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First Principles Calculations Toward Understanding SERS of 2,2′‐Bipyridyl Adsorbed on Au, Ag, and Au–Ag Nanoalloy
Author(s) -
Takenaka Masato,
Hashimoto Yoshikazu,
Iwasa Takeshi,
Taketsugu Tetsuya,
Seniutinas Gediminas,
Balčytis Armandas,
Juodkazis Saulius,
Nishijima Yoshiaki
Publication year - 2019
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.25603
Subject(s) - adsorption , raman spectroscopy , alloy , binding energy , materials science , spectral line , dispersion (optics) , chemical physics , molecule , molecular dynamics , cluster (spacecraft) , chemistry , computational chemistry , atomic physics , optics , composite material , physics , astronomy , computer science , programming language , organic chemistry
First principles electrodyanmics and quantum chemical simulations are performed to gain insights into the underlying mechanisms of the surface enhanced Raman spectra of 22BPY adsorbed on pure Au and Ag as well as on Au–Ag alloy nanodiscs. Experimental SERS spectra from Au and Ag nanodiscs show similar peaks, whereas those from Au–Ag alloy reveal new spectral features. The physical enhancement factors due to surface nano‐texture were considered by numerical FDTD simulations of light intensity distribution for the nano‐textured Au, Ag, and Au–Ag alloy and compared with experimental results. For the chemical insights of the enhancement, the DFT calculations with the dispersion interaction were performed using Au 20 , Ag 20 , and Au 10 Ag 10 clusters of a pyramidal structure for SERS modeling. Binding of 22BPY to the clusters was simulated by considering possible arrangements of vertex and planar physical as well as chemical adsorption models. The DFT results indicate that 22BPY prefers a coplanar adsorption on a (111) face with trans‐conformation having close energy difference to cis‐conformation. Binding to pure Au cluster is stronger than to pure Ag or Au–Ag alloy clusters and adsorption onto the alloy surface can deform the surface. The computed Raman spectra are compared with experimental data and assignments for pure Au and Ag models are well matching, indicating the need of dispersion interaction to reproduce strong Raman signal at around 800 cm –1 . This work provides insight into 3D character of SERS on nanorough surfaces due to different binding energies and bond length of nanoalloys. © 2018 Wiley Periodicals, Inc.