scholarly journals Non-Radiative Processes and Vibrational Pumping in Surface-Enhanced Raman Scattering

2021 ◽  
Author(s):  
◽  
Christopher Galloway
Keyword(s):  
Cross Section ◽  
Single Molecule ◽  
Cross Sections ◽  
Plasmon Resonance ◽  
Additional Contribution ◽  
Vibrational Modes ◽  
Silver Colloids ◽  
Surface Enhanced ◽  
Vibrational Population ◽  
Anti Stokes

<p><b>The main focus of this thesis was the physical interpretation of the pumping cross-section. This was achieved by performing a statistical analysis of single molecule vibrational pumping events in which both the SERS and pumping cross-sections could be measured simultaneously. Samples were constructed in which small aggregates of silver colloids were evenly distributed on a dry surface.</b></p> <p>The sample was then cooled to 77K so that the main mechanism for creating a vibrational population was through Stokes scattering. Spatial mappings were then performed which measured how the SERS spectrum varied with positionon the sample and the single molecule events were identified. The SERS cross-sections were determined from the Stokes intensity while the pumping cross-sections were determined from the ratio of the anti-Stokes and Stokes peaks. It was observed that the pumping cross-section was often significantly larger than the SERS cross-section, as much as four orders of magnitude in some cases. Several attempts were made to explain this discrepancy including the possibility ofthe surface plasmon resonance favouring anti-Stokes scattering, underestimated lifetimes for the vibrational modes, and additional pumping from fluorescence. However, the most likely candidate was non-radiative Stokes scattering by the observed molecule which would increase the vibrational population but would not increase the Stokes intensity. To estimate the proportion of scattered light that is radiative or non-radiative,single molecule measurements were performed under both surface-enhanced and unmodified conditions. By comparing the fluorescence and Raman intensities under these scenarios, it was possible to estimate the radiative and non-radiative enhancement factors. It was found that the non-radiative SERS cross-section was typically much larger than the radiative cross-section for samples consisting of aggregated silver colloids. The discrepancy between the pumping and SERS cross-section (which is the radiative cross-section) could therefore be explained by non-radiative scattering dominating the creation of the vibrational population, along with an additional contribution due to the plasmon resonance favouring certain vibrational modes. Furthermore, the lifetime of a molecule after it has been excited to the first electronic state was estimated to be as short as 25 fs. It would be impossible to measure lifetimes of this order of magnitude in single molecules using time-resolved techniques. Furthermore, to the very best of our knowledge, this is the first time that an experimental determination of the non-radiative SERS cross-section has been made.</p>

scholarly journals Non-Radiative Processes and Vibrational Pumping in Surface-Enhanced Raman Scattering

2021 ◽  
Author(s):  
◽  
Christopher Galloway
Keyword(s):  
Cross Section ◽  
Single Molecule ◽  
Cross Sections ◽  
Plasmon Resonance ◽  
Additional Contribution ◽  
Vibrational Modes ◽  
Silver Colloids ◽  
Surface Enhanced ◽  
Vibrational Population ◽  
Anti Stokes

<p><b>The main focus of this thesis was the physical interpretation of the pumping cross-section. This was achieved by performing a statistical analysis of single molecule vibrational pumping events in which both the SERS and pumping cross-sections could be measured simultaneously. Samples were constructed in which small aggregates of silver colloids were evenly distributed on a dry surface.</b></p> <p>The sample was then cooled to 77K so that the main mechanism for creating a vibrational population was through Stokes scattering. Spatial mappings were then performed which measured how the SERS spectrum varied with positionon the sample and the single molecule events were identified. The SERS cross-sections were determined from the Stokes intensity while the pumping cross-sections were determined from the ratio of the anti-Stokes and Stokes peaks. It was observed that the pumping cross-section was often significantly larger than the SERS cross-section, as much as four orders of magnitude in some cases. Several attempts were made to explain this discrepancy including the possibility ofthe surface plasmon resonance favouring anti-Stokes scattering, underestimated lifetimes for the vibrational modes, and additional pumping from fluorescence. However, the most likely candidate was non-radiative Stokes scattering by the observed molecule which would increase the vibrational population but would not increase the Stokes intensity. To estimate the proportion of scattered light that is radiative or non-radiative,single molecule measurements were performed under both surface-enhanced and unmodified conditions. By comparing the fluorescence and Raman intensities under these scenarios, it was possible to estimate the radiative and non-radiative enhancement factors. It was found that the non-radiative SERS cross-section was typically much larger than the radiative cross-section for samples consisting of aggregated silver colloids. The discrepancy between the pumping and SERS cross-section (which is the radiative cross-section) could therefore be explained by non-radiative scattering dominating the creation of the vibrational population, along with an additional contribution due to the plasmon resonance favouring certain vibrational modes. Furthermore, the lifetime of a molecule after it has been excited to the first electronic state was estimated to be as short as 25 fs. It would be impossible to measure lifetimes of this order of magnitude in single molecules using time-resolved techniques. Furthermore, to the very best of our knowledge, this is the first time that an experimental determination of the non-radiative SERS cross-section has been made.</p>

scholarly journals Linking classical and molecular optomechanics descriptions of SERS

2017 ◽  
Vol 205 ◽  
pp. 31-65 ◽  
Author(s):  
Mikołaj K. Schmidt ◽  
Ruben Esteban ◽  
Felix Benz ◽  
Jeremy J. Baumberg ◽  
Javier Aizpurua
Keyword(s):  
Cross Sections ◽  
Quantum Dynamics ◽  
Optical Cavity ◽  
Raman Signal ◽  
Classical Approach ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Enhanced Raman Scattering ◽  
Anti Stokes ◽  
Full Quantum

The surface-enhanced Raman scattering (SERS) of molecular species in plasmonic cavities can be described as an optomechanical process where plasmons constitute an optical cavity of reduced effective mode volume which effectively couples to the vibrations of the molecules. An optomechanical Hamiltonian can address the full quantum dynamics of the system, including the phonon population build-up, the vibrational pumping regime, and the Stokes–anti-Stokes correlations of the photons emitted. Here we describe in detail two different levels of approximation to the methodological solution of the optomechanical Hamiltonian of a generic SERS configuration, and compare the results of each model in light of recent experiments. Furthermore, a phenomenological semi-classical approach based on a rate equation of the phonon population is demonstrated to be formally equivalent to that obtained from the full quantum optomechanical approach. The evolution of the Raman signal with laser intensity (thermal, vibrational pumping and instability regimes) is accurately addressed when this phenomenological semi-classical approach is properly extended to account for the anti-Stokes process. The formal equivalence between semi-classical and molecular optomechanics descriptions allows us to describe the vibrational pumping regime of SERS through the classical cross sections which characterize a nanosystem, thus setting a roadmap to describing molecular optomechanical effects in a variety of experimental situations.

Transmission Electron Diffraction at 200 eV and Damage Thresholds below the Carbon K Edge

2000 ◽  
Vol 6 (4) ◽  
pp. 368-379
Author(s):  
Michael R. Stevens ◽  
Qing Chen ◽  
Uwe Weierstall ◽  
John C.H. Spence
Keyword(s):  
Electron Diffraction ◽  
Cross Section ◽  
Single Molecule ◽  
Cross Sections ◽  
Threshold Energy ◽  
Low Energy ◽  
Transmission Electron Diffraction ◽  
Transmission Electron ◽  
Minimum Number ◽  
Shell Ionization

Abstract Transmission electron diffraction patterns from ultra-thin aromatic and aliphatic organic films at beam energies of 200 eV–1 keV have been recorded in a custom low energy electron transmission (LEET) chamber. A significant reduction of the molecular damage cross-section, measured by fading of diffraction spots, was found for thin films of the aromatic perylene when the beam energy was reduced from 400 to 200 eV. The corresponding measurements for the aliphatic tetracontane showed a smaller “threshold energy” and the differences are discussed. Electron beam damage from other aromatic materials has also been studied at low energy. Comparison of the carbon K shell ionization cross-section and the measured damage cross-sections show that carbon K-shell ionization is strongly correlated with the damage observed in aromatics at beam energies higher than 284 eV. Calculation of the minimum number of unit cells needed for imaging a single molecule, and comparison of calculated elastic with measured damage cross-sections both indicate new possibilities for imaging biomolecules with low energy electrons.

Single-Molecule Detection of a Cyanine Dye in Silver Colloidal Solution Using Near-Infrared Surface-Enhanced Raman Scattering

1998 ◽  
Vol 52 (2) ◽  
pp. 175-178 ◽  
Author(s):  
Katrin Kneipp ◽  
Harald Kneipp ◽  
Geurt Deinum ◽  
Irving Itzkan ◽  
Ramachandra R. Dasari ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Single Molecule ◽  
Near Infrared ◽  
Colloidal Solution ◽  
Single Molecule Detection ◽  
Cyanine Dye ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Enhanced Raman Scattering ◽  
Anti Stokes

Single-molecule Raman spectroscopy of a cyanine dye in aqueous silver colloidal solution with the use of surface-enhanced Raman scattering at near-infrared excitation (NIR-SERS) is reported. A characteristic Poisson distribution of SERS signals due to the Brownian motion of single dye molecule-loaded silver particles reflects the probability of finding 0, 1, or 2 1,1'-diethyl-2,2'cyanine (PIC) molecules in the probed volume during an actual measurement and is evidence that single-molecule detection by SERS has been achieved. Spectra measured in 1 s collection time with 100 mW nonresonant 830 nm excitation provide a clear “fingerprint” of a single PIC molecule by showing its typical Raman lines between 700 and 1700 cm−1. Single-molecule Raman signals are also detected for the first time at the anti-Stokes side of the excitation laser. Effective Raman cross sections for PIC of ∼10−16 cm2 per molecule can be inferred from the ratio between “pumped” anti-Stokes and Stokes signals.

scholarly journals Quantification of the Enhancement Factor in Surface-Enhanced Raman Scattering

2021 ◽  
Author(s):  
◽  
Evan Blackie
Keyword(s):  
Cross Section ◽  
Single Molecule ◽  
Cross Sections ◽  
Enhancement Factor ◽  
Density Functional ◽  
Practical Applications ◽  
Surface Enhanced Raman ◽  
Scattering Volume ◽  
Rhodamine Dye

<p>This thesis presents a rigorous stepwise methodology towards the accurate measurement and quantification of the SERS enhancement factor (EF), the key parameter in describing the SERS effect. The work represents, we believe, a successful attempt to resolve some of the inconsistencies in the literature and to refocus the field by emphasizing the importance of consistent definitions and rigorous quantification to elucidate matters of fundamental importance in SERS. The success in our approach is that it combines careful experimental measurements upon a sound theoretical framework, and utilizes a 'toolbox' of techniques developed in recent years, such as bi-analyte SERS (BiASERS) techniques for single-molecule (SM) detection, and isotopic editing. In experimental work, we measure the bare Raman cross-sections of five common probes used in SERS as a first step in measuring the analytical enhancement factor (AEF) and single-molecule enhancement factor (SMEF). The methodology in measuring these EFs involved the use of a reference standard of known cross-section along with a careful characterization of the scattering volume through beam profiling experiments. As a guide to validating the reference cross-section we make extensive use of density functional theory (DFT) calculations to obtain estimates for the intrinsic Raman cross-sections of small, non-resonant probes. The results of this work showed that previous upper limits for the EF reported in the literature of 1014 were based on a faulty normalization of the EF. In fact, EFs of 108 were sufficient to see single molecules, which is much lower than previously expected; under optimum conditions, even lower EFs, possibly down to 105 could be sufficient for the SM detection of resonant probes. As a valuable extension of BiASERS, we elaborate on the synthesis of isotopic analogues of a rhodamine dye as ideal partners for SM experiments. The synthesis and definitive characterization of these probes enable their use in an experiment to determine the SM regime in a liquid colloidal sample. Isotopically edited dyes such as these, in combination with the methodologies of EF quantification outlined herein, set the standard for those interested in accurate quantification of the SERS effect. This approach is useful in terms of both basic theoretical questions and applications such as the effective comparison of SERS substrates. Finally, we extend the techniques developed over the thesis to a long-standing and largely unresolved question in SERS: What is the minimum intrinsic Raman cross-section that can be measured as a single molecule in standard SERS conditions. In this work, we explore the SM detection non-resonant probes, which are the molecules of interest for many practical applications such as forensics and biological assays. Specifically, we demonstrate the successful SM detection of isotopically edited adenine probes.</p>

Surface Enhanced Vibrational Spectroscopy of Proteins with Plasmonic Nanoantenna Arrays

2010 ◽  
Vol 1248 ◽  
Author(s):  
Ronen Adato ◽  
Ahmet A. Yanik ◽  
Jason J. Amsden ◽  
David Kaplan ◽  
Fiorenzo Omenetto ◽  
...  
Keyword(s):  
Single Molecule ◽  
Cross Sections ◽  
Near Field ◽  
Molecular Layer ◽  
Direct Access ◽  
Functional Studies ◽  
Intrinsic Absorption ◽  
Surface Enhanced ◽  
Infrared Spectral ◽  
Fluorescent Molecules

AbstractInfrared absorption spectroscopy is a powerful tool for structural and functional studies of biomolecules. The technique enables direct access to the vibrational fingerprints of molecular bonds in the mid-infrared spectral region (3-20μm). Although intrinsic absorption cross-sections are nearly ten orders of magnitude greater than corresponding Raman cross-sections, they are still small in comparison with those of fluorescent molecules. Sensitivity improvements are therefore required for the method to be applicable to single molecule / molecular layer studies. In this work, we demonstrate the use of lithographically patterned arrays of nanoantennas to enhance the absorption signature of the protein amide-I and II backbone vibrations. Strong absorption signals from monolayer thickness films are obtained. By arranging ensembles of tailored antennas in specific lattices, higher quality factor resonances and increased near-field intensities are possible. These features are leveraged to obtain 104-105 fold signal enhancements and the direct measurement of vibrational spectra of proteins at zepto-mole sensitivity levels.

Surface enhanced anti-Stokes one-photon luminescence from single gold nanorods

Nanoscale ◽  
2015 ◽  
Vol 7 (2) ◽  
pp. 577-582 ◽  
Author(s):  
Yingbo He ◽  
Keyu Xia ◽  
Guowei Lu ◽  
Hongming Shen ◽  
Yuqing Cheng ◽  
...  
Keyword(s):  
Surface Plasmon Resonance ◽  
Fermi Level ◽  
Surface Plasmon ◽  
Gold Nanorods ◽  
Plasmon Resonance ◽  
Gold Nanorod ◽  
Surface Enhanced ◽  
Anti Stokes

Anti-Stokes one-photon luminescence from single gold nanorod was determined to be enhanced by surface plasmon resonance and strongly related with the distribution of electrons near the Fermi level.

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