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1
Yang, Fu-Liang. "Interdiffusion in metallic multilayers." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360566.
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Moffat, Jonathan. "Assembly of biopolymer multilayers." Thesis, University of East Anglia, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435024.
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Conyers, James Scott. "Diffusion in metallic multilayers." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621609.
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Skubic, Björn. "Spin Dynamics and Magnetic Multilayers." Doctoral thesis, Uppsala University, Department of Physics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8168.
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<p>Theoretical studies based on first-principles theory are presented for a number of different magnetic systems. The first part of the thesis concerns spin dynamics and the second part concerns properties of magnetic multilayers. The theoretical treatment is based on electronic structure calculations performed by means of density functional theory.</p><p>A method is developed for simulating atomistic spin dynamics at finite temperatures, which is based on solving the equations of motion for the atomic spins by means of Langevin dynamics. The method relies on a mapping of the interatomic exchange interactions from density functional theory to a Heisenberg Hamiltonian. Simulations are performed for various magnetic systems and processes beyond the reach of conventional micromagnetism. As an example, magnetization dynamics in the limit of large magnetic and anisotropy fields is explored. Moreover, the method is applied to studying the dynamics of systems with complex atomic order such as the diluted magnetic semiconductor MnGaAs and the spin glass alloy CuMn. The method is also applied to a Fe thin film and a Fe/Cr/Fe trilayer system, where the limits of ultrafast switching are explored. Current induced magnetization dynamics is investigated by calculating the current induced spin-transfer torque by means of density functional theory combined with the relaxation time approximation and semi-classical Boltzmann theory. The current induced torque is calculated for the helical spin-density waves in Er and fcc Fe, where the current is found to promote a rigid rotation of the magnetic order.</p><p>Properties of magnetic multilayers composed of magnetic and nonmagnetic layers are investigated by means of the Korringa-Kohn-Rostocker interface Green's function method. Multilayer properties such as magnetic moments, interlayer exchange coupling and ordering temperatures are calculated and compared with experiments, with focus on understanding the influence of interface quality. Moreover, the influence on the interlayer exchange coupling of alloying the nonmagnetic spacer layers with small amounts of a magnetic impurity is investigated.</p>
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Skubic, Björn. "Spin dynamics and magnetic multilayers /." Uppsala : Acta Universitatis Upsaliensis Acta Universitatis Upsaliensis, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8168.
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Baxter, C. S. "The structure of metal multilayers." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377256.
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Genc, Arda. "Phase Stability in Metallic Multilayers." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204506282.
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Turner-Valle, Jennifer 1970. "Nonlinear multilayers as optical limiters." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/288788.
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In this work we present a non-iterative technique for computing the steady-state optical properties of nonlinear multilayers and we examine nonlinear multilayer designs for optical limiters. Optical limiters are filters with intensity-dependent transmission designed to curtail the transmission of incident light above a threshold irradiance value in order to protect optical sensors from damage due to intense light. Thin film multilayers composed of nonlinear materials exhibiting an intensity-dependent refractive index are used as the basis for optical limiter designs in order to enhance the nonlinear filter response by magnifying the electric field in the nonlinear materials through interference effects. The nonlinear multilayer designs considered in this work are based on linear optical interference filter designs which are selected for their spectral properties and electric field distributions. Quarter wave stacks and cavity filters are examined for their suitability as sensor protectors and their manufacturability. The underlying non-iterative technique used to calculate the optical response of these filters derives from recognizing that the multi-valued calculation of output irradiance as a function of incident irradiance may be turned into a single-valued calculation of incident irradiance as a function of output irradiance. Finally, the benefits and drawbacks of using nonlinear multilayer for optical limiting are examined and future research directions are proposed.
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Holmström, Erik. "Magnetism and Structure in Metallic Multilayers." Doctoral thesis, Uppsala University, Department of Physics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3556.
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<p>The interplay between magnetism and structure has been studied in magnetic multilayers by electronic structure calculations based on density functional theory and analyzed in terms of models. The main ideas behind the Korringa-Kohn-Rostocker Green’s function method are described and the implementation of the coherent potential approximation is outlined.</p><p>A simple model for the bilinear magnetic interlayer coupling in metallic multilayers is derived that elucidates the main characteristics of the effect such as coupling period and origin of damping. An analysis of two exotic effects on the magnetic interlayer coupling, Fermi surface nesting and magnetic enhancement is also performed. The Fermi surface nesting in CuPd for the (110) direction is shown to induce a sharp peak in the magnetic interlayer coupling amplitude for a Fe/CuPd/Fe system when the Cu concentration is 60% in the CuPd alloy. The high magnetic susceptibility in Pd is shown to have strong influence on the magnetic interlayer coupling in a Fe/Pd/Fe (100) system where it changes the amplitude, phase and induces an offset.</p><p>The relation between surface structure and magnetic properties in metallic multilayers is investigated in terms of a theory that is based on a symbiosis between experiment and theory. By calculating the total magnetic moment of a sample for a large range of possible interface structures and comparing to experimental results for equivalent samples a parameter that describes the interface structure is determined. This parameter is then shown to be universal for the particular combination of elements in the structure both as regards the calculated total magnetic moment as well as the magnetic interlayer coupling and the critical temperatures. </p>
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Ajib, Rabih. "Propagation of light in Plasmonic multilayers." Thesis, Université Clermont Auvergne (2017-2020), 2017. http://www.theses.fr/2017CLFAC040/document.
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La plasmonique vise à utiliser des nanostructures métalliques très petites devant la longueur d’onde pour manipuler la lumière. Les structures métalliques sont particulières parce qu’elles contiennent un plasma d’électrons libres qui conditionne complètement leur réponse optique. Notamment, lorsque la lumière se propage à proximité des métaux, sous forme de mode guidés comme les plasmons et les gap-palsmons, elle est souvent lente, présentant une vitesse de groupe faible. Dans ce travail, nous présentons une analyse physique qui permet de comprendre cette faible vitesse en considérant le fait que l’énergie se déplace à l’opposé de la lumière dans les métaux. Nous montrons que la vitesse de groupe est égale à la vitesse de l’énergie pour ces modes guidés, et proposons la notion de ralentissement plasmonique. Finalement, nous étudions comment cette « trainée plasmonique » rend une structure aussi simple qu’un coupleur à prisme sensible à la répulsion entre les électrons du plasma<br>The field of plasmonics aims at manipulating light using deeply subwavelength nanostructures. Such structures present a peculiar optical response because of the free electron plasma they contain. Actually, when light propagates in the vicinity of metals, usually under the form of a guided mode, it presents a low group velocity. Such modes, like plasmons and gap-plasmons, are said to be slow. In this work we present a general physical analysis of this phenomenon by studying how the energy propagates in metals in a direction that is opposite to the propagation direction of the mode. We show that the group velocity and the energy velocity are the same, and finally introduce the concept of plasmonic drag. Finally, we study how slow guided modes make structures as simple as prism couplers sensitive to the repulsion between electrons inside the plasma
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Holmström, Erik. "Magnetism and structure in metallic multilayers /." Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3556.
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Stanciu, Victor. "Magnetism of Semiconductors and Metallic Multilayers." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5844.
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Kim, Young-Hee. "Studies of magnetic films and multilayers." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386598.
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Springwell, Ross Stuart. "Growth and characterisation of uranium multilayers." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1445107/.
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This thesis investigates the extents of the 5f-3d and 5f-4f electronic interactions in U/Fe, U/Co and U/Gd thin films, where electronic hybridisation effects are expected to influence the magnetism of the U 5f states. The samples were prepared by DC magnetron sputtering and included niobium buffer and capping layers to instigate crystalline growth and prevent oxidation of the multilayer stack. Layer thicknesses were varied between 5A and 90A with up to 30 bilayer repeats. The majority of the samples were grown at room temperature, but selected compositions were grown at elevated substrate temperatures. Many well-defined Bragg peaks were evident in the X-ray reflectivity spectra of multilayers of all three systems, indicating a low impurity contamination and a well-reproduced bilayer structure. High-angle X-ray diffraction spectra of the transition metal multilayers revealed poorly crystalline, oriented transition metal layers with a non-crystalline component of Fe and Co of 17A. U/Gd X-ray diffraction spectra displayed intensities up to two orders of magnitude greater than those observed for U/Fe or U/Co samples of similar composition and contained satellite peaks, indicating some degree of coherency between the two species. An intense peak was observed, arising from a crystalline uranium component at a position close to that expected for an exotic hep U phase, oriented in the 001 direction. Bulk magnetisation measurements revealed magnetically 'dead' Fe and Co layers of 15A and magnetic moments tending towards the bulk values of 2.2/zb and 1.7/iB for thick Fe and Co layers respectively. A study of the bulk magnetic properties of the U/Gd system did not indicate the presence of any significant 'dead' layer, but reported a saturation magnetic moment for thick Gd layers of 4.5//b> considerably reduced from the bulk value of 7.63//B- Calculations of the magnetic anisotropy for U/Gd samples revealed a possible transition from the gadolinium moments aligned within the plane of the film to samples displaying perpendicular magnetic anisotropy (PMA), at a gadolinium layer thickness of 5A. This transition could be achieved for thicker Gd layers if the thickness of the U layers were increased. A finite-size scaling effect was observed in a gadolinium layer thickness dependent study of the Curie temperature, indicating a transition from three to two dimensional behaviour for very thin Gd layers. Polarised neutron reflectivity spectra were taken in the specular geometry at magnetic saturation, and were simulated with separate, reduced moment and bulk moment ferromagnetic layers for U/Fe and U/Co samples and a simple bilayer structure for U/Gd samples. This simultaneous measurement of both the physical composition and bulk magnetisation measurements supported results obtained by X-ray reflectivity and magnetometry. The hybridisation of the electronic states in U/Fe and U/Gd resulted in an induced polarisation, detected using element selective techniques. X-ray magnetic circular dichroism measurements at the U Mrv and My edges were used to investigate the spin and orbital components of the uranium magnetic moment and a total magnetic moment on the U site of 0.1/b for the case of U/Fe multilayers, 0.01/zb in U/Gd samples and a signal only barely detectable above the statistical noise in the U/Co system were revealed. A uranium layer thickness dependent study of the magnetic moment values was used to indirectly deduce the profile of uranium magnetisation within the layers. X-ray resonant magnetic reflectivity measurements provided a depth dependent measure of the induced U 5f moment for selected U/Fe samples, which indicated a more complicated interfacial structure than that deduced by X- ray and neutron reflectivity techniques and showed that the majority of the U 5f moment was located at the interface region.
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Warren, Julian Guy. "Optical studies of organized dye multilayers." Thesis, Durham University, 1992. http://etheses.dur.ac.uk/5609/.
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The optical studies of organized dye multilayers constructed by the Langmuir- Blodgett technique are described. A number of different organic dye materials are examined; and some warrant special attention. They are S120 a cyanine, the squaraines and perylene. It is shown that these dyes form particularly well ordered films with unique optical properties. S120 forms J-aggregates, Sql and Sq3 both squaraines form hypsochromicaly shifted complexes (possibly H-aggregates) and Sq2 another squaraine exhibits band splitting (possibly Davydov). Fluorescence studies of perylene:tricosanoic acid films show that monomer and dimer species exist at room temperature, whilst at low temperature a third emitter is observed (excimer).Structural studies of perylene:tricosanoic acid films reveal a high degree of order. From the isotherms and polarized absorption spectra it is seen that the molecules are on their edges, tilted with respect to the substrate. RHEED measurements confirm the high degree of structural order. The dependence of surface plasmon resonance on the overlayers is demonstrated. The silver thickness and history are shown to be important in subsequent surface plasmon resonance measurements. An overlayer containing a dye with a sharp intense absorption band can interact with the surface plasmons to give anomalous dispersion (backbending). Only single backbending is observed for 8120 and Sql, indicating anisotropic films. Good agreement is found between 8120 backbending and data reported in the literature.
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Jordan, Simon Mark. "The MOKE characterisation of magnetic multilayers." Thesis, University of York, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284135.
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Berg, Michael C. Ph D. Massachusetts Institute of Technology. "Biological applications of weal polyelectrolyte multilayers." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33599.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005.<br>Includes bibliographical references.<br>This thesis research focused on biological applications of ultra-thin weak polyelectrolyte multilayers with specific emphasis on cell patterning, drug delivery, and antibacterial coatings. All of these very different applications were studied using three different polymers - polyacrylic acid (PAA), poly(allylamine hydrochloride) (PAH), polyacrylamide (PAAm). The first part of this thesis focuses on patterning polyelectrolyte multilayers found to resist mammalian cell adhesion, with ligands that promote specific interactions for adhesion. It was found that by patterning PAH on polyelectrolyte multilayers, the patterned functional group density and thickness could be tuned through ink pH adjustment. By changing the surface density of amine groups in the PAH patterns, the ligand density could also be altered using specific chemistry to attach peptides containing the tri-peptide sequence, RGD, which is known to promote cell adhesion in a number of cell types. The RGD density in the patterned regions determined the number of cells attached and the amount of cytoskeletal protein organization. The second part is an evaluation of porous polyelectrolyte multilayers as a delivery system for controlled release of small molecule drugs. The loading and releasing properties of porous PAH/PAA multilayers were investigated using the two drugs, ketoprofen and cytochalasin D. It was determined that the amount of drug released was proportional to the number of porous layers. Nanoporous films showed zero-order release, whereas microporous films displayed Fickian diffusion. The efficacy of the released drugs was checked by monitoring the effect of released cytochalasin D on fibroblasts' division.<br>(cont.) In the final part of this thesis, the antibacterial properties of both silver-loaded polyelectrolyte multilayers and superhydrophobic multilayers are examined. It was found that silver loaded multilayers killed bacteria to an extent greater than 99.99% for both airborne and waterborne models. Superhydrophobic films showed excellent anti-fouling properties for proteins, mammalian cells, and bacteria.<br>by Michael C. Berg.<br>Ph.D.
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Kok, Kuan Ying. "Microstructural analysis of giant magnetoresistive multilayers." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627229.
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Rao, Shraddha M. S. "Coherent optical interactions in graphene multilayers." Thesis, Heriot-Watt University, 2016. http://hdl.handle.net/10399/3202.
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The work discussed in this thesis deals with the generation, control and modulation of optical interactions in two-dimensional materials, specifically in unpatterned, subwavelength graphene multilayers, using the process of Coherent Perfect Absorption (CPA). It aims to address the problem of inefficient light-matter coupling at the nanoscale by studying new geometries for enabling total absorption in 50% absorbing graphene films. Total optical absorption is demonstrated and a 80% modulation of the absorption and scattering is achieved by controlling the relative phases of the interacting optical beams. Degenerate four-wave mixing (DFWM) in graphene multilayers leads to the generation of optical phase conjugation and negative refraction. These nonlinear responses are generated with a conversion efficiency of 5 x 10-5, and using the CPA arrangement their amplitudes are modulated with a modulation contrast of 100%. It is shown that the two-dimensionality of graphene gives rise to a ‘phase-dependent’ nonlinearity, which differs significantly from that in bulk materials. The optical nonlinearity in graphene is seen to be controlled by the relative phases of the interacting optical fields in a manner such that the nonlinear polarisation itself can be switched on or off. The phase-dependent nonlinearity of the two-dimensional medium is then explored in three alternative geometries. The first one uses only two input beams, and a light-with-light modulation of the nonlinear signals is observed with a contrast of 90%. The second geometry involves a single beam interacting with the sample, wherein, nonlinear signals are generated in a self-pumping mode, due to reflection from a mirror placed very close to the graphene sample. The last configuration also uses a mirror in order to require only a single light beam and leads to the observation of a ‘negative reflection’ signal. Finally, a nonlinear imaging technique ‘phase-contrast imaging’ is performed using a traditional DFWM configuration with three input optical fields. A phase-object applied on one of the pump beams is transformed into an intensity object in the resulting negative refraction. A few basic phase objects are imaged on the negatively refracted beam and are reported in this work, offering a possible application for the advantages offered by two-dimensional optical nonlinearities.
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Loos, Enrico. "Elektronenmikroskopie zum Wachstum von Siliziden." Master's thesis, [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10673673.
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Tanji, T., S. Hasebe, Y. Nakagami, K. Yamamoto, and M. Ichihashi. "Observation of Magnetic Multilayers by Electron Holography." Cambridge University Press, 2004. http://hdl.handle.net/2237/10296.
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Erdelen, C., André Laschewsky, H. Ringsdorf, J. Schneider, and A. Schuster. "Thermal behaviour of polymeric Langmuir-Blodgett multilayers." Universität Potsdam, 1989. http://opus.kobv.de/ubp/volltexte/2008/1737/.
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Langmuir-Blodgett multilayers of hydrocarbon and fluorocarbon polymers with hydrophilic spacer, lipid-polyelectrolyte complexes and mesogenic polymers have been prepared. The thermal behaviour of the multilayers was studied by small angle X-ray scattering, IR and UV—visible spectroscopy. Good thermal stabilities were found for the various classes of polymers. In addition, for both complexed multilayers and mesogenic polymer films, reorientation processes were observed.
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Lee, Dok Won. "Structural and magnetic properties of copperiron multilayers." Thesis, McGill University, 1997. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20264.
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The structural and magnetic properties of Diamagnetic/Ferromagnetic: Cu/Fe multilayers, prepared by DC-magnetron sputtering, were studied as a function of Fe layer thickness tFe. Structural characterization reveals the successful growth of high-quality layered structures along the film growth direction. However, the increasing contribution of the interface roughness was visible with decreasing tFe . X-ray diffraction data indicate the dissolution of Fe atoms in fcc Cu medium due to interfacial mixing.<br>The magnetic transition from ferromagnetism to paramagnetism with decreasing tFe was confirmed by conversion-electron Mossbauer spectroscopy (CEMS), vibrating sample magnetometry, and magnetotransport measurements. The monotonic decrease in the average hyperfine field with t Fe indicates that the transition is a gradual process as t Fe decreases from 34 A down to 7 A. The isomer shift of the singlets in the CEM spectra suggests the presence of fcc Fe, while the observed doublet is assigned to the Cu-Fe alloy phase at the interfaces.<br>The variation of magnetoresistance (MR) with t Cu indicates that for a nominal t Fe of 20 A the multilayer has a well-defined superlattice structure, whereas multilayers with nominal tFe, of 5 A have a granular-alloy-like structure. AC susceptometry provided direct evidence for island formation for nominal tFe = 5 A by exhibiting the blocking characteristics of superparamagnets. The temperature-dependence of the magnetization suggests that for nominal tFe = 5 A, 75% of the Fe atoms are in the superparamagnetic bcc phase, leaving the remaining 25% in the Cu-Fe alloy and fcc Fe phases.<br>The observed magnetic transition is likely due to superparamagnetic relaxation rather than a structural transition from bcc Fe to fcc Fe as t Fe decreases below a critical thickness tC at which a multilayer structure becomes an island structure.
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Cheng, Li 1973. "Magnetic polarisation of palladium in palladiumiron multilayers." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85061.
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This thesis is devoted to the studies of structural and magnetic properties of Pd/Fe multilayers with the principal goal of determining the extent to which the Pd layers are polarised by the Fe atoms and the average moment induced on each Pd atom. Although Pd/Fe multilayers have been the subject of several previous studies, no consensus on the behavior of magnetically polarised Pd has emerged. This work has the novel feature of applying a wide range of characterization techniques on the same sample. These techniques included x-ray diffraction, conversion electron Mossbauer spectroscopy (CEMS), magnetometry and polarised neutron reflectometry. Ag/Fe multilayers were first characterized to confirm the validity of the analysis of the small-angle x-ray reflectivity to obtain layer thicknesses, as well as to determine the temperature dependence of the Fe moment from GEMS data.<br>From the intersection of the results from the complementary measurements on Pd/Fe multilayers, for the first time, an unequivocal understanding of the behavior of magnetically polarised Pd has been achieved. We find, there is a clear excess magnetisation associated with Pd polarisation. At 4.5 K, the Pd in contact with an Fe surface is polarised with an average moment of 0.32 +/- 0.02 muB to a depth of 20 +/- 4 A (9 +/- 2 atomic layers). These results indicate a large exchange splitting of the Pd d-bands for a significant distance from the Fe surface, leaving the spin-up band full, and a moment in the Pd arising from the 0.36 holes in the spin-down band. We also find that the Fe moment at the Pd/Fe interface is slightly enhanced to 2.42 +/- 0.05 muB for about 2.0 +/- 0.3 atomic layers, suggesting that the magnetic properties of Fe is less affected by Pd as compared to the influence of Fe on Pd. Neither the extent of Pd polarisation nor the interface Fe moment agree with values predicted by theoretical calculations (the calculated Pd polarisation depth is 2 atomic layers, and the interface Fe moment is 2.7 muB). The band structure calculations will have to be refined in the light of the results from current study.
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Freitag, James M. (James Mac). "Structural and magnetotransport properties of nickelcobalt multilayers." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=24003.
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Ferromagnetic/ferromagnetic Ni/Co multilayers with component layer thicknesses ranging from 40 A down to 5 A were prepared by DC-magnetron sputtering. Due to the fact that Ni and Co alloys share a common d band, it is expected that the total resistance of the multilayers, including the elemental resistance of the layers and the resistance of the interdiffused alloyed region at the interfaces, will be lower than for other 3d transition metal combinations. Consequently, the magnetoresistance ratio $ Delta rho/ rho$ is expected to be enhanced.<br>Structural characterization by grazing-angle X-ray reflectivity reveals high-quality layered structures with a well-defined composition modulation along the film growth direction. Wide-angle X-ray diffraction scans display the polycrystalline nature of the Ni/Co multilayers which grow in an FCC phase with a preferred (111) orientation and a fraction of (200) structural domains.<br>Measurements of the magnetotransport properties of these multilayers indicate that the magnetoresistance (MR) effect, $ Delta rho sim0.35 mu Omega cdot$cm, is roughly constant over the entire compositional range. The MR ratio $ Delta rho/ rho,$ which is as high as 3.0% in a Si/(Ni40A/Co5A) $ times$ 6 multilayer, is therefore more strongly dependent on the zero-field resistivity $ rho.$ By fitting a semi-classical model to the resistivity compositional variation, we determined the interface contribution to the resistivity. The MR measurements as well as the magnetic anisotropy of the films, studied by vibrating sample magnetometry (VSM) and magneto-optical Kerr effect (MOKE) magnetometry, are consistent with the origin of the observed MR effect being anisotropic magnetoresistance (AMR). The highest magnetic sensitivity measured at zero-field and constant in the range from ${ sim}{-}10$ Oe to +10 Oe was 0.1%/Oe. This value compares well with other alloys being developed as magnetic sensors. (Abstract shortened by UMI.)
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Hetherington, C. "Transmission electron microscopy of GaAs/AlGaAs multilayers." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379967.
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Rozatian, Amir Sayid Hassan. "Anisotropy and interface structure in magnetic multilayers." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/2825/.
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It is believed that the interfacial structure can significantly affect the magnetic properties of magnetic multilayer thin films. X-ray scattering techniques provide a powerful method with which to study the bulk and interface morphology in these systems, and are therefore crucial in developing an understanding of the dominant factors influencing the magnitude of the perpendicular magnetic anisotropy (PMA).The inter-relation between magnetic and structural properties of a series of magnetic multilayer thin films is investigated. Magnetometry measurements on a series of Fe/Au multilayers showed that some samples exhibited in-plane magnetization. X-ray data and simulations showed that the interface roughness was high in these samples. However, the formation and propagation of uncorrelated roughness followed a systematic trend for surface growth. On the other hand, x-ray data and simulations for a single 100-bilayer sample showed that the interfaces are much better defined with significantly lower roughness. This was the only sample to show perpendicular anisotropy supposing the suggestion that the absence of PMA in all other samples is associated with high interface roughness. Magnetometry measurements of the PMA in Co/Pt multilayers show an increase in effective anisotropy at about 15 bilayers. X-ray data showed that the roughness of the interfaces was correlated in all samples and that the interfaces were sharp with no detectable interdiffusion. No systematic trend in roughness or crystallographic texture is detected with increasing bilayer repeat X-ray measurements on four series of Co/Pd multilayers show interface roughness independent of bilayer repeat number. For Co/Pt, the in-plane correlation length was independent of bilayer number while for Co/Pd and Fe/Au it increased. A saturation of the in-plane correlation length for the Au/Fe system where island growth of the Au occurs was observed. The out-of-plane correlation length increased with bilayer repeat for Co/Pt and Co/Pd. The interfaces in samples with higher PMA had a fractal parameter close to unity.
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Hase, Thomas Paul Anselm. "X-ray scattering from magnetic metallic multilayers." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4652/.
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Study of structure and interface morphology of magnetic thin films is crucial in obtaining a better understanding of the coupling mechanisms in such systems. In this thesis various x-ray scattering techniques are applied to a series of Co/Cr trilayers, Cu/Co multilayers and spin valve structures. It is demonstrated that modifications to the distorted wave Born approximation allow the modelling of grazing incidence diffuse scatter originating from graded systems such as Co/Cr. Grazing incidence scattering techniques are also employed to investigate the out of plane correlations of lateral roughness in Cu/Co multilayers, as well as in miscible trilayer structures. The use of soft x-rays in the investigation of 3d transition metal multilayers is also presented. Such experiments are sensitive to the component of magnetisation aligned with the direction of the incident beam. In a series of magnetisation experiments, the dependence of the x-ray scatter sensitive to this component of magnetisation are analysed. For the first time evidenced is found for correlated magnetic roughness, which has lateral correlation lengths far greater than the structural roughness length scales. This magnetic roughness is measured in detail, and the correlation length is found to vary with applied field direction. Grazing incidence x-ray fluorescence is applied to two spin valve structures. These experiments provide a direct measure of buried layer thicknesses which is not possible by other x-ray scattering techniques. This novel method for the determination of the copper layer thickness in spin valves shows the versatility of non-destructive x-ray methods for the characterisation of magnetic metallic multilayers.
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Molina, Aldareguia Jon Mikel. "Processing and nanoindentation behaviour of nitride multilayers." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620432.
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Sadki, El Hadi Smail. "Vortex matter in low temperature superconducting multilayers." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620238.
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Lloyd, Stephen John. "Structure-property relationships in iron-copper multilayers." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624742.
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Backer-Meurke, Fredrik. "Finite-size effect in CoAlZr/AlZr multilayers." Thesis, Uppsala universitet, Materialfysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355721.
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The structural and magnetic properties of amorphous Cox(Al80Zr20)1-x multilayers with varying thicknesses of the magnetic bilayers have been investigated. The reduction of the thickness causes a reduction of the critical temperature, Tc, this is known as the finite-size effect. The multilayers were grown using DC magnetron sputtering, co-sputtering was used with cobalt and an Al80Zr20 alloy target to create an amorphous CoAlZr alloy. The total thickness of the multilayers was chosen to be held constant at 60 nm and the Al80Zr20 spacing layers were thick enough to suppress any interlayer exchange coupling effects. Estimating the composition using RBS proved difficult with great uncertainties in the measured amount of aluminium in the samples. The amorphousness of the samples was investigated using GIXRD and all measured samples display x-ray amorphousness. Fits of XRR measurements showed that the bilayers displayed a rather large roughness, the origin of this roughness is unknown. MOKE measurements showed that the CoAlZr alloys exhibit a noncollinear spin structure at magnetic bilayer thicknesses of 6 nm and below. The samples’ noncollinear spin structure lead to the loss of remanence. Attempts at measuring the critical temperature with DC measurements using the remanence at zero field were therefore unsuccessful. AC susceptibility with SQUID should allow an accurate measurement of the critical temperature.
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Mibu, Ko. "Magnetic Properties of Fe/Rare Earth Multilayers." 京都大学 (Kyoto University), 1993. http://hdl.handle.net/2433/168948.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである<br>Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(理学)<br>甲第5514号<br>理博第1493号<br>新制||理||834(附属図書館)<br>UT51-94-B158<br>京都大学大学院理学研究科化学専攻<br>(主査)教授 新庄 輝也, 教授 坂東 尚周, 教授 小菅 皓二<br>学位規則第4条第1項該当
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Ghosh, Suchismita. "Thermal conduction in graphene and graphene multilayers." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://proquest.umi.com/pqdweb?index=0&did=1957308711&SrchMode=2&sid=2&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1268427434&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2009.<br>Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 12, 2010). Includes bibliographical references (p. 96-107). Also issued in print.
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Marrows, Christopher Hugh. "Indirect exchange coupling in sputtered magnetic multilayers." Thesis, University of Leeds, 1997. http://etheses.whiterose.ac.uk/2761/.
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This thesis describes the design, construction, and use of a sputter deposition facility at the University of Leeds for the growth of magnetic multilayer samples. Now completed, the machine is a UHV sputtering facility, capable of growing up to 15 samples of arbitrary complexity under computer control in a single vacuum cycle. The system currently has five sputter targets. The system was used to grow Co/Cu multilayers. It was found that the level of residual gas in the chamber is of primary importance in determining the final quality of the samples. A good vacuum is required to achieve good antiferromagnetic coupling between adjacent Co layers in the multilayer stack. Consequentially the giant magnetoresistance of such samples is very high. A poor vacuum leads to poor coupling between Co layers, and the magnetoresistance of such samples is minimal. When grown under clean conditions the giant magnetoresistance of the Co/Cu multilayers was very high - as much as 75% at room temperature, rising to 130% at 4.2K. Coupling oscillations as the Cu spacer thickness was varied were strong, whilst none were detected as a function of Co thickness. It was found that the >< Cu spacer layer was the part of the multilayer where the effects of damage by residual gases were most severe, and that damage to this area could cause biquadratic coupling. This form of the coupling arranges spins in adjacent layers at 90° to one another, rather than antiparallel, reducing the giant magnetoresistance response of the sample. The saturation magnetisation, bilinear and biquadratic coupling energies of 180° and 90° coupled samples were measured. These three quantities were found to scale as a function of temperature.
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Miller, Joe. "The magnetic and magneto-optical properties of PtCo thin films." Thesis, Coventry University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251862.
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Bergmann, Andre. "Antiferromagnetic dipolar ordering in [Co2MnGe/V]N multilayers." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980629276.
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Kyselov, Mykola. "Phenomenological theories of magnetic multilayers and related systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-63594.
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In this thesis multidomain states in magnetically ordered systems with competing long-range and short range interactions are under consideration. In particular, in antiferromagnetically coupled multilayers with perpendicular anisotropy unusual multidomain textures can be stabilized due to a close competition between long-range demagnetization fields and short-range interlayer exchange coupling. These spatially inhomogeneous magnetic textures of regular multidomain configurations and irregular networks of topological defects as well as complex magnetization reversal processes are described in the frame of the phenomenological theory of magnetic domains. Using a modified model of stripe domains it is theoretically shown that the competition between dipolar coupling and antiferromagnetic interlayer exchange coupling causes an instability of ferromagnetically ordered multidomain states and results in three possible ground states: ferromagnetic multidomain state, antiferromagnetic homogeneous and antiferromagnetic multidomain states. The presented theory allows qualitatively to define the area of existence for each of these states depending on geometrical and material parameters of multilayers. In antiferromagnetically coupled superlattices with perpendicular anisotropy an applied magnetic bias field stabilizes specific multidomain states, so-called metamagnetic domains. A phenomenological theory developed in this thesis allows to derive the equilibrium sizes of metamagnetic stripe and bubble domains as functions of the antiferromagnetic exchange, the magnetic bias field, and the geometrical parameters of the multilayer. The magnetic phase diagram includes three different types of metamagnetic domain states,
namely multidomains in the surface layer and in internal layers, and also mixed multidomain states may arise. Qualitative and quantitative analysis of step-like magnetization reversal shows a good agreement between the theory and experiment. Analytical equations have been derived for the stray field components of these multidomain states in perpendicular multilayer systems. In particular, closed expressions for stray fields in the case of ferromagnetic and antiferromagnetic stripes are presented. The theoretical approach provides a basis for the analysis of magnetic force microscopy (MFM) images from this class of nanomagnetic systems. Peculiarities of the MFM contrast have been calculated for realistic tip models. These characteristic features in the MFM signals can be employed for the investigations of the different multidomain modes. The methods developed for stripe-like magnetic domains are employed to calculate magnetization processes in twinned microstructures of ferromagnetic shape-memory materials. The remarkable phenomenon of giant magnetic field induced strain transformations in such ferromagnetic shape memory alloys as Ni-Mn-Ga, Ni-Mn-Al, or Fe-Pd arises as an interplay of two physical effects: (i) A martensitic transition creating competing phases, i.e. crystallographic
domains or variants, which are crystallographically equivalent but have different orientation. (ii) High uniaxial magnetocrystalline anisotropy that pins the magnetization vectors along certain directions of these martensite variants. Then, an applied magnetic field can drive a microstructural transformation by which the martensitic twins, i.e. the different crystallographic domains, are redistributed in the martensitic state. Within the phenomenological (micromagnetic) theory the equilibrium parameters of multivariant stripe patterns have been derived as functions of the applied field for an extended single-crystalline plate. The calculated magnetic phase diagram allows to give a detailed description of the magnetic field-driven martensitic twin rearrangement in single crystals of magnetic shape-memory alloys. The analysis reveals the crucial role of preformed twins and of the dipolar stray-field energy for the magnetic-field driven transformation process in magnetic shape-memory materials. This work has been done in close collaboration with a group of experimentalists from Institute of Metallic Materials of IFW Dresden, Germany and San Jose Research Center of
Hitachi Global Storage Technologies, United States. Comparisons between theoretical and experimental data from this cooperation are presented throughout this thesis as vital part of my work on these different subjects.
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Laschewsky, André, and H. Ringsdorf. "Polymerization of amphiphilic dienes in Langmuir-Blodgett multilayers." Universität Potsdam, 1988. http://opus.kobv.de/ubp/volltexte/2008/1717/.
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Amphiphilic derivatives of octadiene and docosadiene were investigated in monolayers and Langmuir-Blodgett multilayers, with respect to their self-organization and their polymerization behavior. All amphiphiles investigated form monolayers. However, only acid and alcohol derivatives were able to build up multilayers. Those multilayers are rapidly photopolymerized in the layers via a two-step process: Irradiation with long-wavelength UV light yields soluble polymers, whereas additional irradiation with sfiort-wavelength
UV light produces insoluble and presumably cross-linked polymers. The reaction meclianism is discussed according to the polymer characterization by UV spectroscopy, small-angle X-ray scattering, NMR spectroscopy, and gel permeation chromatography. All multilayers undergo structural changes during the polymerization; substantial changes result in defects in the polymerized layers as observed by scanning electron microscopy.
In contrast to the acids and alcohols, the deposition of monolayers of the aldehyde derivatives did not yield well-ordered multilayers, but rather amorphous films. In this different film structure, the photopolymerization
process differs from the one observed in multilayers.
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Saha, Naresh. "Mechanically micropatterned polyelectrolyte multilayers to control cell behavior." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENI100.
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Les films polyélectrolytes ont émergé comme un outil polyvalent dans le domaine desbiomatériaux et de l’ingénierie tissulaire. Dans cette étude, nous avons conçu des films à base debiopolymère, dont la rigidité peut être modulée par photo-réticulation. L’adhésion de bactéries etde cellules mammifères sur ces films a été étudiée. Une telle manipulation de rigidité superficielleconduit à une réponse différentielle des bactéries et des cellules mammifères. Les bactéries àGram négatif présentent une meilleure croissance sur des films nous alors que les cellulesmammifères préféraient les films plus rigides. Ces films ont été spatialement structurés à l’aided’un photomasque, permettant de créer des zones adjacentes de rigidité variable et de formecontrôlée. Les motifs photostructurés ont conduit les cellules à s’organiser préférentiellement surles zones les plus rigides. Une étude comparative a été réalisée avec des micropatronsbiochimiques. Les résultats ont montré des réponses similaires pour trois types cellulairesdifférents. Ces films offrent des perspectives intéressantes pour l’ingénierie tissulaire et pour letest de médicaments<br>Polyelectrolyte multilayers have emerged as a versatile tool in the field of biomaterials and tissueengineering. In this study, photocrosslinkable polyelectrolyte films based on biopolymers whosestiffness can be easily tuned by UV irradiation were prepared. Then, they were tested againstbacteria and mammalian cells to address the influence of the film stiffness on cell behavior. Suchsuperficial stiffness manipulation resulted in differential response of bacteria and mammaliancells. Gram negative bacteria evidenced better growth on softer films while various mammaliancells preferred stiffer films. Stiffness patterns of various geometries and sizes were generated byexposing the films to the UV light through a photomask incorporated in transparent substrates.The patterned films composed of stiff motifs distributed in a soft background induced apreferential spatial organization, which depended on pattern shape and size. A comparative studywith commercial biochemical patterns revealed similar pattern fidelity for three differentmammalian cell types. Such mechanical patterns on a 2D film appear promising for futureapplications in tissue engineering or for drug screening
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Séon, Lydie. "Polymer multilayers : fundamental aspects and application for biomaterials." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE014/document.
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La surface d'un matériau est le lieu privilégié des interactions entre le matériau et son environnement. La technique couche-par-couche, qui consiste en un dépôt alterné de polyanions et de polycations, ouvre de nouvelles perspectives dans le domaine des biomatériaux pour le contrôle de ces interactions. La cohésion des films multicouches de polyélectrolytes est principalement assurée par des interactions électrostatiques mais a été étendue à d'autres forces motrices telles que les interactions hôte-invité. Nos travaux s’articulent autour de deux axes principaux. D’une part, nous nous sommes intéressés aux films multicouches de polymères neutres basés sur des interactions hôte-invité et en particulier à l'influence de la force du complexe d’inclusion b-cyclodextrine/ferrocène sur la topographie de ces films. La force de l’interaction hôte-invité a d’abord été modulée en associant différents invités (l’adamantane, le ferrocène et le pyrène) avec la β-cyclodextrine. La force du complexe b-cyclodextrine/ferrocène a été ensuite modulée par la présence de différents sels de sodium à différentes forces ioniques au cours de la construction du film. Une force d'interaction intermédiaire du complexe semble être nécessaire pour former des films continus, tandis que, si elle est trop faible, la force d'interaction limite la construction du film.D’autre part, motivé par le fait que la prévention des infections microbiennes des dispositifs médicaux implantables constitue un problème médical et financier majeur, nous avons développé de nouveaux revêtements antimicrobiens grâce à la technique couche-par-couche. Des films multicouches à base de polysaccharides contenant la cateslytine, un peptide antimicrobien, permettent l’inhibition en 24h du développement de Candida albicans et Staphylococcus aureus, qui sont des agents pathogènes communs et virulents rencontrés dans les maladies nosocomiales. La libération des peptides antimicrobiens est déclenchée par la dégradation enzymatique du film en présence des agents pathogènes. Le revêtement est ainsi qualifié d’auto-défensif. La non-cytotoxicité du film vis-à-vis des cellules humaines permet une application cliniquement pertinente pour prévenir les infections sur les cathéters. Des dimères à base de cateslytine de différentes longueurs et un dendrimère ont été synthétisés afin d'améliorer l'activité biologique du peptide d'origine, i.e. ses propriétés antimicrobiennes et antiinflammatoires. Afin d’élaborer des films antimicrobiens mécaniquement robustes, le polyuréthane (polymère entrant dans la composition des cathéters) a été fonctionnalisé par une couche de polydopamine qui peut ensuite réagir avec des groupements thiol ou amine, permettant la fixation covalente des films de polysaccharides antimicrobiens réticulés étape par étape<br>The surface of a material is the privileged location, where the interactions between the material and its environment take place. In the field of biomaterials, the challenge is to control these interactions. A very versatile coating technique is the layer-by-layer deposition, which consists in the alternated deposition of polyanions and polycations. The cohesion of polyelectrolyte multilayer films is primarily ensured by electrostatic interactions but was extended to other driving forces such as host-guest interactions. Our work was constituted of two main parts.In the first part, the buildup of neutral polymer multilayer films based on host-guest interactions was studied and in particular the influence of β-cyclodextrin/ferrocene interaction strength on the topography of these films. The host-guest interaction strength was first modulated by involving different guests (adamantane, ferrocene and pyrene) in the buildup. Then, β -cyclodextrin/ferrocene interaction strength was tuned by the presence of different types and concentrations of salts during the multilayer buildup. Intermediate interaction strength seems to be required to form continuous films, whereas, if too low, the interaction strength limits the film buildup.In the second part, motivated by the fact that the prevention of pathogen colonization of implantable medical devices constitutes a major medical and financial issue, polyelectrolyte multilayers were used as tools to develop new antimicrobial coatings. Polysaccharide multilayer films containing cateslytin, an antimicrobial peptide, fully inhibited in 24h the development of Candida albicans and Staphylococcus aureus, which are common and virulent pathogens agents encountered in care-associated diseases. The release of the antimicrobial peptides was triggered by the enzymatic degradation of the film due to the pathogens themselves introducing the concept of self-defensive coating. The non-cytotoxicity of the film, towards human cells, highlights a medically relevant application to prevent infections on catheters. Different cateslytin based dimers with various lengths and one dendrimer were synthesized in order to improve the bioactivity of the original peptide, i.e. antimicrobial and anti-inflammatory properties. In order to obtain mechanically robust antimicrobial films, polyurethane (polymer that composes catheters) was functionalized with a polydopamine layer that can further react with thiol or amine groups, allowing the covalent attachment of step-by-step cross-linked antimicrobial polysaccharide films
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Lee, Dok Won. "Structural and magnetic properties of copper/iron multilayers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ44203.pdf.
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Patel, Pritesh Arjunbhai. "Polyelectrolyte multilayers simulations, experiments, and applications in biomineralization /." online version, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1193430461.
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Nedelcu, Ileana. "Interface structure and interdiffusion in Mo/Si multilayers." Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/57926.
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Meng, Xiadong. "Surface magneto-optic Kerr effect of NiCoCu multilayers." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22775.
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A phenomenological theory of magneto-optic Kerr effect (MOKE) is presented to illustrate the connection between the magnetization and the polarization of light reflection in an isotropic medium. An apparatus measuring the MOKE of magnetic medium was designed and constructed. The surface magneto-optic Kerr effect (SMOKE) of a magnetic multilayer is a measurement of the average magnetization of several layers within the penetration depth of the light.<br>SMOKE measurements on a series of sputtered $ rm Ni sb{80}Co sb{20}15 A$/CU$(t sb{Cu}),$ where $t sb{Cu}$ is the thickness of Cu spacer layer, multilayers confirms that the coupling strength in these multilayers oscillates from antiferromagnetic (AF) coupling to ferromagnetic coupling as a function of Cu spacer layer thickness. Low-angle x-ray diffraction and SMOKE measurements on a series of AF-coupled $ rm (Ni sb{80}Co sb{20}15 A$/Cu20A) $ times$ N multilayers with bilayer numbers N ranging from 8 to 100 shows that cumulative interface roughness increases with increasing N, as do the saturation field and coercivity. This is possibly due to the out-of-plane anisotropy associated with cumulative interface roughness in multilayers.<br>An AF-coupled $ rm (Ni sb{70}Co sb{30}15 A$/Cu20A) $ times$ 10 was continually annealed up to 400$ sp circ$C in several steps, and the magnetic behaviour of the sample was evaluated as a function of annealing temperatures. $ rm (Ni sb{70}Co sb{30}15 A$/CU20A/Ni$ rm sb{70}Co sb{30} A$/CU20A) $ times$ 5 multilayer was used for investigating the AF coupling between magnetic layers of unequal thicknesses. Finally, an AF-coupled $ rm (Ni sb{70}Co sb{30}15 A$/Cu20A/Ni$ rm sb{70}Co sb{30}15 A$/Cu35A) $ times$ 5 multilayer was sputtered and used to study the magnetization of an AF-coupled multilayer with two different coupling strengthes.
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Ferreira, Mauro Santos. "Oscillatory interlayer exchange coupling in metallic magnetic multilayers." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265777.
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Fenn, Michael. "Electrical resistivity of thin metal films and multilayers." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325924.
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Kryukov, Sergiy A. "MAGNETIC PROPERTIES OF Nb/Ni SUPERCONDUCTING / FERROMAGNETIC MULTILAYERS." UKnowledge, 2012. http://uknowledge.uky.edu/physastron_etds/7.
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Magnetic properties of Nb/Ni superconducting (SC) / ferromagnetic (FM) multilayers exhibit interesting properties near and below SC transition. A complex Field (H) – Temperature (T) phase boundary is observed in perpendicular and parallel orientation of ML with respect to DC field. We address the critical need to develop methods to make reliable magnetic measurements on SC thin films and ML, in spite of their extreme shape anisotropy and the strong diamagnetic response of the SC state.
Abrupt, highly reproducible “switching” of the SC state magnetization near the normal-state FM coercive fields has been observed in Nb/Ni ML. The SC penetration depth l(Nb) > the SC coherence length xo(Nb) » 40 nm >> the FM layer thickness y(Ni) = 5 nm, abrupt magnetic reversals might be driven by strong supercurrent densities (J x M torques) that have the potential to flow into the Ni layers. Alternatively, sharp magnetization anomalies also can result from strong flux pinning by the periodic layered structure of ML, including “lock-in” of quantized flux lines (FL) parallel to the ML plane. Strong confinement of the supercurrents within ML planes might also lead to various phase transitions of the FL lattice (FLL) composed of one-dimensional chains and other unusual structures.
Possible mechanisms for the switching anomalies must be evaluated while considering other experimental properties of Nb(x)/Ni(y) ML:
1) The upper critical magnetic field Hc2(T) exhibits a highly unusual anisotropy where the SC transition temperature Tc (H®0) for DC field H ^ ML plane exceeds the value for H || ML by ~ 0.5 K.
2) Nb/Ni ML samples do not consistently exhibit magnetic signatures for the onset of superconductivity, depending on the details of the sample mounting procedure and the AC or DC method used in SQUID magnetometry experiments.
3) Unusual “wiggles” or oscillations of order 10-30 mK were observed in Hc2(T) in AC SQUID experiments with H || ML and can be even larger (~0.16 K), depending upon the AC drive amplitude ho and frequency f .
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Zschintzsch-Dias, Manuel. "Self organized formation of Ge nanocrystals in multilayers." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-86838.
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The aim of this work is to create a process which allows the tailored growth of Ge nanocrystals for use in photovoltic applications. The multilayer systems used here provide a reliable method to control the Ge nanocrystal size after phase separation.
In this thesis, the deposition of GeOx/SiO2 and Ge:SiOx~ 2/SiO2 multilayers via reactive dc magnetron sputtering and the self-ordered Ge nanocrystal formation within the GeOx and Ge:SiOx~ 2 sublayers during subsequent annealing is investigated.
Mostly the focus of this work is on the determination of the proper deposition conditions for tuning the composition of the systems investigated. For the GeOx/SiO2 multilayers this involves changing the GeOx composition between elemental Ge (x = 0) and GeO2 (x = 2), whereas for the Ge:SiOx~ 2/SiO2 multilayers this involves changing the stoichiometry of the Ge:SiOx~ 2 sublayers in the vicinity of stochiometric silica (x = 2). The deposition conditions are controlled by the variation of the deposition rate, the deposition temperature and the oxygen partial pressure.
A convenient process window has been found which allows the sequential deposition of GeOx/SiO2 or Ge:SiOx ~2/SiO2 without changing the oxygen partial pressure during deposition. For stoichiometry determination Rutherford back-scattering spectrometry has been applied extensively.
The phase separation in the spatially confined GeOx and Ge:SiOx ~2 sublayers was investigated by X-ray absorption spectroscopy at the Ge K-edge. The Ge sub-oxides content of the as-deposited multilayers diminishes with increasing annealing temperature, showing complete phase separation at approximately 450° C for both systems (using inert N2 at ambient pressure). With the use of chemical reducing H2 in the annealing atmosphere, the temperature regime where the GeOx phase separation occurs is lowered by approximately 100 °C. At temperatures above 400° C the sublayer composition, and thus the density of the Ge nanocrystals, can be altered by making use of the reduction of GeO2 by H2.
The Ge nanocrystal formation after subsequent annealing was investigated with X-ray scattering, Raman spectroscopy and electron microscopy. By these methods the existence of 2 - 5 nm Ge nanocrystals at annealing temperatures of 550 (GeOx) - 700° C (Ge:SiOx ~2) has been confirmed which is within the multilayer stability range.
The technique used allows the production of extended multilayer stacks (50 periods ~ 300 nm) with very smooth interfaces (roughness ~ 0.5 nm). Thus it was possible to produce Ge nanocrystal layers with ultra-thin SiO2 separation layers (thickness ~ 1 nm) which offers interesting possibilities for charge transport via direct tunneling.
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Fulthorpe, Brian David. "X-ray scattering in giant magneto-resistive multilayers." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4300/.
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The scattering mechanisms responsible for Giant Magneto-Resistance (OMR) in magnetic multilayers are believed to be related to many aspects of the multilayer structure. X-ray scattering techniques provide a powerful method with which to study the bulk and interface morphology in these systems, and are therefore crucial in developing an understanding of the dominant factors influencing the magnitude of the OMR. Reflectivity measurements performed on a series of Co/Cu multilayers, sputter deposited onto etched silicon, reveal no variation in the interface roughness with etching voltage, the thickness of the individual layers also remaining constant. The observed decrease in the OMR cannot, therefore, be attributed to variations in spacer thickness or interfacial spin-independent scattering. Electron and X-ray Diffraction measurements suggest the reduction in GMR is due to a loss of antiferromagnetic coupling associated with a transformation of the texture from a randomly oriented to well oriented (111) polycrystalline texture, and subsequent reduction in the volume fraction of (100) oriented grains. Interfaces within Co/Cu are found to propagate with a high degree of conformality with increasing bilayer number, with an out-of-plane correlation length well in excess of 300Å. In contrast, the Co/Pt system exhibits a limiting out-of-plane correlation length of the order of 350Å arising from a columnar growth mode. X-ray Reflectivity and Diffraction measurements provide no structural interpretation for the 3-fold enhancement in the rate of increase of the saturation conductivity, as a function of spacer thickness, in Fe/Au (100) compared to Fe/Au (111), or why large oscillations in the GMR occur for the (100) orientation only. Such observations are, however, consistent with the existence of a channelling mechanism in Fe/Au (100). Grazing Incidence Fluorescence data indicates that Nb acts as a surfactant in Fe/Au (111) growth on sapphire. The influence of different defect types within multilayers has also been observed.