Using Ultraviolet-visible Research Articles

Surface modification of polybutadiene facilitated by supercritical carbon dioxide

The hydrophilicity of polymers can be improved through surface modification, traditionally done with conventional organic solvents, but these may cause the deterioration of polymer bulk properties due to irreversible polymer swelling. However, supercritical carbon dioxide (scCO2) not only swells the polymer reversibly, but also acts as a convenient transport medium for monomeric solutes, which may be subsequently polymerized. Thus we are able to modify the polymer surface without affecting its bulk strength and durability. Here we report scCO2 surface modification of polybutadiene using ultraviolet-visible (UV/Vis) and Fourier transform infrared (FTIR) spectroscopy. Monomers such as 3-vinylbenzoic acid and crotonic acid are used to study the effects of pressure, solute structure, and reaction mechanism on the diffusion rates and partitioning of monomers between the fluid phase and the polymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 522–530, 2003

Photochromic and thermal properties of poly(vinyl alcohol)/H 6P 2W 18O 62 hybrid membranes

Poly(vinyl alcohol) (PVA) films, which contained different content of heteropolyacid (HPA) with Dawson–Wells structure, were prepared. The photochromic behavior was investigated by using ultraviolet–visible (UV-Vis) absorption spectroscopy. The result indicated that the film was reduced photochemically to yield a blue species under UV irradiation, and the color of the film changed to deep blue with increasing irradiation time and HPA content. The photochromic sensibility of different UV wavelength was investigated. In the UV-Vis spectra of the irradiated films, an isobestic point was observed at about 352 nm. The reduction mechanism of the heteropolyanion (W 6+→W 5+) was suggested. The thermal property and the conductivity of the film were also studied. The thermal degradation step and the melting point of the film were influenced by different content of the HPA. Notably, the conductivity of 8.33×10 −6 S cm −1 was observed when the HPA content was 80 wt.%.

Semiconducting CuClxBr1−x(x = 0–1) nanocrystals in thin films: synthesis and characterization

Thin films containing semiconducting nanocrystals of CuClxBr1−x (x = 0–1) were synthesized by the sol–gel process, by stepwise substitution of chloride ions by bromide ions. Cuprous oxide was used as the precursor for copper, HCl and HBr as halide sources, and the matrix sol was synthesized from 3-glycidoxypropyl(trimethoxy)silane (GPTS) and tetraethoxysilane (TEOS). The films were characterized using ultraviolet–visible (UV-VIS) spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction analysis. Thin films (thickness 0.7–1.0 µm) containing cubic CuClxBr1−x (x = 1–0) nanoparticles were obtained. For the samples having no bromide, the absorption spectrum showed a sharp absorption edge at 371 nm. Addition of HBr shifted the peak towards a higher wavelength, giving a peak that is characteristic of CuClxBr1−x; the addition of 1.85 × 10−2 mole of HBr leads to the complete substitution of chloride by bromide ions. The same observations were also made using X-ray diffraction.

Single-Shot Excimer Laser Annealing and In Process Ellipsometry Analysis for Ultra Shallow Junctions

AbstractSingle-shot Excimer Laser Annealing (ELA) was performed onto Si surface that was previously B+ implanted with or without Ge+ pre-amorphization. As a result, p+ type USJ (Ultra-Shallow Junction) has been formed. In process analysis, using Infrared Spectroscopic Ellipsometry (IR-SE) has been performed and compared with conventional 4-point probe method. Also, the corresponding crystallinity for the USJ of Si surface has been studied using Ultraviolet-Visible (UV-Vis) Spectroscopic Ellipsometry. In the case of pre-amorphization by Ge+ implantation, the laser energy density threshold required for melting the surface, and therefore for electrical activation, decreased drastically because of the difference in the thermodynamic properties of the amorphized Si. Estimation of the junction depth shows a shallower junction when using UV-SE, as compared to IR-SE. This can be explained by the fact that, in the UV range, the crystallinity of the top layer is predominant while IR-SE is more sensitive to dopant activation. This efficient single-shot ELA is a candidate for the USJ formation for sub-0.1 νm CMOS transistors. The effective method for investigating the activation state related to the crystallinity by using UV-SE and IR-SE is expected to apply as a non-contact analytical tool for USJ formation.

Binding of Nucleotides by T4 DNA Ligase and T4 RNA Ligase: Optical Absorbance and Fluorescence Studies

The interaction of nucleotides with T4 DNA and RNA ligases has been characterized using ultraviolet visible (UV-VIS) absorbance and fluorescence spectroscopy. Both enzymes bind nucleotides with the K d between 0.1 and 20 μM. Nucleotide binding results in a decrease of absorbance at 260 nm due to π-stacking with an aromatic residue, possibly phenylalanine, and causes red-shifting of the absorbance maximum due to hydrogen bonding with the exocyclic amino group. T4 DNA ligase is shown to have, besides the catalytic ATP binding site, another noncovalent nucleotide binding site. ATP bound there alters the π-stacking of the nucleotide in the catalytic site, increasing its optical extinction. The K d for the noncovalent site is ∼1000-fold higher than for the catalytic site. Nucleotides quench the protein fluorescence showing that a tryptophan residue is located in the active site of the ligase. The decrease of absorbance around 298 nm suggests that the hydrogen bonding interactions of this tryptophan residue are weakened in the ligase-nucleotide complex. The excitation/emission properties of T4 RNA ligase indicate that its ATP binding pocket is in contact with solvent, which is excluded upon binding of the nucleotide. Overall, the spectroscopic analysis reveals important similarities between T4 ligases and related nucleotidyltransferases, despite the low sequence similarity.

Thermal and photochemical formation of small gold colloids in sol-gel films

The formation of small gold colloids in SiO 2TiO 2 sol-gel films on soda-lime glass was investigated using ultraviolet-visible (UV-VIS) sectroscopy and electron microscopy. Conventional thermal reduction of gold ions in sol-gel films tended to form large particles due to growth or aggregation causing a hazy appearance in the high concentration range. It was found that a haze-free deep blue tinted film could be prepared by UV irradiations of the dried gel film before annealing at 500°C. Colloids with a narrow size distribution were formed in this film. Sufficient photoreduction of metallic species from gold salts is a key factor for the excellent coloration.