A spectroscopic prism coupler for measuring the refractive indices and thicknesses of dielectric films

A spectroscopic prism coupler is created for measuring refractive indices n_f and thicknesses H_f of dielectric films. The operating principle of the device is based on the simultaneous resonance excitation of several waveguide modes in a film by a focused TE or TM polarized light beam in the geometry of frustrated total internal reflection. Calculations of n_f and H_f are performed using measured angular positions θ_m of dark m-lines in the cross section of the specularly reflected beam. Using obtained angles θ_m, we can calculate effective refractive indices β_m of modes. By solving a set of nonlinear dispersion equations for the modes of a planar waveguide, we can calculate refractive index n_f and thickness H_f of a film. The proposed prism coupler has no moving parts and allows us to measure the optical parameters of films 0.5–10 μm thick in the 400–1100 nm range of wavelengths. The device can also be used as a spectroscopic refractometer for measuring the refractive indices of bulk media. The device is used to measure refractive index and thickness of a SiO film and the refractive index of TF4 glass.     

Magneto-optical and optical properties of polycrystalline Со–Р films with nanometer thickness

Features of the optical and magneto-optical properties of polycrystalline Со–Р films with nanometer thickness are established experimentally. It is found that the spectra of optical parameters n and k and magnetic circular dichroism depend largely on film thickness, suggesting that magneto-optical activity is governed by different mechanisms in thin films and bulk materials.     

Effect of bias voltage polarity of a substrate on the texture,microstructure, and magnetic properties of Ni films prepared by magnetron sputtering

The influence of the bias voltage polarity U_s on microstructure, crystallographic texture and magnetic properties has been investigated for Ni films with a thickness of ≈15–420 nm, which are obtained via magnetron sputtering at a working gas pressure P corresponding to the collision-deficient flight mode of atoms of the sputtered target between the target and the substrate. The Ni(111)-textured films have been shown to form at U_s ≈–100 V, whose microstructure and magnetic parameters are almost unchanged with a thickness. In contrast, the Ni(200) films are formed at U_s ≈ +100 V, whose magnetic properties and micro-structure depend significantly on the thickness d that manifests in a critical thickness d* ≈ 150 nm, when the structure of the film becomes inhomogeneous in the thickness, the remagnetization loops are changed from rectangular to supercritical with the formation of the band domain structure.     

IR spectra of the optical constants of an industrial high-pressure polyethylene film

The IR spectra of the real n(ν) and imaginary κ(ν) parts of the complex refractive index of an industrial high-pressure polyethylene film are measured by the methods of transmission and attenuated total reflectance spectroscopy in the range 700–750 cm^?1 taking into account the anisotropy and the structural inhomogeneity of the film over its thickness. It is proposed to use these spectra as the reference spectra for polyethylene films in the range around 720 cm^?1.     

Donor-Acceptor Conjugated Linear Polyenes: A Study of Excited State Intramolecular Charge Transfer,Photoisomerization and Fluorescence Probe Properties

Numerous studies of donor-acceptor conjugated linear polyenes have been carried out with the goal to understand the exact nature of the excited state electronic structure and dynamics. In this article we discuss our endeavours with regard to the excited state intramolecular charge transfer, photoisomerization and fluorescence probe properties of various donor-acceptor substituted compounds of diphenylpolyene [Ar(CH = CH) _n Ar] series and ethenylindoles.     

Peculiarities of Photoprocesses in Poly(9,9-di-<Emphasis Type="Italic">n</Emphasis>-octylfluorenyl-2,7-diyl) Films Doped with Potassium Iodide

The spectral-luminescence properties of poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) films doped with potassium iodide are investigated. It is found that the addition of potassium iodide at concentrations of 0.1–1% leads to a drop in the degree of ordering of the PFO films and decreases the fluorescence intensity and lifetime of the polymer. The kinetics of photoluminescence of PFO–KI films is studied in nano-, micro-, and millisecond time bands. Analysis of the experimental data on long-term luminescence using the percolation model showed that the addition of potassium iodide to the polymer increases the degree of disordering of the film. Investigations of the effect of an external magnetic field on the PFO luminescence over a wide time range indicate a complex character of the time dependence of the magnetic effect. The changes in both the magnitude and sign of the magnetic effect g(B) are observed over the entire measured time range.     

Monomers with a High Refraction Index Based on Acryloyl Derivatives of Spirocyclic Piperidin-4-One Thioacetals

Dithioazaspiroheterocyclic derivatives are synthesized by condensing dithiols with piperidin-4-one in the presence of catalytic amounts of Lewis acids. Acrylic dithioazaspiroheterocyclic derivatives are obtained by the reaction with acryloyl chloride. The polymerization of monomers yields transparent polymer films of optical quality. The refractive indices for the synthesized monomers and polymers are in the range of n = 1.59–1.64.     

Determination of the Steady State Leakage Current in Structures with Ferroelectric Ceramic Films

Steady state leakage currents have been investigated in capacitor structures with ferroelectric solgel films of lead zirconate titanate (PZT) formed on silicon substrates with a lower Pt electrode. It is established that Pt/PZT/Hg structures, regardless of the PZT film thickness, are characterized by the presence of a rectifying contact similar to p–n junction. The steady state leakage current in the forward direction increases with a decrease in the film thickness and is determined by the ferroelectric bulk conductivity.     

On the possibility of regulating the rate of enzymatic destruction of chitosan in an acetic acid solution

The enzymatic destruction of chitosan in an acetic acid solution in the presence of sodium chloride and sulfate was considered. It was shown that the addition of these low-molecular electrolytes is accompanied by a tightening of the macromolecular coil, as indicated by a decrease in the α constant in the Mark–Kuhn–Houwink equation and the intrinsic viscosity of chitosan. As a consequence, the chitosan units become less accessible for interaction with the enzyme, and the kinetic parameters of the process (Michaelis constant K _M and the maximum rate of enzymatic destruction V _max) change accordingly. This suggests that the resistance of this polymer to the enzyme action can be enhanced by introducing low-molecular electrolyte salts in the solution or film coating to suppress the polyelectrolyte swelling of chitosan.     

Activation conduction in metallic island films

The differential conductivity of metallic island films of Ti, Co, W, and FeNi is investigated in the vicinity of liquid nitrogen temperatures. It is found that the temperature dependence of the conductivity of metallic island films in the insulator phase varies in accordance with the activation law σ ∝T ⁿ exp(?E/kT). It is shown that the power of temperature in the preexponential factor varies from n = 2 to 1 upon an increase in the film thickness. In thicker films, in which a transition from the insulator to the metal conductivity phase takes place, the temperature dependence of the conductivity increases in proportion to temperature. The mechanism of conduction in metallic island films is discussed.     

Spin−wave resonance as a way of studying the constant of surface anisotropy,using films of Fe–Ni alloy as an example

The effect the thickness and concentration composition of a ferromagnetic thin film have on surface anisotropy constant K _S is investigated. Spin–wave resonance is chosen as a way of detecting and measuring the K _S value. Fe–Ni thin films are synthesized via chemical deposition. Dependences of K _S on the content of Ni in the alloy and a film’s thickness are established.     

Size effects and magnetization of (Fe/Si)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> multilayer film nanostructures

The temperature dependence of the magnetization of (Fe/Si) _n multilayer films with nanometer layers is investigated. The films are prepared through thermal evaporation under ultrahigh vacuum onto Si(100) and Si(111) single-crystal substrates. It is revealed that the thickness of individual iron layers in (Fe/Si) _n multilayer films affects the magnetization and its temperature dependence. The inference is made that this dependence is associated with the formation of a chemical interface at the Fe-Si boundaries. The characteristics of the chemical interface in the (Fe/Si) _n films are estimated.     

Formation of textured Ni(200) and Ni(111) films by magnetron sputtering

The effect of the working gas pressure (P ≈ 1.33–0.09 Pa) and the substrate temperature (T_s ≈ 77–550 K) on the texture and the microstructure of nickel films deposited by magnetron sputtering onto SiO₂/Si substrates is studied. Ni(200) films with a transition type of microstructure are shown to form at growth parameters P ≈ 0.13–0.09 Pa and T_s ≈ 300–550 K, which ensure a high migration ability of nickel adatoms on a substrate. This transition type is characterized by a change of the film structure from quasi-homogeneous to quasi-columnar when a film reaches a critical thickness. Ni(111) films with a columnar microstructure and high porosity form at a low migration ability, which takes place at P ≈ 1.33–0.3 Pa or upon cooling a substrate to T_s ≈ 77 K.     

Energy disorder in polysilanes

The absorption spectra (T=295 K), photoluminescence spectra (T=5–295 K), and thermally stimulated luminescence curves (T=5–295 K) of poly(di-n-hexylsilane) (PDHS), poly(methyl-n-hexylsilane) (PMHS), poly(methylcyclohexylsilane) (PMCHS), and poly(methylphenylsilane) (PMPS) films are measured. The results obtained are analyzed within the model of random hoppings of excitons and charge carriers over sites with a Gaussian distribution of the density of states. It is established that the variance parameters of the density-of-state functions of excitons and charge carriers characterize the energy disorder and depend on the chemical nature of side groups of the polymer, the conformation of segments of the main chain of the polymer macromolecule, and the temperature. At room temperature, the energy disorder in crystalline regions of the PDHS film is explained in terms of fluctuations in the number of monomer units in chain segments. In polymers with nonsymmetric side groups (such as PMHS, PMCHS, and PMPS), the disorder is more pronounced due to the formation of conformers in which silicon atoms occupy different positions in the chain. In the PMPS polymer, the disorder occurs through one more mechanism associated with fluctuations of the angle between the plane of the phenyl ring and the axis of the polymer segment due to mixing of σ-and π-electron states.     

Influence of “ytterbium nanofilm–silicon Si(111)” interfaces on the valence of ytterbium

The work function of ytterbium films of nanometer thickness (from 1 to 16 monolayers) has been measured. The films have been prepared by sputtering of ytterbium in an ultrahigh vacuum on n- and p-type Si(111)7 × 7 silicon substrates with an electrical resistivity from 1 to 20 Ω cm. It has been shown that, in the films with a thickness of less than 8 monolayers, the work function depends nonmonotonically on the amount of ytterbium deposited on the surface (Friedel oscillations), whereas in the films with a thickness of more than 8 monolayers, the work function takes on a constant value (3.3 eV) that exceeds the work function for macroscopic samples (2.6 eV). This difference is associated with the fact that, during the formation of an Yb–Si interface, the large difference in the work functions of ytterbium and silicon (4.63 eV) leads to the transfer of a significant fraction of electrons from the metal to the semiconductor. This transfer of electrons from the film to silicon is accompanied by the lowering of the Yb 5d level below the Fermi level. As a result, the valence of the metal and, accordingly, the work function increase.     

Effective refractive index of a quasi-two-dimensional polydomain film of a conjugated polymer

The relation between the effective ordinary refractive index n* = (n _o n _e )^1/2 of a quasi-two-dimensional polydomain uniaxial film of a conjugated polymer F8BT in the visible transparency region and the refractive indices (n _o,e ) of uniaxial domains with the optical axes randomly oriented in the plane of the film has been confirmed experimentally. The permissible interval of variations in n* has been established and a strong spectral dispersion of this interval near the long-wavelength electronic absorption band of the film has been demonstrated.     

Magnetorefractive effect and giant magnetoresistance in Fe(<Emphasis Type="Italic">t</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)/Cr superlattices

The magnetorefractive effect in Fe(t _x , Å)/Cr(10 Å) samples grown by molecular-beam epitaxy with a variable thickness of the iron layer (superlattices, cluster-layered nanostructures) has been studied in the IR region (λ = 2–13 µm) in s and p polarizations of light. The magnetoresistive effect in a dc magnetic field, H ≤ 32 kOe, has been measured on the same samples. The iron layer thickness required for the magnetorefractive response to appear has been found to be t _Fe ≥ 3 Å. The correlation between the magnitude of the magnetorefractive effect in the mid-IR region and magnetoresistance has been discussed.     

Deactivation pathways of the electronic excitation of ions of lanthanide complexes in polymers with functional groups

Complexes Eu(TTA)₃phen and Eu(MBTA)₃phen, as well as complexes Tb(MBTA)₃phen and Tb(TTA)₃phen, which do not luminesce in solutions, are shown to luminesce in polymer films (TTA is thenoyltrifluoroacetone, MBTA is n-methoxybenzoyltrifluoroacetone, and phen is o-phenanthroline). Luminescence of complexes of Eu and Tb in films of a polymer, poly(methylene-bis-anthranilamide) 1,6-hexamethylenedicarboxylic acid (PAA-5), having a high concentration of functional anthranilate groups, is studied. From the behavior of the luminescence intensity (I _lum), the luminescence decay time, and the luminescence spectra of complexes of these lanthanides in polymer films, the following regular features were revealed. (i) During the film preparation at 90°C, Ln complexes are attached to PAA-5 via anthranilate groups. (ii) Irradiation of these films in the range of the absorption band of ligands (TTA or MBTA) leads to deactivation of the electronic excitation of ions according to the diketone detachment mechanism and to further binding of complexes to polymers. In this case, I _lum(Eu(III)) decreases because the introduction of anthranilate groups of the polymer into the first coordination sphere of Eu(III) complexes enhances the nonradiative deactivation of these ions, whereas I _lum(Tb(III)) increases since the introduction of these groups suppresses the nonradiative deactivation of Tb complexes through triplet states of ligands (TTA and MBTA). (iii) Upon storage of films in the dark (20°C), complexes detach themselves from the polymer and return to their initial structure. In PAA-5 films into which Eu and Tb complexes were simultaneously introduced, the color of the emission from the irradiation spot changes from red to green.     

Generation of acoustic waves by power microwave pulses with the use of thin metal films

We study the features of excitation of acoustic waves by high-power microwave pulses in thin metal films bordering on liquid. Aluminum films with thicknesses 1–10 nm deposited onto a quartz substrate were used in experiments. It is shown theoretically that the absorption coefficient of microwaves is maximum for film thickness from 2 to 3 nm and the value of this maximum is determined by the dielectric permittivity of the bordering liquid. Theoretical calculations and experiments are performed for water and ethyl alcohol. The sound generation in a layered system quartz-aluminum film-liquid is analyzed with the help of the step-by-step approach. At the first step, microwave energy is absorbed in the film and heat is released. Then heat almost instantly diffuses into a liquid whose thermal expansion creates an acoustic signal. Profiles of acoustic signals excited in aluminum films by microwave pulses with a 5-ns duration and an energy of up to 1 mJ are experimentally detected. The most efficient transduction was observed for an aluminum film 3.5 nm thick.     

Self-polarization and migratory polarization in thin lead zirconate-titanate films

This paper reports on a study of the electrical properties of 0.7–1-μm-thick textured PZT ferroelectric films prepared by rf magnetron sputtering of a PbZr_0.54Ti_0.46O₃ target which additionally contained 10 mol % lead oxide. Such films are shown to feature a combination of a self-polarized state and migratory polarization. The totality of the data obtained suggest that the films had n-type conduction. As shown by the laser beam modulation technique, the polarization was distributed nonuniformly in depth, with most of the poled state localized near the lower interface of the thin-film ferroelectric capacitor. The mechanism underlying the onset of this self-polarization is related to the charging of the lower interface of the structure by electrons, which occurs during the cooling following the high-temperature treatment of the PZT film, and to poling of the bulk of the film by the charged interface. This mechanism of the self-polarization of ferroelectric films is believed to have a universal character. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 4, 2002, pp. 739–744. Original Russian Text Copyright ? 2002 by Pronin, Kaptelov, Tarakanov, Shaplygina, Afanas’ev, Pankrashkin.