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 title 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-Kronig analysis (KKA) of its s-polarized 20 degrees 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) hut 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.54450250

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

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 TiO2 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. (C) 2002 Elsevier Science B.V. All rights reserved.4430130

Sol-gel titanium dioxide thin films on platinum substrates: preparation and characterization

Titanium dioxide was prepared by hydrolysis and polycondensation of titanium tetraisopropoxide. TiO2 films were obtained by spin-coating platinum substrates with the precursor solution. Infrared reflection-absorption spectroscopy, Raman spectroscopy and X-ray diffractrometry showed that films prepared at 100 degreesC were amorphous, films dried at 400 and 600 degreesC were composed of anatase and those prepared at 800 degreesC were rutile. Independent of the drying temperature, field emission scanning electron microscopy of the electrode surface showed that films have a cracked morphology. Cyclic voltammetry carried out at different scan rates showed that in films dried from 100 to 600 degreesC, the mass transport occurs by a semi-infinite linear diffusion. For rutile, however, the cyclic voltammetry results were better fitted considering a linear peak current, I-p, dependence on scan rate, i.e., the mass transport can be characterized by a surface reaction where the diffusion occurs only on the electrode I film interface (thin layer diffusion). Films were also characterized by electrochemical impedance spectroscopy. For an ac frequency equal to 10,000 Hz, the flatband potentials shifted toward more positive potentials as the drying temperature increased. The S800 sample showed lower donor densities (1.2 x 10(18) cm(-3) at 10,000 Hz) compared with the other samples. The electrochemical behavior of the films was discussed in the light of structural differences. (C) 2003 Elsevier Science B.V. All rights reserved.544475

Infrared and Raman studies on films of organosiloxane networks produced by PECVD

The effect of the incorporation of oxygen and nitrogen on the structure of films obtained by PECVD of hexamethyldisiloxane (HMDSO)-He-N-2 and HMDSO-He-O-2 mixtures is investigated using infrared and Raman spectroscopies. From transmittance spectra of films deposited onto single-crystal KBr disks, the transverse optical (TO) and longitudinal optical (LO) functions in the mid-infrared region were calculated. To correlate structural aspects with the observed LO-TO splittings, an identification analysis of functional group based on the infrared and Raman literature was made. It was concluded that the structure of the films deposited from HMDSO-He-O-2 discharges was strongly dependent on the proportion of oxygen in the gas feed. In the absence of oxygen, i.e., for a discharge of a HMDSO-He mixture, the resulting film consisted of a network of interconnected siloxane and carbosilane units. Addition of O-2 precluded the formation of methylene bridges and induced the formation of a material enriched with Si-O-Si groups. Films formed from the HMDSO-He-N-2 plasmas, on the other hand, consisted mainly of interconnected siloxane and carbosilane units in addition to a small quantity of silazane units. On the basis of these results, we propose an interpretation for the variation of the LO-TO splitting amplitude for the asymmetrical stretching mode (AS1) of Si-O in Si-O-Si groups as a function of the oxygen or nitrogen incorporation into the films.37245946

Effect of thickness, chemical nature of dopants and an alkyl substituent on absorption bands of polyaniline

The effect of thickness, an alkyl substituent in the ortho position and the chemical nature of the counterion on the absorption spectra of polyaniline films was studied. Previous work performed using the electrochemical quartz crystal microbalance technique (EQCM) has shown a greater participation of anions in the ionic exchange process when the thickness of the film is increased. This fact was attributed to morphological changes leading to different densities of the polymer film, which was demonstrated by SEM experiments. Changes in absorption spectra provoked by conformational changes due to the presence of a substituent and the effect of the chemical nature of the anions art analyzed for Cl-, ClO4- and p-toluene sulfonate (PTS-).21242

LO-TO splittings in plasma-deposited siloxane films

The present work presents LO and TO functions in the mid-infrared region for thin films deposited from glow discharge plasmas of tetramethylsilane (TMS) diluted either in Ar or O-2 or in mixtures of these two gases. These functions were calculated through the Kramers-Kronig analysis of transmittance spectra of the films supported on KBr disks. To correlate structural aspects of the films with the observed LO-TO splittings, a group frequency analysis based on the literature was made. Such an analysis indicated that the films deposited from the TMS Ar mixture were formed mainly by a polycarbosilane skeleton, whereas those deposited from TMS-O-2 and TMS-O-2-Ar were formed by a random network of four types of distorted tetrahedra: (CH3)(3)SiO0.5, (CH3)(2)SiO, (CH3SiO1.5), and SiO2. From the LO-TO splitting for the asymmetrical stretching mode of Si-O-Si groups, the density and the presence of defects in samples obtained from TMS-O-2 and TMS-O-2-Ar mixtures were evaluated. The number of defects increased as the Ar-to-O-2 flow rate decreased. We also report for the first time LO-TO splittings for bands related to the bending of CH3 and to the stretching of the Si-C bond in Si(CH3)(x) groups. The knowledge of such splittings is very important for a correct evaluation of the infrared reflection -absorption spectra taken at oblique incidence of thin films containing Si-O bonds and Si(CH3)(x) groups deposited on metals.10739106991070

Modification of plasma-polymerized organosiloxane films by irradiation with He+, Ne+, Ar+, and Kr+ ions

The effects of ion irradiation on the composition, structure, compactness, and surface hardness of polyorganosiloxane films synthesized by plasma-enhanced chemical vapor deposition were investigated as a function of the ion mass and fluence. The films were obtained from a glow discharge plasma of a hexamethyldisiloxane (HMDSO)-O-2-Ar mixture, and the irradiations were carried out with 170 keV He+, Ne+, Ar+, and Kr+ ions at fluences between 1 x 10(14) and 1 x 10(16) cm(-2). To characterize the film elemental composition, two ion-beam analysis techniques were used: Rutherford backscattering spectroscopy (RBS) and forward recoil spectroscopy (FRS). The ion-beam-induced hydrogen loss from the films was significant. For the He+-irradiated samples, a H loss of about 50% with respect to the pristine or unirradiated film was observed for the highest fluence. The surface hardness measurements, performed with a nanoindenter, in films irradiated at a fluence of 1 x 10(16) cm(-1) were 8.1, 6.0, 4.7, and 1.6 GPa for He+, Ne+, Ar-,(+) and Kr+, respectively. To examine the ion-induced structural transformations in the films, infrared reflection-absorption spectroscopy (IRRAS) was employed. From analysis of the spectra of the irradiated samples several conclusions could be drawn. For example, as the ion fluence increased, (i) the densities of methyl- and Si-O-related groups changed, (ii) film disorder increased, and (iii) groups such as Si-CH2-Si, and Si-OH, which were not present in the pristine film, were formed at lower fluences but disappeared when the latter attained their highest values. Furthermore, some of the absorption peaks that appeared at low fluences and increased with increasing fluence strongly indicate formation of carbon domains in the film. Finally, differences in the ion-induced modifications produced by the different ion species were analyzed in terms of the electronic and nuclear collisions of the ions traversing the film using the well-known SRIM simulation program.17235789579

Nanocomposites of amorphous hydrogenated carbon and siloxane networks produced by PECVD

16456756

Helium ion irradiation of polymer films deposited from TMS-Ar plasmas

Polymer films synthesized from plasmas of a tetramethylsilane - Ar mixture were modified by irradiation with 170 keV He ions at fluences ranging from 1 x 10(14) to 1 x 10(16) cm(-2). As revealed by infrared spectroscopy, the ion beam produced intense bond rearrangements, such as the depletion of bonding groups (C-H and Si-H), and induced the formation of new ones, such as O-H and Si-O. From the nanoindentation measurements, a remarkable increase in the surface hardness of the films was observed as the ion fluence was increased. The increases in hardness were accompanied by an increase in the film compaction as shown by using a combination of RBS and film thickness measurements. From both hardness and infrared measurements A was concluded that, under the He ion bombardment, the polymer structure is transformed into a silicon oxycarbide network.4448949