Browsing by Author "Yu, Ziwei"

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    Data for Wavelength Dependence of Plasmon-Induced Vibrational Energy Transfer in Fluorophore–Plasmonic Systems
    (2024-08-01) Christenson, Gerrit N; Yu, Ziwei; Frontiera, Renee R; rrf@umn.edu; Frontiera, Renee R; Materials Research Science & Engineering Center
    Understanding, predicting, and controlling plasmon–molecule energy transfer are important for improvements to plasmonic photocatalysis and photothermal therapies. Here, we use continuous wave surface-enhanced anti-Stokes and Stokes Raman spectroscopy to quantify the vibrational kinetic energy, equivalent to a molecular temperature under a Boltzmann approximation, of Raman-active vibrational modes of molecules at plasmonic interfaces. In previous work from our group, we observed an anomalous steady-state reduction in vibrational kinetic energies in benzenethiols absorbed onto the surface of gold nanoparticles. To further explore this effect, here, we quantify the wavelength dependence of vibrational energy in plasmon–fluorophore systems, where molecules can undergo electronic transitions with resonant excitation. We used three excitation wavelengths and three molecules with varying electronic resonance energies. We observe wavelength-dependent vibrational energy distributions, which we attribute to competing effects of on-resonance heating and off-resonance decrease in the population ratio. This work thus quantifies the resonance wavelength dependence of vibrational energy in plasmon molecular systems and helps to suggest future applications of tailored systems with controllable energy transfer pathways.
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    Probing Plasmon-Molecules Interactions with Surface-enhanced Raman Spectroscopy: Towards the Guided Design of Plasmonic Photocatalysts
    (2023-03) Yu, Ziwei
    Plasmonic materials have proven their strong candidacy as photocatalysts with their unique optical properties and strong interactions with light. The possibility of driving chemical reactions with sunlight to achieve high efficiency and selectivity has driven a lot of research exploring plasmonic photocatalysts. However, the progress has been slow due to a lack of mechanistic understanding. My thesis work aims to provide guidelines for plasmonic catalysts design through investigating plasmon-molecules interaction with various spectroscopic techniques.In this thesis, I will discuss my investigation of the energy transfer processes in the plasmonic-molecules systems on the ultrafast and steady state timescales with surface-enhanced Raman thermometry. Our results reveal that following the initial transient energy deposition, there is a quick energy dissipation between the molecules through intermolecular interactions on the ultrafast timescale (within 30 ps). On the steady state, surprisingly, we observed a “plasmon refrigerator” where the molecules are cooled below room temperature. In later work, I will discuss our work on developing surface-enhanced Raman optical activity spectroscopy and our investigation of the chiral interactions between molecules and plasmons. Our initial results suggest chirality transfer in the plasmonic-molecules systems. Lastly, I will propose a series of future directions to further the study of plasmon-molecules interactions. Herein, I show that surface-enhanced Raman spectroscopy (SERS) is a powerful technique, especially when coupled with other techniques such as Raman thermometry and Raman optical activity. Our studies on plasmon-molecules interactions will help with the development of plasmonic catalysis by providing guidelines for the design and optimization of plasmonic catalysts.
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    Supporting data for Intermolecular Forces Dictate Vibrational Energy Transfer in Plasmonic–Molecule Systems
    (2022-02-22) Yu, Ziwei; Frontiera, Renee; rrf@umn.edu; Frontiera, Renee
    These files contain data along with associated output from described analysis supporting all results reported in Yu, Z.; Frontiera, R. R. Intermolecular Forces Dictate Vibrational Energy Transfer in Plasmonic–Molecule Systems. ACS Nano, 2022, 16, 1, 847–854. Anti-Stokes and Stokes scattering from aromatic thiols adsorbed on gold nanoparticles are monitored with ultrafast surface-enhanced Raman spectroscopy (SERS). Vibration population ratio changing kinetics of the aromatic thiols is obtained by conducting peak fitting with the acquired ultrafast anti-Stokes and Stokes SERS spectra and performing Boltzmann analysis. The as-obtained kinetic traces are fitted with exponential decay convoluted with the instrument response function to extract the temporal increase and lifetime of the population ratio kinetics, which are found to be correlated with the molecular property in a fashion that molecules with a stronger intermolecular interaction experience less temporal population ratio increase and shorter excited vibrational state lifetime.