Surface-enhanced Raman spectroscopy substrate preparation

Possible applications include optical coatings [98], catalysts [99-101], substrates for Surface Enhanced Raman spectroscopy [102] or biosensor electrodes [103], Mesoporous gold can be prepared by de-aHoying a suitable precursor such as a... 

Sampling in surface-enhanced Raman and infrared spectroscopy is intimately linked to the optical enhancement induced by arrays and fractals of hot metal particles, primarily of silver and gold. The key to both techniques is preparation of the metal particles either in a suspension or as architectures on the surface of substrates. We will therefore detail the preparation and self-assembly methods used to obtain films, sols, and arrayed architectures coupled with the methods of adsorbing the species of interest on them to obtain optimal enhancement of the Raman and infrared signatures. Surface-enhanced Raman spectroscopy (SERS) has been more widely used and studied because of the relative ease of the sampling process and the ready availability of lasers in the visible range of the optical spectrum. Surface-enhanced infrared spectroscopy (SEIRA) using attenuated total reflection coupled to Fourier transform infrared spectroscopy, on the other hand, is an attractive alternative to SERS but has yet to be widely applied in analytical chemistry. 

Surface-Enhanced Raman Spectroscopy, Fig. 4 Overview of the broad diversity of SERS substrates (a) aggregates of silver nanoparticles fabricated by means of a modified Lee-Meisel protocol, (b) aggregates of gold nanoparticles, (c) enzymatic generated silver nanoparticles with flowerlike shape, (d) nanosized gold cores coated by a silica shell for an application as SERS label, (e) silver nanotriangle structures prepared by means... 

Mulvaney, S.P., He, L, Natan, M.). and Keating, C.D. (2003) Three-layer substrates for surface-enhanced Raman scattering preparation and preliminary evaluation. Journal of Raman Spectroscopy, 34, 153-71. 

SURFACE ENHANCEMENT BY SAMPLE AND SUBSTRATE PREPARATION TECHNIQUES IN RAMAN AND INFRARED SPECTROSCOPY... 

The observation and understanding of SERS are clearly very important developments in the study of surface chemistry and surface physics. The combination of molecular information and extraordinary sensitivity provides a valuable probe of surface structure and behavior. Out of the broad study of SERS by both chemists and physicists have emerged several approaches to using SERS for chemical analysis. A common analytical situation involves preparation of a SERS active substrate by one of several methods, then exposure of the substrate to a liquid or gaseous sample. Subsequent Raman spectroscopy of the adsorbed layer provides the analytical signal, enhanced by whatever chemical or field enhancement is provided by the adsorbate-substrate interaction. The current and next section are not intended to address SERS substrates comprehensively, but several of analytical interest are described. 

In summary, the utility of micro-SERS spectroscopy for the evaluation of potential-dependent interfacial com-petititve and displacement reactions at chargwl surface has been demonstrated. The data obtained allow the determination of the chemical identity, structure, orientation, competitive and displacement adsorption of cationic surfactants and nitrophenol in the first adsorption layer. The examples of these measurements in the field of surfactants and organic pollutants reviewed in this article were selected to illustrate the sensitivity, molecular specificity of adsorption processes, accuracy, ease of substrate preparation, and manifold applications of Raman analysis. The spatial resolution of the laser microprobe, coupled with the 10 enhancement of the Raman cross-section, means that picogram quantities of material localized to pm-sized surfaces areas can be detected and identified by SERS vibrational spectroscopy. 

The simplest way to prepare a plasmonic nanostructure is thermal and electron beam deposition in vacuum on a flat substrate that is either hydrophilic or hydrophobic. Even though the roughness of the structure depends on the contact angle between the metal and substrate, which is less controllable, the method can be well applied to some metals. DUV plasmonic nanostructures were readily formed by thermal deposition of indium onto a glass substrate. The size of indium nanostructures can be controlled from 15 to 50 nm by the evaporation speed, pressure, and the deposited thickness. The resulting extinction peaks due to the dipole resonance were tuned to between 260 and 600 nm, which were used for surface enhancement of Raman spectroscopy by DUV excitation [7]. Self-assembled arrays of hemispherical gallium nanoparticles were deposited by molecular beam epitaxy on a sapphire support as a substrate for UV plasmonics. The mean NanoParticle radii of 23, 26, and 70 nm were fabricated at LSPR frequencies... 

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