We present here a detailed study of the specific nanoparticle structures that give rise to single-molecule surface-enhanced Raman scattering (SMSERS). A variety are observed, but simplest dimers Ag nanocrystals. chose one these for using electrodynamics calculations and found electromagnetic SERS enhancement factors 10(9) easily obtained consistent with activity.

After its discovery more than 30 years ago, surface-enhanced Raman spectroscopy (SERS) was expected to have major impact as a sensitive analytical technique and tool for fundamental studies of surface species. Unfortunately, the lack reliable reproducible fabrication methods limited applicability. In recent years, SERS has enjoyed renaissance, there is renewed interest in both fundamentals applications SERS. New techniques nanofabrication, design substrates that maximize electromagnetic...

The surface-enhanced Raman excitation profiles (REPs) of rhodamine 6G (R6G) on Ag surfaces are studied using a tunable optical parametric oscillator source and versatile detection scheme. These experiments afford the ability to finely tune wavelength near molecular resonance R6G (i.e., approximately 500-575 nm) perform wavelength-scanned measurements single molecule. ensemble-averaged REPs measured for collections molecules island films. relative contributions 0-0 0-1 vibronic transitions...

A chemical warfare agent (CWA) gas detector based on surface-enhanced Raman spectroscopy (SERS) using robust nanostructured substrates and a portable spectrometer is promising alternative to existing modalities. gas-dosing apparatus was constructed simulate exposure provide platform for quantitative analysis of SERS detection. As first step toward characterizing detection from the phase, benzenethiol (BT) has been chosen as test analyte. spectra were monitored during BT adsorption onto...

A probe mediated SERS-based strategy is developed to selectively detect hydrazine with superb sensitivity. Ortho-phthaldialdehyde, a simple probe, reacts specifically form phthalazine, molecule that possesses larger Raman cross section and better affinity toward the SERS substrate. We observed limit of detection 8.5 × 10–11 M. Our method shows both qualitative quantitative measurement high sensitivity, low cost, fast analysis time.

Plasmonics is a rapidly growing field, yet imaging of the plasmonic modes in complex nanoscale architectures extremely challenging. Here we obtain spatial maps localized surface plasmon high-aspect-ratio silver nanorods using electron energy loss spectroscopy (EELS) and correlate to optical data classical electrodynamics calculations from exact same particles. EELS mapping thus demonstrated be an invaluable technique for elucidating overlapping modes.

Hydrogen peroxide (H2O2) is known as a key molecule in variety of biological processes, well crucial byproduct many enzymatic reactions. Therefore, being able to selectively and sensitively detect H2O2 not only important monitoring, estimating, decoding relevant physiological pathways but also very helpful developing enzymatic-based biosensors for other analytes interest. Herein, we report plasmonic probe based on 3-mercaptophenylboronic acid (3-MPBA) modified gold nanoparticles (AuNPs)...

A computational analysis of the electron- and photon-driven surface-plasmon resonances monomer dimer metal nanorods is presented to elucidate differences similarities between two excitation mechanisms in a system with well-understood optical properties. By correlating nanostructure's simulated electron energy-loss spectrum loss-probability maps its induced polarization scattered electric field we discern how certain plasmon modes are selectively excited they funnel energy from source into...

Controlling light from single emitters is an overarching theme of nano-optics. Antennas are routinely used to modify the angular emission patterns radio wave sources. "Optical antennas" translate these principles visible and infrared wavelengths have been recently fluorescence quantum dots molecules. Understanding properties molecules, however, would be advanced were one able observe their vibrational spectra through Raman scattering in a very reproducible manner but it hugely challenging...

N-Heterocyclic carbenes (NHCs) are an attractive alternative to thiol ligands when forming self-assembled monolayers on noble-metal surfaces; however, relative the well-studied monolayers, comparatively little is known about binding, orientation, and packing of NHC monolayers. Herein, we combine surface-enhanced Raman spectroscopy (SERS) first-principles theory investigate how alkyl "wingtip" groups, i.e., those attached nitrogens N-heterocyclic carbenes, affect orientation gold...

Energy transfer from plasmonic nanoparticles to semiconductors can expand the available spectrum of solar energy-harvesting devices. Here, we spatially and spectrally resolve interaction between single Ag nanocubes with insulating semiconducting substrates using electron energy-loss spectroscopy, electrodynamics simulations, extended plasmon hybridization theory. Our results illustrate a new way characterize plasmon–semiconductor energy at nanoscale bear impact upon design next-generation

The ability to detect molecules at low concentrations is highly desired for applications that range from basic science healthcare. Considerable interest also exists ultrathin materials with high optical absorption, e.g. microbolometers and thermal emitters. Metal nanostructures present opportunities achieve both purposes. nanoparticles can generate gigantic field enhancements, sufficient the Raman spectroscopy of single molecules. Thin layers containing metal ("metasurfaces") near-total...

Owing to its extreme sensitivity and easy execution, surface-enhanced Raman spectroscopy (SERS) now finds application for a wide variety of problems requiring sensitive targeted analyte detection. This widespread has prompted proliferation different SERS-based sensors, suggesting the need framework classify existing methods guide development new techniques. After brief discussion general SERS modalities, we sensors according origin signal. Three major categories emerge from this analysis:...

Electron energy-loss spectroscopy (EELS) offers a window to view nanoscale properties and processes. When performed in scanning transmission electron microscope, EELS can simultaneously render images of objects with sub-nanometer spatial resolution correlate them spectroscopic information $\sim10 - 100$ meV spectral resolution. Consequently, is near-perfect tool for understanding the optical electronic individual few-particle plasmonic metal nanoparticles assemblies, which are significant...

Nanoporous metal films are promising substrates for surfaced-enhanced Raman scattering (SERS) measurement, owing to their homogeneity, large surface area, and abundant hot-spots. Herein, a facile procedure was developed fabricate nanoporous Ag film on various substrate surfaces. Thermally deposited first treated with O2 plasma, resulting in porous Ag/AgxO (AgxO-NF) nanoscale feature. Sodium citrate then used reduce AgxO Ag, forming (AgNF) similar morphology. The AgNF demonstrates 30-fold...

Surface-enhanced Raman spectroscopy (SERS) underpins a wide range of commercial and fundamental applications. SERS often relies on ligands, usually thiols, bound to noble metal surface. The difficulty straightforward thiol synthesis combined with their instability surfaces highlights the need for alternative ligand design. We present first example utilizing N-heterocyclic carbene ligands. A general three step is presented functionalized NHC-CO2 adducts. These ligands are deposited...

The importance of reactive trajectories straying far from the minimum energy path is demonstrated for bimolecular reaction H + HBr --> H2(v', j') Br at 53 kcal/mol collision energy. Product quantum state distributions are measured and calculated using quasi-classical trajectory technique, calculations indicate that highly internally excited H2 products result indirect with bent transition states. A general argument made suggesting internal exceeding a kinematic constraint can, in general, be...

Through numerical simulation, we predict the existence of Fano interference effect in electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) symmetry-broken nanorod dimers that are heterogeneous material composition asymmetric length. The differing selection rules probe comparison to photon a plane wave allow for simultaneous excitation both optically bright dark plasmons each monomer unit, suggesting resonances will not arise EELS CL. Yet, interferences manifested dimer's...

Since the observation of single-molecule surface-enhanced Raman scattering (SMSERS) in 1997, questions regarding nature electromagnetic hot spots responsible for such observations still persist. For first time, we employ electron-energy-loss spectroscopy (EELS) a scanning transmission electron microscope (STEM) to obtain maps localized surface plasmon modes SMSERS-active nanostructures, which are resolved both space and energy. Single-molecule character is confirmed by bianalyte approach...

Surface enhanced Raman scattering (SERS) is undergoing a renaissance, spurred largely by developments in the burgeoning field of plasmonics. This paper reviews current status and future directions plasmonic nanostructures for SERS. We show that engineered enable exciting new functionalities, including beamed highly reproducible chips single molecule furthermore silicon photonics enables SERS to be performed using optically trapped Ag nanoparticle clusters.

Surface functionalization is an essential component of most applications noble-metal surfaces. Thiols and amines are traditionally employed to attach molecules surfaces, but they have limitations. A growing body research, however, suggests that N-heterocyclic carbenes (NHCs) can be readily for surface with superior chemical stability compared thiols. We demonstrate the power surface-enhanced Raman scattering combined theory present a comprehensive picture NHC binding gold In particular, we...

The remarkable resilience of N-heterocyclic carbene (NHC) gold bonds has quickly made NHCs the ligand choice when functionalizing surfaces. Despite rapid progress using deposition from free or CO2 -protected NHCs, synthetic challenges hinder functionalization NHC surfaces with protic functional groups, such as alcohols and amines, particularly on larger nanoparticles. Here, we synthesize NHC-functionalized gold(I) complexes aqueous nanoparticles without need for additional reagents, enabling...

The effects of two nearly isoenergetic C-H stretching motions on the gas-phase reaction atomic chlorine with methane are examined. First, a 1:4:9 mixture Cl(2), CH(4), and He is coexpanded into vacuum chamber. Then, either antisymmetric stretch (nu(3)=3019 cm(-1)) CH(4) prepared by direct infrared absorption or infrared-inactive symmetric (nu(1)=2917 stimulated Raman pumping. Photolysis Cl(2) at 355 nm generates fast Cl atoms that initiate collision energy 1290+/-175 cm(-1) (0.16+/-0.02 eV)....