.1021/ja807458x


Oxidation of the Ag nanoparticle surface has a dramatic effect on the adsorption, orientation, and SERS detection limit of nitroaromatic molecules in aqueous solutions. Ultrasensitive SERS detection of p-nitrophenol can be achieved when oxidation of surface-immobilized Ag nanoparticles is inhibited by replacing the oxygen dissolved in water with argon gas. The presence of silver oxide at the nanoparticle surface hinders charge transfer between the aromatic ring and the underlying Ag metal surface and drastically decreases the overall detection sensitivity.

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    • "We suggest instead that an insulating interfacial layer with properties unlike those of either IO:H or silver is formed during annealing. This layer may, for example, be composed of silver oxide (Ag 2 O) which has been observed to form on the surface of silver nanoparticles in oxygen and water environments [22] [23] [24] "
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    ABSTRACT: The front transparent conductive oxide layer is a source of significant optical and electrical losses in silicon heterojunction solar cells because of the trade-off between free-carrier absorption and sheet resistance. We demonstrate that hydrogen-doped indium oxide (IO:H), which has an electron mobility of over 100 cm2/V s, reduces these losses compared to traditional, low-mobility transparent conductive oxides, but suffers from high contact resistance at the interface of the IO:H layer and the silver front electrode grid. This problem is avoided by inserting a thin indium tin oxide (ITO) layer at the IO:H/silver interface. Such IO:H/ITO bilayers have low contact resistance, sheet resistance, and free-carrier absorption, and outperform IO:H-only or ITO-only layers in solar cells. We report a certified efficiency of 22.1% for a 4-cm2 screen-printed silicon heterojunction solar cell employing an IO:H/ITO bilayer as the front transparent conductive oxide.
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    • "In contrast to these methods, x-ray photoelectron spectroscopy (XPS) is capable of showing the chemical state of detected elements, and is thus better suited to determine the origin of tarnishing of AgNPs. In a recent study [12], XPS was used to show the oxidation of colloidal AgNPs in air and its deleterious effect on surface enhanced Raman spectroscopy (SERS) [17]. Another recent work combined XPS with x-ray absorption fine structure spectroscopy providing detailed information on the local atomic structure and chemical nature of silver nanoparticles functionalized with the organic thiols [18]. "
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    ABSTRACT: We investigate the optical and morphological effects of silver island films exposed to atmosphere. Silver nanoparticles with an average radius below 5 nm were highly tarnished after one week, showing significant morphological changes. Using x-ray photoelectron spectroscopy we demonstrate that the tarnishing is predominantly caused by oxidation and not sulfidation for exposed silver nanostructures under normal conditions. Post-deposition annealing of tarnished nanoparticle films results in further morphological changes which are highly dependent on the exposure time and nominal film thickness. Our results suggest that the size and density of the nanoparticles can be pre-designed by controlling the deposition thickness, tarnishing and annealing. The processing causes a red-shift in the localized surface plasmon resonance due to reduced particle interactions.
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