Photoinduced kinetics of SERS in bioinorganic hybrid systems. a case study: dopamine-TiO2.
The reported observation of SERS on semiconductors has confirmed the feasibility of distinguishing the charge-transfer mechanism from the electromagnetic one responsible for the enhancement of the signal in metal nanoparticles. Experimental investigation of the well characterized dopamine-TiO(2) system revealed an unexpected dependence on coverage and size. We propose here a theoretical model applicable to SERS on semiconducting substrates that explains this remarkable behavior. The model is based on a competition mechanism arising from the formation of an electron gas in the conduction band of the semiconductor due to the photoexcitation of a charge-transfer complex. Taking into account the two competing effects, a linear increase in the Raman intensity arising from increasing coverage and a quenching effect due to the photon absorption by the electron gas, provides excellent agreement between our model and the experiment for 5 nm nanoparticles. Discrepancies for the case of 2 nm nanoparticles are attributed to quantum confinement, an effect that is investigated elsewhere.
Finkelstein-Shapiro
Daniel
D
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA. d-finkelstein-shapiro@northwestern.edu
Tarakeshwar
Pilarisetty
P
Rajh
Tijana
T
Mujica
Vladimiro
V
D004298:Dopamine / Q000737:chemistry*; D004579:Electron Transport; D007700:Kinetics; D053758:Nanoparticles / Q000737:chemistry; D010316:Particle Size; D055668:Photochemical Processes; D012666:Semiconductors; D013059:Spectrum Analysis, Raman; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
C009495:titanium dioxide; D014025:Titanium; D004298:Dopamine