UV-visible Optical Absorption Spectroscopy Research Articles

An Organic Acid-induced Synthesis and Characterization of Selenium Nanoparticles

A simple wet chemical method has been developed to synthesize selenium nanoparticles (size 40–100 nm), by the reaction of sodium selenosulphate precursor with different organic acids in aqueous medium, under ambient conditions. Polyvinyl alcohol has been used to stabilize the selenium nanoparticles. The synthesized nanoparticles can be separated from its sol by using a high-speed centrifuge and can be redispersed in aqueous medium with a sonicator. UV-visible optical absorption spectroscopy, X-ray diffraction, energy dispersive X-rays, differential scanning calorimetry, atomic force microscopy, and transmission electron microscopy techniques have been employed to characterize the synthesized selenium nanoparticles.

Structure and Properties of - Nanocomposite Films for Biomedical Applications

The hemocompatibility of La2O3-doped TiO2 films with different concentration prepared by radio frequency (RF) sputtering was studied. The microstructures and blood compatibility of TiO2 films were investigated by scan electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-visible optical absorption spectroscopy, respectively. With the increasing of the La2O3 concentrations, the TiO2 films become smooth, and the grain size becomes smaller. Meanwhile, the band gap of the samples increases from 2.85 to 3.3 eV with increasing of the La2O3 content in TiO2 films from 0 to 3.64%. La2O3-doped TiO2 films exhibit n-type semiconductor properties due to the existence of Ti2+ and Ti3+. The mechanism of hemocompatibility of TiO2 film doped with La2O3 was analyzed and discussed.

Effect of surface microstructure and wettability on plasma protein adsorption to ZnO thin films prepared at different RF powers

In this paper, the adsorption behavior of plasma proteins on the surface of ZnO thin films prepared by radio frequency (RF) sputtering under different sputtering powers was studied. The microstructures and surface properties of the ZnO thin films were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible optical absorption spectroscopy and contact angle techniques. The results show that the ZnO thin films have better orientation of the (0 0 2) peak with increasing RF power, especially at around 160 W, and the optical band gap of the ZnO films varies from 3.2 to 3.4 eV. The contact angle test carried out by the sessile drop technique denoted a hydrophobic surface of the ZnO films, and the surface energy and adhesive work of the ZnO thin films decreased with increasing sputtering power. The amounts of human fibrinogen (HFG) and human serum albumin (HSA) adsorbing on the ZnO films and reference samples were determined by using enzyme-linked immunosorbent assay (ELISA). The results show that fewer plasma proteins and a smaller HFG/HSA ratio adsorb on the ZnO thin films' surface.

Synthesis and Characterization of Sodium Selenosulphate Induced PVA-Capped Gold Nanoparticles

A new method has been developed for the synthesis of gold nanoparticles by the reaction of auric acid with sodium selenosulphate, under ambient conditions. Gold nanoparticles were efficiently stabilized by polyvinyl alcohol even at a low concentration. Further, the effect of auric acid, sodium selenosulphate and stabilizer concentrations on the size of the gold nanoparticles has also been studied. The synthesized gold nanoparticles have been characterized by UV-visible optical absorption spectroscopy, X-ray powder diffraction, energy dispersive X-ray analysis, dynamic light scattering, atomic force microscopy and transmission electron microscopy techniques.

Riley oxidation: A forgotten name reaction for synthesis of selenium nanoparticles

A simple wet chemical method, involving reaction of acetone with selenium dioxide, has been developed, to synthesize polyvinyl alcohol-stabilized selenium nanoparticles. The method is capable of producing nanoparticles in the size range of about 100-300 nm, under ambient conditions. The synthesized nanoparticles can be separated easily from the aqueous sols by a high-speed centrifuge, and can be re-dispersed in aqueous medium by a sonicator. The effect of concentrations of selenium dioxide, acetone and PVA on the size of the selenium nanoparticles has been studied. The size of the selenium nanoparticles has been found to increase with increase in the reaction time as well as the concentration of selenium dioxide, while it decreases with increase in the concentration of the stabilizer, PVA. The synthesized selenium nanoparticles have been characterized by UV-visible optical absorption spectroscopy, X-ray diffraction, energy dispersive X-ray analysis, differential scanning calorimetry, atomic force microscopy, scanning electron microscopy and transmission electron microscopy techniques.

On the Thermal Stability of Extracellular Hemoglobin of glossoscolex Paulistus: Optical Spectroscopic Studies

Hemoglobin of Glossoscolex paulistus (HbGp) in the oxy- and cyanomet- forms was studied by dynamic light scattering (DLS) and optical absorption spectroscopy (OAS). At 25°C, oxy-HbGp, in the pH range 5.0-8.0, is stable presenting a mono-disperse size distribution with hydrodynamic diameter (Dh) of 27±1 nm. Cyanomet-HbGp behaves in a similar way up to pH 9.0. More alkaline pH, above 9.0, induced an irreversible dissociation process, resulting in smaller Dh of 10±1 nm, suggesting oligomeric dissociation. At pH 7.0, no oligomeric dissociation is observed as a function of temperature and denaturation occurs at 52°C and 57°C, respectively, for oxy- and cyanomet-HbGp. Dissociation temperatures were lower at higher pH, for both forms of HbGp. Based on the higher critical denaturation and dissociation temperatures cyanomet-HbGp is more stable than the oxy- form. Kinetic studies were performed for oxy-HbGp using UV-VIS OAS and DLS. Rate constants as a function of temperature and the activation energy (Ea) have been estimated by DLS for oxy-HbGp at pH 7.5 and 8.0, giving Ea values of 278 and 262 kJ/mol, respectively. Auto-oxidation kinetics monitored by UV-VIS at pH 8.0 in the temperature range 38-44°C is mono-exponential with an Ea value of 333 kJ/mol. Oligomeric protein dissociation promotes an increase in auto-oxidation rate and vice-versa. The present work shows that DLS is suitable to follow quantitatively the changes on the oligomerization of multisubunit proteins. Support: FAPESP, CNPq and CAPES Brazilian and FCT-MCTES Portuguese agencies.

Structure and haemocompatibility of ZnO films deposited by radio frequency sputtering

ZnO films were first deposited on silicon and glass substrates using radio frequency sputtering and then annealed in air at different temperatures from 300 to 700 °C. The microstructures, surface energy and optical properties of ZnO films were examined by x-ray diffraction, Raman spectroscopy, contact angle test and UV–visible optical absorption spectroscopy, respectively. Results show that a perfectly oriented ZnO (0 0 2) thin film is obtained in all ZnO samples. Raman spectroscopy, in combination with those derived by UV–visible optical absorption spectroscopy, provides us with an accurate description of ZnO nature, revealing that, after annealing, ZnO films exhibit better crystallinity and narrower optical energy gap. The contact angle test denotes that the adhesive work and polar component of the surface energy of ZnO films increase steadily with the annealing temperature, which leads to more active interaction between annealed ZnO films and blood plasma. The platelet adhesion experiment shows that there are fewer platelets adhered to the surface of ZnO films compared to the polyurethane (PU) used in clinical application, suggesting ZnO's better compatibility with blood. As the annealing temperature increases, the number of platelets adhered to ZnO films increases correspondingly, which we believe is due to the narrower optical energy gap. Therefore, the appropriate surface properties and the wide optical energy gap of ZnO thin films are believed to be the main factors responsible for the excellent haemocompatibility.

Vinyl monomers-induced synthesis of polyvinyl alcohol-stabilized selenium nanoparticles

A simple wet chemical method has been developed to synthesize selenium nanoparticles (size 100–200 nm), by reaction of sodium selenosulphate precursor with different vinyl monomers, such as acrylamide, N,N′-dimethylene bis acrylamide, methyl methacrylate, sodium acrylate, etc., in aqueous medium, under ambient conditions. Polyvinyl alcohol has been used to stabilize the selenium nanoparticles. Average size of the synthesized selenium nanoparticles can be controlled by adjusting concentration of both the precursors and the stabilizer. Rate of the reaction as well as size of the resultant selenium nanoparticles have been correlated with the functional groups of the different monomers. UV–vis optical absorption spectroscopy, X-ray diffraction, energy dispersive X-rays, differential scanning calorimetry, atomic force microscopy, scanning electron microscopy and transmission electron microscopy techniques have been employed to characterize the synthesized selenium nanoparticles. Gas chromatographic analysis of the reaction mixture established the non-catalytic role of the vinyl monomers, which were found to be consumed during the course of the reaction.

Growth of ordered silver nanoparticles in silica film mesostructured with a triblock copolymer PEO–PPO–PEO

Elaboration of mesostructured silica films with a triblock copolymer polyethylene oxide–polypropylene oxide–polyethylene oxide, (PEO–PPO–PEO) and controlled growth of silver nanoparticles in the mesostructure are described. The films are characterized using UV–visible optical absorption spectroscopy, TEM, AFM, SEM, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Organized arrays of spherical silver nanoparticles with diameter between 5 and 8 nm have been obtained by NaBH 4 reduction. The size and the repartition of silver nanoparticles are controlled by the film mesostructure. The localization of silver nanoparticles exclusively in the upper-side part of the silica-block copolymer film is evidenced by RBS experiment. On the other hand, by using a thermal method, 40 nm long silver sticks can be obtained, by diffusion and coalescence of spherical particles in the silica-block copolymer layer. In this case, migration of silver particles toward the glass substrate-film interface is shown by the RBS experiment.

Clustering of germanium atoms in silica glass responsible for the 3.1 eV emission band studied by optical absorption and X-ray absorption fine structure analysis

Correlation between the 3.1 eV emission band and local atomic configuration was systematically examined for Ge + implanted silica glass by UV–vis optical absorption spectroscopy and X-ray absorption fine structure (XAFS) analysis. The 2.7 eV emission band, commonly observed in defective silica, was replaced by the sharp and intense 3.1 eV emission band for the Ge + fluence > 2 × 10 16 cm −2, in which UV–vis absorption spectra suggested clustering of Ge atoms with the size ∼1 nm. XAFS spectroscopy indicated that the Ge atoms were under coordinated with oxygen atoms nearly at a neutral valence state on average. The present results are consistent with the previous ESR study but imply that the small Ge clusters rather than the O=Ge: complexes (point defects) are responsible for the 3.1 eV emission band.

Effect of annealing on structure and haemocompatibility of tetrahedral amorphous hydrogenated carbon films

Tetrahedral amorphous hydrogenated carbon (ta–C:H) films with higher sp3 C fraction were prepared using a magnetic-field-filter plasma stream deposition system. The influences of annealing on the microstructure, optical properties and blood compatibility of ta–C:H films were investigated by using Raman spectra, UV–visible optical absorption spectroscopy and tests of platelet adhesion, respectively. Results show that the graphitization of ta–C:H films is significantly promoted when annealing temperature over 400 °C, resulting in a decrease of optical band gap from 2.3 to 0.2 eV in a annealing temperature range of 200 °C–600 °C. The quantity and morphology of the adherent platelets on the surface of samples indicated that the blood compatibility of ta–C:H films significantly depend on annealing temperature, and retrogression origin of the blood-compatibility of ta–C:H films were analyzed and discussed.

Structure and optical properties of M/ZnO (M=Au, Cu, Pt) nanocomposites

Metal (Au, Cu, Pt)/zinc oxide nanocomposite films were prepared with different metal contents by radio frequency co-sputtering technique. The films were annealed at different temperatures in an argon atmosphere for 2 h. Formation of metal nanoparticles was studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD). UV-Vis optical absorption spectroscopy was used for optical characterization of the samples. With the increase of annealing temperature, the size of the metal particles in the ZnO matrix varied. Surface plasmon resonance bands were observed in the Au/ZnO and Cu/ZnO composite films due to the formation of nanometer-size Au and Cu particles in the matrix. However, a similar behavior was not seen with Pt/ZnO composites. Upon incorporation of Pt nanoparticles in the ZnO matrix, the optical band gap of the matrix was drastically reduced.

Spin control of the lifetime of an intramolecular charge-transfer excited state.

Triplet-sensitized generation of a long-lived intramolecular charge-separated excited state is described in an electron donor-acceptor molecule with a short distance between the donor and the acceptor. Time-resolved UV-Vis optical absorption spectroscopy shows that the lifetime of this triplet excited state is 1.4 micros in acetonitrile at 298 K, i.e. five orders of magnitude greater than that of the corresponding singlet charge-separated state. In slightly less polar alkane nitrile solvents, the local and CT triplet states coexist, which allows determination of their relative energies.

Effect of high temperature annealing on optical and thermal properties of CVD diamond

Structural changes in diamond films of different qualities caused by annealing in vacuum up to 1600°C have been studied by IR and UV-visible optical absorption, Raman and photoluminescence spectroscopy. An internal degradation of the diamond films and a strong optical absorption enhancement in the whole UV-vis-IR range take place at T>1300°C, and correlate with the loss of bonded hydrogen. At least 25% of the total amount of hydrogen is found to be in the unbound state in some of the as-grown (untreated) films. The diamond darkening is ascribed to appearance of graphite-like phases presumably at grain boundaries. Activation energy of GB transformation process is much lower (250–530 kJ/mol) compared to surface graphitization of single crystal diamond. No evidence of charge transfer altering the concentration of substitutional nitrogen N 0 S and N A−N D (in B-doped films) upon annealing was found. Thermal conductivity measured by laser flash technique remains almost constant (20 W/cmK) even after annealing to 1575°C, then catastrophically drops because of crack development in the film.

Sol–Gel Synthesis and Characterization of Ag and Au Nanoparticles in SiO2, TiO2, and ZrO2 Thin Films

Silver and gold nanoparticles were synthesized by the sol–gel process in SiO2, TiO2, and ZrO2 thin films. A versatile method, based on the use of coordination chemistry, is presented for stabilizing Ag+ and Au3+ ions in sol–gel systems. Various ligands of the metal ions were tested, and for each system it was possible to find a suitable ligand capable of stabilizing the metal ions and preventing gold precipitation onto the film surface. Thin films were prepared by spin‐coating onto glass or fused silica substrates and then heat‐treated at various temperatures in air or H2 atmosphere for nucleating the metal nanoparticles. The Ag particle size was about 10 nm after heating the SiO2 film at 600°C and the TiO2 and ZrO2 films at 500°C. After heat treatment at 500°C, the Au particle size was 13 and 17 nm in the TiO2 and ZrO2 films, respectively. The films were characterized by UV–vis optical absorption spectroscopy and X‐ray diffraction, for studying the nucleation and the growth of the metal nanoparticles. The results are discussed with regard to the embedding matrix, the temperature, and the atmosphere of the heat treatment, and it is concluded that crystallization of TiO2 and ZrO2 films may hinder the growth of Ag and Au particles.

Microstructure, microhardness, composition, and corrosive properties of stainless steel 304

Tetrahedral amorphous carbon films (ta-C) and nitrogen-containing ta-C films have been prepared using a magnetic-filtered plasma-deposition method in pure Ar, and Ar with N2 ambient, respectively. The structural and optical properties of these films have been studied using UV-visible optical absorption spectroscopy, Raman spectroscopy, and measurements of electrical conductivity in the temperature range from 300 to 500 K. The value of the optical band gap for the ta-C films deposited at suitable conditions were found to be larger than 3 eV. For nitrogen-containing ta-C films deposited at low partial pressure of nitrogen, the incorporation of a small amount of nitrogen will result in a slight drop in activation energy of conductivity and a decrease in band gap, which indicates that there are evidently both doping effect of nitrogen and graphitization of bonding. The study of surface morphology has been performed using atomic force microscopy (AFM), and results show that the surface roughness increases with the amount of nitrogen incorporated in ta-C films. The correlation between surface roughness and configuration of N atoms in ta-C network is also discussed.

Formation and characteristics of undoped and doped tetrahedral amorphous carbon films

Abstract Synthesis of undoped and doped tetrahedral amorphous carbon (ta-C) films has been achieved using magnetic field filtered plasma stream system in an ambient gas of pure Ar and Ar with N 2 , respectively. The optical and electrical properties of these films as a function of the substrate bias voltages ( V b ) or nitrogen partial pressures ( P N ) have been studied using UV-visible optical absorption spectroscopy, Fourier-transform infra-red spectroscopy (FTIR) and measurements of electrical conductivity. The results show that ta-C films with a high sp 3 fraction were formed when the V b was in the range of −10 to −50 V. The optical band gap of such ta-C films was found to be larger than 3 eV. The incorporation of nitrogen into the ta-C films deposited at low P N ( P N

Development of Fourier transform spectrometry for UV–visible differential optical absorption spectroscopy measurements of tropospheric minor constituents

Concentration measurements of trace gases in the atmosphere require the use of highly sensitive and precise techniques. The UV-visible differential optical absorption spectroscopy technique is one that is heavily used for tropospheric measurements. To assess the advantages and drawbacks of using a Fourier transform spectrometer, we built a differential optical absorption spectroscopy optical setup based on a Bruker IFS 120M spectrometer. The characteristics and the capabilities of this setup have been studied and compared with those of the more conventional grating-based instruments. Two of the main advantages of the Fourier transform spectrometer are (1) the existence of a reproducible and precise wave-number scale, which greatly simplifies the algorithms used to analyze the atmospheric spectra, and (2) the possibility of recording large spectral regions at relatively high resolution, enabling the simultaneous detection of numerous chemical species with better discriminating properties. The main drawback, on the other hand, is due to the fact that a Fourier transform spectrometer is a scanning device for which the scanning time is small compared with the total measurement time. It does not have the signal integration capabilities of the CCD or photodiode array-based grating spectrographs. The Fourier transform spectrometer therefore needs fairly large amounts of light and is limited to short to medium absorption path lengths when working in the UV.

Effects of nitrogen on the structure and properties of highly tetrahedral amorphous carbon films

Nitrogen-containing tetrahedral amorphous carbon films (ta-C) have been prepared using a magnetic field filtered plasma stream deposition method. The plasma stream was first formed by sputtering of a graphite target in nitrogen-argon atmospheres. The partial pressure of nitrogen, , was in the range 0-7 Pa at total pressure of deposition Pa. The optical and electrical properties of samples were studied using x-ray photoelectron spectroscopy (XPS), Fourier transform infrared absorption spectroscopy (FTIR), UV-visible optical absorption spectroscopy and measurements of electrical conductivity in the temperature range 300-500 K. The incorporation of small amounts of nitrogen will result in an increase in electrical conductivity, a slight drop of the band gap and an increase in band-tail absorption. These suggest that incorporation of a small amount of nitrogen into ta-C films will induce graphitization of bonding. For samples deposited at Pa, nitrogenation of films is very pronounced. The actual nitrogen content in films in terms of atomic percentage can be as much as 47%. The films have a wide band gap of 4.05 eV and an extremely low electrical conductivity. These suggest that a carbon nitride film is formed. The configurations of N atoms in the ta-C network are identified and discussed.