Near-Infrared Surface-Enhanced Raman Scattering of Ultrathin Films of C_nAzoNaph(1,4)C_mN⁺Br^- (n = 7, 10, 12; m = 4, 6)

Abstract

Near-infrared (NIR) Fourier transform (FT) Raman spectra have been measured for a series of 4-[4‘-[[(4‘ ‘-alkyloxy)phenyl]azo]naphthyloxy] alkyltrimethylammonium compounds [C n AzoNaph(1,4)C m N+Br-] in a solid state, in a cast film on a CaF2 plate, and in dipping films on etching silver foils and for one- and three-layer Langmuir−Blodgett (LB) films of C10AzoNaph(1,4)C4N+−sodium dextran sulfate (SDS) on a CaF2 plate and etching silver foils. The one-monolayer LB film on the silver foil shows much more intense Raman signals than the 75-layer film on the CaF2 plate, showing a great surface-enhanced Raman scattering (SERS) effect for the LB film on the silver foil. Since SDS plays a role as a spacer, C10AzoNaph(1,4)C4N+ is not directly adsorbed on the silver surface. Therefore, the strong SERS effect for the LB films of C10AzoNaph(1,4)C4N+−SDS may be explained by an electromagnetic mechanism. The one-monolayer dipping film of C10AzoNaph(1,4)C4N+Br- on the silver foil shows about 10 times stronger Raman signals than the one-monolayer LB film and the spectral intensity pattern is quite different between the dipping and LB films. It is very likely that the direct adsorption of C10AzoNaph(1,4)C4N+Br- on the silver foil gives a much stronger SERS effect for the dipping film. The different intensity pattern between the two kinds of films may be due to the differences in the molecular orientation and/or aggregation in the films. The dipping film of C7AzoNaph(1,4)C4N+Br- yields a much smaller SERS enhancement factor. The alkyl tail is too short to have well-organized molecular aggregation and/or orientation in the film, and the enhancement factor may be sensitive to the molecular aggregation and/or orientation in the film.

Silver‐bacterial cellulosic sponges as active SERS substrates

“…These two compounds were first chosen because they show a strong Raman enhancement effect using conventional Ag colloids. 6,19 Also the adsorption modes of these ligands to the silver surface are different, which allow us to compare the cellulosic nanocomposites as SERS substrates for ligands with distinct chemisorption behavior. Additionally, Ag colloids were also used for comparative purposes.…”

“…Several solid SERS substrates have been proposed, such as acid-etching silver foil, 6 metal islands on films formed through thermal evaporation 7 and laser-ablated silver plates, 8 just to enounce some examples. However, these procedures imply relatively complicated experimental conditions, which make the practice of SERS difficult.…”

Simple method for electrochemical preparation of silver dendrites used as active and stable SERS substrate

“…Currently, there are many kinds of SERS-active substrates used in the wide range of SERS applications. Some examples are electrochemically roughened metal electrodes [8][9][10][11][12], negatively or positively charged silver colloidal solutions [13][14][15], acid etching silver foil [16], metal island films formed through thermal evaporation [17,18], and laser-ablated silver plate [19,20]. The versatility of SERS techniques is underlined by the variety of methods using different types of substrates satisfying the requirements of a particular application.…”

Experimental (SERS) and theoretical (DFT) studies on the adsorption of p-, m-, and o-nitroaniline on gold nanoparticles

“…One of the most important factors that could affect the molecules' adsorption behavior is the surfaces characteristic of the SERS-active substrates. Because of differences in the adsorption configuration the SERS spectra would have more or less differences for the same molecules adsorbed on different substrates [8][9][10][11][12][13][14][15]. Another important factor that could affect the molecules' adsorption behavior is the surface configuration of the molecules themselves.…”