Dispersion Of Thin Films Research Articles

Dispersion changes of platinum supported on silica glass during thermal treatment in oxygen and hydrogen atmospheres

Dispersion and chemical composition changes of thin platinum films supported on fused silica, caused by thermal treatment at temperatures of 773 and 823 K in hydrogen and oxygen atmospheres at pressures of 10 −1 to 10 −3 Pa, have been investigated by electron microscopy and electron diffraction. Heating the Pt SiO 2 system in hydrogen leads to an increase of the metal-support interaction, resulting in the flattening of the metal particles, formation of platinum-silicon intermetallic compounds, and generation of strain. During a subsequent heating in oxygen, redispersion of the platinum by splitting of the particles has been observed. Redispersion by spreading of platinum oxide over the support has been found after long (10 h) heating of the Pt SiO 2 system at 823 K in oxygen at a pressure of ~10 −2 Pa. The mechanisms of platinum redispersion presented above are documented by electron micrographs.

Waveguide modes in ferroeixctric films

Abstract The calculation of the polariton dispersion in thin dielectric films is carried out using the quantum Green function method. The oscillator strength of the transition into the vibronical state is shown to decrease with decreasing crystal thickness.

Temperature-dependent dispersion of cadmium sulfide thin film in a slab-type optical waveguide

A previously reported optical guided-wave method for determining the optical constants of high-index thin films has been used to measure the temperature-dependent dispersion in vacuum-evaporated cadmium sulfide thin films. Measurements were carried out over the spectral range from 4579 to 6328 Å using Ar and He–Ne lasers at 18 K, 83 K, and room temperature in an optical cryostat.

Refractive index dispersion of light-guiding thin films by a spectroscopically extended dark m-lines method: application to Garnet and amorphous hydrogenated silicon layers

Refractive index dispersion of light-guiding thin films by a spectroscopically extended dark m-lines method: application to Garnet and amorphous hydrogenated silicon layers

Faraday effect dispersion in nickel and permalloy thin films

Faraday rotations in nickel and permalloy films up to 80-20 Ni-Fe compositions have been obtained at both normal and oblique incidence. Incident light was parallel to the magnetic field which ranged up to 8 kilogauss. For oblique incidence a graphic analysis of Faraday rotation vs. applied field yields both the magnetization and specific rotation. The dispersion curves for both the nickel and the permalloys show rotations which increase in moving from higher to lower energies in the range 0.7 to 3.0 eV. Rotation peaks occur at 1.2 eV for the nickel and at 1.7 eV for 80-20 permalloy. We identify the peak in nickel with that shown in earlier MOKE conductivity measurements. Identical structure with shift to higher energies is exhibited by the permalloys. We attribute the shift primarily to an equivalent lowering of the Fermi level as iron is added to the nickel.

Measurements of refractive-index dispersion by optical waveguiding

A technique for measuring the refractive-index dispersion in light-guiding thin films by means of the prism-coupling method is reported. A collimated polychromatic light beam is employed, and the wavelength dependence of synchronous angles is determined spectroscopically. A representative experiment performed on an amorphous specimen reveals its usefulness for investigating the detailed dispersion characteristics of thin films with accuracies better than 0.001.

Dielectric dispersion and polarization effects in thin transition metal oxide films : B. Lalevic, N. Annamalai, B. Leung, G. Taylor and W. Slusark, Jr.Vacuum27, (4) 249

Dielectric properties of thin polycrystalline and amorphous films of NiO, NiO(Li), CoO, CoO(Li), Nb2O5 and TiO2 in the thickness range 0.14–15 ωm were studied as a function of frequency, temperature, applied voltage and dopant concentration in the frequency range 3–108 Hz. These films were prepared either by anodization or thermal oxidation and in some cases by reactive sputtering. Experimental data for the real ϵ1 and imaginary ϵ2 parts of the dielectric constant, ac conductivity σ(ω) and loss tangent tan δ indicate the existence of several dispersion mechanisms. Cole-Cole plots and the modified Debye relations were used to derive the values for relaxation times at low frequencies. The frequency dependence of σ(ω) in the frequency region 103–106 Hz where σ(ω)αωn indicates that the dispersion mechanism is due to charge carriers hopping between sites with either correlated or non-correlated potentials. The observed quadratic dependence of σ(ω) on frequency in the frequency region 106–108 Hz is attributed to a Debye type loss resulting from thermally activated hopping. Polarization effects at lower frequencies <103Hz indicate the existence of Schottky barriers at the metal-insulator interfaces in agreement with Simmons theory of MIM structures.

2.12 Dielectric dispersion and polarization effects in thin transition metal oxide films

Dielectric properties of thin polycrystalline and amorphous films of NiO, NiO(Li), CoO, CoO(Li), Nb 2O 5 and TiO 2 in the thickness range 0.14–15 ωm were studied as a function of frequency, temperature, applied voltage and dopant concentration in the frequency range 3–10 8 Hz. These films were prepared either by anodization or thermal oxidation and in some cases by reactive sputtering. Experimental data for the real ϵ 1 and imaginary ϵ 2 parts of the dielectric constant, ac conductivity σ( ω) and loss tangent tan δ indicate the existence of several dispersion mechanisms. Cole-Cole plots and the modified Debye relations were used to derive the values for relaxation times at low frequencies. The frequency dependence of σ( ω) in the frequency region 10 3–10 6 Hz where σ( ω) αω n indicates that the dispersion mechanism is due to charge carriers hopping between sites with either correlated or non-correlated potentials. The observed quadratic dependence of σ( ω) on frequency in the frequency region 10 6–10 8 Hz is attributed to a Debye type loss resulting from thermally activated hopping. Polarization effects at lower frequencies <10 3 Hz indicate the existence of Schottky barriers at the metal-insulator interfaces in agreement with Simmons theory of MIM structures.

Refractive Index Dispersion in Semiconductor-related Thin Films

A technique is described for determining refractive index dispersion throughout the uv-visible spectrum in semiconductor-related transparent thin films. The dispersion constants that have been measured can be used in the design of optical systems and in photolithography. Measurements were made with the LASER-VAMFO interferometer. Calculations and analyses are also described which show the accuracy and repeatability of the technique. Data were taken for 28 different thin-film materials, and representative refractive index dispersion curves are shown for some of them. The dispersion constants for each material evaluated are also presented.

Influence de la structure locale de l'anisotropie magn&amp;#233;tique induite sur la dispersion de l&amp;#769;aimantation dans les couches minces ferromagn&amp;#233;tiques polycristallines

A study is made of the magnetization dispersion of polycrystalline thin ferromagnetic films with induced uniaxial magnetic anisotropy. The general formula for the so-called magnetization-induced anisotropy in a crystallite of cubic symmetry is established in order to prove that in a polycrystalline thin film this anisotropy necessarily varies from one crystallite to the next. A calculation is then made to see how these variations and the variations of the magnetocrystalline anisotropy directions affect the magnetization dispersion. It is found that in general the resulting dispersion is larger than that obtained from a superposition of magnetocrystalline anisotropy and a uniform uniaxial anisotropy. It also seems that, contrary to what is generally assumed, the dispersion does not decrease monotonically with increasing uniaxial anisotropy (K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</inf> ), but that it initially decreases (for K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</inf> < magnetocrystalline anisotropy energy) until it reaches a minimum, and then increases with K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</inf> . On the other hand, the dispersion does not vanish even if magnetostriction and magnetocrystalline energy are zero. Thus it is shown how the experimental results of Wolf [13], on the dispersion of Ni Fe Co thin films, could be qualitatively explained by this theory.

Spin Wave Dispersion in Thin Cobalt Films

AbstractA dispersion law for the energy spectrum of thin films of hexagonal cobalt is obtained on the basis of the Heisenberg Hamiltonian and the Holstein‐Primakoff approximation. The general formulation is discussed for an arbitrary system of ferromagnetic thin films. The calculations include an effective anisotropy field.

Dispersion in thin magnetic films

Dispersion in thin magnetic films

Dependence of the Anisotropy Axis Dispersion on Thickness of Thin Nickel–Iron–Cobalt Films

THE measurement of easy axis dispersion in thin ferromagnetic films is of interest in connexion with the explanation of their magnetic behaviour. Clow1 has reported the variation of the dispersion of easy axis with film thickness for evaporated specimens of 82–18 per cent nickel–iron alloy in the thickness-range 50–2000 A. In the work reported here, measurements of dispersion were made by a slightly different method on films of nickel–iron–cobalt alloy in the range 400–6000 A in thickness.

Measurement of Easy Direction Dispersion in Magnetic Thin Films

WITH reference to the foregoing communication by Peacock and Winsor, I agree that my measurements of the angle β′ gives values which depend on the dispersion of the magnitude of the anisotropy field HK. Further, the method of measurement described in their communication would generally be considered to be more accurate than mine.

Measurement of Easy Direction Dispersion in Magnetic Thin Films

CLOW1 has described a method for the measurement of the dispersion of the easy direction of magnetization in a single nickel–iron thin film. In this method “a field pulse HA, greater than the anisotropy field HK, was applied along the average difficult direction, and during the latter part of this pulse a small pulse HD was applied along the average easy direction. The flux change parallel to the easy axis, due to the application of HA, was measured with a single pick-up loop, and the minimum value of HD giving full output was taken to be proportional to the maximum value of β (the angular dispersion of the anisotropy axis). In practice, the approach to full output was too gradual for accurate measurement of this minimum value, and a level of HD, H′D say, giving 80 per cent full output, was used. An angle β′ given by sinβ′ = H′D/HK therefore gives the maximum dispersion in anisotropy over some 80 per cent of the film. Hence, 20 per cent of the film has hard directions at angles to the mean greater than β′, and 80 per cent at angles less than β′”.

Dispersion of Zinc Sulfide and Magnesium Fluoride Films in the Visible Spectrum

The dispersion and aging effects of thin films of MgF2 and ZnS were investigated in the spectral range of 4000 A to 7500 A. The method of evaporating ZnS is reported. The index of refraction was calculated from spectrophotometric reflectance measurements at extremes of reflectance.