Celso U. Davanzo

Properties of titanium oxide films obtained by PECVD

Abstract Amorphous TiO 2 films containing carbon and excess oxygen were deposited from glow discharge plasmas of titanium tetraisopropoxide Ti(OC 3 H 7 ) 4 , helium, oxygen and argon mixtures. The discharge was generated in a stainless steel vacuum chamber by two parallel-plate electrodes connected to a 13.56 MHz power supply. A substrate holder, to which a d.c. bias voltage could be applied, was positioned outside the region between the two electrodes, i.e. in a region of lower plasma density. The substrate voltage bias, V B , and the ratio of the partial pressures of O 2 to Ti(OC 3 H 7 ) 4 [oxygen to precursor (OTP) ratio] in the chamber were adopted as the principal deposition parameters. Details of the molecular structure of the films were investigated by infrared spectroscopy and X-ray photoelectron spectroscopy. The latter was also used to determine the O/Ti and C/Ti atomic ratios at the film surface. The total (surface and bulk) O/Ti and C/Ti atomic ratios were determined using Rutherford backscattering spectroscopy. While neither the surface nor the total O/Ti ratio varied significantly with V B and the OTP ratio, both the surface and total C/Ti ratios varied strongly with these parameters. The refractive index, determined by ultraviolet-visible spectroscopy, and the electrical conductivity, measured by a two-point probe, were influenced by the polarity and magnitude of V B .

Influence of Curing Mode and Time on Degree of Conversion of One Conventional and Two Self-adhesive Resin Cements

This study evaluated the effect of curing mode (auto- and dual-polymerizing mode) and time interval (5, 10 and 15 minutes) on the degree of conversion of resin cements. One conventional dual-cured resin cement (Panavia F 2.0 [Kuraray Medical Inc]) and two self-adhesive cements (RelyX Unicem [3M ESPE] and BisCem [BISCO, Inc]) were evaluated. The products (n = 5) were manipulated according to the manufacturers instructions and applied to the surface of a horizontal attenuated reflectance unit attached to an infrared spectrometer. The materials were either light-cured for 40 seconds (dual-polymerizing mode) or allowed to auto-polymerize. The degree of conversion was calculated according to changes in the aliphatic-to-aromatic peak ratios prior to and 5, 10 and 15 minutes after light-activation or after mixing when the specimens were allowed to auto-polymerize. Data (%) were analyzed by two-way repeated measure ANOVA (curing mode and time interval) and Tukeys post-hoc test (alpha = 0.05%). The light-activating mode led to a higher degree of conversion values than the self-curing mode in self-adhesive cements (RelyX Unicem and BisCem), while there was no difference in the degree of conversion between the self- and light-cured groups of Panavia F 2.0 resin cement. All products showed a higher degree of conversion at 15 minutes postcuring than any other evaluation interval. The self-adhesive cements provide a higher degree of conversion values when light-activated. After 15 minutes of polymerization initiation, the degree of conversion was higher in all resin cements, regardless of the curing mode.

Antimony(v) oxide grafted onto a silica gel surface: acidic properties and thermal stability

Antimony(v) oxide grafted onto a silica gel surface was obtained in highly dispersed form, with antimony density of 0.65 atoms nm–2. The material presents Bronsted and Lewis acid properties different from pyrochlore, Sb2O5. These sites disappear upon thermal treatment at 500 °C owing to reaction of antimony oxide with the silica surface.

Simultaneous determination of ash content and protein in wheat flour using infrared reflection techniques and partial least-squares regression (PLS)

Partial Least Square (PLS) multivariate calibration associated to Near Infrared Reflection Spectroscopy (NIRRS) or Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) were used to establish methods for simultaneous determination of protein and ash content on commercial wheat flour samples of Triticum aestivum L. Duplicate spectra of 100 samples with protein content between 8.85-13.23% (Kjeldahl method) and ash content between 0.330-1.287% (gravimetric method) were employed to build calibration methods. The spectra were used in log (1/R) format as well as in the first and second derivatives and they were also pre-processed by mean centering (MC) or variance scaling (VS) or both. The samples were divided in two sets, one with 55 samples and the other with 45 used as calibration and validation sets, respectively. Calibration methods were obtained by using minimum values of root mean square error of calibration (RMSEC) and root mean square error of validation (RMSEV). Methods of calibration with RMSEC and RMSEV values lower than 0.33 in the determination of protein content and lower than 0.07 in the determination of ash content. The proposed methods are environmentally non aggressive as they avoid the use of reagents and do not generate hazardous waste. Furthermore, they allow fast and non destructive simultaneous and direct determination of ash and protein content in wheat flour samples.

Photoluminescence spectrum redshifting of porous silicon by a polymeric carbon layer

Photoluminescence of porous silicon at room temperature shifts to a larger wavelength in low‐resistivity Si samples (0.006 Ω cm) when compared to the one emitted by high resistivity samples (0.4 Ω cm). This shift is associated with a coating of hydrocarbon over the porous silicon structure. The hydrocarbon coating was identified by electron energy loss spectroscopy imaging together with infrared spectroscopy.

Determination of intrinsic viscosity of poly(ethylene terephthalate) using infrared spectroscopy and multivariate calibration method

A methodology was developed to determine the intrinsic viscosity of poly(ethylene terephthalate) (PET) using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and multivariate calibration (MVC) methods. Multivariate partial least squares calibration was applied to the spectra using mean centering and cross validation. The results were correlated to the intrinsic viscosities determined by the standard chemical method (ASTM D 4603-01) and a very good correlation for values in the range from 0.346 to 0.780dLg(-1) (relative viscosity values ca. 1.185-1.449) was observed. The spectrophotometer detector sensitivity and the humidity of the samples did not influence the results. The methodology developed is interesting because it does not produce hazardous wastes, avoids the use of time-consuming chemical methods and can rapidly predict the intrinsic viscosity of PET samples over a large range of values, which includes those of recycled materials.

Infrared reflection-absorption characterization of TiO2 films on ITO: detection of LO modes

Abstract By exploiting the high reflectivity of ITO substrates in the infrared and the detection of longitudinal optical (LO) modes provided by oblique incidence of radiation (Berreman effect), we showed that reflection-absorption experiments in the MID-IR can be successfully performed when thin inorganic oxide films deposited on ITO are used as samples. The samples we used were TiO 2 films deposited on ITO by a sol-gel method. After being annealed at different temperatures, the films presented different structures, which could be detected by the IR spectra. Cyclic voltammograms of the samples were also presented and correlated to the IR spectra. Since we expect that other inorganic oxides can yield similar results, this simple, non-destructive and inexpensive technique can be routinely used in an electrochemical laboratory.

Observation of the Berreman Effect in Infrared Reflection-Absorption Spectra of Amorphous Titanium Oxide Thin Films Deposited on Aluminum

Infrared reflection-absorption spectra of plasma-enhanced chemical vapor deposition (PECVD) amorphous TiO2 thin films on aluminum were obtained with s- and p-polarized light and oblique incidence angles. Such spectra were analyzed by means of spectral simulations based on a Fresnel equation for a three-layered system. The optical constants used in the simulations were obtained through the Kramers–Krönig analysis of the reflectance spectra of a pellet of powdered amorphous TiO2. LO-TO energy-loss functions were also calculated from these optical constants, and a splitting was observed. A good qualitative agreement between experimental and simulated spectra was achieved, and the Berreman effect was observed in both cases when p-polarized light was used. It was shown, therefore, that the Berreman effect makes infrared reflection-absorption spectroscopy a successful technique for the characterization of an amorphous TiO2 thin layer on aluminum.

Influence of the donor strength of the ligands on the structure of the hexacoordinated complexes of tin(IV) chloride. A vibrational spectroscopy study

Abstract Twenty three tin(IV) tetrahalide adducts with various monodentate ligands, cis - and trans - L 2 ·SnX 4 , were studied by IR and Raman spectroscopy at room temperature and above. The observed SnX stretching frequencies as well as the structure, are correlated with the donor number of the ligands. In some cases the basicity or the bulkiness of the ligand are not the prevalent factors in determining the structure of the complex.

s - and p -Polarized Infrared Specular Reflectance of Vitreous Silica at Oblique Incidences: Detection of LO Modes

Infrared (IR) specular reflectance spectra of a semi-infinite sample of vitreous silica (v-SiO2) were obtained with the use of both s- and p-polarized light and oblique incidence angles. The optical constants of the material and hence its longitudinal optic/transverse optic (LO-TO) functions were determined through the Kramers–Krönig analysis (KKA) of its s-polarized 20° off-normal reflectance spectrum. p-Polarized spectra had their reflection maxima blue-shifting as the incidence angle increased, while they remained unchanged for the s-polarized spectra. Since an LO mode generally lies at wavenumbers higher than its respective TO mode, such a blue shift may be due to the detection of the LO mode in addition to the TO mode as incidence angle increased. The only exception to this observation was the high-frequency shoulder, which underwent a sharp intensification as the incidence increased. The present work shows that it is indeed brought about by the weakly IR active asymmetrical mode (AS2) but only because it takes place immediately after the intense AS1 mode, which causes the refraction index spectrum to have a broad dip below unity. Such a dip is proven to be responsible for the sharp increase in the high-frequency shoulder of the reflectance spectra.