Raman scattering from amorphous ice films

The Raman spectrum from thin films of amorphous ice has been obtained by using a new laser beam trapping technique. Both the OH-stretching region of the spectrum and the always present intense scattering background have been interpreted.     

Surface-enhanced Raman scattering (SERS) from different azobenzene self-assembled monolayers and sandwiches

Self-assembled monolayers (SAMs) of functionalized azobenzene thiols (RAzoCnSH, n=3-6 for R=H, abbreviated as AzoCnSH; and n=4 for R=CH(3)CONH, abbreviated as aaAzoC4SH) on different substrates RAzoCnSz.sbnd;z.sfnc;S (S represents substrates of vacuum-deposited gold (Au), silver foil (Ag), HNO(3) etched silver foil (EAg), and silver mirror (mAg)) have been studied by SERS in the near-infrared region. SERS of the SAMs on EAg and/or mAg exhibit SERS effects that vary with etching time and/or deposition time. The most appropriate time is 5 s for etching in 1:1 HNO(3) and 40 s for deposition in 0.1 M Ag(NH(3))(2)NO(3). Further, a layer of Ag mirror was conveniently deposited on the top of the SAMs on different substrates, yielding a more efficient SERS-active system possessing a "sandwiched" structure of mAgz.sfnc;RAzoCnS-z.sfnc;S. An appropriate surface roughness is required for the strongest SERS effect. Scanning electron microscopy (SEM) indicates that there exist a large number of projects around 100 nm on the surface showing the strongest SERS effect. When the surface roughness is decreased or increased, the SERS effect decreases sharply. The relationship between the SERS effect and the structural nature was investigated and showed that the enhancement factor decays exponentially with increasing in distances of the azobenzene group from the underlying substrate or the overlying silver mirror. This result reveals that the SERS effect may be the result of the electromagnetic coupling effect between two metal layers.     

Raman scattering from thin polystyrene films on gold diffraction gratings

Raman spectra from gold-coated sinusoidal diffraction gratings overcoated with thin films of polystyrene have been examined using laser beams of several wavelengths. The angular and polarization dependence of the Raman spectral intensity is reported and is shown to correlate with variations in the zero-order grating reflectivity. Surface enhancement and multiple resonance effects in the Raman spectra are demonstrated.     

Approaching the electromagnetic mechanism of surface-enhanced Raman scattering: from self-assembled arrays to individual gold nanoparticles

Surface-enhanced Raman scattering (SERS) has been intensively explored both in theory and applications and has been widely used in chemistry, physics and biology for decades. A variety of SERS substrates have been developed in order to investigate the mechanisms behind, which give rise to the enormous enhancement even enabling single molecule detection. The Raman enhancement, which involves an electromagnetic enhancement (EM) and a chemical enhancement (CM), reflects both the physical principle of light/metal interactions and the molecule/metal interactions. In this tutorial review, we focus on the EM enhancement of SERS active substrates made of colloidal gold nanoparticles (GNPs), varying from self-assembled arrays down to single particles, for the purpose of investigating the EM coupling effect and probing the distribution of the induced electric field of single GNPs.     

Essential nanogap effects on surface-enhanced Raman scattering signals from closely spaced gold nanoparticles

We have demonstrated the essential nanogap effects on surface-enhanced Raman scattering (SERS) signals obtained from two diagonally aligned gold nanoparticles with several nanometre separations, which were precisely fabricated on a glass substrate. This is the first proof of principle for extracting the light localization effects on SERS due to the formation of nanogaps from experimentally observed SERS signals.     

Tuning the critical temperature of cuprate superconductor films with self-assembled organic layers

Control over the T(c) value of high-T(c) superconductors by self-assembled monolayers is demonstrated (T(c) = critical temperature). Molecular control was achieved by adsorption of polar molecules on the superconductor surface (see scheme) that change its carrier concentration through charge transport or light-induced polarization.     

Flame temperatures from Raman scattering

Pure rotational, as well as vibrational Raman scattering has been observed from stable diatomic molecules in high-temperature flames. Accurate (rotational) flame temperatures may be determined from the rotational line intensities. For a hydrogen diffusion flame in air T_rot(N₂) = 1880 ± 21K, T_rot(H₂) = 1890 ± 80 K, T_vib(N₂) = 1995 ± 130 K, and T_vib(H₂) =1900 ± 150 K.     

Surface enhanced Raman scattering of p-aminothiophenol self-assembled monolayers in sandwich structure fabricated on glass

A sandwich structure consisting of Ag nanoparticles (NPs), p-aminothiophenol (p-ATP) self-assembled monolayers (SAMs), and Ag NPs was fabricated on glass and characterized by surface enhanced Raman scattering (SERS). The SERS spectrum of a p-ATP SAM in such sandwich structure shows that the electromagnetic enhancement is greater than that on Ag NPs assembled on glass. The obtained enhancement factors (EF) on solely one sandwich structure were as large as 6.0 +/- 0.62 x 10(4) and 1.2 +/- 0.62 x 10(7) for the 7a and 3b(b(2)) vibration modes, respectively. The large enhancement effect of p-ATP SAMs is likely a result of plasmon coupling between the two layers of Ag NP (localized surface plasmon) resonance, creating a large localized electromagnetic field at their interface, where p-ATP resides. Moreover, the fact that large EF values (approximately 1.9 +/- 0.7 x 10(4) and 9.4 +/- 0.7 x 10(6) for the 7a- and b(2)-type vibration modes, respectively) were also obtained on a single sandwich structure of Au NPsp-ATP SAMsAg NPs in the visible demonstrates that the electromagnetic coupling does not exist only between Ag NPs but also between Au and Ag NPs. The lower EF values on Au-to-Ag NPs compared to those on Ag-to-Ag NPs demonstrate that the Au-to-Ag coupling must be less effective than the Ag-to-Ag coupling for the induction of SERS in the visible.     

Grafting of porphyrins on cellulose nanometric films

Ultrathin films of cellulose were functionalized with iron protoporphyrin IX (FePP). Spin-coating allows the production of silylated cellulose films in a controlled way. Cellulose regeneration is achieved through the hydrolyzation of the silane groups, exposing the film to acidic vapors. To enhance the reactivity of the cellulose surface to the protoporphyrin, carbonyldiimidazole (CDI) was used as an activator. The effect of different spacers on the porphyrin grafting such as 1,8-diaminooctane and 1,4-phenylenediamine was studied. The highest level of cellulose functionalization with FePP was achieved when both the cellulose film and FePP were activated by CDI and a diaminoalkane was used as a spacer between the surface and the FePP. ATR/MIR (attenuated total reflection in multiple internal reflections) was performed in situ to follow the kinetics of the different chemical reactions with the cellulose surface. ATR/MIR proved again to be a powerful tool for probing the surface reaction. X-ray photoelectron spectroscopy permitted the elemental analysis of the cellulose surface after the chemical modification.     

Au nanoparticle micropatterns prepared from self-assembled films

A kind of hybrid multilayer film based on mercaptobenzoic acid-capped Au nanoparticles (MBA-Au-NPs) and photoreactive nitrodiazoresin (NDR) has been fabricated via electrostatic self-assembly. Upon exposure to UV light, the initial ionic bonds between the layers of the film convert into covalent bonds and the film stability toward polar solvents, salt, or surfactant solutions increases significantly. The micropatterned NDR/MBA-Au-NP film with the covalently linked architecture was formed by selecting exposure of the film through a photomask and later developed in sodium dodecyl sulfate (SDS) aqueous solution. The metallic Au-NP micropatterns, furthermore, are produced by sintering the micropatterned NDR/MBA-Au-NP film at 550 degrees C, at which the organic components are removed completely. The well-defined micropatterns were characterized with atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), microscope with a charge-coupled device (CCD) camera, and X-ray photoelectron spectroscopy (XPS).     

Cuttlebone-derived organic matrix as a scaffold for assembly of silver nanoparticles and application of the composite films in surface-enhanced Raman scattering

Biologically derived materials provide a rich variety of approaches toward new functional materials because of their fascinating structures and environment-friendly features, which is currently a topic of research interest. In this paper, we show that the cuttlebone-derived organic matrix (CDOM) is an excellent scaffold for the one-step synthesis and assembly of silver nanoparticles (AgNPs), which can be further used as substrate for surface-enhanced Raman scattering (SERS). Formation of AgNPs–CDOM composite was accomplished by the reaction of CDOM with AgNO₃ and NH₃·H₂O solution at 80 °C without using any other stabilizer and reducing agents. UV–vis spectra and TEM were utilized to characterize the AgNPs and investigate their formation process. Results demonstrate that the size and distribution of AgNPs can be partly regulated by changing incubation time; the concentration of NH₃·H₂O is critical to the formation rate of AgNPs. As a proof of principle, we show that the AgNPs–CDOM composite can be employed in trace analysis using SERS.     

Surface-enhanced Raman scattering on silver nanostructured films prepared by spray-deposition

Silver nanostructured films were directly prepared by spray deposition of preformed polyol-based Ag-PVP nanoparticles. These homogeneous films of high optical quality were tested as SERS-active substrates. Laser excitation at 514.5 nm within the red part of the plasmon band leads to intense and reproducible SERS spectra of acridine, used as the probe molecule. From SERS measurements at different pH values, it was possible to determine the apparent pK(a) of acridine and to obtain specific surface properties of the film. Finally, these SERS titrations along with enhancement factor estimates allowed us to further depict the nature of the films.     

Librational Raman scattering from solid polymers

Broad, low frequency Raman bands (below 100 cm^?1 were observed in several solid polymers (polymethylmethacrylate) (PMMA), polystyrene, poly n-butyl methacrylate and poly 4-methyl pentene-1) and attributed to the librational motions of the side groups. A structural model for the librating side group is proposed which exhibits the observed frequency dependence on mass.     

Surface enhanced Raman scattering of biospecies on anodized aluminum oxide films

Traditionally, aluminum and anodized aluminum oxide films (AAO) are not the platforms of choice for surface-enhanced raman scattering (SERS) experiments despite of the aluminum’s large negative permittivity value. Here we examine the usefulness of aluminum and nanoporous alumina platforms for detecting soft biospecies ranging from bacterial spores to protein markers. We used these flat platforms to examine SERS of a model protein (cytochrome c from bovine heart tissue) and bacterial cells (spores of Bacillus subtilis ATCC13933 used as Anthrax simulant) and demonstrated clear Raman amplification.     

Surface-enhanced Raman scattering from silver-coated opals

We describe surface-enhanced Raman scattering measurements from a benzenethiol monolayer adsorbed on a silver-coated film that is, in turn, deposited on an artificial opal, where the latter is a close-packed three-dimensional dielectric lattice formed from polystyrene spheres. Data for a range of sphere sizes, silver film thicknesses, and laser excitation wavelengths are obtained. Enhancement factors can be in the range of 10(7). To partially explain these large enhancements, we have performed model finite-difference time domain simulations of the position-dependent electric fields generated at the opal surfaces for several experimentally studied laser wavelengths and sphere diameters.     

Probing dynamic generation of hot-spots in self-assembled chains of gold nanorods by surface-enhanced Raman scattering

Further progress in the applications of self-assembled nanostructures critically depends on developing a fundamental understanding of the relation between the properties of nanoparticle ensembles and their time-dependent structural characteristics. Following dynamic generation of hot-spots in the self-assembled chains of gold nanorods, we established a direct correlation between ensemble-averaged surface-enhanced Raman scattering and extinction properties of the chains. Experimental results were supported with comprehensive finite-difference time-domain simulations. The established relationship between the structure of nanorod ensembles and their optical properties provides the basis for creating dynamic, solution-based, plasmonic platforms that can be utilized in applications ranging from sensing to nanoelectronics.     

Brillouin scattering from polymer films

Many polymers cannot be prepared as clear amorphous blocks suitable for classical light scattering studies. However, most linear polymers can be prepared as films which are somewhat transparent. With the advent of high contrast multipass interferometers, these films can now be studied by Brillouin scattering. This work demonstrates the wide range of polymeric materials that can now be studied by Brillouin spectroscopy.     

Raman scattering from the longitudinal acoustic mode of oligo-oxyethylene

Low-frequency Raman spectra are reported for monodisperse oligo-oxyethylenes with hydroxy and alkoxy end groups. Assignments are made to the longitudinal acoustic modes. The results are modeled by a rod with a longitudinal modulus E ≥ 2.2 × 10¹⁰ N m^?2 and perturbing forces as large as (alkoxy-ended oligomers) or larger than (hydroxy-ended oligomers) those suggested for the n-alkanes.