Anomalous temperature dependence of resistance observed for high TC Y-Ba-Cu-O thin films

Anomalies in the resistance versus temperature plots of some Y-Ba-Cu-O sputtered thin films have been observed. Compositional variations over some portion of the film are found responsible for the appearance of the anomalies. The need for exercising caution in the interpretation of such anomalies is emphasized.     

Casimir force between thin films of real metals

The Casimir force between two finite-thickness metal films has been calculated for realistic plasma frequencies of metals. The result obtained indicates the possibility of weakening of the Casimir force for real films by approximately an order of magnitude at the appropriate choice of the parameters in qualitative agreement with the existing experimental data.     

Anomalous temperature dependence of the electrical conductivity of zinc oxide thin films

The temperature dependence of the conductivity of Ga-doped ZnO thin films was examined in humid and dry atmospheres. The conductivity initially increases to the maximum (range 1) and then decreases to the minimum (range 2) and again increases (range 3) in the heating run under humid air atmosphere. The subsequent cooling reduces the conductivity to less than that for the heating run. The extent of the reduction becomes large as the cooling rate increases. The extrema character in the conductivity versus temperature curves does not disappear under nitrogen gas atmosphere provided it is humid. On the other hand, the conductivity in the ranges 1 and 2 decreases so significantly that the extrema character disappears in the driest air as possible. These behaviors are explained by assuming that the dissociatively chemisorbed states of water vapor act as electron donors and desorb at the higher temperature, and the desorption as well as the chemisorption require a time for attaining equilibrium. With this in view, a theoretical analysis is given of semiconducting films thinner than the depletion boundary layer thickness, and numerical curves fitting to the experimental results are obtained. The heat of chemisorption of nonionized water q° is 1.35 eV and the energy levels of water chemisorption donors and oxygen chemisorption acceptors are at 0.66 and 0.59 eV below the conduction band edge, respectively.     

Isotopic dependence of the Casimir force

We calculate the dependence of the Casimir force on the isotopic composition of the interacting objects. This dependence arises from the subtle influence of the nuclear masses on the electronic properties of the bodies. We discuss the relevance of these results to current experiments utilizing the isoelectronic effect to search at very short separations for new weak forces suggested by various unification theories.     

On the shape dependence of the tangential Casimir force

The normal and tangential Casimir force for the rack gear is calculated numerically in the case of ideal boundary conditions for the electromagnetic field—perfect reflection on the boundaries. The resulting tangential force appears to be essentially shape-dependent. Relatively small shape variations lead to the essential changes in tangential force, whereas normal force remains almost unchanged.     

Linear temperature correction to the Casimir force

We discuss the temperature correction to the Casimir force between nonideal metallic bodies which caused disagreement in the literature. A general method to find the troubling term is proposed that does not require a direct reference to the Lifshitz formula. The linear temperature correction is shown to survive for nonideal metals. It is important for small separations between bodies tested in the recent experiments.     

Anomalous magnetoresistance of thin copper films

Thin copper films exhibit the anomalous magnetoresistance (AMR), which depends on the magnetic field orientation versus the film plane and is due to electron localization. Spin-orbit interaction and spin-flip scattering by paramagnetic impurities strongly affect the character of the field and temperature AMR dependences.     

Anomalous optical constants of thin films

The explanation of anomalous optical constants in thin chemically distinct layers on substrates offered by Plumb is re-examined and extended. The model invokes the concept of the space charged boundary layer and treats the charge carrier population as a free-electron gas to derive the optical behaviour of thin surface films. The implication of the space charge means that the optical constants of a dielectric film on a metal will vary over a distance directly proportional to the dielectric constant of the film and inversly proportional to the concentration of the electrons at the metal/film interface. Similarly as the temperature increases this space charge region should extend to larger distances from the interface.     

Analytic approach to the thermal Casimir force between metal and dielectric

The analytic asymptotic expressions for the Casimir free energy, pressure and entropy at low temperature in the configuration of one metal and one dielectric plate are obtained. For this purpose we develop the perturbation theory in a small parameter proportional to the product of the separation between the plates and the temperature. This is done using both the simplified model of an ideal metal and of a dielectric with constant dielectric permittivity and for the realistic case of the metal and dielectric with frequency-dependent dielectric permittivities. The analytic expressions for all related physical quantities at high temperature are also provided. The obtained analytic results are compared with numerical computations and good agreement is found. We demonstrate for the first time that the Lifshitz theory, when applied to the configuration of metal-dielectric, satisfies the requirements of thermodynamics if the static dielectric permittivity of a dielectric plate is finite. If it is infinitely large, the Lifshitz formula is shown to violate the Nernst heat theorem. The implications of these results for the thermal quantum field theory in Matsubara formulation and for the recent measurements of the Casimir force between metal and semiconductor surfaces are discussed.     

Casimir force at both nonzero temperature and finite conductivity

We find the combined effect of nonzero temperature and finite conductivity onto the Casimir force between real metals. Configurations of two parallel plates and a sphere (lens) above a plate are considered. Perturbation theory in two parameters (the relative temperature and the relative penetration depth of zero-point oscillations into the metal) is developed. Perturbative results are compared with computations. Recent improper computations based on the Lifshitz formula for the temperature Casimir force are discussed.     

Substrate temperature dependence of properties of ZnO thin films deposited by LP-MOCVD

ZnO films were prepared on (0002) sapphire by metal-organic chemical vapor deposition (MOCVD) with fixed Zn and O gas flow rates. The film properties displayed complex dependencies on temperature over the range 330–460 °C. All films were preferentially oriented along the (0002) direction and the integrated intensity of the (0002) peak increased with increasing substrate temperature, indicative of an increasing deposition rate. Furthermore, high substrate temperatures promoted the growth of columnar grains, and improved the crystallinity, as the decreasing FWHM of the (0002) ZnO peak suggests. However, it was not the highest temperature sample, but the sample deposited at 390 °C that had the best UV band emission characteristics, with no defect-related luminescence in the photoluminescence (PL) spectra, as well as the highest transmission and sharpest absorption edge in the transmittance spectra. PACS 81.15.Gh; 78.55.Et; 68.55.Jk; 61.10.Kw     

Thickness and temperature dependence of subsidiary absorption thresholds in yttrium-iron-garnet thin films

The microwave subsidiary absorption threshold in tangentially magnetized yttrium-iron-garnet (YIG) films was measured as a function of the static magnetic field, film thickness and decrease in the 0.3–3 μm range is observed. The effect is explained quantitatively by using modified Damon-Eshbach dispersion relations which take into account exchange interactions.

The effect of temperature on h_crit, the smallest threshold field amplitude, in the 250<T< 450 K temperature range can be expressed by an empirical relationship h_crit M_s(T)^-1.6 where M_s is the saturation magnetization. This h_crit vs M_s relationship is similar to that obtained for the magnetization dependence of parallel pump thresholds in Li-Ti ferrite compounds.     

Thickness dependence of the Curie temperature and critical concentration in diluted ferromagnetic thin films

A thickness-dependent critical concentration of an Ising ferromagnetic thin film is predicted. The calculated values of the Curie temperature are bounded by those known for diluted two- and three-dimensional ferromagnets.     

Anomalous properties of thin films of ferromagnetic superconductors

Anomalous magnetic and superconducting behavior which originates from the electromagnetic interaction between the persistent current and the rare earth magnetic moments is theoretically predicted in thin films of ferromagnetic superconductors. It is shown that the ferromagnetic ordering can coexist with superconductivity for films of thickness smaller than the London penetration depth. The ferromagnetic phase transition is of the second order and its critical temperature depends on the thickness of the film.     

Anomalous transmission of electromagnetic wave through periodic arrays of subwavelength slits arranged on thin metal films

We study the optical properties of periodic structures, each of which consists of arrays of subwavelength slits in thick films that are placed directly against a continuous thin film. We find that the transmittance of the entire system including the thin film is higher than the transmittance of the isolated thin film alone. Our investigations are performed through numerical simulations with the Fourier modal method.     

Anomalous Hall effect in perpendicular CoFeB thin films

Our recent research achievements in the perpendicular magnetic anisotropy （PMA） properties of the CoFeB sand- wiched by MgO and tantalum layers are summarized. We found that the PMA behaviors of Ta/CoFeB/MgO and MgO/CoFeB/Ta thin films are different. The larger PMA in the latter film is related to the lower magnetization of CoFeB deposited on MgO. Furthermore, we have demonstrated a large anomalous Hall effect in perpendicular CoFeB thin fihn. Our results show large anomalous Hall resistivity, large longitudinal resistivity, and low switching field can be achieved, all at the same time, in the perpendicular CoFeB thin film. Anomalous Hall effect with high and linear sensitivity is also found in an MgO/CoFeBFFa thin film with a thick MgO layer, which opens a door tbr future device applications of perpendicular ferromagnetic thin films.     

Anomalous electron diffusion in irradiated thin gold films

We report on topographical and electrical properties of an evaporated (as-prepared) thin gold film before and after irradiation with 200 keV Ar⁺ ions. TEM-investigations reveal for the as-prepared film voids and channels of small size, and a pronounced percolative structure with large scale inhomogeneities after irradiation. Magnetoresistance measurements carried out before and after irradiation yield the temperature dependence of the phase coherence lengthL , when analysing the experimental data within current theories for 2-dimensional (2d) weak localization. The results can be explained by normal electron diffusion if-for the as-prepared film-L is larger than the size of structural inhomogeneities, and-for the irradiated film-by anomalous electron diffusion ifL becomes smaller. The analysis ofL (T) for the irradiated film yields critical exponents for 2d-percolation, in good agreement with predictions of percolation theory.     

Thickness dependence of the phase transition temperature in Ag2Te thin films

Electrical resistance measurements of Ag₂Te thin films of different thicknesses, vacuum deposited on clean glass substrates held at room temperature in a vacuum of 5 × 10^?5 Torr, have been carried out from about 300 to 450 K. A semiconducting-to-metallic-phase transition, which takes place during heating, is indicated by a sharp change in the slope of the resistance-vs-temperature curve. For films of different thicknesses the phase transition is found to occur at different temperatures. The size-dependent phase transition is explained by taking into account the varying surface and intergrain surface (interface) energy contributions to the total energy of the stable phase as a function of thickness and the difference in specific surface and integrain surface energies of the two phases. An order of magnitude of the difference in the function of specific surface and interfacial energies of the two phases is also made.