Infrared Absorption Enhancement of Octadecanethiol on Colloidal Silver Particles

Abstract

Infrared absorption measurements at normal incidence of radiation have been carried out on octadecanethiol (ODT) deposited from ethanol-water mixed solutions onto colloidal silver particles (ca. 30 nm diameter) on Si(111) substrates. The infrared absorption spectra taken as functions of silver mass thickness and ODT concentration show that the intensities of the CH 2 asymmetric and symmetric stretch modes of ODT are twice enhanced in comparison to those observed in the absence of the particles. The spectra also reveal that at any ODT concentration the absorption intensities exhibit a maximum for a particular mass thickness of the particles, indicating that the enhancement is linked to the aggregation of the particles. Contribution of the surface plasmon resonance apparently does not play a major role in the present systems. Approximately the same magnitude of enhancement is obtained for silver hydrosol particles exposed to ODT from the solution followed by depositing on the substrates. Scanning electron morphological inspection has been done on the aggregates in relation to the enhancement.

Assessing the Gold Standard: The Complex Vibrational Nonlinear Susceptibility of Metals

“…n , and n are the amplitude, frequency, and width of each of the n ODT resonant modes. Eight vibrational modes 38,39 were included in fits of the model given in eq 2 to the data. The major peaks at 2877 and 2937 cm 1 result from the symmetric stretch of the terminal methyl group on ODT.…”

In situ UV–visible and IR absorption study of the aggregation of silver colloidal particles via chemisorption of octadecanethiol

“…In addition, the particular marked decrease in intensity of the plasma band must be ascribed to ethanol: some evidence shows that addition of ethanol alone to the hydrosol causes severe aggregation (agglomeration), engendering complete precipitation. 31 Quite different features were observed after addition of ethanol containing 1.00 mM ODT to the silver hydrosol. The UV-visible spectra taken as a function of elapsed time are shown in Fig.…”

“…The original hydrosol (without ODT and ethanol) exhibits a relatively narrow band peaking at 395 nm because of the plasma resonance of the spherical silver particles with radii of ¾ 15 nm, as judged by our scanning electron microscope inspection. 31 This band broadens and shifts to 424 nm after 10 min of admixture. A more intense broadening and a small red-shift occur after 1440 min.…”

“…Infrared absorption measurements of ODT were performed after depositing ODT-dosed silver hydrosols onto Si(111) substrates. The results revealed that the magnitude of absorption enhancement depends upon the aggregation state of the particles on the substrate surface 31 and yielded in situ information regarding surface modification and its influence upon colloidal aggregation. Consequently, the present study performs UV-visible transmission and infrared attenuated total reflection (ATR) measurements for the silver hydrosol as a function of time elapsed since ODT-dissolved ethanol was dosed to the hydrosol.…”

“…8,29 -31 In our recent study of spherical silver colloidal particles, 31 the plasma resonance band of the particles was observed as a function of the concentration of octadecanethiol (CH 3 CH 2 17 SH; ODT) that had been added to the hydrosol. The band features, frequency and width were dependent upon the ODT concentration.…”