SERS chemical enhancement of 2,4,5-trichlorophenoxyacetic acid absorbed on Au₂₀, its Au-Ag and Au-Cu bimetallic clusters: A DFT study

Abstract

The surface-enhanced Raman scattering (SERS) phenomenon of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) adsorbed on Au₂₀ pyramidal cluster is studied by Density Functional Theory. All possible adsorption configurations between the adsorbate and the Au₂₀ clusters are evaluated and the vibrational assignments of normal Raman and SERS spectra are analyzed. The result shows that the most stable adsorption configuration of the adsorbate on Au₂₀ cluster is formed by the interaction of O13 (-COOH group) and Au atom. The SERS activities of 2,4,5-T adsorbed on 1:1 Au-Ag and Au-Cu bimetallic clusters are also investigated. For bimetallic clusters, the substitution of 1, 4 or 10 Au atoms by Ag/Cu is performed by replacing the respective number of Ag/Cu atoms in 1, 2 and 3 parallel layers of the Au₂₀ cluster. While the Raman scattering activity of the Au₁₀Ag₁₀ cluster is comparable to that of the Au20 cluster, it is remarkably higher than the Au₁₀Ag₁₀ cluster. This observation is explained by the molecule-to-cluster charge transfer process. The obtained results are hoped to contribute to better design of SERS-based analytical sensors for mobile and on-site applications.