0000000000451564
AUTHOR
Ullrich Pietsch
Kinetic behaviour of a structural phase transition in Langmuir-Blodgett multilayers studied by energy dispersive x-ray reflectivity
Various multilayers of Cd stearate were prepared by means of the Langmuir-Blodgett technique and investigated at T = Ts - ΔT (Ts, melting point of LB film). The x-ray scattering spectrum was recorded in several time intervals using an energy dispersive set up. For ΔT = 3 ... 9 K the observed intensity reduction of Bragg peaks, which corresponds to the multilayer periodicity, is recorded as a function of time. In addition new peaks appear. This is interpreted in terms of a kinetically driven phase separation of the metastable LB-phase. The time needed for phase disorder and the nucleation of the new phase decreases for smaller ΔT. The measured layer spacing of the new phase is larger than th…
Measurements of ultrafast spin-profiles and spin-diffusion properties in the domain wall area at a metal/ferromagnetic film interface
AbstractExciting a ferromagnetic material with an ultrashort IR laser pulse is known to induce spin dynamics by heating the spin system and by ultrafast spin diffusion processes. Here, we report on measurements of spin-profiles and spin diffusion properties in the vicinity of domain walls in the interface region between a metallic Al layer and a ferromagnetic Co/Pd thin film upon IR excitation. We followed the ultrafast temporal evolution by means of an ultrafast resonant magnetic scattering experiment in surface scattering geometry, which enables us to exploit the evolution of the domain network within a 1/e distance of 3 nm to 5 nm from the Al/FM film interface. We observe a magnetization…
Probing ultrafast changes of spin and charge density profiles with resonant XUV magnetic reflectivity at the free-electron laser FERMI
We report the results of resonant magnetic XUV reflectivity experiments performed at the XUV free-electron laser FERMI. Circularly polarized XUV light with the photon energy tuned to the Fe M2,3 edge is used to measure resonant magnetic reflectivities and the corresponding Q-resolved asymmetry of a Permalloy/Ta/Permalloy trilayer film. The asymmetry exhibits ultrafast changes on 240 fs time scales upon pumping with ultrashort IR laser pulses. Depending on the value of the wavevector transfer Qz, we observe both decreasing and increasing values of the asymmetry parameter, which is attributed to ultrafast changes in the vertical spin and charge density profiles of the trilayer film.
Light Induced Modifications of Langmuir-Blodgett-Multilayer Assemblies Containing Amphotropic Azocopolymer
Abstract Photochromic LB-multilayers of amphotropic copolymers having rod-like azobenzene moieties as side groups which exhibit thermotropic liquid crystalline behaviour in the bulk have been characterized by UV-VIS spectroscopy as well as by angular dependent and energy dispersive SAXS. Upon irradiation with UV-light the initial optical in-plane anisotropy and the vertical layered structure of LB-films can be destroyed. A new layered structure can be rebuilt on irradiation with visible light or by annealing. Using linearly polarized light for the irradiation an optical anisotropy (POA) has been induced or reversibly modified by a photoselection process.
Chemical modification of Topaz surfaces
In chemisorption, one is typically faced with the problem that the two-dimensional structure of the organic layer does not match the structure of the inorganic substrate. This work describes the first steps toward an induced epitaxial correlation of organic compounds on an inorganic surface. The idea of this work was to use a single crystal with a two-dimensional surface structure, Topaz (001), that matches an alkyl chain lattice better than existing substrates. X-ray reflectivity and FTIR experiments prove the surface modification of the Topaz, which is probably an etherification of the reactive OH-groups on the Topaz (001) surface.