Publications

2021

Complex plasmon-exciton dynamics revealed through quantum dot light emission in a nanocavity

Plasmonic cavities can confine electromagnetic radiation to deep sub-wavelength regimes. This facilitates strong coupling phenomena to be observed at the limit of individual quantum emitters. Here, we report an extensive set of measurements of plasmonic cavities hosting one to a few semiconductor quantum dots. Scattering spectra show Rabi splitting, demonstrating that these devices are close […]

Glutathione Self-Assembles into a Shell of Hydrogen-Bonded Intermolecular Aggregates on “Naked” Silver Nanoparticles

A detailed understanding of the molecular structure in nanoparticle ligand capping layers is crucial for their efficient incorporation into modern scientific and technological applications. Peptide ligands render the nanoparticles as biocompatible materials. Glutathione, a γ-ECG tripeptide, self-assembles into aggregates on the surface of ligand-free silver nanoparticles through intermolecular hydrogen bonding and forms a few nanometer-thick […]

2020

Surface-enhanced ultrafast two-dimensional vibrational spectroscopy with engineered plasmonic nano-antennas

Development of noble metal nanostructure substrates that provide strong near-field enhancements enables applications of linear and nonlinear infrared (IR) spectroscopies to study minute sample quantities, such as nanometer thick films and molecular monolayers. Large near-field enhancements of the electric fields used for spectroscopic interrogation of molecules at the nanostructure surface result in enhancement of the […]

Dual-frequency surface-enhanced two-dimensional vibrational spectroscopy of thin layers at an interface

Ultrafast spectroscopy of molecular systems involving hydrogen- (H−) bonding has been at the forefront of fundamental chemical and physical research for several decades. Among the spectroscopic observables of the ultrafast dynamics is the pure dephasing of vibrationally excited molecules. Using third-order nonlinear vibrational spectroscopy, including polarization-selective transient grating measurements of vibrational lifetime and orientational diffusion […]

2019

Intense-field interaction regime with weak laser pulses and localized plasmonic enhancement: Reference-free demonstration by 3rd- and 5th-order infrared spectroscopies

In bulk materials, intense field interaction is accompanied by undesired nonresonant processes. Plasmonic nanostructures localize enhanced fields exclusively in their vicinity. We report a 4-fold vibrational population inversion between all the excited and the ground states in the molecular monolayer on the surface of gold nanoantennas. Excited population assessment relies on a novel reference-sample-free evaluation […]

Plasmonic Trimers for Dual-Frequency Surface-Enhanced Two-Dimensional Infrared Spectroscopy

Extension of surface-enhanced two-dimensional infrared spectroscopy (SE-2DIR) to dual-frequency experiments allows studying dynamics and energy transport in thin molecular films by tagging and probing vibrational modes on different sites of the molecule. Measurements of cross-peaks involving transitions largely separated in frequency by SE-2DIR require plasmonic nanostructures with resonant excitations at the corresponding frequencies, where the […]

Two-Dimensional Infrared Spectroscopy Reveals Molecular Self-Assembly on the Surface of Silver Nanoparticles

The conformation of molecules, peptides, and proteins, self-assembled into structured monolayers on the surface of metal nanoparticles (NPs), can strongly affect their properties and use in chemical or nanobiomedical applications. Elucidating molecular conformations on the NP surface is highly challenging, and the microscopic details mostly remain elusive. Using polarization-selective third-order two-dimensional ultrafast infrared spectroscopy, we […]

2018

Quantifying conformations of ester vibrational probes with hydrogen-bond-induced Fermi resonances

Solvatochromic shifts of local vibrational probes report on the strength of the surrounding electric fields and the probe’s hydrogen bonding status. Stretching vibrational mode of the ester carbonyl group is a popular solvatochromic reporter used in the studies of peptides and proteins. Small molecules, used to calibrate the response of the vibrational probes, sometimes involve […]

Two-Dimensional Infrared Spectroscopy with Local Plasmonic Fields of a Trimer Gap-Antenna Array

Half-wavelength plasmonic antennas tuned to resonance with molecular vibrational excitations have been demonstrated to enhance 2DIR signals by multiple orders of magnitude. We design doubly degenerate in-plane plasmonic normal modes of the symmetric trimer gap-antenna, which have orthogonal dipole moments excited by light of the appropriate polarization, to localize the enhanced field into the antenna’s […]

Artificial plasmonic molecules and their interaction with real molecules

Plasmonic molecules are small assemblies of nanosized metal particles. Interactions between the particles modify their optical properties and make them attractive for multiple applications in spectroscopy and sensing. In this review, we focus on basic properties rather than on applications. Plasmonic molecules can be created using either nanofabrication methods or self-assembly techniques in solution. The […]

Radiative Enhancement of Linear and Third-Order Vibrational Excitations by an Array of Infrared Plasmonic Antennas

Infrared gold antennas localize enhanced near fields close to the metal surface, when excited at the frequency of their plasmon resonance, and amplify vibrational signals from the nearby molecules. We study the dependence of the signal enhancement on the thickness of a polymer film containing vibrational chromophores, deposited on the antenna array, using linear (FTIR) […]

Surface-Enhanced Dual-Frequency Two-Dimensional Vibrational Spectroscopy of Thin Layers at an Interface

The development of spectroscopic approaches to study molecules at interfaces is important as the molecular properties often differ from those in the bulk. Implementation of surface-enhanced two-dimensional infrared (SE 2DIR) spectroscopy using lithographically fabricated plasmonic nanoarrays is demonstrated for nanometer thick films. The sample, 4-azidobutyrate-N-hydroxysuccinimide ester (azNHS), dispersed in polystyrene was deposited onto the nanoarray. […]

Communication: Probing the interaction of infrared antenna arrays and molecular films with ultrafast quantum dynamics

Narrowband vibrational molecular transitions interacting with the broadband resonance of infrared plasmonic antennas lead to Fano lineshapes observed in linear (FTIR) and third-order (transient absorption and 2DIR) spectroscopic experiments. Both molecular and plasmonic components are inherently dissipative, and the effects associated with their coupling can be observed, in principle, when measuring the corresponding ultrafast quantum […]

2017

Two-dimensional Fano lineshapes in ultrafast vibrational spectroscopy of thin molecular layers on plasmonic arrays

Two-dimensional femtosecond infrared (2DIR) spectroscopy routinely provides insights into molecular structure and ultrafast dynamics in 1–100 μm thick bulk samples. Confinement of molecules to surfaces, gaps, crevices, and other topographic features, frequently encountered on the nanometer length scale, significantly alters their structure and dynamics, affecting physical and chemical properties. Amplification of 2DIR signals by the […]

A Spin-Boson Screening approach for unraveling dominant vibrational energy transfer pathways in molecular materials

Vibrational energy transfer driven by anharmonicity is the major mechanism of energy dissipation in polyatomic molecules and in molecules embedded in condensed phase environment. Energy transfer pathways are sensitive to the particular intra-molecular structure as well as to specific interactions between the molecule and its environment, and their identification is a challenging many-body problem. This work introduces a theoretical approach which enables to identify […]

2016

Vacuum Rabi splitting in a plasmonic cavity at the single quantum emitter limit

The strong interaction of individual quantum emitters with resonant cavities is of fundamental interest for understanding light–matter interactions. Plasmonic cavities hold the promise of attaining the strong coupling regime even under ambient conditions and within subdiffraction volumes. Recent experiments revealed strong coupling between individual plasmonic structures and multiple organic molecules; however, strong coupling at the […]

2D-IR spectroscopy of hydrogen-bond-mediated vibrational excitation transfer

Vibrational excitation transfer along the hydrogen-bond-mediated pathways in the complex of methyl acetate (MA) and 4-cyanophenol (4CP) was studied by dual-frequency femtosecond two-dimensional infrared spectroscopy. We excited the energy-donating ester carbonyl stretching vibrational mode and followed the transfer to the energy-accepting benzene ring and cyano stretching vibrations. The complexes with no, one, and two hydrogen-bonded […]

2015

Kinetics of Exchange between Zero-, One-, and Two-Hydrogen-Bonded States of Methyl and Ethyl Acetate in Methanol

It has recently been shown that the ester carbonyl stretching vibration can be used as a sensitive probe of local electrostatic field in molecular systems. To further characterize this vibrational probe and extend its potential applications, we studied the kinetics of chemical exchange between differently hydrogen-bonded (H-bonded) ester carbonyl groups of methyl acetate (MA) and […]

2014

The simplest plasmonic molecules: Metal nanoparticle dimers and trimers

This review discusses research on the plasmonic properties of small clusters of metal nanoparticles, with two and three particles. These are the simplest examples of ‘plasmonic molecules’. Coupling between two particles leads to new surface plasmon resonances and to the creation of a hot spot of a strong electric field in the gap between the […]

Non-linear infrared spectroscopy of the water bending mode: direct experimental evidence of hydration shell reorganization?

The structure and dynamics of liquid water are further studied by investigating the bend vibrational mode of HDO/D2O and pure H2O via two-dimensional infrared spectroscopy (2D-IR) and linear absorption. The experimental findings and theoretical calculations support a picture in which the HDO bend is localized and the H2O bend is delocalized. The HDO and H2O bends present […]

Effect of Nanoparticle Symmetry on Plasmonic Fields: Implications for Single‐Molecule Raman Scattering

The strong electromagnetic field localization required for the observation of single‐molecule surface‐enhanced Raman scattering (SMSERS) is readily obtained when the studied molecule is adsorbed inside the gap between closely adjacent nanoparticles. The interactions of adsorbed molecules with the electric field of light are influenced by the nanoparticle arrangement. This chapter discusses a series of spectroscopic […]