Optical Nanocomposite Planar Waveguides Doped with Rare-Earth and Noble Metal Elements

The present paper is focused on multilayer Er³⁺-doped silica-titania planar waveguides, co-doped with silver, which were prepared by spin-coating on silica glass, or buffered single crystal silicon substrates. The single layer thickness (0.4 m) and refractive index (1.60–1.63) were measured by spectroscopic ellipsometry at 715 nm. The thickness of the waveguides (measured by mechanical profilometry) was 1 m and their optical propagation losses were measured at different laser wavelengths (488 nm, 514 nm and 633 nm), exhibiting an approximately Rayleigh-like behavior. The thermal precipitation of silver nanocrystallites was achieved, both in air and under a controlled atmosphere (dry nitrogen) and these were characterized by visible absorption spectroscopy, which clearly showed the development of a plasmon absorption band near 415 nm, by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The Er³⁺ metastable level lifetimes for the emission at ca. 1.54 m were found to be ca. 4–6 ms, for Er³⁺ concentrations varying between 0.2–2.0 mol% (or (0.4–4.4) × 10²⁰ ions/cm³), but no significant variation was observed with the Ag concentration added (up to 2.5 mol%).     

Optical and Electrical Characteristics of Polymer Films Modified with Nanostructured Silver Aggregates

To study the formation of a new dispersed phase in polymer layers, the absorption of radiation-generated silver aggregates in cellophane films was examined. Stable silver nanoparticles were prepared by the radiation-chemical reduction of silver ions in a solution of inverted micelles of the composition AgNO₃(AgClO₄)/H₂O/AOT/octane. On irradiation of cellophane films immersed in a micellar solution, the formed silver aggregates Ag^m+ _nbecame incorporated into the films. The modified films exhibited a stable yellow color. The intensity of an optical absorption band of the films with _max 420–440 nm increased proportionally to the radiation dose absorbed by an aqueous micellar solution. The light sensitivity of these films was examined. A 35-min exposure of the films at = 365 nm resulted in an increase in the intensity of the main absorption band by 17% and in a bathochromic shift of the maximum. The electrical characteristics of modified films were determined depending on the radiation dose. It was found that the incorporation of nanostructured silver clusters exhibiting the characteristic optical absorption band with _max 420–440 nm increased the conductivity of cellophane films by two to three orders of magnitude.     

Borohydride reduction of AgNO<Subscript>3</Subscript> in polyacrylate aqueous solutions: Two-stage synthesis of “blue silver”

Two-stage synthesis of blue silver, complex compound of metal clusters and polyacrylic acid anion having a typical absorption band at 750 nm was performed by the partial oxidation of unstable products resulted from the borohydride reduction of silver cations in polyacrylate aqueous solutions.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 243–247.Original Russian Text Copyright © 2005 by B. Sergeev, Lopatina, Prusov, G. Sergeev.     

An EELS and EXELFS study of amorphous hydrogenated silicon carbide

A series of thin films of amorphous hydrogenated silicon carbide (a-SiCH) produced by RF plasma decomposition of propane and silane has been studied by electron energy-loss spectroscopy (EELS) and extended energy-loss fine structure (EXELFS) studies. The composition of the films has been determined by EELS and the nearest neighbour spacings have been determined by EXELFS. These results, along with the energy of the plasmon loss peaks, have been compared with the deposition conditions for each film. The results show that for a large gas ratio (C₃H₈/(C₃H₈+SiH₄)) the films have a high proportion of carbon and are similar to a-CH in structure, whereas those films prepared with Y = 0.4 or 0.5 have nearest neighbour spacings consistent with those for tetrahedrally bonded carbon. The films prepared with lowest Y have nearest neighbour spacings similar to those for amorphous silicon carbide. The results for a-SiCH have been compared with the results of EELS and EXELFS of CVD diamond films, amorphous carbon and amorphous silicon.     

Accuracy of film thickness determination in electron probe microanalysis

The thickness of copper films (100–450 nm) on silicon substrates was determined by electron probe microanalysis (EPMA) applying (z) procedures of Pouchou and Pichoir. Film thickness was calculated from experimental k-ratios analyzed with electron energies between 6 and 30 keV using commercial software (LAYERF distributed by CAMECA). The influence of the incident electron energy and X-ray line chosen for analysis on the results was investigated. Accuracy of film thickness determination was evaluated by comparison with Rutherford backscattering spectroscopy (RBS) and secondary ion mass spectrometry (SIMS). The difference between layer thicknesses determined with EPMA and RBS is in general less than 2%, if EPMA measurements are performed with various electron energies. Layer thicknesses determined with Cu-L are mostly closer to values obtained by RBS than those derived from Cu-K radiation. Preliminary SIMS measurements yielded inconsistent results and, thus, cannot be used in this case to determine the layer thickness of Cu films on Si accurately.     

Thickness Determination of Ultra-Thin Films on Si Substrates by EPMA

Results from thickness determination of single-element ultra-thin (<10nm) films by electron probe microanalysis (EPMA) are presented. The studied samples were Ge, Sn, Ag and Au thin films deposited by resistive evaporation on Si substrates. The thickness of the films was controlled during evaporation by means of a quartz crystal, previously calibrated using samples with overlayers of different thicknesses (>20nm) measured by Rutherford backscatter spectrometry and optical interferometry. EPMA measurements were performed on an electron microprobe CAMECA SX-50, with incident electron energies ranging from 4keV to 20keV. Film thicknesses were derived from the measured k-ratios using the analytical programs X-Film and Layerf and the Monte Carlo simulation code Penelope. The ionization cross sections used in the simulations were calculated with the distorted-wave Born approximation. Film thicknesses obtained from the EPMA measurements using the various computational methods are compared with those measured with the quartz crystal. The maximum relative difference between results from the different techniques does not exceed 5%.     

Insertion of 3d- and 4f-Elements into Silver Iodide

The interaction of manganese and some 4f-metals (M) with silver iodide is studied. The samples are obtained by sputtering M onto the surface of polycrystalline AgI films (0.2 m, 300 K) in a vacuum. Optical absorption in the samples is interpreted as the insertion of M ions into AgI with the formation of dopants AgI:M. A new phase with an optical bandgap of 3.7 eV emerges in the samples with elevated concentrations of La, Ce, Pr, Nd, Sm, or Dy (n _M/n _Ag 0.1). X-ray diffraction patterns for such samples with Sm correspond to structures with large interfacial distances, for example, 0.99, 0.87, 0.76, and 0.67 nm. In air, AgI forms in the samples with a new phase; this process is hindered by the sputtered protective coatings. According to optical absorption data, X-ray diffraction, and local microanalysis the Mn insertion into AgI is followed by the formation of a new phase (2Ag:Mn:4I), which may belong with solid electrolytes Ag₂MI₄, where nonmagnetic M are known (Zn, Cd, Sn, Hg, Pb).     

Sol-Gel Derived Titania/γ-Glycidoxypropyltrimethoxysilane and Methyltrimethoxysilane Hybrid Materials for Optical Waveguides

We report here on titania/organically modified silane hybrid materials produced by the sol-gel technique for optical waveguide applications. Acid catalyzed solutions of -glycidoxypropyltrimethoxysilane and methyltrimethoxysilane mixed with tetrapropylorthotitanate have been used as precursors for the hybrid materials. Waveguide films with a thickness about 1.3-m have been prepared on a silicon substrate by a single-coating process and low-temperature heat treatment. Atomic force microscopy (AFM), thermal gravimetric analysis (TGA), UV-visible spectroscopy (UV-VIS), and Fourier transform infrared (FTIR) spectroscopy have been used to investigate the optical and structural properties of these waveguide films. The results have shown that dense, pore-free, and highly transparent films can be obtained by low temperature heat treatment. The planar waveguide propagation loss of the hybrid films has also been measured.     

“Blue silver”: transformation of clusters and metal coagulation

The formation and transformations of blue silver ( _max 700 nm) during -irradiation of a weakly alkaline (pH 9) aqueous solution containing AgClO₄, polyacrylic acid (PAA), and isopropanol were studied. We believe that blue silver is a linear silver cluster stabilized on a polymeric molecule. During radiation-chemical reduction the cluster is transformed into new clusters ( _max = 365 and 460 nm). When all of the Ag⁺ ions present in the solution have been reduced, clusters coalesce and a new phase,i.e., colloidal silver particles, forms. The mechanism of the radiation-chemical transformations is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–37, January, 1995.     

Hydrogen determination by means of the1H(19F, αγ)16 O and1H(15N, αγ)12C resonance reactions

Hydrogen surface contamination and depth profiles can be measured by the resonant nuclear reactions¹H(¹⁹F, )¹⁶O and¹H(¹⁵N, )¹²C. The method was applied to study hydrogen-implanted silicon, amorphous silicon layers and silicon oxide films produced by anodic oxidation.     

Electrochemical Production of Ultrathin Silicon Dioxide Films

Low-temperature synthesis of ultrathin (20 nm) SiO₂ films, by anodizing semiconductor single-crystal silicon wafers, is studied. Effects of physicochemical properties of electrolyte and single-crystal silicon on the films' dielectric characteristics are considered.     

Characterization of ion-implanted silicion by Rutherford backscattering spectrometry and ellipsometry

It is demonstrated that the information obtained by Rutherford backscattering spectrometry and channeling technique can substantially help in the construction of a realistic optical model for the ellipsometry of ion-implanted silicon. In the case of fully amorphous ion-bombarded layers, the ellipsometry is a fast, non-destructive and contactless method to estimate the thickness of these films. For buried and partially disordered layers a qualitative interpretation of different trajectories in the - plance can be given on the basis of channeling measurements.     

Characterisation of thin sputtered silicon nitride films by NRA, ERDA, RBS and SEM

Summary Thin, amorphous silicon nitride (a-SIN_x) films were deposited on n-type (100) silicon substrates using an argon ion beam for sputtering a HPSN block under high vacuum conditions. The substrates were kept at room temperature. Nitrogen depth distributions were determined by NRA using the resonance reaction ¹⁵N(p,)¹²C at 429 keV. Hydrogen profiles were analysed by NRA (¹H(¹⁵N,)¹²C at E_o=6.385 MeV) and by ERDA (²⁰Ne²⁺, E_o=10 MeV). The NRA was used to determine the depth distributions (concentration vs. areal density) of nitrogen and hydrogen taking calibration standards into consideration. The silicon depth distributions and the N/Si ratios of the deposited a-SiN_x films were determined by RBS (⁴He⁺, E_o=2.0 MeV). Film thicknesses were obtained by SEM. The density of the deposited a-SiN_x films was found to be =2.7 (±0.1) g/cm³ by correlating RBS data and real film thicknesses as obtained by SEM.     

Preparation of TiO2 coating films containing Pd fine particles by sol-gel method

TiO₂ coating films of 0.3–0.4 m in thickness that contain fine Pd particles have been prepared by sol-gel method using Ti(OC₃H ₇ ⁱ )₄ and PdCl₂ as starting materials in an attempt to obtain optical materials that show surface plasma resonance in the visible range. A temperature higher than 900°C was required for formation of Pd metal particles when the heat-treatment was conducted in air. Heat-treatment of pre-heated amorphous films in air at 800°C resulted in precipitation of PdO particles, the size of which could be varied by changing the time of heat-treatment, and subsequent heat-treatment in H₂/Ar gas converted the PdO particles into Pd metal particles. Heat-treatment of pre-heated amorphous films in H₂/Ar gas also resulted in precipitation of Pd metal particles. The size of the Pd metal particles precipitated in the films was 6 to 90 nm, depending on the conditions of heat-treatment. The resultant TiO₂ films containing Pd metal particles were brownish grey in color and showed optical absorption in the visible range over 400 nm, which is attributed to surface plasma resonance of Pd metal particles.     

Brightness Reversion of Mechanical Pulps. Part XVII: Diffuse Reflectance Study on Brightness Stabilization by Additives Under Various Atmospheres

Brightness reversion of softwood (SW) and hardwood (HW) bleached chemithermomechanical pulps (BCTMP) with a 300–400nm light source under argon, oxygen, and air were studied in the absence and presence of UV-screens using UV–Vis reflectance difference spectroscopy. The UV-Vis difference absorption spectra of control SW and HW BCTMP testsheets indicate that as the concentration of atmospheric oxygen is increased, the absorption at max 360nm increases and a blue shift occurs. In all of the cases studied, brightness reversion was observed to occur under an argon atmosphere. The addition of benzophenone and benzotriazole additives to BCTMP testsheets resulted in a significant decrease in formation of chromophores absorbed at 400nm and 360nm. The possible mechanisms contributing to these effects are discussed in terms of the photoformation of lignin chromophoric structures.     

Vapochromism of a Pyrrolizinato-nickel(II) Complex Incorporated in Polyvinylbutyral. An Optochemical Detecting System for Alcohols in Air

The bis(1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinido)nickel(II ) complex (NiL2, L = C11H2N7-) has been incorporated as dispersed monomer in polyvinylbutyral (PVB) at a fairly high concentration (0.021 M). NiL2/PVB spin coated thin films (thickness, 2 m) on glass and silicon and evaporated free standing thicker films (thickness, 50 m) have been studied by means of absorption or reflectivity visible as well as infrared spectroscopy. The light-blue NiL2/PVB film fades slightly on heating (for 7 min at 90 °C) and remains as such after cooling to room temperature. The optical spectrum of the thermally activated NiL2/PVB system, in contact with organic solvent vapors at room temperature, changes with time evolving towards the initial spectrum before the thermal treatment. The system is therefore amenable for sensing organic solvents in air. Several ordinary solvents have been tested. After 12 min exposure to air saturated with vapor a steady-state absorbance signal at the most sensitive wavelength (661 nm) is reached for any tested solvent. The system is most sensitive to alcohols. Response cycles are reported for methanol as solvent.     

Charge Accumulation in Nanoheterogeneous Iridium Oxide Films

Iridium oxide films with different values of crystallinity degree K are synthesized. Properties of the films and their morphological features are examined. The charging of the films in a 1 M H₂SO₄solution is studied voltammetrically. The most amorphous films (K = 0.08–0.26) acquire the largest overall charge q(in a fixed potential range) relative to films with higher crystallinity degrees; however, the qvs. K dependence is not additive, and the charge remains virtually invariant beginning with K 0.26. The contribution of slow charging processes, which is quite perceptible in the amorphous films, is absent in samples with higher crystallinity degrees, which have faster charge kinetics. The fast charging processes, which are not limited by diffusion, occur in boundary regions of IrO₂crystallites (and/or the oxide part of a crystalline hydrated iridium oxide) and the amorphous phase. The transport of charge-compensating ions in the boundary regions occurs without considerable complications, as in the loose network of amorphous phase IrO₂· xH₂O. The assumption about the formation of a metallic highly-conducting IrO₂cluster at K 0.26 is substantiated. The cluster rules out large resistances in the course of charge transport, which is a possible reason for the slow charging of amorphous films with K < 0.26.     

Theory of spin-dependent recombination of radicals in homogeneous solution

The kinetic equations of spin-dependent radical recombination are described. The theory takes into account all reencounters of two radicals. The magnetic field dependence of the recombination rate constants is calculated in two cases: for a reaction of radicals with different g-factors and for a reaction in which one of the partners has a magnetic nucleus.

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. g- , . .

     

Absorption spectra of hexachlorobenzene adsorbed on SiO2 powders

Summary Photoacoustic spectra of hexachlorobenzene adsorbed on SiO₂ powders of different particle sizes were investigated. A comparison of the measured PA spectra with the calculated optical absorption lengths led to the conclusion that only absorption bands for which is much larger than the particle size, i.e. in the case of carrier transparency, appear in the PA spectrum. This indicates that the particle diameter determines the thickness of the sample. Compared to their solution spectra the PA spectra of HCB on the silica carriers do not show a red shift of the various absorption bands as was claimed in the literature. Permanent address: Institute of Public Health, B. Kidria, 52a, YU-51000 Rijeka, Yugoslavia