Crystallization of amorphous antimony films on silver films

The crystallization process in amorphous antimony films 70–330 Å thick evaporated onto silver films 10–150 Å thick which have previously been evaporated onto glass is directly observed through an optical microscope. The conditions under which the crystallization process in the amorphous antimony films is observed are found to be severely limited by the preparation conditions of the silver films. The crystallization can only be observed on silver films thinner than 30–40 Å which have previously been exposed to oxygen or nitrogen gas. The crystallization thickness of amorphous antimony films on these substrates is estimated to be 123-75 Å as the substrate temperature varies from 20 to 80 °C and the activation energy for crystallization to be 0.23-0.30 eV as the film thickness varies from infinity to 200 Å.     

2.24 Structural and electrical properties of discontinuous gold films on glass

In the present work thin gold films are investigated in the thickness interval 10–160 Å. The films are deposited in UHV on to glass substrates at room temperature and with an electric field in the substrate plane. In the thickness interval 10–45 Å the film is discontinuous and the size distribution of the islands as determined from electron micrographs is described with a log-normal distribution function. The onset of the in situ electrical conduction at the average thickness 45 Å makes it possible to measure the film resistance as a function of the film thickness during the condensation. At the thickness 53 Å stable metallic continuous paths are formed and the film achieves metallic properties. The fraction of the surface covered with material and the island density are measured 20 h after the deposition. Both these entities change rapidly at the stage when the film grows to be metallic continuous.     

Study of thermocapillary film rupture using a fiber optical thickness probe

Rupture of a subcooled water film flowing down an inclined plate with a 150×150 mm heater is studied using a fiber optical thickness probe. The main governing parameters of the experiment and their respective values are: Reynolds number (3.2–30.2), plate inclination angle from the horizon (3–90 deg), heat flux (0–1.53 W/cm²). The effect of the heat flux on the film flow leads to the formation of periodically flowing rivulets and thin film between them. As the heat flux grows the film thickness between rivulets gradually decreases, but, upon reaching a certain critical thickness, the film spontaneously ruptures. The critical film thickness is practically independent on the film Reynolds number as well as on the plate inclination angle and lies in the neighborhood of 60 µm (initial film thickness varies from 93 to 368 µm). The heater surface temperature prior to rupture is also independent of Re and Θ, and is about 45°C (initial film temperature is 24°C). The process of rupture involves two stages: 1) abrupt film thinning down to a very thin residual film remaining on the heater; 2) rupture and dryout of the residual film. The threshold heat flux required for film rupture is scarcely affected by the plate inclination angle but grows with the Reynolds number.     

Longitudinal Magneto-Optical Kerr Effect in Magneto-Plasmonic Heterostructures

In this paper, the effect of Au nanoparticles and a Bragg reflector mirror on the optical and longitudinal magneto-optical Kerr effect of a new magneto-plasmonic structure has been investigated. The new magneto-plasmonic heterostructure consists of a Bragg reflector mirror beside a crystalline Ce:YIG thin film incorporating gold nanoparticles. Our results indicate sufficient broad band longitudinal magneto-optical Kerr effect enhancement in this new structure using the combination of surface plasmon resonance and Bragg reflector mirror.     

Caractérisation de l'interface métal-diélectrique par l'étude de l'impédance complexe des structures Al/CdS/Au obtenues par pulvérisation cathodique

The interfacial phenomena in sputtered sandwich films were investigated by studying the complex impedance of Al/CdS/Au structures in which the dielectric thickness was less than 800 Å. The experimental results are interpreted using Maxwell-Wagner theory in which the dielectric film is considered as two layers. Semiconductive regions appear when a specific heat treatment is applied. The activation energy associated with conduction variations as a function of temperature is in the range 0.4–1 eV. Comparative studies with restructuring of the aluminium electrode show a correlation between the surface state of the metal and interfacial properties. We show that specific properties of sputtered photocells may be modified by approaching a limit of temperature of 440 K.     

Strain insensitive Ni-Co films over a wide composition range

The magnetic properties of vacuum deposited Ni-Co films have been studied as a function of film composition, film thickness, and substrate temperature. The experimental parameters ranged from 400-1000 Å for thickness 17-41-percent Ni for composition and room temperature to 300°C for the substrate temperature. It was found that the magnetoelastic strain coefficient approaches zero in the vicinity of 35-percent Ni in agreement with Tolman's result[1] and remains insensitive to film composition from 30-40- percent Ni. These results are in reasonably good agreement with calculations based on single crystal data and the expression of Callen and Goldberg [10]. The coercive force and anisotropy field are an order of magnitude larger than of nonmagnetostrictive Permalloy films. An unexpected result is an increased coercive field with increasing film thickness while the anisotropy field remains practically constant; the films become inverted at a critical thickness in the order of 750 Å For a wide variation of preparation parameters the crystallite size remained less than 100 Å     

Controlled layer-by-layer formation of ultrathin TiO2 on silver island films via a surface sol-gel method for surface-enhanced Raman scattering measurement

A surface sol-gel process has been demonstrated to be an effective method for the surface modification of silver island films as unique SERS substrates for monitoring molecular adsorption on a dielectric titania surface. This layer-by-layer approach allows control of the thickness of the dielectric surface with a monolayer precision on silver surfaces. The enhancement of Raman scattering from adsorbed Rhodamine 6G molecules is inversely proportional to the thickness of the titania film, which is consistent with the decay of electromagnetic enhancement. Despite a reduction in the sensitivity of the film, a substantial improvement in the film was achieved as a result of the enhanced stability of this substrate compared to the silver island film without a TiO(2) coating.     

The effect of spatial dispersion of the dielectric permittivity on the capacitance of thin insulating films: Non-linear dependence of the inverse capacitance on film thickness

An apparently non-linear relation between the inverse capacitance of thin insulating films and the film thickness is often observed in the thickness region up to a thousand ångströms and is commonly ascribed to film inhomogeneity, lattice imperfections or field penetration into the metal electrodes. This effect is considered in terms of the theory of non-local dielectrics for which the dielectric response to an electric field at different points is correlated over regions comparable with the local microstructure. The general theory is adapted to thin metal-film-metal junctions and the effective dielectric permittivity in the classical capacitance expression for a planar condenser is calculated as a function of the film thickness for various model systems. The resulting effects are predicted to be larger than those expected for field penetration. Comparison with experimental data for ionic oxide and sulphide films shows that the observed effects are most probablu too large to be ascribed solely to the non-local nature of the dielectric response, whereas the effects observed for films of organic acid salts have the order expected (corresponding to correlation lengths of one or two molecular layers).     

Zero-Field Vortex-Induced Hall Effect and Polar Kerr Effect in Chiral p-Wave Superconductors near Kosterlitz-Thouless Transition

In this work, we investigate polar Kerr effect and Ohmic conductivity induced by vortex dynamics in a chiral p-wave superconducting thin film near Kosterlitz-Thouless (KT) transition without explicitly applying magnetic field. Due to the broken time reversal symmetry in the superconducting state and the breaking of Galilean invariance by forces originated from impurities, a conductivity tensor with nonzero off-diagonal element is expected. We generalize the dynamical theory developed by Ambegaokar, Halperin, Nelson, and Siggia to obtain a matrix dielectric function describing vortex screening, which is further related to the conductivity tensor. Polar Kerr effect due to the nonzero Hall conductivity is studied. The corresponding Kerr angle is shown to be proportional to the imaginary part of off-diagonal component of the dielectric function in certain parameter regime. While the frequency and temperature dependence of dissipation in chiral p-wave context behave similarly to those of s-wave results, the Kerr angle exhibits some novel features near the KT transition. As a result, Kerr angle measurement in experiment can provide a probe of vortex dynamics described in this work.     

Photoconduction et effets photovoltaïques dans des couches minces pulverisées de ZnS

Data concerning photoelectric effects in Al/ZnS/Au structures (dielectric thickness from 150 to 600 Å) are presented. In this structure we have observed a photovoltaïc open-circuit voltage which reaches about 0.3 V and whose polarity changes with the wavelength of the incident illumination; furthermore, the observed photocurrent varies linearly with the intensity of the incident light. We propose that these photoeffects are due to interband transitions in the dielectric for photon energies above the ZnS band gap, and to photoexcitation of coulombic centres for lower photon energies.     

Étude de la croissance des couches minces à partir de mesures optiques et électriques pendant leur dépôt

The variation of the effective complex dielectric constant of a thin gold film with its mass thickness during deposition has been determined from measurements of the film reflectivity and transmittivity at λ=6328 Å. We propose an analysis based on the theory of Cohen et al. which allows the evolution of the “filling coefficient” of the film to be followed and also the formation of its grains. The resistivity measurements performed simultaneously confirm the results obtained from optical measurements. We have succeeded in determining two critical thicknesses for our deposition conditions that separate the different stages of film growth.     

The variation in electrical resistance with temperature for Bi/Ag bilayer films

The variation in the electrical resistance of vacuum-evaporated Bi/Ag bilayers with different layer thicknesses was studied as a function of temperature. A silver overlayer 50 Å thick increased the variation in R_T/R with temperature of the bismuth film (R_T is the resistance of the film at temperature T and R the resistance at room temperature). It increased the resistance of the film and made the temperature coefficient of resistance at room temperature more negative. In addition, the resistance minimum was shifted to higher temperatures. The variation in resistance with temperature is explained on the basis of the Kaidanov and Regal model. When the total thickness of the bilayer film was kept constant (approximately 1000 Å), the variation in resistance on annealing was dependent on the thickness of the silver layer. The rapid rise in resistance above 100 °C observed in films with silver layers between 100 and 600 Å thick is explained on the basis of diffusion at the interface and aggregation of the silver film on the surface. By controlling the thickness of the layers it is possible to keep the variation in resistance with temperature of the film to a minimum.     

Comparison of magnetic behavior of cylindrical and flat films from Kerr effect probe measurements

The magnetic characteristics of flat and cylindrical permalloy films are compared. 1000 Å-flat films and 10 000-Å cylindrical films electrodeposited onto 5-mil-diameter wires show very similar magnetic properties. Geometrical differences arise largely in the relative ease or difficulty with which fields may be applied to the films and signals extracted. The greater thickness of the cylindrical films described gives rise to enhanced magnetostatic effects apparent in the Kerr effect probe measurements and to strong self-shielding against nonaxial external fields.     

Unambiguous determination of thickness and dielectric function of thin films by spectroscopic ellipsometry

We present a spectroscopic method of determining both thickness and dielectric functions of thin films on previously characterized substrates. The method requires that spectroscopic ellipsometric data be taken over an energy range where the substrate has a sharp optical structure, e.g. a critical point. These data are used to determine a “pseudodielectric” function for the film, which necessarily depends on the assumed film thickness. We develop a general first-order theory which shows that the correct thickness and dielectric function of the film are those for which the substrate feature vanishes in the calculated pseudodielectric function. The theory is also used to investigate sensitivity and applicability. We show that sensitivity can be enhanced by differentiating the pseudodielectric function with respect to energy. The method is demonstrated with several numerical and experimental examples, which illustrate that monolayer thickness accuracy can be achieved.     

Galvanomagnetic and magnetic properties of evaporated thin nickel films II. Thickness dependence of the Hall coefficients,the magnetoresistivity and the saturation magnetization

The film thickness dependence of the Hall coefficients, the magnetoresistivity and the saturation magnetization was studied in the range 10–2000 Å. An oscillation of the ordinary Hall coefficient as a function of thickness was observed. These oscillations were interpreted as magnetomorphic oscillations. Similar oscillations of the extraordinary Hall coefficient and of the magnetoresistivity were also observed. The saturation magnetization approaches a value of 1.8 kG for very thin films (d < 70 Å).     

Unusual thickness dependence of the dielectric constant of erbium oxide films

The thickness dependence of the dielectric constant of Er₂O₃ films was studied. It was found that for films less than 700 Å thick and greater than 1300 Å the dielectric constant ε shows the usual behaviour of increasing with increasing thickness and then assuming the limiting bulk value. However, for films of intermediate thicknesses (700–1300 Å) the dielectric constant first decreases, attains a minimum value and then increases to obtain the bulk value. It is suggested, based on electron microscope observations, that this curious thickness dependence of ε arises because of the transformations from (i) amorphous to crystalline and (ii) f.c.c. type to b.c.c. type crystalline phases in the films.     

Capping effects of Au on Fe/GaAs(001) studied by magneto-optical Kerr effect

Molecular beam epitaxially grown Fe on GaAs(001) capped by Au overlayer with variable thickness had been investigated in situ by magneto-optical Kerr effect (MOKE). It is observed that the MOKE intensity as a function of Au film thickness decays much faster than that derived from the well-known Zak's theory. This can be explained by different optical parameters of ultrathin films from bulk values. It is also found that a minimum thickness of 1.4 nm Au is needed to effectively prevent the oxidation of Fe film at 300 K in atmosphere.     

Magnetooptical memory experiments on a rotating Mn-Cu-Bi disk medium

A thin film of a new magnetooptical memory medium, Mn-Cu-Bi, was prepared on a glass disk and their dynamic memory characteristics were examined with an experimental rotating disk exerciser. The Curie temperature of the medium was about 200°C. Curie-point writing was made on it. The written information was read by the Kerr effect. The Kerr rotation was ±1.3° at an Ar ion laser wavelength of 5145 Å, where the Kerr rotation of the medium was made maximum by an SiO overcoating. For track selection, a moving coil with a linear motion air bearing, whose shaft was rectangular in form, was used. By utilizing a laser for the light source of a moiré fringe measurement technique, an accurate track access was made possible. The accuracy was within 1 μm and the track-to-track transfer time was about 5 ms. Writing and reading were accomplished under computer control with the direct memory access mode. A 5.09 × 10^-6medium error rate without error correction was obtained for a 2.5 × 10⁵bit/cm²packing density at a data transfer rate of 0.5 MHz.     

Analytical investigation of solitary waves in nonlinear Kerr medium

We study analytically the solution of nonlinear equation which result from the propagation of electromagnetic waves within a nonlinear Kerr medium. The medium is characterized by a dielectric constant which varies periodically and depends on the local field intensity. As a first step, we detail the resolution of the nonlinear equations with a quadratic nonlinearity. After that, we apply the slowly varying envelope approximation to obtain a Sine–Gordon equation. In this kind of nonlinearity, a gap solitons occurs. Moreover we verify that the solutions of the nonlinear equation for all frequencies within the gap are solitons solutions. After that we study the conditions of apparition of these particular solutions (i.e. soliton or anti-soliton) which are very suitable in experiments.     

Enhanced Polar Magneto-optical Kerr Rotation in Cobalt Thin Film Incorporating Ag Nanoparticles

We report an experimental study on the effect of Ag nanoparticles on the polar magneto-optical Kerr effect in cobalt thin film. The magneto-optical cobalt thin film was prepared by electron beam deposition method onto the Ag nanoparticles which were synthesized by laser ablation in liquid technique. Our results indicate that we have sufficient enhancement of polar magneto-optical Kerr effect of cobalt thin film around the surface plasmon resonance of Ag nanoparticles. Moreover, combination of surface plasmon resonance of the Ag nanoparticles and very thin Au layer can be attained the enhancement factor in all of visible spectral region.