Adsorption of 4-Biphenylmethanethiolate on Different-Sized Gold Nanoparticle Surfaces

Adsorption of 4-biphenylmethanethiolate (BPMT) has been studied for different-sized gold nanoparticles, with mean diameters of 6, 11, 15, 27, 35, 43, and 97 nm, using surface-enhanced Raman scattering (SERS). Transmission electron microscopy (TEM) images and UV−visible absorption spectra were obtained to examine the monodispersity and BPMT derivatization of the gold nanoparticle samples. Changes in the UV−vis spectra indicated that BPMT-derivatized gold particles appeared to aggregate more extensively with increasing mean diameter. The SERS enhancement was found to be weak in diameter ranges smaller than 11 nm. BPMT was assumed to adsorb on gold, with a standing geometry on the surface, from the presence of the ν 2 mode at ∼3065 cm - 1 in the SERS spectra of 35-, 43-, and 97-nm particles. The disappearance of the ν as (CH 2 ) band in the SERS spectra of all the gold particle samples denoted a preference of sp 3 hybridization for the sulfur atom in BPMT on gold particle surfaces. The TEM images showed that monodisperse 15-nm gold nanoparticles derivatized with BPMT could be arranged in a two-dimensional close-packed array. The results of simulated annealing molecular dynamics simulations showed that the close-packed structures of BPMT on a Au(111) surface exhibit ordered herringbone arrangements with almost vertical orientations.