Abstract: We are reporting an unexpected metal insulator transition at the ferromagnetic phase-transition temperature for thin films of La0.9Sr0.1MnO3 (< 50 nm), grown on a (100) face of SrTiO3 substrate. For the thicker films (> 50 nm), similar to the single crystal, no such transition is observed below T-C. Additionally, we observe the suppression of the features associated with charge or orbital ordering in intentionally La-deficient thin films of La0.88Sr0.1MnO3 (< 75 nm). In thin films, transmission electron microscopy reveals a compressive strain due to the epitaxial growth, that is, lattice parameters adopt those of the cubic lattice of SrTiO3. As the film thickness increases, coherent microtwinning is observed in the films and the films relax to a orthorhombic structure. (C) 2000 American Institute of Physics. [S0003-6951(00)00402-2].

Abstract: The superconducting state. of a thin superconducting disk with a hole is studied within the, nonlinear Ginzburg-Landau theory in which the demagnetization effect is accurately taken into account. We find that the flux through the hole is not quantized, the superconducting state is stabilized with increasing size of the hole for fixed radius of the disk, and a transition to a multivortex state is found if the disk is sufficiently large. Breaking the circular symmetry through a non-central-location of the hole in the disk favors the multivortex state.

Abstract: Catalytic synthesis and transmission electron microscopy (TEM) of multi-wall carbon nanotubes are presented. Silica, zeolite and alumina supported cobalt catalysts were prepared by different methods (impregnation and ion-adsorption precipitation) and were used to produce nanotubes. The synthesis was carried out in a fixed bed flow reactor and the process was optimized in order to produce carbon nanotubes on a gram scale. The influence of various parameters such as the method of catalyst preparation, the nature of the support, cobalt concentration and reaction conditions on the formation of nanotubes was investigated. The carbon deposits were measured and the quality of nanotubes was determined by low and high resolution TEM. Multi-wall straight and coiled nanotubes were found to be fairly regular with an average inner (outer) diameter of 4-7 nm (8-23 nm) and with lengths up to 0.1 mm.

Abstract: The electron distribution function (EDF) in an electron cyclotron resonance (ECR) discharge is far from Maxwellian. The self-consistent simulation of ECR discharges requires a calculation of the EDF on every magnetic line for various ion density profiles. The straightforward self-consistent simulation of ECR discharges using the Monte Carlo technique for the EDF calculation is very computer time expensive, since the electron and ion time scales are very different. An electron Boltzmann kinetic equation averaged over the fast electron bouncing and pitch-angle scattering was derived in order to develop an effective and operative tool for the fast modeling (FM) of low-pressure ECR discharges. An analytical solution for the EDF in a loss cone was derived. To check the validity of the FM, one-dimensional (in coordinate) and two-dimensional (in velocity) Monte Carlo simulation codes were developed. The validity of the fast modeling method is proved by comparison with the Monte Carlo simulations. The complete system of equations for FM is presented and ready for use in a comprehensive study of ECR discharges. The variations of plasma density and of wall and sheath potentials are analyzed by solving a self-consistent set of equations for the EDF.

Abstract: We present a detailed analysis of the point-defect clustering in strained Si/Si(1-x)Ge(x)/(001)Si structures, including the interaction of the point defects with the strained interfaces and the sample surface during 400 kV electron irradiation at room temperature. Point-defect cluster formation is very sensitive to the type and magnitude of the strain in the Si and Si(1-x)Ge(x) layers. A small compressive strain (-0.3%) in the SiGe alloy causes an aggregation of vacancies in the form of metastable [110]-oriented chains. They are located on {113} planes and further recombine with interstitials. Tensile strain in the Si layer causes an aggregation of interstitial atoms in the forms of additional [110] rows which are inserted on {113} planes with [001]-split configurations. The chainlike configurations are characterized by a large outward lattice relaxation for interstitial rows (0.13 +/-0.01 nm) and a very small inward relaxation for vacancy chains (0.02+/-0.01 nm). A compressive strain higher than -0.5% strongly decreases point-defect generation inside the strained SiGe alloy due to the large positive value of the formation volume of a Frenkel pair. This leads to the suppression of point-defect clustering in a strained SiGe alloy so that SiGe relaxes via a diffusion of vacancies from the Si layer, giving rise to an intermixing at the Si/SiGe interface. In material with a 0.9% misfit a strongly increased flow of vacancies from the Si layer to the SiGe layer and an increased biaxial strain in SiGe bath promote the preferential aggregation of vacancies in the (001) plane, which relaxes to form intrinsic 60 degrees dislocation loops.