The fabrication of substrates for Surface Enhanced Raman Scattering (SERS) applications matching the needs for high sensitive and reproducible sensors remains a major scientific and technological issue. We correlate the morphological parameters of silver (Ag) nanostructured thin films prepared by sputter deposition on flat silicon (Si) substrates with their SERS activity. A maximum enhancement of the SERS signal has been found at the Ag percolation threshold, leading to the detection of thiophenol, a non-resonant Raman probe, at concentrations as low as 10−10M, which corresponds to enhancement factors higher than 7 orders of magnitude. To gain full control over the developed nanostructure, we employed the combination of in-situ time-resolved microfocus Grazing Incidence Small Angle X-ray Scattering with sputter deposition. This enables to achieve a deepened understanding of the different growth regimes of Ag. Thereby an improved tailoring of the thin film nanostructure for SERS applications can be realized.

This work reports on the formation of different types of structures on the surface of polymer films upon UV laser irradiation. Poly(ethylene terephthalate) was irradiated with nanosecond UV pulses at 193 and 266 nm. The polarization of the laser beam and the irradiation angle of incidence were varied, giving rise to laser induced surface structures with different shapes and periodicities. The irradiated surfaces were topographically characterized by atomic force microscopy and the chemical modifications induced by laser irradiation were inspected via micro-Raman and fluorescence spectroscopies. Contact angle measurements were performed with different liquids, and the results evaluated in terms of surface free energy components. Finally, in order to test the influence of surface properties for a potential application, the modified surfaces were used for mesenchymal stem cell culture assays and the effect of nanostructure and surface chemistry on cell adhesion was evaluated.

This article describes a procedure for either amperometric or potentiometric determination of iodine formed by the oxidation of iodide by chlorine dioxide, chlorine, chlorite, and chlorate. Either phenylarsine oxide or sodium thiosulfate can be used as the titrant. Sample pretreatment and pH adjustment are used to differentiate among the various chlorine species.

In this Letter, we report on the successful fabrication of low loss, high refractive index contrast waveguides via ion migration upon femtosecond laser writing in phosphate glass. Waveguides were produced in two different phosphate glass compositions with high and low La 2 O 3 content. In the La-rich glass, a large refractive index increase in the guiding region was observed due to the incoming migration of La accompanied by the out-diffusion of K. The much smaller refractive index change in the La-less glass is caused by rearrangements of the glass structure. These results confirm the feasibility of adapting the glass composition for enabling the laser writing of high refractive index contrast structures via spatially selective modification of the glass composition. The origin of the refractive index modification caused by femtosecond (fs) laser irradiation in phosphate glasses has been investigated by several research groups. In such reports, mostly commercial glass from Kigre, Inc. (QX and MM2) and Schott AG (IOG) are used [1][2][3][4][5]. Most of these glasses were developed for telecommunication research and industry as base materials for waveguide fabrication by Ag-Na ion exchange [6][7][8]. With the advent of fs-laser-inscription techniques, demand for new glasses grew even higher due to the ability of fast prototyping and fabrication of complex 3D custom components [5]. Still, little effort was made to optimize the glass composition for this new technique. Due to the versatility of fs-laser writing, many problems were surmounted by adjusting the processing conditions to produce excellent results in various glasses [1,5]. However, there is little doubt that glass composition is a key parameter for further optimizing fs-laser-written optical devices. Among various commercial phosphate glass compositions, we have identified and isolated a set of glass with and without La 2 O 3 to demonstrate the importance of optimizing the glass matrix composition for fs-laser writing. We show that the presence of La 2 O 3 enables us to achieve a large positive refractive index contrast (RIC) in the written structures. The responsible mechanism is identified as the migration of La to form a region of increased refractive index accompanied by out-diffusion of K. The compositional changes unambiguously correlate to positive and negative refractive index modifications. Indeed, the refractive index changes observed via La migration are far beyond what can be attributed to changes in the glass structure.In the present work, we have investigated in detail the role of La 2 O 3 in the photo-inscription mechanisms in phosphate glasses. The addition of La 2 O 3 to P 2 O 5 -Al 2 O 3 glasses is known to increase the refractive index of the glass [9,10] as well as to improve its thermal, mechanical, and optical properties. We have used two different QX special melt phosphate glass samples from Kigre, Inc., both doped with 2 wt. % Er and 4 wt. % Yb (QX was introduced as a laser glass capable of withstanding high thermal loading and shoc...

No abstract

aIn this work we present the formation of laser induced periodic surface structures (LIPSS) on spin-coated thin films of several model aromatic polymers including poly(ethylene terephthalate), poly(trimethylene terephthalate) and poly carbonate bis-phenol A upon irradiation with femtosecond pulses of 795 and 265 nm at fluences well below the ablation threshold. LIPSS are formed with period lengths similar to the laser wavelength and parallel to the direction of the laser polarization vector. Formation of LIPSS upon IR irradiation at 795 nm, a wavelength at which the polymers absorb weakly, contrasts with the absence of LIPSS in this spectral range upon irradiation with nanosecond pulses. Real and reciprocal space characterization of LIPSS obtained by Atomic Force Microscopy (AFM) and Grazing Incidence Small Angle X-ray Scattering (GISAXS), respectively, yields well correlated morphological information. Comparison of experimental and simulated GISAXS patterns suggests that LIPSS can be suitably described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice. Fluorescence measurements, after laser irradiation, provide indirect information about dynamics and structure of the polymer at the molecular level. Our results indicate that the LIPSS are formed by interference of the incident and surface scattered waves. As a result of this process, heating of the polymer surface above its glass transition temperature takes place enabling LIPSS formation.

No abstract

Natural extracts possess several kinds of antioxidants (anthocyanins, betalains, thymol, carvacrol, and resveratrol) that have also demonstrated antimicrobial properties. In order to study these properties, extracts from cranberry, blueberry, beetroot, pomegranate, oregano, pitaya, and resveratrol (from grapes) were obtained. Growth inhibition tests of mesophilic aerobes, coliforms, and fungi were conducted in films prepared from the extracts in accordance with Mexican Official Norms (NOM). Optical properties such as transparency and opacity, mechanical properties, and pH were also analyzed in these materials. The films with beetroot, cranberry, and blueberry extracts demonstrated the best antimicrobial activity against various bacteria and fungi in comparison with unmodified chitosan–starch film. This study shows that the addition of antioxidants improved the antimicrobial performance of these films. It was also found that antimicrobial properties are inherent to the films. These polymers combined with the extracts effectively inhibit or reduce microorganism growth from human and environmental contact; therefore, previous sterilization could be unnecessary in comparison with traditional plastics. The presence of extracts decreased transmittance percentages at 280 and 400 nm, as well as the transparency values, while increasing their opacity values, providing better UV–VIS light barrier properties. Despite diminished glass transition temperatures (Tg), the values obtained are still adequate for food packaging applications.