Optical Characterization of Electronic-Transitions Arising from the Au/S Interface of Self-Assembled N-Alkanethiolate Monolayers


J. Shi, B. Hong, A. N. Parikh, R. W. Collins, D. L. Allara, Chemical Physics Letters 246, 90 (1995)

Analyses of optical frequency ellipsometric spectra obtained in situ upon completion of the self-assembly of n-alkanethiolate monolayers on gold substrates immersed in methanol reveal the presence of a thick S/Au interface layer. This layer exhibits unique optical transitions, modeled as two Lorentzian oscillators with imaginary parts peaked at ≈ 570 nm (≈ 2.2 eV) and ≈ 290 nm (≈ 4.3 eV), indicating a perturbation of the near-surface gold electronic structure upon thiol chemisorption. A further, more rigorous, spectral analysis involving an anisotropic, uniaxially oriented chain assembly reveals the presence of significant microscopic void defects in the otherwise densely packed monolayers.

DOI: 10.1016/0009-2614(95)01085-N