Effect of Chemical Nature of the Surface on the Mechanism and Selection Rules of Charge-Transfer Surface-Enhanced Raman Scattering

Abstract

The intrinsic challenge in the elucidation of charge-transfer surface-enhanced Raman scattering (SERS) has inspired the present study. It is believed that changing the surface may serve as illustrative evidence for studying the influence of the chemical nature and electronic structure of the substrate on the resonance and nonresonance chemical mechanism of SERS. With the aim of investigating the important parameters which are effective on the ground- and excited-state properties, in this work we have focused on changing the composition of the substrate. Therefore, 6- and 20-atom pure as well as bimetallic silver and gold clusters have been used as models, and the adsorption of pyridine on these clusters has been studied. It has been found that through the nonresonant chemical mechanism, the Au adsorption site becomes favorable. Therefore, the static chemical enhancement of the Au binding site is more than that of Ag, and it is related to the greater binding energy of gold. To determine the effect of the surface on the resonance chemical mechanism, we have calculated the relative intensity of the pyridine–metal cluster on the charge-transfer (CT) resonance condition. The relative intensities of simulated spectra match well with the available experimental results and suggest that changing the surface, which reveals the trend by applying negative potential on a given surface, could be explained by variation of the effective charge of the cluster. These calculations also show the importance of variation of the excited-state vector gradient and dimensionless displacement for different surfaces and their effects on the selection rules. An illuminating insight about the absolute SERS-CT intensity has been provided that shows the higher average scattering cross sections in the order of 105 for binding through Ag in comparison to 103 for binding through Au. In addition, the enhancement factor for the silver binding site has been obtained as 104 in comparison to that of gold, which is 102. This factor is the intermediate value of 103 for alloys, which confirms the idea that alloying improves the enhancement factor of gold.

Theoretical simulation of surface‐enhanced resonance Raman spectroscopy of cytosine and its tautomers

“…Additionally, the electronic UV spectra of isolated Ag cluster in comparison with the complexes reveal the rather decrease in the intensity and slightly shift of energy for high‐intensity plasmon‐like excitation after complexation. It is also confirmed with our previous study for adsorption of pyridine molecule on the same metal cluster . However, it is apparent that adsorption of the studied molecules (Cyt, T1, T2, and T3,) splits this excitation and decreases the intensity.…”

“…Madzharova et al experimental SERS spectrum of Cyt with citrate‐capped silver nanoparticles (an incident light of 532 nm) was displayed in Figure . In their study and also Freeman et al observation, two strong signals, around 800 and 1,307 cm ‐1 and the lower mode at 1,636 cm ‐1 , were recorded clearly . The experimental SERS spectra of Cyt (in Figure ) collected in the presence of citrate background.…”

Molecular sensitivity of metal nanoparticles decorated graphene‐family nanomaterials as surface‐enhanced Raman scattering (SERS) platforms

“…To gain insights into graphene‐metal interface creating localized hybridization pocket, promoting charge transfer and/or exchange/sharing of electrons between the metal nanoparticles surface adsorbed on graphene and the probe molecule as basic process for chemical SERS enhancement, suggested by an independent parametric study, we performed density functional theory calculations paired with high‐quality adatom basis sets . Figure shows the optimized geometries of Ag and Au, respectively, adsorbed on graphene, GO, and GO* structures at metal/C ~6%.…”

“…Graphene‐decorated with metal nanocrystals are attracting a great deal of attention. For instance, the inclusion of metal (Fe, Gd, and Al), alkali metal (Li, Na, and K), and coinage metal nanoparticles (Cu, Ag, and Au) onto GFNs result in SERS, better electrocatalytic activity, increased sensitivity, and specificity in chemical, electrochemical sensing, and DNA detection . The GFNs are proposed for Raman enhancement, termed as graphene‐mediated surface‐enhanced Raman scattering (G‐SERS) in comparison with other substrates .…”

Nanostructured silver dendrites for photon-induced Cysteine dimerization

“…On the surface of the SERS-active substrate, both the physically adsorbed and chemisorbed molecules exhibit an enhanced Raman signal due to the effect of the additive effect 26 . Generally, chemisorbed molecules show an effect more pronounced than that of physically adsorbed molecules 27 . In other words, chemisorbed molecules show the most significant enhancement effects, namely, the highest intensity electromagnetic mechanism (EM) and chemical mechanism (CM) effects 28 .…”