Surface-enhanced Raman scattering active substrates by liquid flame spray deposited and inkjet printed silver nanoparticles

Surface-enhanced Raman scattering (SERS) active substrates were made via liquid flame spray deposition and inkjet printing of silver nanoparticles. Both processes are suitable for cost-effective fabrication of large-area SERS substrates. Crystal violet (CV) solutions were used as target molecules and in both samples the detection limit was approximately 10 nM. In addition, sintering temperature of the inkjet printed silver nanoparticles was found to have a large effect on the SERS activity with the higher curing temperature of 200 °C resulting in contamination layer on silver and cancelation of the SERS signal. This layer was characterized using an X-ray photoelectron spectroscopy (XPS).     

Picosecond bismuth-doped fiber MOPFA for frequency conversion

We report the development of a bismuth-doped fiber master oscillator power fiber amplifier system. The system operates at 1177 nm, producing 28 ps pulses at 9.11 MHz repetition rate, with an output power of 150 mW and a peak pulse power of 580 W. We subsequently frequency double the output, resulting in a picosecond pulsed visible source operating at 588.5 nm, with a maximum average output power of 13.7 mW.     

Spectral control in anisotropic resonance-domain metamaterials

We introduce a concept to control the spectral and dichroic properties of metamaterials. The approach is based on anisotropic metal nanoparticles and on varying their mutual orientation in a periodic lattice. Even seemingly inconsequential changes in particle ordering strongly modify the dichroic properties of the arrays and result in either very narrow resonances or ultrabroad extinction ranges. The results arise from long-range diffractive coupling between the particles, as determined by the dependence of the array unit cell size on particle ordering.     

Adsorption of bacteria and polycations on model surfaces of cellulose, hemicellulose and wood extractives studied by QCM-D

Quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) were used as the tools to study the adsorption of bacteria onto surfaces of silica and polystyrene coated with materials related to papermaking. Cationic polyelectrolytes used as fixatives and retention aids in paper industry were found to promote irreversible adsorption of the ubiquitous white water bacterium, Pseudoxanthomonas taiwanensis, onto model surfaces of cellulose (pH 8). The high charged low molecular weight polyelectrolyte, poly(diallyldimethyl) ammonium chloride (pDADMAC) adsorbed to silica surface as a flat and rigid layer, whereas the low charged cationic polyacryl amide (C-PAM) of high molecular weight adsorbed as a thick and loose layer. AFM images showed that the polyelectrolytes accumulated as layers around each bacterial cell. In the presence of wood hemicellulose (O-acetyl-galactoglucomannan) the bacteria adsorbed massively, as large, tightly packed rafts (up to 0.05mm in size) onto the polystyrene crystal surface coated with wood extractives (pH 4.7). AFM and FESEM micrographs also showed large naked areas (with no bacteria) in between the bacterial rafts on the crystal surface. In this case, QCM-D only incompletely responded to the massiveness of the bacterial adsorption. The results indicate that cationic polymers can be used to increase the retention of bacteria from the process water onto the fibre web and that, depending on the balance between hemicelluloses and wood extractives and pH of the process waters, bacteria can be drawn from process waters onto surfaces.     

Stepwise 1D growth of luminescent Au(I)-Ag(I) phosphine-alkynyl clusters: synthesis, photophysical, and theoretical studies

Reactions between the diphosphino-gold cationic complexes [Au(2)(PPh(2)-C(2)-(C(6)H(4))(n)-C(2)-PPh(2))(2)](2+) (n = 0, 1, 2, 3) and polymeric acetylides (AuC(2)Ph)(n) and (AgC(2)Ph)(n) lead to the formation of a new family of heterometallic clusters with the general formula [Au(8+2n)Ag(6+2n)(C(2)Ph)(8+4n)(PPh(2)C(2)(C(6)H(4))(n)C(2)PPh(2))(2)](2+), n = 0 (1), 1 (2), 2 (3), 3 (4). Compounds 1-4 were characterized in detail by NMR and ESI-MS spectroscopy. Complex 1 (n = 0) crystallizes in two forms (orange (1a) and yellow (1b)), one of which (1a) has been analyzed by X-ray crystallography. The luminescence behavior of 1-4 has been studied. Compounds 2 and 3 exhibited orange-red phosphorescence with quantitative quantum efficiency in both aerated and degassed CH(2)Cl(2), implying O(2)-independent phosphorescence due to efficient protection of the emitting chromophore center by the organic ligands. Complex 3 exhibits reasonable two-photon absorption (TPA) property with a cross section of σ ≈ 45 GM (800 nm), which is comparable to the value of commercially available TPA dyes such as coumarin 151. Computational studies have been performed to correlate the structural and photophysical features of the complexes studied. The metal-centered triplet emission within the heterometallic core is suggested to play a key role in the observed phosphorescence. The luminescence spectrum of 1 in CH(2)Cl(2) shows dual phosphorescence maximized at 575 nm (the P(1) band) and 770 nm (the P(2) band). Both P(1) and P(2) bands possess identical excitation spectra, i.e., the same ground-state origin, and the same relaxation dynamics throughout the temperature range of 298-200 K. The dual emission of 1 arises from fast structural fluctuation upon excitation, perhaps forming two geometry isomers, which exhibit distinctly different P(1) and P(2) bands. The scrambling dynamics might require large-amplitude motion and, hence, is hampered in rigid media, as evidenced by the single emission for 1a (610 nm) and 1b (570 nm) observed in solid.     

Isomerism of [64Cu-NOTA-Bn]-labeled radiotracers: separation of two complex isomers and determination of their interconversion energy barrier using ion pair chromatography

The model complex [(64)Cu((S)-p-NH(2)-Bn-NOTA)](-) ([(64)Cu]1) was used to study the isomerism of [(64)Cu-NOTA-Bn]-labeled radiotracers. Two complex isomers [(64)Cu]1a and [(64)Cu]1b, which were formed at a ratio of 1:9 during the complexation of [(64)Cu]Cu(2+) with (S)-p-NH(2)-Bn-NOTA, were separated using ion pair chromatography. To study the interconversion, the nonradioactive complex isomers Cu1a and Cu1b were separated and thermally treated at 90 °C in both ammonium acetate solution and deionized water. A faster interconversion rate was observed for both isomers with lower concentrations of ammonium ions. At the end of reaction, the thermodynamic Cu1a to Cu1b equilibrium ratio was 6:94. The particular energy barriers of the interconversion for Cu1a and Cu1b were 130 kJ mol(-1) and 140 kJ mol(-1). Spectrophotometric measurements with Cu1a and Cu1b revealed two isomers adopting different geometrical configurations.     

Soy protein–nanocellulose composite aerogels

Organic aerogels based on two important and widely abundant renewable resources, soy proteins (SP) and nanofibrillar cellulose (NFC) are developed from precursor aqueous dispersions and a facile method conducive of channel- and defect-free systems after cooling and freeze-drying cycles that yielded apparent densities on the order of 0.1 g/cm³. NFC loading drives the internal morphology of the composite aerogels to transition from network- to fibrillar-like, with high density of interconnected cells. Composite aerogels with SP loadings as high as ca. 70 % display a compression modulus of 4.4 MPa very close to that obtained from reference, pure NFC aerogels. Thus, the high compression modulus of the composite system is not compromised as long as a relatively low amount of reinforcing NFC is present. The composite materials gain moisture (up to 5 %) in equilibrium with 50 % RH air, independent of SP content. Furthermore, their physical integrity is unchanged upon immersion in polar and non-polar solvents. Fast liquid sorption rates are observed in the case of composite aerogels in contact with hexane. In contrast, water sorption is modulated by the chemical composition of the aerogel, with an important contribution from swelling. The potential functionalities of the newly developed SP–NFC composite green materials can benefit from the reduced material cost and the chemical features brought about the amino acids present in SPs.     

An example concerning the zero set of the Jacobian

Let f∈W1,1(Ω,Rn) be a homeomorphism of finite distortion K. It is known that if K1/(n−1)∈L¹(Ω), then the Jacobian Jf of f is positive almost everywhere in Ω. We will show that this integrability assumption on K is sharp in any Orlicz-scale: if α is increasing function (satisfying minor technical assumptions) such that limt→∞α(t)=∞, then there exists f such that K1/(n−1)/α(K)∈L¹(Ω) and Jf vanishes in a set of positive measure.     

Effects of intermediate zinc pulses on properties of TiN and NbN films deposited by atomic layer epitaxy

The reasons for the improvements gained by using intermediate zinc pulses in atomic layer epitaxy growth of TiN and NbN films were examined by a comprehensive characterization and comparison of films prepared from TiCl₄ or NbCl₅ and NH₃ with and without zinc. The characterization techniques used comprise time-of-flight elastic recoil detection analysis, secondary ion mass spectrometry, Rutherford backscattering spectrometry, nuclear resonance broadening, proton backscattering spectrometry, deuteron induced reactions, proton induced X-ray emission, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and Hall effect and reflectance measurements. The effect of zinc was found to be manifold: both compositional and structural changes were observed. In the case of TiN the major improvement gained by using zinc was significantly decreased oxygen contamination whereas a marked increase of grain size was the dominant effect observed with NbN. A clear correlation between the compositional and structural changes and the improvements of the electrical properties was established.     

Molecular dynamics simulations of water droplets on polymer surfaces

Molecular dynamics simulations were used to study the wetting of polymer surfaces with water. Contact angles of water droplets on crystalline and two amorphous polyethylene (PE) and poly(vinyl chloride) (PVC) surfaces were extracted from atomistic simulations. Crystalline surfaces were produced by duplicating the unit cell of an experimental crystal structure, and amorphous surfaces by pressing the bulk polymer step by step at elevated temperature between two repulsive grid surfaces to a target density. Different-sized water droplets on the crystalline PE surface revealed a slightly positive line tension on the order of 10(-12)-10(-11) N, whereas droplets on crystalline PVC did not yield a definite line tension. Microscopic contact angles produced by the simple point charge (SPC) water model were mostly a few degrees smaller than those produced by the extended SPC model, which, as the model with lowest bulk energy, presents an upper boundary for contact angles. The macroscopic contact angle for the SPC model was 94 degrees on crystalline PVC and 113 degrees on crystalline PE. Amorphicity of the surface increased the water contact angle on PE but decreased it on PVC, for both water models. If the simulated contact angles on crystalline and amorphous surfaces are combined in proportion to the crystallinity of the polymer in question, simulated values in relatively good agreement with measured values are obtained.