Surface plasmon resonance and surface-enhanced Raman scattering activity of SiO2–Au core-cap nanostructure arrays

SiO₂–Au core-cap nanostructure arrays were prepared by dip-coating technique combined with wet chemical reduction method. The surface morphologies, structures, and optical properties of the obtained samples were characterized by scanning electron microscopy, X-ray diffraction, and ultraviolet–visible spectrophotometer, respectively. The surface-enhanced Raman scattering (SERS) activity of SiO₂–Au core-cap nanostructure arrays substrates was investigated using leucine as probe molecule. And the relationship between the SERS effect and the surface plasmon resonance (SPR) peaks was discussed. High-quality, stable, and reproducible SERS spectra of leucine were successfully obtained. When the maximum SPR peak matched with the excitation wavelength, the substrate gave rise to the highest SERS enhancement. Furthermore, six different fluorescent dyes were also chosen as probe molecules. It was found that the substrate showed good Raman enhancement and highly efficient fluorescence quenching characteristic on these fluorescent dyes.     

SERS scaling rules

We demonstrate the qualitative analysis of surface-enhanced Raman scattering (SERS) intensity and optical extinction by experimentally and numerically. This analytical methods are well matched not only the simple square lattice array of nanostructures, but also the rectangular lattices. We also demonstrate SERS selectivity of modes controlling the optical extinction of excitation and scattering wavelength. Both square lattice and rectangular lattice have similar tendency, but the rectangular lattice structures have much higher selectivity of SERS modes.     

Direct laser writing of symmetry-broken nanocorrals and their applications in SERS spectroscopy

We propose a simple and fast approach to prepare surface-enhanced Raman scattering (SERS) substrates over a large area with high flexibility by using direct laser writing (DLW) technique. The proposal is demonstrated by the direct fabrication of an array and a complex of symmetry-broken nanocorrals with DLW followed by a metal deposition process. SERS measurements show significant SERS enhancement, which can be controlled through engineering the focused “hot spots” by changing the structural parameters. The experimental observations are further confirmed by our simulations with a finite-difference time-domain tool. The studies can be extended to versatile SERS substrates with arbitrary geometries.     

Surface-enhanced Raman scattering (SERS)-based volatile organic compounds (VOCs) detection using plasmonic bimetallic nanogap substrate

In this paper, we present surface-enhanced Raman scattering (SERS)-based volatile organic compounds (VOCs) detection with bimetallic nanogap structure substrate. Deep UV photolithography at the wavelength of 250 nm is used to pattern circular shape nanostructures. The nanogap between adjacent circular patterns is 30 ± 5 nm. Silver (30 nm) and gold (15 nm) plasmonic active layers are deposited on the nanostructures subsequently. SERS measurements on different concentrations of acetone vapor ranged from 0.7, 1.5, 3.5, 10.3, 24.5 % and control have been performed with the substrate. The measurement results are found reproducible, and the detection limit is found to be 9.5 pg (acetone molecule). The detection sensitivity is 28.7 % higher than that of the recent reported leaning silicon nanopillar substrate. With further system miniaturization, the sensing technique can work as a portable SERS-based VOCs detection platform for point-of-care breath analysis, homeland security, chemical sensing and environmental monitoring.     

Combined taper-and-cylinder optical fiber probes for highly sensitive surface-enhanced Raman scattering

A combined taper-and-cylinder optical fiber fabricated by simple tube-etching and modified with silver nanoparticles is developed for surface-enhanced Raman scattering (SERS) sensing. It has the advantages of high light transmission efficiency and large interaction areas for light and silver nanoparticles. The detection of rhodamine 6G in remote mode indicates that the sensitivity could realize 10^?13 M. The fiber SERS probe with high flexibility and sensitivity shows great potential for molecule detection in various sensing applications.     

Investigation of the catalysis and SERS properties of flower-like and hierarchical silver microcrystals

Noble metal nano/microstructures have attracted considerable attention because of their unique properties and their various applications. Controlling the shape of noble metal nano/microstructures is a promising strategy to tailor their physical and chemical properties for various applications in fields such as biological labeling and imaging, catalysis, and sensing. Among various specific structures, flower-like and hierarchical silver nano/microstructures have attracted increasing interest because exploration of these novel nano/microstructures with unusual optical properties can provide new perspectives into the rational design of novel materials. It is significantly more challenging to develop facile and effective solution approaches for systematic manipulation of the shape of Ag nano/microstructures. In this article, we revisited the ascorbic acid reduction method to prepare flower-like silver microcrystal with plate petals and hierarchical Ag microcrystal on a large scale and in high purity. Ascorbic acid plays two roles of a reducing agent and a crystal growth regulator. Therefore, the molar ratio of ascorbic acid and silver nitrate is critical to the formation of Ag microcrystal. The controlling of the two different Ag microstructures can be achieved by adjusting the molar ratio of the reactants in aqueous medium at room temperature. The as-prepared Ag microcrystals were characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The flower-like Ag microcrystal with plate petals and hierarchical Ag microcrystal with nanoscale sharp tips and gaps could exhibit high catalytic activity and strong surface-enhanced Raman spectroscopy (SERS) activity due to the high surface area and the local electromagnetic field intensity enhancement, respectively. The potential application of the as-prepared Ag microcrystals in catalysis and SERS was investigated, which revealed that these two kinds of Ag microcrystals exhibit high catalytic activities to the NaBH₄-catalyzed reduction of 4-nitrophenol and significant SERS effect to 4-aminothiophenol molecular due to their nanoscale sharp tips and gaps. Therefore, the flower-like Ag microcrystal and hierarchical Ag microcrystal investigated here could be promising candidates for single particle catalyst and SERS.     

Optimized AC conductivity correlated to structure,morphology and thermal properties of PVDF/PVA/Nafion composites

Polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) composites were prepared by controlled loading of Nafion (5 to 15 wt%) by solution casting using water and dimethylformamide (DMF) as a solvent. The surface morphology of composite analyzed by atomic force microscopy (AFM) reveals the presence of Nafion ionomers. The increase in interlayer spacing of modified PVDF/PVA polymer system as a function of Nafion was detected by X-ray diffraction (XRD). The major change in Fourier transform infrared (FTIR) spectroscopy confirms the chemical bond C=O stretching around 1,700 cm^?1 due to Nafion. Differential scanning calorimetry (DSC) demonstrates the thermal stability of polymer composites and the decrease in melting temperature (T _m). The optimized AC conductivity (σ) of the prepared composite was evaluated by using an impedance analyzer as a function of temperature (40 to 150 °C) at constant 30-MHz frequency. The highest conductivity of 1.3?×?10^?2 S m^?1 was observed at 80 °C for 10 wt% of Nafion and correlated with structure, morphology and thermal properties of modified PVDF/PVA/Nafion composites. The experimental results may be useful for sensors, fuel cells and battery application domains.     

Plasma-assisted hot filament chemical vapor deposition of AlN thin films on ZnO buffer layer: toward highly c-axis-oriented,uniform, insulative films

c-Axis-oriented aluminum nitride (AlN) thin film with improved quality was deposited on Si(111) substrate using ZnO buffer layer by plasma-assisted hot filament chemical vapor deposition. The optical and electrical properties and surface morphology as well as elemental composition of the AlN films deposited with and without ZnO buffer layer were investigated using a host of measurement techniques: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and current–voltage (I–V) characteristic measurement. The XRD and XPS results reveal that the AlN/ZnO/Si films are free of metallic Al particles. Also, cross-sectional FESEM observations suggest formation of a well-aligned, uniform, continuous, and highly (002) oriented structure for a bi-layered AlN film when Si(111) is covered with ZnO buffer. Moreover, a decrease in full width at half maximum of the E₂ (high)-mode peak in Raman spectrum indicates a better crystallinity for the AlN films formed on ZnO/Si substrate. Finally, I–V curves obtained indicate that the electrical behavior of the AlN thin films switches from conductive to insulative when film is grown on a ZnO-buffered Si substrate.     

System design considerations for precision measurement of high magnetic fields by Faraday effect

Practical and technical considerations for an instrument designed to measure high magnetic fields by Faraday effect are given. Magnetic fields up to 2 Tesla were measured and the results compared to those of Nuclear Magnetic Resonance technique. Results of measurements at low temperatures are also reported.     

Synthesis of fluorescent carbon dots from one-step pyrolysis of frontal-polymerized poly(acrylamide-co-4-vinylpyridine)

We report herein the synthesis of carbon dots (CDs) by a one-step pyrolysis from poly(acrylamide-co-4-vinylpyridine) [poly(AAM-co-4-VP)]. The poly(AAM-co-4-VP) was fabricated using frontal polymerization within 5 min in an easy and rapid way and then was pyrolyzed to afford CDs. The as-prepared CDs show crystalline structure and excellent dispersibility with particle sizes in the range of 2–4 nm. The optical properties were throughly investigated, and we found the CDs exhibit strong blue fluorescence with quantum yield of ~18 % and excellent photoluminescent stability, which is rarely influenced by the external conditions. This process can be exploited as an effective path for synthesis CDs with polymers by a facile and rapid way.     

Radiative lifetimes of some energy levels of doubly ionized Xenon

Using 1–5 MeV Xenon ions we have studied the beam-foil spectrum of Xenon between 105 nm and 500 nm. Radiative lifetimes were measured for levels of Xenon III. For those lifetimes which have been measured previously (Andersen et al. [l]) good agreement is obtained. The interpretation of the decay curves and the assignment of a measured value, were done with the help of theoretical lifetimes obtained by Coulomb-approximation calculations [2].     

The KLL Auger spectrum of fluorine

The KLL Auger spectrum of fluorine (Z=9) has been studied in three different fluoride salts. Five Auger lines are observed in each compound in accordance with extreme LS coupling theory. A cation dependence of the Auger transition energies and line-widths is observed. The energy shifts are in agreement with a theoretical model.     

Synthesis at the nanoscale of ZnO into poly(methyl methacrylate) and its characterization

In this paper, PMMA/ZnO nanocomposites have been prepared by a very simple, facile and versatile chemical approach. The prepared PMMA/ZnO nanocomposites possess no color, high transparency, good thermal stability, UV-shielding capability, luminescence and homogeneity. The chemical process involved solution mixing of ZnO nanoparticles dispersed in DMAc with the Polymethylmethacrylate (PMMA) matrix dissolved in the same solvent. The effect of ZnO content on the physical properties of the PMMA matrix is investigated by X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, UV–Vis absorption and photoluminescence spectroscopy. It was found that pure hexagonal ZnO nanoparticles with an average particle size of 4–8 nm were homogeneously dispersed in the PMMA matrix. A significant improvement in thermal properties was observed with the incorporation of 1.0 wt% ZnO nanoparticles. The prepared nanocomposite films are highly transparent and a clear excitonic peak is observed in their absorption spectra. Measurement of room temperature photoluminescence spectra shows intensive near-band edge emission peak at 3.28 eV without any structural defects for a nanocomposite film with a filler content of 1.0 wt%.     

Beam-foil lifetime measurements on energy levels of singly ionized Xenon

Radiative lifetimes were measured for levels of Xenon II by use of the beam-foil technique. Results are compared with other experimental and theoretical data. The coulomb approximation [1] was used to calculate lifetimes of the higher levels of Xenon II to facilitate an unambiguous assignment of the measured lifetime to a level.     

The secondary-electron background problem in electron excited auger electron spectroscopy

Dynamic background subtraction is used to demonstrate that the recently suggested spline-polynomial scheme for characterizing the secondary electron background neglects an important aspect of the Auger feature. As a consequence of this neglect, area measurements using the spline approximation are difficult to relate to the true Auger current.     

Double-walled core-shell structured Si@SiO2@C nanocomposite as anode for lithium-ion batteries

Double-walled core-shell structured Si@SiO₂@C nanocomposite has been prepared by calcination of silicon nanoparticles in air and subsequent carbon coating. The obtained Si@SiO₂@C nanocomposite demonstrates a reversible specific capacity of about 786 mAh g^?1 after 100 cycles at a current density of 100 mA g^?1 with a capacity fading of 0.13 % per cycle. The enhanced electrochemical performance can be due to that the double walls of carbon and SiO₂ improve the electronic conductivity and enhance the compatibility of electrode materials and electrolyte as a result of accommodating the significant volumetric change during cycles. The interlayer SiO₂ may release the mechanical strain and enhance the interfacial adhesion between carbon shell and silicon core.     

Beam-foil-excited Auger transitions in neon

Energy spectra of electrons ejected from collisions between a carbon foil and Ne projectiles with energies between 1.4 and 20 MeV have been measured. Continuous and discrete electron energy distributions are observed. Auger transitions of foil-excited Ne have been studied. Using relativistic Dirac-Fock multiconfiguration calculations, most of the measured Auger transitions have been identified.     

Methods of IR spectroscopy in monitoring of chemotherapy of oncological pathologies using palladium complexes

FTIR spectroscopy is used to study mammary-gland tissues of mice with a sarcoma tumor (strain 180). Spectral features that are typical of malignant tumors are revealed in the FTIR spectra in the sarcoma-tumor tissues. Tumor tissues are studied after treatment using coordination compounds based on palladium complexes with 3-amino-1-hydroxypropylidene-1,1-diphosphonic acid and zoledronic acid. A therapeutic effect is not revealed after treatment using palladium complex with 3-amino-1-hydroxypropylidene-1,1-diphosphonic acid. The suppression of tumor growth amounts to 59% when palladium complexes with zoledronic acid are used. Suppression of tumor growth is accompanied by variations in spectral characteristics. With respect to diagnostic features, the FTIR spectra of tumor tissues after treatment with the palladium complexes with zoledronic acid are similar to the FTIR spectra of tissues that are free of malignant tumors. Specific spectroscopic characteristics that make it possible to control the chemotherapy of oncological pathologies are determined.     

Luminescent properties of Eu2+ ions in AlN at low and high intensity of excitation

Luminescent properties of powder AlN∶Eu²⁺ phosphors were studied by excitation of 2-nd harmonic of ruby laser (hv=3·56 eV). It was shown that emission spectra of AlN∶Eu²⁺ phosphors consist of five or two overlapping bands according to the concentration of europium and the intensity of excitation. Decay times of luminescence of Eu²⁺ centres in different peaks lie between 0·9 and 1·5 μsec which is in agreement with the value of decay time of 4f⁶ 5d→47⁷ transition of Eu²⁺ ions. It is evident from the decomposition of emission spectra of Eu²⁺ centres that there exist several types of Eu²⁺ centres in AlN as was already demonstrated in the case of oxygen centres in AlN.