In situ surface-enhanced Raman scattering shows ligand-enhanced hot electron harvesting on silver, gold, and copper nanoparticles

Abstract

Hot carriers (electrons and holes) generated from the decay of localized surface plasmon resonances can take a major role in catalytic reactions on metal nanoparticles. By obtaining surface enhanced Raman scattering (SERS) spectra of p-aminothiophenol as product of the reduction of p-nitrothiophenol by hot electrons, different catalytic activity is revealed here for nanoparticles of silver, gold, and copper. As a main finding, a series of different ligands, comprising halide and non-halide species, are found to enhance product formation in the reduction reaction on nanoparticles of all three metals. A comparison with the standard electrode potentials of the metals with and without the ligands and SERS data obtained at different electrode potential indicate that the higher catalytic activity can be associated with a higher Fermi level, thereby resulting in an improved efficiency of hot carrier generation. The concept of such a ligandenhanced hot electron reduction provides a way to make light-to-chemical energy conversion more efficient due to improved electron harvesting.

Surface Molecular Patterning by Plasmon-Catalyzed Reactions

“…The data in Figure b demonstrate the possibility to introduce positions that are selectively functionalized by an amino group before a background of nitro groups using the six-electron reduction of PNTP to PATP that is induced at an acidic pH by hot electrons as well. Our recent work has indicated that Cl – as a ligand, introduced here as well, can greatly accelerate this reduction on gold nanoparticles . Here, the intensity ratio I 1595 / I 1346 of the band at 1595 cm –1 ( I 1595 ) of PATP and I 1346 , of the band at 1346 cm –1 , present in the SERS spectra of PNTP, was used to map the relative amount of PATP that is formed in the hot-electron reduction.…”

“…The possibility to exploit localized surface plasmons as drivers of very different types of reactions enables modifications of other molecules in a SAM as well. Figure a shows the possibility to generate a DMAB pattern from PNTP in a reaction mechanism that involves a four-electron reduction, which is equipped by hot electrons generated upon the decay of the localized surface plasmon of the gold nanoparticles . The characteristic bands in the SERS spectra collected from the illuminated spot clearly indicate the formation of DMAB (Figure a).…”

“…As seen in the SERS map of Figure a and the corresponding line profile (Figure S2a), the pattern also shows a gradient of the DMAB signal strength from the center to the edge of the spots, in agreement with the profile of DMAB spots formed from PATP (Figure g). As was shown previously when this reaction was reported to occur on gold nanoparticles and studied in detail, the efficiency of the generation of hot carriers can be improved significantly in the presence of halide ions and other ligands so that fabrication of the DMAB pattern could also be achieved at a lower intensity than the one chosen here. Nevertheless, the reaction was not found to occur at the laser intensity of 5 kW/cm 2 used for SERS readout here.…”

“…The possibility to utilize hot carriers that are generated in a plasmonic excitation for both oxidation and reduction reactions of adsorbed organic species has been discussed in varying contexts, including a better understanding of the reaction mechanism and the role of the hot carriers. ,,,,− The plasmon-catalyzed oxidation of PATP to form DMAB on immobilized gold nanoparticles depends on specific excitation conditions, , specifically with respect to excitation intensity, providing control of separate writing and readout process here.…”

“…As will be shown using the well-characterized plasmon-catalyzed oxidation of p -aminothiophenol (PATP) to 4,4′-dimercaptoazobenzene (DMAB), − as well as two hot-electron-based reduction reactions, the four-electron reduction of p -nitrothiophenol (PNTP) to DMAB at neutral pH, − and the six-electron reduction of PNTP to PATP at an acidic pH, , microscopic patterns with different structures and functionalities can be fabricated in a conventional microscope. The information encoded by the structures can be directly read out by Raman imaging, suggesting utilization for information storage in SERS-based security labels.…”