Papers by Keyword: Ultrathin Film

Abstract: The magnetic susceptibility dependence on temperature near phase transition point was investigated by theoretical analysis. It is shown that with decreasing of the film thickness the magnetic susceptibility shape curve becomes more rounded finite-size function, centered about the lowered temperature Tc (L). The obtained results are in good agreement with experimental data.

Abstract: Ultrathin MgB₂ film is essential for the fabrication of MgB₂ superconducting single photon detectors (SSPDs). In this paper, we prepared 20nm and 10nm MgB₂ film using ex-situ annealing of Mg-B multilayer method. The precursor films were prepared by electron beam evaporation. A flowing Mg vapour and H₂ was introduced in the annealing process to keep MgB₂ thin film thermodynamically stable. The annealing temperature was between 680 and 740 and annealing time was 1-10min. 20nm MgB₂ films on MgO(111) substrates had the critical temperature (T_c) of 32.2K. The films grew along c-axes direction. As the substrate changed to SiC(001) and Al₂O₃(001), T_c decreased to 30.3K and 10.2K respectively. For 10nm MgB₂ film on SiC(001) substrate, T_c was 24.2K. The self-field critical current density for 10nm and 20nm film on SiC(001) substrate was 2.1×10⁶A/cm² and 2.3×10⁶A/cm², respectively. AFM image showed that the film had a flat surface with mean roughness of 0.899nm for 10nm MgB₂ film.

Abstract: The lamellar crystal orientation and crystal instable growth in polymer ultrathin films were studied. The orientation of lamellar crystal transforms from edge-on to flat-on with decreasing film thickness due to the enhancement of restriction effect of polymer-substrate on the edge-on lamellar crystals. Lamellar crystals in ultrathin films have a instable growth and become a dendrite at the growth front because of the diffusion-controlled growth.

Abstract: The properties of ultrathin films have been studied within the framework of Ising model and the method of random-field interactions. It is shown that the Curie temperature is inversely proportional to the number of layers. Critical exponent has been obtained and it is shown that it does not depend on the type of crystalline lattice.

Abstract: By the Langmuir-Blodgett(LB) technique, the zinc ion containing multilayer was prepared by transferring the zinc acetate, spread on the surface of subphase of ultrapure water and stearic acid-chloroform mixtures, onto a hydrophilic silicon wafer or glass plate. Then the multilayer was converted into ZnO ultrathin films after pre-heating and annealing. The optimized parameters for monolayer formation, such as concentration of subphase, barrier speed and spreading volume, were determined by the measurement of the surface pressure-surface area (Π-A) isotherms. The expended areas after deposition with zinc ions inferred the interaction of stearic acid with zinc ion during the formation of monolayer at air-water interface. The optimized parameters for multilayer deposition, such as surface pressure and lifting speed were determined by the measurement of the transfer coefficient. The X-ray diffraction(XRD) was used to investigate the crystal structures of ZnO nanoparticles and ultrathin film. The surface morphologies of the LB multilayer and ultrathin film were observed by the atomic force microscopy (AFM). A uniform and flat surface of ZnO ultrathin film within nanometer ranges(<35nm) were obtained.

Abstract: The magnetic properties of an ultrathin cobalt film were modified by a focused femtosecond pulsed laser beam. The Co wedge, with a thickness ranging from 0 to 2 nm, sandwiched by Au films was prepared using ultra-high vacuum magnetron sputtering on a mica substrate. The modifications of the laser induced magnetic anisotropy were investigated using magneto-optic Kerr microscopy and MFM/AFM techniques. The laser induces: (i) local reorientation of magnetization from an in-plane to a perpendicular state and (ii) an increase of the coercivity field. A corresponding increase of the perpendicular magnetic anisotropy is discussed considering an improvement of the Co/Au interfaces.

Abstract: Ultrathin film of polyisoprene was formed on silica surface in the two dimensional adsorbed surfactant by gamma-ray induced polymerization. The effect of gamma irradiation total doses on polymeric film formation was investigated. The modified silica and formed film were characterized. The results showed the potential of the surface modification by polymer film-surfactant-silica hybrid.

Abstract: A modified model of simply supported ultrathin film for incorporating the surface effects and geometrically nonlinear conditions is proposed on basis of Kirchhoff’s hypothesis. The governing equations and non-classical boundary conditions are derived via using Hamilton’s principle. The residual membrane force and bending moment, in which the contributions of surface stresses and nonlinear terms are taken into account, are explicitly expatiated. Comparison between the modified model and conventional plate theory is also given. Using the simply supported bending strip-like film as an example, results indicate that the mechanical behaviors of the film are size-dependent when the thickness of the film is nanometer.