SERS signal response and SERS/SERDS spectra of fluoranthene in water on naturally grown Ag nanoparticle ensembles

We present experimental results of the time‐dependent Raman signal response of fluoranthene adsorbed on a naturally grown Ag nanoparticle ensemble, which serves as surface enhanced Raman scattering (SERS) substrate. In addition, SERS characteristics such as the concentration‐dependent calibration curves and the limit of detection (LOD) for fluoranthene in distilled water will be shown. The SERS substrate was prepared by Volmer–Weber growth under ultrahigh vacuum condition and exhibits a plasmon resonance wavelength at 491 nm. For the measurement of SERS signal response and SERS/shifted excitation Raman difference spectroscopy spectra of fluoranthene in water, experimental Raman setup containing a microsystem light source with two emission wavelengths (487.61 nm and 487.91 nm) was used. We experimentally demonstrate that the maximum SERS intensity is achieved 9 min after changing the analyte concentration from 0 nmol/l to 600 nmol/l. This response time is explained by a time‐dependent adsorption of the probe molecules onto the nanoparticles. The LOD for fluoranthene in water was evaluated applying shifted excitation Raman difference spectroscopy (SERDS) at different molecule concentrations. For SERDS, two emission wavelengths of a prototype microsystem light source have been used for Raman excitation. The experimental results reveal that the LOD for the probe molecules is very low. Experimentally, we have detected a fluoranthene concentration of only 4 nmol/l, which is very close to our estimated LOD of 2 nmol/l. Thus, the presented Raman setup, with a SERS substrate, whose plasmon resonance coincides with the excitation wavelength for SERS measurements, is well suited for in‐situ trace detection of pollutant chemicals in water. Copyright © 2013 John Wiley & Sons, Ltd.     

High‐power HgGa2S4 optical parametric oscillator pumped at 1064 nm and operating at 100 Hz

The defect chalcopyrite crystal HgGa₂S₄ has been employed in a 1064‐nm pumped optical parametric oscillator operating at 100 Hz, to generate ∼5 ns long idler pulses near 4 µm with energies as high as 6.1 mJ and average power of 610 mW. At crystal dimensions comparable to those available for the commercial AgGaS₂ crystal, operation of the 1064‐nm pumped HgGa₂S₄ OPO is characterized by much lower pump threshold and higher conversion efficiency, with the most important consequence that such a device might become practical at pump levels sufficiently lower than the optical damage threshold.     

Turbulence in noninteger dimensions by fractal Fourier decimation

Fractal decimation reduces the effective dimensionality D of a flow by keeping only a (randomly chosen) set of Fourier modes whose number in a ball of radius k is proportional to k(D) for large k. At the critical dimension D(c)=4/3 there is an equilibrium Gibbs state with a k(-5/3) spectrum, as in V. L'vov et al., Phys. Rev. Lett. 89, 064501 (2002). Spectral simulations of fractally decimated two-dimensional turbulence show that the inverse cascade persists below D=2 with a rapidly rising Kolmogorov constant, likely to diverge as (D-4/3)(-2/3).     

Solutions for the storage and handling of SPINE standard pucks

Currently there is no rack system for the long‐term storage of SPINE pucks in spite of their commercial availability and heavy usage at the ESRF. The only way to store pucks is in transport dewar canisters which presents a number of limitations and drawbacks. Here a simple affordable rack for storing SPINE pucks is described, which we believe is accessible to not only synchrotrons but also both academic and industrial research laboratories.     

Utilizing Experiment and Theory to Evaluate Rhodamine B ethylenediamine as a Fluorescent Sensor for G-type Nerve Agents

Nerve gas mimic binding with Rhodamine B ethylenediamine (1) was studied in organic media. Binding of the nerve gas mimic, diethyl chlorophosphate (DCP), with the probe generated a non-fluorescent intermediate and a fluorescent product. Fluorescent and non-fluorescent products generated were identified using mass spectrometry and X-ray crystallography. Time-dependent density functional theory calculations were also used to investigate the electronic structure of the fluorescent probe in the ground and lowest lying π?→?π* singlet excited state. Though good agreement between theory and experiment can be obtained for the intense peak in the experimental spectrum using non-hybrid functionals, care must be taken when modelling these complexes due to the appearance of an n?→?π* transition that is too low in energy and appears to fall in the shoulders of the π?→?π* transitions.

     

Interactions between oligopeptides and oxidised titanium surfaces detected by vibrational spectroscopy

Five alternating polar/hydrophobic oligopeptides derived from EAK 16 (AEAEAKAKAEAEAKAK) were examined in comparison with EAK 16 (peptide 1) both after solubilisation/lyophilisation and deposition on oxidised titanium surfaces. The peptides were synthesised for their possible use as biomimetic materials due to their self‐assembling properties and the presence, in one of them, of the arginine‐glycine‐aspartic (RGD) sequence, an active modulator of cell adhesion. Infrared (IR) and Raman spectroscopies were used to investigate the influence of the amino acid substitution on the self‐assembling properties of the peptides under both experimental conditions. In the lyophilised peptides, β‐sheet was the prevailing conformation (65–69%) as in EAK 16, irrespective of acid substitution (E→D, peptide 2), basic substitution (K→O, peptide 3), hydrophobic spacer substitution (A→Abu, peptide 4 and A→Y, peptide 5) and RGD insertion (peptide 6). After deposition on oxidised titanium, the main conformation remained β‐sheet. The side‐chain shortening of the acidic amino acid residue (peptide 2) or the insertion of a rigid and bulky residue such as Y (peptide 5) decreased the self‐assembling ability more than the side‐chain shortening of the basic amino acid residue (peptide 3) or the insertion of the RGD head (peptide 6). The interaction with the oxidised titanium surface was mainly due to carboxylate groups with a bidentate bridging coordination and C  O peptidic groups. Copyright © 2010 John Wiley & Sons, Ltd.     

Spectroscopy of the hyperfine structure of antiprotonic 4He and 3He

The spin magnetic moment $\mu^{\overline{p}}_{s}$ of the antiproton can be determined by comparing the measured transition frequencies in $\overline{p}^4$ He^?+? with three-body QED calculations. A comparison between the proton and antiproton can then be used as a test of CPT invariance. The highest measurement precision of the difference between the proton and the antiproton spin magnetic moments to date is 0.3%. A new experimental value of the spin magnetic moment of the antiproton was obtained as $\mu^{\overline{p}}_{s} = -2.7862(83)\mu_{N}$ , slightly better than the previously best measurement. This agrees with $\mu^{p}_{s}$ within 0.24%. In 2009, a new measurement with antiprotonic ³He has been started. A comparison between the theoretical calculations and experimental results would lead to a stronger test of the theory and address systematic errors therein. A measurement of this state will be the first HF measurement on $\overline{p}^3$ He^?+?. We report here on the new experimental setup and the first tests.     

Hexadecapolar Kondo effect in URu2Si2?

We derive the coupling of a localized hexadecapolar mode to conduction electrons in tetragonal symmetry. The derivation can be easily adapted to arbitrary multipoles in an arbitrary environment. We relate our model to the two-channel Kondo (2CK) model and show that for an f(2) configuration a relevant crystal field splitting in addition to the 2CK interaction is intrinsic to tetragonal symmetry. We discuss possible realizations of a hexadecapolar Kondo effect in URu(2)Si(2). Solving our model we find good agreement with susceptibility and specific heat measurements in Th(1-x)U(x)Ru(2)Si(2) (x?1).     

Current status of the TwinMic beamline at Elettra: a soft X‐ray transmission and emission microscopy station

The current status of the TwinMic beamline at Elettra synchrotron light source, that hosts the European twin X‐ray microscopy station, is reported. The X‐ray source, provided by a short hybrid undulator with source size and divergence intermediate between bending magnets and conventional undulators, is energy‐tailored using a collimated plane‐grating monochromator. The TwinMic spectromicroscopy experimental station combines scanning and full‐field imaging in a single instrument, with contrast modes such as absorption, differential phase, interference and darkfield. The implementation of coherent diffractive imaging modalities and ptychography is ongoing. Typically, scanning transmission X‐ray microscopy images are simultaneously collected in transmission and differential phase contrast and can be complemented by chemical and elemental analysis using across‐absorption‐edge imaging, X‐ray absorption near‐edge structure or low‐energy X‐ray fluorescence. The lateral resolutions depend on the particular imaging and contrast mode chosen. The TwinMic range of applications covers diverse research fields such as biology, biochemistry, medicine, pharmacology, environment, geochemistry, food, agriculture and materials science. They will be illustrated in the paper with representative results.