Interfacial Charge-Transfer Effects in Semiconductor–Molecule–Metal Structures: Influence of Contact Variation

Abstract

The charge-transfer resonance of Raman measurements in nanosized semiconductor−molecule−metal interfaces as a function of the excitation energy with four models (Cu−ZnO− PATP−Ag, Cu−Ag−PATP−ZnO, Cu−ZnO−Ag−PATP, and Cu− Ag−ZnO−PATP assemblies) to describe this dependence provides a powerful tool to study the chemical mechanism of surface enhanced Raman scattering (SERS).We measured the SERS spectra of self-assembled p-aminothiophenol (PATP) molecule junctions at 488, 514, 633, and 785 nm excitation wavelengths. We followed changes at the molecule junctions during the conditioning and eventually effect of charge-transfer (CT) through molecule−ZnO interfaces. Our results demonstrate that the interaction between the semiconductor bands and molecular energy levels can lead to novel charge behavior. The typical ZnO-PATP interfacial electron−hole recombination causes an increase in the CT resonance enhancement of Raman scattering, which is mainly responsible for the drastic change in molecular polarizability. We also proposed a complementary interpretation of the mechanism responsible for the highly variable enhancement observed in SERS.

Surface-enhanced Raman scattering of amorphous TiO2 thin films by gold nanostructures: Revealing first layer effect with thickness variation

“…Most of the enhancement comes from the layer closest to the gold surface, which is clearly the signature of an interfacial effect consistent with charge transfer contributions. 27 As the Klarite substrate is designed to supply surface plasmon resonance in its active area and because SERS of TiO 2 only occurs in this area, the SERS process is mainly due to SPR-induced charge transfer mechanisms. Considering now the electromagnetic contribution to the enhancement, SPR increases the local electric field intensity through an evanescent wave, the amplitude of which decreases exponentially with distance from the interface.…”

Semiconductor materials in analytical applications of surface‐enhanced Raman scattering

“…The measurements were carried out by monitoring the spectral changes in PATP upon adjusting the relative orientation of PATP in the ZnO/PATP/Ag sandwich structure. Furthermore, multiple contacts have also been constructed by coupling the ZnO/PATP/Ag sandwich structure with different metal substrates . Lombardi et al .…”

“…However, these advances remain short of increasing demand for sensing applications. Semiconductor materials inject new vitality into traditional SERS and may lead to promising functions based on their unique optical, chemical, electrical, and catalytic properties …”

Ag-Nanoparticle-Decorated Ge Nanocap Arrays Protruding from Porous Anodic Aluminum Oxide as Sensitive and Reproducible Surface-Enhanced Raman Scattering Substrates

“…The latter originates from the charge transfer between the analyte and the conducting sublayer, usually a semiconductor. 11,12 Thus, hybrid substrates consisting of semiconductors and noble metals are beneficial to high SERS sensitivity for rapid trace analysis. To date, various semiconductors (Si, 13 ZnO, 14,15 ZnS, 16 TiO 2 , 17 and Cu 2 O 18 ) and noble metals (Au and Ag) have been chosen to build hybrid substrates with higher SERS activity.…”