Dissertations / Theses on the topic 'Surface properties of condensed matter'
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Caramella, Lucia. "Theoretical spectroscopy of realistic condensed matter systems." Paris 6, 2009. http://www.theses.fr/2009PA066019.
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Le sujet de cette these porte sur des calculs ab initio de proprietes d'etat fondamental et excite de systemes differents, dans le cadre de la dft et de la tddft. Du cote numerique, nous avons mis en oeuvre une methode originale pour l'evaluation de la polarisabilite dynamique a particules independantes, et generalise un code au spin dans le but d'etudier les proprietes magnetiques de systemes reels. Nous avons etudie des spectres de reflectivite anisotrope et de perte d'energie pour la surface (100) du silicium, propre ou oxydee. La comparaison entre les spectres mesures et simules, nous ont permis d'exclure la reconstruction p(2x1). En suite, nous avons mis en evidence le probleme de la description des excitations des systemes a couche ouverte presente un etude des proprietes optiques d'alliage magnetique interessants pour des applications en spintronique. Nous avons evalue les proprietes d'etat fondamental de ces alliages et la conductivite du fer ccc.
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DiLisi, Gregory Anthony. "Oligomeric liquid crystals: Viscoelastic properties and surface interactions." Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1060023040.
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Delage, Patrick. "Growth mode and frictional properties of ultrathin films of sodium chloride on copper surfaces." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84022.
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The epitaxial growth of ultrathin films of NaCl was achieved on a Cu(100) substrate at room temperature. The growth mode was observed to be of the Stranski-Krastanov type using non-contact AFM, with well-oriented square islands growing on top of the first monolayer of NaCl. The frictional properties of different monolayers were measured using contact mode AFM. The friction contrast between the different monolayers of NaCl was found to be too small to be measured within the noise. Atomic stick-slip measurements were performed on a NaCl island. The results are discussed in comparison with relevent literature on thin films of alkali halides.
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Haider, Muhammad Baseer. "Surface and Bulk Properties of Magnetically Doped GaN and Their Dependence on the Growth Conditions." Ohio University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1132011994.
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Patra, Abhirup. "Surface properties, adsorption, and phase transitions with a dispersion-corrected density functional." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/516784.
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PhysicsPh.D.
Understanding the “incomprehensible” world of materials is the biggest challenge to the materials science community. To access the properties of the materials and to utilize them for positive changes in the world are of great interest. Often scientists use approximate theories to get legitimate answers to the problems. Density functional theory (DFT) has emerged as one of the successful and powerful predictive methods in this regard. The accuracy of DFT relies on the approximate form of the exchange-correlation (EXC) functional. The most complicated form of this functional can be as accurate as more complicated and computationally robust method like Quantum Monte Carlo (QMC), Random Phase Approximation (RPA). Two newest meta-GGAs, SCAN and SCAN+rVV10 are among those functionals. Instantaneous charge fluctuation between any two objects gives rise to the van der Waals (vdW) interactions (often termed as dispersion interactions). It is a purely correlation effect of the interacting electrons and thus non-local in nature. Despite its small magnitude it plays a very important role in many systems such as weakly bound rare-gas dimers, molecular crystals, and molecule-surface interaction. The traditional semi-local functionals can not describe the non-local of vdW interactions; only short- and intermediate-range of the vdW are accounted for in these functionals. In this thesis we investigate the effect of the weak vdW interactions in surface properties, rare-gas dimers and how it can be captured seamlessly within the semi-local density functional approximation. We have used summed-up vdW series within the spherical-shell approximation to develop a new vdW correction to the meta-GGA-MS2 functional. This method has been utilized to calculate binding energy and equilibrium binding distance of different homo- and hetero-dimers and we found that this method systematically improves the MGGA-MS2 results with a very good agreement with the experimental data. The binding energy curves are plotted using this MGGA-MS2, MGGA-MS2-vdW and two other popular vdW-corrected functionals PBE-D2, vdW-DF2. From these plots it is clear that our summed-up vdW series captures the long-range part of the binding energy curve via C6, C8, and, C10 coefficients. The clean metallic surface properties such as surface energy, work functions are important and often play a crucial role in many catalytic reactions. The weak dispersion interactions present between the surfaces has significant effect on these properties. We used LDA, PBE, PBSEsol, SCAN and SCAN+rVV10 to compute the clean metallic surface properties. The SCAN+rVV10 seamlessly captures different ranges of the vdW interactions at the surface and predicts very accurate values of surface energy ( ) , and work function (𝞥) and inter-layer relaxations (𝞭%). Our conclusion is adding non-local vdW correction to a good semi-local density functional such as SCAN is necessary in order to predict the weak attractive vdW forces at the metallic surface. The SCAN+rVV10 has also been employed to study the hydrogen evolution reaction (HER) on 1T-MoS2. We have chosen as a descriptor differential Gibbs free energy (𝚫 GH ) to understand the underlying mechanism of this catalytic reaction. Density functional theory calculations agree with the experimental findings. In the case of layered materials like 1T-MoS2, vdW interactions play an important role in hydrogen binding, that SCAN+rVV10 calculation was able to describe precisely. We have also used SCAN and SCAN+rVV10 functionals to understand bonding of CO on (111) metal surfaces, where many approximations to DFT fail to predict correct adsorption site and adsorption energy. In this case SCAN and SCAN+rVV10 do not show systematic improvements compared to LDA or PBE, rather, both SCAN and SCAN+rVV10 overbind CO more compared to PBE but less compared to the LDA. This overbinding of CO is associated with the incorrect charge transfer from metal to molecule and presumably comes from the density-driven self-interaction error of the functionals. In this thesis we assessed different semi-local functionals to investigate molecule surface systems of 𝞹-conjugated molecules (thiophene, pyridine) adsorbed on Cu(111), Cu(110), Cu(100) surfaces. We find the binding mechanism of these molecules on the metallic surface is mediated by short and intermediate range vdW interactions. Calculated values of binding energies and adsorbed geometries imply that this kind of adsorption falls in the weak chemisorption regime. Structural phase transitions due to applied pressure are very important in materials science. However, pressure induced structural phase transition in early lanthanide elements such as Ce are considered as abnormal first order phase transition. The Ce 𝝰-to-𝝲 isostructural phase transition is one of them. The volume collapse and change of magnetic properties associated with this transition are mediated by the localized f-electron. Semi-local density functionals like LDA, GGA delocalize this f-electron due to the inherent self-interaction error (SIE) of these functionals. We have tested the SCAN functional for this particular problem, and, it was found that the spin-orbit coupling calculations with SCAN not only predicts the correct magnetic ordering of the two phases, but also gives a correct minima for the high-pressure 𝝰-Ce phase and a shoulder for the low-pressure 𝝲-Ce phase.
Temple University--Theses
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Torrance, David Britt. "Growth and electronic properties of nanostructured epitaxial graphene on silicon carbide." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50205.
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The two-dimensional phase of carbon known as graphene is actively being pursued as a primary material in future electronic devices. The goals of this thesis are to investigate the growth and electronic properties of epitaxial graphene on SiC, with a particular focus on nanostructured graphene. The first part of this thesis examines the kinetics of graphene growth on SiC(0001) and SiC(0001 ̅) by high-temperature sublimation of the substrate using a custom-built, ultra-high vacuum induction furnace. A first-principles kinetic theory of silicon sublimation and mass-transfer is developed to describe the functional dependence of the graphene growth rate on the furnace temperature and pressure. This theory can be used to calibrate other graphene growth furnaces which employ confinement controlled sublimation. The final chapter in this thesis involves a careful study of self-organized epitaxial graphene nanoribbons (GNRs) on SiC(0001). Scanning tunneling microscopy of the sidewall GNRs confirms that these self-organized nanostructures are susceptible to overgrowth onto nearby SiC terraces. Atomic-scale imaging of the overgrown sidewall GNRs detected local strained regions in the nanoribbon crystal lattice, with strain coefficients as high as 15%. Scanning tunneling spectroscopy (STS) of these strained regions demonstrate that the graphene electronic local density of states is strongly affected by distortions in the crystal lattice. Room temperature STS in regions with a large strain gradient found local energy gaps as high as 400 meV. Controllable, strain-induced quantum states in epitaxial graphene on SiC could be utilized in new electronic devices.Per request of the author and the advisor, and with the approval of the graduate office, the Acknowledgements page was replaced with an errata.
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Alcantara, Ortigoza Marisol. "Theoretical studies of electronic, vibrational, and magnetic properties of chemisorbed surfaces and nanoalloys." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/496.
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Regoutz, Anna. "Structural and electronic properties of metal oxides." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6f425890-b211-4b35-b438-b8de18f7ae64.
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Metal oxides are of immense technological importance. Their wide variety of structural and electronic characteristics leads to a flexibility unrivalled by other groups of materials. However, there is still much debate about the fundamental properties of some of the most widely used oxides, including TiO2 and In2O3. This work presents high quality, in-depth characterisation of these two oxides in pure and doped form, including soft and hard X-ray photoelectron spectroscopy and X-ray diffraction. Bulk samples as well as thin film samples were prepared analysed. For the preparation of thin films a high quality sol-gel dip-coating method was developed, which resulted in epitaxial films. In more detail the organisation of the thesis is as follows: Chapter 1 provides an introduction to key ideas related to metal oxides and presents the metal oxides investigated in this thesis, In2O3, Ga2O3, Tl2O3, TiO2, and SnO2. Chapter 2 presents background information and Chapter 3 gives the practical details of the experimental techniques employed. Chapters 4 presents reciprocal space maps of MBE-grown In2O3 thin films and nanorods on YSZ substrates. Chapters 5 and 6 investigate the doping of In2O3 bulk samples with gallium and thallium and introduce a range of solid state characterisation techniques. Chapter 7 describes the development of a dip-coating sol-gel method for the growth of thin films of TiO2 and shows 3D reciprocal space maps of the resulting films. Chapter 8 concerns hard x-ray photoelectron spectroscopy of undoped and Sn-doped TiO2. Chapter 9 interconnects previous chapters by presenting 2D reciprocal space maps of nano structured epitaxial samples of In2O3 grown by the newly developed sol-gel based method. Chapter 10 concludes this thesis with a summary of the results.
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Bekele, Selemon. "Structural and Dynamical Properties of Water and Polymers at Surfaces and Interfaces: A Molecular Dynamics Investigation." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1530040420616781.
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Bidermane, Ieva. "Structure and Electronic Properties of Phthalocyanine Films on Metal and Semiconductor Substrates." Doctoral thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-217086.
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The current thesis presents fundamental studies of phthalocyanines (Pcs), a group of organic macro-cycle molecules. The use of phthalocyanine molecular films in devices with a variety of possible technological applications has been the reason of the many studies dedicated to such molecules during the last decades. Core and valence photoelectron spectroscopies (PES), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy (STM) techniques are used to study phthalocyanine molecules in gas phase and adsorbed on gold (111) and silicon Si(100)-2x1 substrates. Density functional theory (DFT) is used to obtain further insights in the electronic structure of the phthalocyanines. The aim of our studies is to get a deeper understanding into the molecule-molecule and molecule-substrate interactions, a fundamental requirement for improving the devices based on such molecular materials. Gas phase PES and XAS studies and single molecule DFT calculations are performed on the valence band (VB) of iron phthalocyanine (FePc), manganese phthalocyanine (MnPc) and metal-free phthalocyanine (H2Pc). The VB simulations have shown how the metal atom of the Pc influences the inner valence states of the molecules. The HOMO of the H2Pc and FePc is formed by mostly C2p states, whereas the HOMO of MnPc has mainly Mn3d character. PES studies of H2Pc on Au(111) have revealed the influence of the surface on the adsorption of the monolayer. XAS studies indicate formation of ordered monolayer with the Pc ligands parallel to the surface and the change of the molecular tilt angle with increasing thicknesses. For LuPc2 adsorbed on Au(111), STM study demonstrates a formation of bilayer instead of a monolayer. A comparison between the results of LuPc2 adsorbed on pristine or passivated Si(100)-2x1 confirmes the different reactivities of these surfaces: LuPc2 retains many molecular-like characters, when adsorbed on the innert passivated Si. Instead, on the more reactive pristine Si surface, the spectroscopic results have indicated a more significant interaction, possible hybridization and charge redistribution between the molecules and the surface. Moreover, STM images show a modification of the geometrical shape of the molecules, which are proposed to adsorb in two different geometries on the pristine Si surface.
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Seel, Jennifer A. "Ion-surface scattering measurements of the (110) surface of titanium dioxide." Thesis, University of Ottawa (Canada), 1997. http://hdl.handle.net/10393/4149.
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The (110) surface of TiO$\sb2$ is examined using a 9.92 keV oxygen ion beam. The positions of the peaks in the emitted ion energy spectrum are consistent with those predicted by ion-surface scattering theory for O$\sp{+}$-O and O$\sp{+}$-Ti collisions. Upon examination of the peaks present in the ion energy spectrum, information about the surface crystallographic structure can be determined. This includes studying the shadowing/blocking effects as the azimuthal and elevation angles are varied. Using this information the dimensions of the surface unit cell are found to be consistent with the bulk dimensions. The height of the oxygen rows that are present above the surface can also be determined and is found to be lower than predicted by the bulk.
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Bulicz, John. "Single crystal surface investigations using RHEED." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7501.
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A RHEED system was assembled and incorporated in the existing ultra-high-vacuum chamber. A system for the production and transport of low energy ions to the ultra-high-vacuum environment was maintained. Samples cut from wafers of Si(100) were investigated using electron diffraction as well as low energy ion scattering techniques. The surface composition, symmetry and orientation of these specimens could be determined. Attempts to adsorb hydrogen onto the Si(100) surface indicated that the procedure in use needs to be modified. An initial RHEED study of the Si(110) surface revealed a complex arrangement of atoms which does not correspond to the "16 x 2" structure reported for the clean surface.
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Zhang, Chang-Hua. "Stability and surface dynamics of metal nanowires." Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/290097.
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In this thesis, we have systematically investigated the stability, surface dynamics, electronic transport, and growth of metal nanowires using a semiclassical free energy functional based on the mean-field interacting electron model, which is simple and general enough. In this model, the ionic degrees of freedom of the wire are modeled as an incompressible fluid, and the conducting electrons are treated as a Fermi gas confined within the wire with Dirichlet boundary conditions. In equilibrium, we prove that the electron-electron interaction is a second-order effect to the total grand canonical free energy, while the shell-correction to the noninteracting grand canonical free energy is a first-order effect. To leading order, the electron-electron interactions just renormalize the Weyl parameters, such as the average energy density, surface tension and mean curvature energy, but not the mesoscopic shell effect. This finding for open mesoscopic systems is a generalization of the well-known Strutinsky theorem for finite-Fermion systems. It is for this reason that self-consistent jellium calculations obtain essentially identical equilibrium mesoscopic effects as calculations based on the free-electron model. However, for systems out of equilibrium, the electron-electron interaction plays important roles. First of all, the Strutinsky theorem breaks down in the non-equilibrium case. Secondly, the gauge invariance condition is violated if the electron-electron interaction is not adequately included. We first derive a thermodynamic phase diagram for jellium nanowires, which predicts that cylindrical wires with certain "magic" conductance values are stable with respect to small perturbations up to remarkably high temperatures and high applied voltage. We have shown that Jahn-Teller-distorted wires can be stable. The derived sequence of stable cylindrical and elliptical geometries explains the experimentally observed shell and supershell structures for alkali metals. Highly deformed wires can explain additional conductance peaks in low temperature experiments on alkali metals and in gold. We then study the surface dynamic properties of different phases. Both surface phonons and surface self-diffusion of atoms are included in the linearized surface dynamics. It is found that inertial dynamics (phonons) always dominate the long-wavelength behavior at small time scales, including the critical points. (Abstract shortened by UMI.)
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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.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.
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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Tabard-Cossa, Vincent. "Microcantilever actuation generated by redox-induced surface stress." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102214.
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Electrochemically-induced changes in surface stress at the solid-liquid interface are measured using a differential cantilever-based sensor. The simultaneous, in situ measurements of the current (charge) and interfacial stress changes are performed by employing an AFM cantilever as both the working electrode (in a conventional three-probe electrochemical cell configuration) and as the mechanical transducer (bending of the cantilever). The custom-built instrument achieves a surface stress sensitivity of 1x10-4 N/m and a dynamic range of 5x105. Combining electrochemistry with cantilever-based sensing provides the extra surface characterization capability essential for the interpretation of the origin of the surface stress.The objective of the present study is to gain a better understanding of the mechanisms responsible for the nanomechanical motion of cantilever sensors during adsorption and absorption processes. The study of these simple model systems will lead to a general understanding of the cantilever-based sensor's response and provide insights into the physical origin of the measured surface stress.
The surface stress generated by the electrochemically-controlled absorption of ions into a thin polypyrrole film is investigated. A compressive change in surface stress of about -2 N/m is measured when the polymer is electrochemically switched between its oxidized and neutral (swollen) state. The volume change of the polymer phase with respect to the gold-coated cantilever is shown to be responsible for the mechanical motion observed.
The potential-induced surface stress and surface energy change on an Au(111)-textured cantilever, in a 0.1 M HClO4 electrolyte, are simultaneously measured. These measurements revealed that for solid electrodes these two thermodynamic parameters are significantly different. In the double layer region, a surface stress change of -0.55 +/-0.06 N/m is measured during ClO4- adsorption whereas the surface energy variation is smaller by one order of magnitude. The origin of the surface stress change at the metal-electrolyte interface is understood by the variation in electron density at the surface which alters the inter-atomic bonds strength between surface atoms, while the specificity of adsorption of ions is found to be mostly responsible for the fine structure of the surface stress profile.
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Rost, A. W. "Magnetothermal properties near quantum criticality in the itinerant metamagnet Sr₃Ru₂O₇ /." St Andrews, 2009. http://hdl.handle.net/10023/837.
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Raymond, Sylvain. "Zero-dimensional properties of self-assembled islands." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ28370.pdf.
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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.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.
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.
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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Triola, Christopher Lawrence Charles. "Electronic properties of chiral two-dimensional materials." W&M ScholarWorks, 2015. https://scholarworks.wm.edu/etd/1539624004.
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In this dissertation we study the electronic properties of certain two-dimensional chiral electron systems. We study the static and dynamic screening of gapped bilayer graphene and find important qualitative differences between the dielectric screening function obtained using a simplified 2-band model and that obtained using a more sophisticated 4-band model. We also formulate a continuum model to study the low-energy electronic properties of heterostructures formed by graphene on a strong three-dimensional topological insulator (TI) both for the case of commensurate and incommensurate stacking. We find that the proximity of the TI induces a strong enhancement of the spin-orbit coupling in graphene that can be tuned via the twist angle. Additionally, we examine the effect of a spin-active interface on the symmetry of proximity-induced superconducting pairing amplitudes in topological insulators. We compare our results to those for normal metals and ferromagnetic materials finding that the nontrivial spin chirality of the TI leads to qualitatively different behavior of the pairing amplitude. Lastly, we study the many-body instabilities of the Dirac states predicted to arise on the surfaces of topological Kondo insulators identifying regions of parameter space in which the system exhibits spin density wave, and charge density wave order.
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Godin, Michel. "Surface stress, kinetics, and structure of alkanethiol self-assembled monolayers." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85551.
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The surface stress induced during the formation of alkanethiol [HS(CH 2)nCH3] self-assembled monolayers (SAMs) on gold from the vapor phase was measured using a differential cantilever-based sensor. This custom-built system is capable of surface stress measurements with a sensitivity of 5 x 10-5 N/m using commercially-available atomic force microscopy cantilevers. A second system combining cantilever-based sensing and ellipsometry was also designed and built, capable of yielding simultaneous in situ surface stress and film thickness measurements. Scanning tunneling microscopy (STM) with molecular resolution was also performed ex situ in order to characterize the structure of the resulting SAMs. The complementary use of these tools has provided an all-around view of the self-assembly process.These measurements were performed in order to gain insight into the mechanisms involved in the self-assembly process and into the origins of the associated surface stress. Moreover, these studies were used to characterize and optimize the response of cantilever-based sensors based on functionalized SAM technology in terms of reliability, sensitivity, and reproducibility.
The evolution of the surface stress induced during alkanethiol SAM formation reveals features associated with coverage-dependent structural phase transitions. These results show that both the kinetics of SAM formation and the resulting SAM structure are strongly influenced by the surface structure of the underlying gold substrate, by the impingement rate of the alkanethiol molecules onto the gold surface, and by the cleanliness of the gold surface. In particular, it was found that a minimum gold grain size is necessary in order for the SAM to achieve the standing-up phase, for which large compressive surface stresses (~10 N/m) are measured. In addition, these results show that alkanethiol SAMs can become kinetically trapped in metastable intermediate states (lying-down phase) for formation on small-grained gold surfaces and/or at low alkanethiol vapor concentrations. Theoretical modeling of the origins of the induced surface stress reveals that inter-molecular Lennard-Jones interactions and electrostatic repulsion between adsorbed species play minimal roles in the development of the surface stress. Changes in the electronic structure of the underlying gold substrate are more likely to account for the large compressive surface stresses observed during alkanethiol SAM formation.
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Finnie, Paul D. "The fabrication and optical properties of quantum wires." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq26116.pdf.
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Kou, Angela. "Microscopic Properties of the Fractional Quantum Hall Effect." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11161.
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The fractional quantum Hall effect occurs when an extremely clean 2-dimensional fermion gas is subject to a magnetic field. This simple set of circumstances creates phenomena, such as edge reconstruction and fractional statistics, that remain subjects of experimental study 30 years after the discovery of the fractional quantum Hall effect. This thesis investigates the properties of excitations of the fractional quantumPhysics
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Helbers, Andrew J. "Magneto-Optical Properties of Rare-Earth Doped Semiconductors." Thesis, Lehigh University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10623187.
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Brackstone, Mark Andrew. "Dynamic properties of models of modulated systems in condensed matter." Thesis, University of Southampton, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255764.
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CamarÃo, Diego de Lucena. "Diffusive properties of soft condensed matter systems under external confinement." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=13612.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorNesta tese estudamos a influÃncia de potenciais de confinamento externos nas propriedades dinÃmicas de sistemas de matÃria condensada mole. Analisamos as propriedades difusivas de dois sistemas especÃficos utilizando simulaÃÃes computacionais (DinÃmica Molecular de Langevin e DinÃmica Browniana). No CapÃtulo 1, introduzimos o tÃpico sobre matÃria condensada mole. Mostramos vÃrios aspectos teÃricos e experimentais neste tipo de sistema. Fazemos uma breve introduÃÃo ao tÃpico de difusÃo, onde discutimos os principais aspectos do movimento Browniano. Introduzimos o problema de difusÃo em linha (SFD, do inglÃs "single-file diffusion") e o discutimos, teorica e experimentalmente, no contexto de sistemas de matÃria condensada mole. No CapÃtulo 2, introduzimos os mÃtodos computacionais utilizados nesta tese. Discutimos os mÃtodos de DinÃmica Molecular e suas variantes, o mÃtodo de DinÃmica de Langevin e DinÃmica Browniana. TambÃm introduzimos algoritmos de integraÃÃo utilizados nos capÃtulos posteriores. Nos Caps. 3, 4 e 5, analisamos dois sistemas distintos, (i) um sistema de partÃculas de Yukawa confinadas em um canal parabÃlico quasi-unidimensional (q1D) e (ii) um sistema de colÃides magnÃticos sob a influÃncia de um potencial parabÃlico e uma modulaÃÃo periÃdica externa ao longo da direÃÃo nÃo confinada. No primeiro sistema, estudamos a transiÃÃo do regime de difusÃo em linha (SFD) para o regime de difusÃo normal (2D). No segundo sistema, estudamos os efeitos de vÃrios parÃmetros que caracterizam o sistema (e.g., a magnitude do campo magnÃtico externo e a presenÃa da modulaÃÃo periÃdica externa) em suas propriedades dinÃmicas. Finalmente, apresentamos um sumÃrio dos principais resultados obtidos nesta tese e mostramos algumas questÃes em aberto como perspectivas para pesquisas futuras na Ãrea de difusÃo em sistemas de matÃria condensada mole.
In this thesis we study the influence of external confinement potentials on the dynamical properties of soft condensed matter systems. We analyze the diffusive properties of two specific systems by means of Langevin and Brownian Dynamics simulations. In Chapter 1, we introduce the subject of soft condensed matter. We show several theoretical and experimental aspects of these type of systems. We make a brief introduction to the topic of diffusion, where we discuss main aspects of Brownian motion. We introduce the single-file diffusion (SFD) problem and discuss it in the context of soft condensed matter systems, both theoretically and experimentally. In Chapter 2, we introduce the computational method used in this thesis. We discuss Molecular Dynamics (MD) and its variants, Langevin and Brownian Dynamics simulations. We also introduce numerical algorithms used in the following chapters. In Chapters 3, 4 and 5, we analyze two different systems, namely (i) a system of interacting Yukawa particles confined in a parabolic quasi-one-dimensional (q1D) channel and (ii) a system of magnetic colloidal particles under the influence of both a parabolic confinement potential and a periodic external modulation along the unconfined direction. In the former, we study the transition from the single-file diffusion (SFD) regime to the two-dimensional (2D) diffusion regime. In the latter, we study the influence of several parameters that characterizes the system, e.g., the strength of an external magnetic field and the periodic modulation along the unconfined direction, on its dynamical properties. Finally, we present the summary of the main findings reported in this thesis and we show some open questions as perspectives for future research in the field of diffusion in soft condensed matter systems.
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Camarão, Diego de Lucena. "Diffusive properties of soft condensed matter systems under external confinement." reponame:Repositório Institucional da UFC, 2014. http://www.repositorio.ufc.br/handle/riufc/11285.
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CAMARÃO, Diego de Lucena. Diffusive properties of soft condensed matter systems under external confinement. 2014. 142 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2014.Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-04-09T20:25:36Z No. of bitstreams: 1 2014_tese_dlcamarao.pdf: 4771668 bytes, checksum: 12d4989237a73eeafcc143c607fa30dd (MD5)
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In this thesis we study the influence of external confinement potentials on the dynamical properties of soft condensed matter systems. We analyze the diffusive properties of two specific systems by means of Langevin and Brownian Dynamics simulations. In Chapter 1, we introduce the subject of soft condensed matter. We show several theoretical and experimental aspects of these type of systems. We make a brief introduction to the topic of diffusion, where we discuss main aspects of Brownian motion. We introduce the single-file diffusion (SFD) problem and discuss it in the context of soft condensed matter systems, both theoretically and experimentally. In Chapter 2, we introduce the computational method used in this thesis. We discuss Molecular Dynamics (MD) and its variants, Langevin and Brownian Dynamics simulations. We also introduce numerical algorithms used in the following chapters. In Chapters 3, 4 and 5, we analyze two different systems, namely (i) a system of interacting Yukawa particles confined in a parabolic quasi-one-dimensional (q1D) channel and (ii) a system of magnetic colloidal particles under the influence of both a parabolic confinement potential and a periodic external modulation along the unconfined direction. In the former, we study the transition from the single-file diffusion (SFD) regime to the two-dimensional (2D) diffusion regime. In the latter, we study the influence of several parameters that characterizes the system, e.g., the strength of an external magnetic field and the periodic modulation along the unconfined direction, on its dynamical properties. Finally, we present the summary of the main findings reported in this thesis and we show some open questions as perspectives for future research in the field of diffusion in soft condensed matter systems.
Nesta tese estudamos a influência de potenciais de confinamento externos nas propriedades dinâmicas de sistemas de matéria condensada mole. Analisamos as propriedades difusivas de dois sistemas específicos utilizando simulações computacionais (Dinâmica Molecular de Langevin e Dinâmica Browniana). No Capítulo 1, introduzimos o tópico sobre matéria condensada mole. Mostramos vários aspectos teóricos e experimentais neste tipo de sistema. Fazemos uma breve introdução ao tópico de difusão, onde discutimos os principais aspectos do movimento Browniano. Introduzimos o problema de difusão em linha (SFD, do inglês "single-file diffusion") e o discutimos, teorica e experimentalmente, no contexto de sistemas de matéria condensada mole. No Capítulo 2, introduzimos os métodos computacionais utilizados nesta tese. Discutimos os métodos de Dinâmica Molecular e suas variantes, o método de Dinâmica de Langevin e Dinâmica Browniana. Também introduzimos algoritmos de integração utilizados nos capítulos posteriores. Nos Caps. 3, 4 e 5, analisamos dois sistemas distintos, (i) um sistema de partículas de Yukawa confinadas em um canal parabólico quasi-unidimensional (q1D) e (ii) um sistema de colóides magnéticos sob a influência de um potencial parabólico e uma modulação periódica externa ao longo da direção não confinada. No primeiro sistema, estudamos a transição do regime de difusão em linha (SFD) para o regime de difusão normal (2D). No segundo sistema, estudamos os efeitos de vários parâmetros que caracterizam o sistema (e.g., a magnitude do campo magnético externo e a presença da modulação periódica externa) em suas propriedades dinâmicas. Finalmente, apresentamos um sumário dos principais resultados obtidos nesta tese e mostramos algumas questões em aberto como perspectivas para pesquisas futuras na área de difusão em sistemas de matéria condensada mole.
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Broussell, Isabelle. "Optical properties of alpha-zinc aluminum sulfide:chromium single crystals." Thesis, University of Ottawa (Canada), 1998. http://hdl.handle.net/10393/4514.
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The optical properties of the chromium doped spinel type semiconductor $\alpha$-$\rm ZnAl\sb2S\sb4$ have been examined over the temperature range 2-540K. From extrinsic absorption and photoluminescence spectra the transitions between the ground state $\rm\sp4A\sb{2g}$ and the excited levels $\rm\sp2E\sb{g}\ (R\sb1$ and R$\rm\sb2),\ \sp2T\sb{2g},\ \sp4T\sb{2g}$ and $\rm\sp4T\sb{1g}$ of the Cr$\sp{3+}$ ions were observed. A fit of the measured temperature dependence of the PL decay, using a four level model, yielded the lifetimes of the $\rm\sp2E\sb{g}\ (R\sb1$ and R$\sb2)$ and $\rm\sp4T\sb{2g}$ levels and the energy gaps between the $\rm\sp2E\sb{g}\sp{(1)}$-$\rm\sp2E\sb{g}\sp{(2)}$ and $\rm\sp2E\sb{g}\sp{(1)}$-$\rm\sp4T\sb{2g}$ states which were found to be very close to the values obtained from steady-state measurements. A configurational coordinate diagram for Cr$\sp{3+}$ ions in a $\alpha$-$\rm ZnAl\sb2S\sb4$:Cr spinel host has been constructed. Optical gain measurements at 198 K, 298 K and 380 K displayed two separate spectral regions associated to the Cr$\sp{3+}$ ions and possibly to Cr$\sp{4+}$ impurity centers. Gain values of up to 25 cm$\sp{-1}$ (730 nm) at 198 K were obtained. Finally the intrinsic photoluminescence measurements revealed an intense UV peak around 380 nm from 20 K to 296 K which corresponds to the indirect band gap of the host crystal, $\alpha$-$\rm ZnAl\sb2S\sb4.$
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Wincheski, Russell A. "Characterization of the physical properties of iron polyimide nanocomposites." W&M ScholarWorks, 1999. https://scholarworks.wm.edu/etd/1539623960.
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The discovery of tunneling magneto-resistance has led to a great deal of interest in the study of ferromagnet-insulator-ferromagnet (FIF) systems due to potential sensor and magnetic storage applications. An analysis of the band structure of the 3d ferromagnets shows that the conduction electrons become spin polarized by the molecular field. The transmission coefficient of these electrons across a tunneling gap therefore depends upon the relative alignment of the molecular field between the two ferromagnets.;In this work the manufacture of such tunneling gaps through compression molding of powdered ferromagnetic iron with a high performance polyimide has been studied for the first time. The percent change in the resistance with applied magnetic field depends critically on the volume percentage of ferromagnetic material in the composite. A peak in the tunneling magnetoresistance (TMR) occurs at a volume concentration just beneath the percolation threshold of the ferromagnetic material. The change in resistance relative to the resistance at zero field, DeltaR/R0, obtains a room temperature peak value of -4.5% at 20% iron volume concentration.;Granular conducting systems near the percolation threshold are also subject to variable range hopping (VRH) conduction. The charging energy of small metallic grains results in an energy barrier for the acceptance of an additional electron. Electronic conduction requires thermal activation over this barrier along with tunneling through the insulating regime. The result of these two combined processes is a temperature dependent tunneling distance and a conductivity of the form ln sigma ∝ T-x, with 1/4 ≤ x ≤ 1/2.;The theoretical development and experimental measurements of TMR and VRH in iron polyimide nanocomposites are thoroughly developed and analyzed in this work. Ferromagnet particle size and band structure effects on TMR are also explored in an effort to optimize the material for sensor applications.
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Church, Christopher J. "The structural, thermal, and magnetic properties of manganese silicon sulfide." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6806.
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$\rm Mn\sb2SiS\sb4$ is a synthetic Olivine in which we have discovered an exceptional temperature dependent magnetic behavior that may lead to interesting applications. A state of spontaneous magnetization was found to exist in this material, but only between 83 and 86.5 K. In order to explain this unusual magnetic phenomena, polycrystalline samples of $\rm Mn\sb2SiS\sb4$ were first prepared from the elements and studied by SQUID magnetometry in low fields, by X-ray and neutron diffraction, by electron spin resonance (ESR) and by specific heat calorimetry. This research, in which the author was a member of a team, is described. His specific contributions include among others; the debugging and extension of some of the computer programs used to analyze the neutron diffraction results, the interfacing of the Bruker ESR spectrometer to a IBM compatible computer and the development of the computer progams to acquire the resonance curves and analyze the line spectra, the analysis of the ESR results, the assembly of parts of an apparatus and the development of a procedure to measure the specific heat of small samples in the 77 to 150 K range as well as some preliminary measurements on a sample of $\rm Mn\sb2SiS\sb4.$ These contributions are emphasized in this thesis. (Abstract shortened by UMI.)
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Vachon, Martin. "Optical properties of single quantum dots in high magnetic field." Thesis, University of Ottawa (Canada), 2008. http://hdl.handle.net/10393/28029.
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The photoluminescence of quantum dots is studied in a high magnetic field regime where the cyclotron frequency is comparable to the confinement energy. Applying a magnetic field perpendicular to the lateral potential plane lifts the shell degeneracy and magneto-photoluminescence spectroscopy therefore provides a probe to investigate the energy shell structure of quantum dots. By isolating a single quantum dot, the inhomogeneous broadening from a distribution of dot sizes and compositions is eliminated and the fine structure of the spectrum is revealed. The orbital splitting of angular momentum states is shown to follow the Fock-Darwin scheme. However, it is also apparent that each angular momentum branch consists of two distinct lines whose magnetic field evolution cannot be explained by a simple Zeeman spin splitting. The dependence of line splitting on orbital state can be described by the addition of spin-orbit coupling to the Fock-Darwin model. Accordingly, a quantitative measurement of the spin-orbit coupling strength in self-assembled quantum dots is obtained for the first time.
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Sabet-Sharghi, Riaz. "Composition dependence of mechanical properties in Al-rich metallic glasses." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26134.
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The effect of composition on the mechanical properties of high Al content Al-Y-Ni metallic glasses has been studied. Nine samples in all were prepared with a composition of ${ rm Al sb{85}Y} sb{x}{ rm Ni} sb{15-x}({ rm x}=3, ...,11).$ The amorphous alloys were first tested using both XRD and DSC. The DSC runs revealed that the samples were made up of two different types: one showing no glass transition and a lower crystallization temperature, and the other showing a distinct glass transition with a higher crystallization temperature indicating that they are truly homogeneous glasses. The samples showed a Young's modulus that does not seem to reveal any distinct compositional dependence whereas, the tensile strengths showed a distinct decreasing trend with increasing Y content. Values of various mechanical properties and crystallization temperatures obtained in this study are compared to those reported by other groups. We find very high specific strengths in these glasses, which combined with their excellent ductility makes them ideal structural materials. The effect of annealing is also examined and it is found that the samples lose a large proportion of their tensile strength and ductility when annealed.
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Pomorski, Pawel. "Theoretical study of conductance, capacitance and transport properties of nanostructures." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84414.
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In the past two decades, significant progress in constructing physical systems of reduced dimensionality has been made. In these systems, quantum effects are observed in the electric current response to an applied bias voltage. Considerable theoretical effort has been made to understand conductance and capacitance which characterize this response. In addition to a fundamental science interest, there has been a significant technological need to build and understand small scale devices in order to maintain the current rate of progress in increasing computer performance.In this thesis, we theoretically investigated the conductance and capacitance of mesoscopic and molecular scale systems. Our approach incorporated Landauer-Buttiker transport theory.
We developed a highly efficient method, based on the solution of the time-dependent Schrodinger equation incorporating a magnetic field, to solve the quantum scattering problem in mesoscopic nanostructures. We studied linear response capacitance in a two plate mesoscopic capacitor with one plate a quantum conductor in the ballistic scattering regime. By determining the scattering wavefunctions in the quantum plate, we were able to obtain relevant densities of states and use them to self-consistently calculate capacitance matrix coefficients for the system. We find the capacitance to be highly dependent on the external magnetic field and the number of probes attached to the quantum conductor.
To study molecular scale systems, our approach was based on Density Functional Theory within Local Density Approximation and non-equilibrium Green's functions, implemented in the simulation package McDcal. For the work in this thesis, we modified McDcal to run on parallel computer architectures. We studied the current-voltage characteristics of silicon cage nanowires sandwiched between aluminum electrodes. We successfully analyzed our results using the complex band structure of the nanowire. Finally, we studied the capacitance properties of carbon nanotube junctions. In junctions with tubes so far apart that their wavefunctions do not overlap, we studied the variation in capacitance for different relative tube positions and radii. We also studied junctions where the nanotubes are in contact but in which there is no current due to a conductance gap. In this system we find an enhancement in the value of capacitance.
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Dikeakos, Maria. "Electronic properties of amorphous and crystalline FexCo1-x-Zr2 alloys." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20141.
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The electronic contribution to the resistivity rho and its temperature dependence were investigated for amorphous and crystalline [Fe xCo1--x] 33.3Zr66.7 (0 ≤ x ≤ 1) alloys in the temperature range 80--300 K. As Fe-rich compositions may exhibit spin fluctuation effects, transport properties were not studied below 80 K where spin fluctuation effects must be taken into consideration. The compositional and structural integrity of the samples was verified by means of X-ray diffractometry, electron-microprobe analysis, and differential scanning calorimetry. It was also confirmed that the first crystallization product for all the compositions is the face-centered cubic phase with the NiTi2-type structure. A true comparison between amorphous and crystalline transport properties was thus possible. For the metallic glasses, it was observed that rho( T) had a temperature dependence of the form: A + Bexp(--T/Delta) in agreement with Mizutani who proposed this relation for glasses containing a significant number of d-electrons at EF. The characteristic temperature, Delta, was found to be related to the Debye temperature, theta D, and the parameter B to the electronic specific heat coefficient, gamma. The resistivity data for the crystalline tenary compounds exhibited a (c -- bT + aT2)-dependence. Both the glasses and their crystalline counterparts were characterized by negative temperature coefficients of the resistivity, alpha. However, for the glasses, alpha increased as the Fe content increased whereas for the crystalline compounds alpha decreased as the Fe content increased.
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Cai, Aiguo. "Study of surface flattening kinetics by low energy electron diffraction on rutile(110)." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ57094.pdf.
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Mativetsky, Jeffrey M. "Understanding and controlling the growth of metals and molecules on an insulating surface." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102682.
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Noncontact atomic force microscopy (NC-AFM) was applied to investigating the creation of monatomic depth rectangular pits, the growth of metals, and the templated growth of molecules on the KBr (001) surface under ultrahigh vacuum conditions. The pits were produced by a new method where the sample is exposed to a controlled dose of charge from an electron beam evaporator. The structure and size distribution of the pits was characterized by NC-AFM. For the metal growth studies, gold, tantalum, and palladium were deposited onto KBr by electron beam deposition. The gold produced tall multiply twinned and epitaxial nanoparticles, while the tantalum formed flatter fractal islands. The palladium growth resulted in the creation of rectangular KBr islands in addition to palladium nanoparticles. Despite the use of a charge deviating grid, charge played an important role during the metal growth. In particular, the number density of gold nanoparticles followed nearly the same temperature dependence as the pits, suggesting that the metal nanoparticles nucleate predominantly at defect sites created by incident charge. The effect of charge was also seen in the tantalum system where pits surrounded the nanoparticles prepared at elevated temperatures. By creating pits before depositing gold, it was shown that the pits edges can be used to template the growth of metals. It was also shown that the pits can be used to trap PTCDA molecules and to align C60 molecules with the <100> direction of the substrate. Molecular resolution NC-AFM measurements were used to determine the structures and lattice constants of the molecular nanostructures. Experiments involving the sequential growth of metals and molecules showed that the order of deposition and the strength of the molecule-metal interaction are key factors in determining the nature of the growth. Furthermore, it was shown that metal structures can be used to nucleate the growth of sufficiently strongly interacting molecules.
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Goudreault, Roger D. "Some properties of the semimagnetic semiconductor alloy system Cd2x(CuGa)yMn2zTe2." Thesis, University of Ottawa (Canada), 1988. http://hdl.handle.net/10393/5499.
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Kadel, Rajesh. "Surface structure study of imidazolium based ionic liquid." Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/1004.
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Marchand, Philippe. "Modèle general de la précipitation aqueuse des solides à surface rugueuse, appliqué à la ferrihydrite." Thesis, University of Ottawa (Canada), 2009. http://hdl.handle.net/10393/28100.
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La ferrihydrite est un oxyde de fer abondant dans les milieux marins et lacustres, qui peut influencer la disponibilité de certains nutriments et purifier l'eau de métaux toxiques. Toutefois, les mécanismes entraînant sa formation et les raisons pour lesquelles elle est toujours nanoparticulaire sont encore mal connus. À partir de la théorie classique de la nucléation, je développe dans cette thèse un modèle simple pour la précipitation aqueuse de phases faiblement cristallines. Il s'agit d'un système d'équations différentielles représentant l'évolution temporelle de la distribution de taille des amas précipités. En utilisant les paramètres physico-chimiques connus pour la ferrihydrite, ce modèle produit des distributions dont le rayon moyen correspond aux valeurs attendues. Pour mieux comparer les distributions simulées et réelles, je devrai préciser les paramètres physico-chimiques de la ferrihydrite et avoir accès à des mesures plus précises de la distribution de taille des échantillons expérimentaux.
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Allard, Louis Bernard. "Optical properties of two-dimensional semiconductor heterostructures: Ion implantation and carrier diffusion." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6664.
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For the most part of this work, we study the effects of focused ion beam implantation in InGaAs/GaAs quantum well structures. The technique of steady-state photoluminescence spectroscopy is utilized to study the compositional disordering occurring in InGaAs/GaAs quantum well structures having been implanted at different doses and subsequently annealed. Photoluminescence results of uniformly implanted regions of InGaAs/GaAs samples are along with a simple formalism permitting the calculation of the interdiffusion lengths. These results, along with SIMS measurements, show that channeling effects play a most important role in disordering quantum wells that lie deep beneath the sample's surface. The observations also show a photoluminescence shift saturation with dose at approximately 2 $\times$ 10$\sp $ Ga$\sp{+}$/cm$\sp2$. Results of pattern-implanted samples give rise to the question of the minimum dose required to induce uniform compositional disordering in InGaAs/GaAs structures. Studies of this "critical" dose, are presented for both AlGaAs/GaAs and InGaAs/GaAs quantum well structures and show that the minimum dose required to induce intermixing in InGaAs/GaAs is approximately two orders of magnitude lower than that observed for the AlGaAs/GaAs structures which was 2 $\times$ 10$\sp $ Bi$\sp{+}$/cm$\sp2$. As another major part of this work, we describe a novel, low light level optical detection system that can be easily configured for various modes of operation. These include (1) time-integrated (steady-state) photoluminescence spectroscopy, (2) transient, spectrally gated photoluminescence decay, (3) time-windowed photoluminescence spectroscopy, (4) two-dimensional, time-integrated photoluminescence mapping, and (5) time-resolved, two-dimensional photoluminescence mapping with time resolution of ${\sim}$100 ps. We use the system in mode (5) to study electron-hole pair expansion in GaAs quantum wells as a function of temperature for a fixed excitation intensity. The results show that the diffusion coefficient rises from an initial value of 26 cm$\sp2$/s at 80 K to 38 cm$\sp2$/s at ${\sim}$100 K and then monotonically decreases to a value of ${\sim}$10 cm$\sp2$/s at room temperature. The rise in the diffusion coefficient is attributable to the gradual decrease of interface roughness scattering with increasing temperature while the decrease of the diffusion coefficient is attributable to the increase of phonon scattering mechanisms with increasing temperature. Results of diffusion at fixed temperature, but as a function of excitation intensity, are also presented and discussed.
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Dai, Ming. "Neutron irradiation damage to avalanche photodiodes and the properties of generated defects." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23880.
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Avalanche Photodiode (APD) is a compact and rugged device, with single photon detection capability and high quantum efficiency. It is a good candidate as a detector to observe irradiation damage to silicon devices and the irradiation induced defects. In this thesis, we have observed the bistable defects and the multistable defects in the APD. We can also observe the time evolution of defect formation and annihilation with time resolution of 10 ms. Also we develop a technique to observe the evolution of defects in real time with an improved time resolution of 1 $ mu s$.
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Bruyère, Michel Jean. "An ultrahigh vacuum system for the scattering of keV ions by a clean silicon(100) surface." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5952.
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An ultrahigh vacuum surface physics system was designed and built to study ion-surface interactions at various incident angles by detection of the forward scattered particles. The proposed initial measurement is the scattering of keV ions by a clean Si(100) surface.
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Ren, Hong 1962. "Effects of exchange frustration on the magnetic properties of iron-rich amorphous alloys." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41224.
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The magnetic properties of amorphous Fe$ sb{ rm x}$T$ sb{ rm 100-x}$ (T = Zr, Hf, Sc; 89 $ le$ x $ le$ 93) alloys have been systematically studied mainly by Mossbauer spectroscopy and magnetization measurements. Two magnetic transitions have been observed in Fe$ sb{92.5}$Hf$ sb{7.5}$ (the only FeHf alloys studied here) and FeZr alloys with Fe content between 90 and 93 at.%. We have ruled out the cluster models which attribute the second transition either to the ordering of AFM clusters or to the freezing of FM clusters, and confirmed that the second transition is due to the homogeneous freezing of the transverse spin components as a result of exchange frustration. On varying the frustration level, the evolution process from a ferromagnetic to a spin glass ordering has been observed. Fe$ sb{89}$Zr$ sb{11}$ essentially exhibits conventional ferromagnetic behavior, while Fe$ sb{90}$Zr$ sb{10}$ shows two magnetic transitions with a noncollinear ground state. As we increase the Fe content further (and thus raise the frustration level), the second transition temperature T$ sb{xy}$ and the noncollinearity of the ground state increase, whereas the first transition temperature T$ sb{c}$ drops. T$ sb{xy}$ and T$ sb{c}$ are expected to meet at x $ simeq$ 94.5, suggesting that Fe$ sb{94.5}$Zr$ sb{5.5}$ (which can not be made by melt-spinning) would be a spin glass. Fe$ sb{91}$Sc$ sb9$ is the most frustrated system studied here and it exhibits a single transition to a spin glass. Extrapolation of the magnetic properties of all systems gives a common limit as the Fe concentration approaches 100%, and suggests that amorphous Fe is a spin glass with the spin freezing temperature about 100K and an average iron moment of $ sim$1.6$ mu sb{B}$. Below the second transition, the transverse spin components are strongly correlated on a nearest neighbor scale in Fe$ sb{92}$Zr$ sb7$Sn, while the correlation length of the longitudinal components shows no detectable change on the local scal
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Godin, Michel. "Design of a differential cantilever-based sensor : surface stress of self-assembled alkanethiols on gold-coated cantilevers." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=30820.
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This exploratory study examined the predictive ability of perceived work environment characteristics on employees' level of motivation to learn and growth need strength. It looked at motivation to learn within the context of two types of training: formal training and on-the-job training. It also examined the existence of group differences in motivation and in perceptions of the work environment. The sample was 117 middle management staff at a Canadian research university, varying in age, level of education, job classification, work unit, and job and institutional tenure. Data was collected using a questionnaire consisting of scales from the management and educational literature. Using multiple regression analysis and MANOVAs, workplace environmental characteristics were found to be predictors of employee motivation. The best predictor of motivation to learn was a composite measure of incentives, while the best predictor of growth need strength was a composite measure of lack of independence and freedom of choice. No group differences in motivational characteristics were found, however, there were differences in perceptions of the work environment.
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Christie, Iain A. D. "The magnetic properties of annite: A SQUID magnetometry and iron-57 Moessbauer spectroscopy study." Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/6646.
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Annite is the Fe rich end-member of the phlogopite-biotite-annite series of micas. The ideal structural formula of annite is: $\{K\sp+\}\lbrack Fe\sbsp{3}{2+}\rbrack\langle Al\sp{3+}Si\sbsp{3}{4+}\rangle O\sbsp {2-}(OH\sp-)\sb2.$ Two samples of annite have been studied, a synthetic, true end-member (in the form of a fine powder) and a natural, near end-member (in the form of single crystal). The samples have been studied using SQUID magnetometry and Mossbauer spectroscopy at temperatures ranging from 4.2 K to 295 K using a purpose-built Mossbauer cryostat and insert. In disagreement with earlier predictions it has been determined that the magnetic ground state of annite consists of planes of predominantly ferromagnetic spins stacked antiferromagnetically along the c* axis. In further contrast to earlier predictions, it has been found that, for annite, the ordering temperature, T$\sb{\rm N}$, is greater than 10 K, with the synthetic sample having T$\sb{\rm N}$ = 58 K. It is proposed that the planar antiferromagnetic structure is part of the intrinsic zero-field magnetic domain structure and that this structure is stabilized by inter-layer dipole-dipole forces. Mossbauer spectroscopy measurements indicate some striking features of the temperature development of magnetic state of both annite samples. In particular, the results indicate that there is a persistent paramagnetic Fe$\sp{2+}$ contribution at temperatures as low as 0.1 T$\sb{\rm N}$; and that the Fe$\sp{3+}$ moments disorder at temperatures significantly below T$\sb{\rm N}.$ Plausible causes for these features are discussed. The first documented attempt to fit the low temperature spectrum of annite is reported. A method for stripping the Fe$\sp{3+}$ contribution from the liquid helium spectrum of synthetic annite is discussed and a hierarchy of simple models is constructed and applied in attempt to fit the remaining Fe$\sp{2+}$ subspectrum. An acceptable fit is not obtained. The consequences of the failure of the simple models are examined.
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Liu, Yi 1971. "First-principles study of transport properties of molecular devices : fullerene and carbon nanotube systems." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85571.
Full textAbstract:
The discovery of fullerenes and carbon nanotubes has been very significant to the field of nanotechnology by providing an abundance of stable, highly symmetric, non-reactive, and relatively large molecules that can, in principle, be manipulated one at a time. At the present stage, a theoretical effort should be carried out in order to find and understand novel phenomena in molecule-based nanostructures which could serve as a basis for fabricating useful molecular devices. In this thesis we investigate from first-principles the transport properties of molecular devices: fullerene and carbon nanotube systems.We begin with charge transport in carbon nanotubes with oxygen, and find that the interaction between oxygen molecules and carbon nanotubes significantly modifies the electronic structure near the Fermi level for both zigzag and armchair tubes. The subtle difference of the adsorption sites of oxygen and the distance between oxygen and nanotubes can cause totally different results of their transport properties.
Then we investigate current flow from the point of view of current density distribution in molecular devices, for current density gives local information of nonequilibrium transport, thereby providing useful and vivid insight to transport properties of molecular electronics. It has been found when an intrinsic carbon nanotube is doped with either a boron or a nitrogen atoms through a replacement of a carbon atom, the local physical properties around the impurity atoms (boron or nitrogen) undergo a significant change, resulting in a dramatic change of the local current distribution. It is suggested that there appears a chiral current flow in the B- and N-doped armchair nanotubes near the impurity. As for a gated C 60 molecular device, the current distribution and the total current flow are both obviously affected by the gate voltage, which indicates the importance of the gate voltage in such a molecular device.
Finally, we discuss the contact effects on transport properties of the molecular devices. We study the effects of the contact geometry as well as the electrode material and find that different orientations of C 60 connected to Au(111) leads can cause significant changes in the current-voltage (I-V) characteristics of such C60 molecular devices. On the other hand, the electrode material is crucial to obtain low resistance ohmic contacts. Our first-principles calculations of transport suggest that Ti has higher affinity for carbide formation. So the choice of proper electrode materials will play an important role in the design of nanoscale devices.
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NGUYEN, TUAN ANH. "INVESTIGATIONS OF ELECTRONIC STRUCTURE AND OPTICAL PROPERTIES OF II-VI SELF-ASSEMBLED QUANTUM DOTS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1143155352.
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Stojak, Kristen L. "Synthesis and Properties of Polymer Nanocomposites with Tunable Electromagnetic Response." Thesis, University of South Florida, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1535889.
Full textAbstract:
Multifunctional polymer nanocomposites (PNCs) are attractive for the design of tunable RF and microwave components such as flexible electronics, attenuators, and antennas due to cost-effectiveness and durability of polymeric matrices. In this work, three separate PNCs were synthesized. Magnetite (Fe 3O4) and cobalt ferrite (CFO) nanoparticles, synthesized by thermal decomposition, were used as PNC fillers. Polymers used in this work were a commercial polymer provided by the Rogers Corporation (RP) and polyvinylidene fluoride (PVDF). PNCs in this thesis consist of Fe3O 4 in RP, CFO in RP, and Fe3O4 in PVDF. Characterization techniques for determining morphology of the nanoparticles, and their resulting PNCs, include x-ray diffraction, transmission electron microscopy and magnetometry.
All magnetometry measurements were taken using a Quantum Design Physical Property Measurement System with a superconducting magnet. Temperature and external magnetic field magnetization measurements revealed that all samples exhibit superparamagnetic behavior at room temperature. Blocking temperature, coercivity and reduced remnant magnetization do not vary with concentration. Tunable saturation magnetization, based on nanoparticle loading, was observed across all PNCs, regardless of polymer or nanoparticle choice, indicating that this is an inherent property in all similar PNC materials.
Tunability studies of the magneto-dielectric PNCs were carried out by adding the PNC to cavity and microstrip linear resonator devices, and passing frequencies of 1–6 GHz through them in the presence of transverse external magnetic fields of up to 4.5 kOe, provided by an electromagnet. Microwave characteristics were extracted from scattering parameters of the PNCs. In all cases, losses were reduced, quality factor was increased, and tunability of the resonance frequency was demonstrated. Strong magnetic field dependence was observed across all samples measured in this study.
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Acharya, Pramod. "Charge regulation of a surface immersed in an electrolyte solution." Thesis, Florida Atlantic University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10172666.
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In this thesis, we investigate theoretically a new model of charge regulation of a single charged planar surface immersed in an aqueous electrolyte solution. Assuming that the adsorbed ions are mobile in the charged plane, we formulate a field theory of charge regulation where the numbers of adsorbed ions can be determined consistently by equating the chemical potentials of the adsorbed ions to that of the ions in the bulk. We analyze the mean-field treatment of the model for electrolyte of arbitrary valences, and then beyond, where correlation effects are systematically taken into account in a loop expansion. In particular, we compute exactly various one-loop quantities, including electrostatic potentials, ion distributions, and chemical potentials, not only for symmetric (1; 1) electrolyte but also for asymmetric (2; 1) electrolyte, and make use of these quantities to address charge regulation at the one-loop level. We find that correlation effects give rise to various phase transitions in the adsorption of ions, and present phase diagrams for (1; 1) and (2; 1) electrolytes, whose distinct behaviors suggest that charge regulation, at the one-loop level, is no longer universal but depends crucially on the valency of the ions.
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Kim, Jeha. "Structural and elastic properties of silver-palladium and copper-palladium superlattices." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186275.
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I prepared Ag/Pd and Cu/Pd superlattices using both sputtering and molecular beam epitaxy. For the Ag/Pd (t(Ag):t(Pd) = 1:1) superlattices, I observed two distinctive behaviors in the structural coherence length ξ as a function of modulation wavelength Λ. Using Brillouin light scattering (BLS) I observed a 50% enhancement of the shear elastic constant c₅₅ and a 16% increase of c₁₁ with decreasing Λ. Annealing study showed that a high structural order of the films in the growth direction was strongly correlated to the increase of c₅₅. For the 3:1 and 1:3 Ag/Pd samples, I also observed a monotonic increase of the Rayleigh velocity υ(R) (or c₅₅) with decreasing Λ and similar behavior in the structural coherence length to the 1:1 samples. In conclusion, the recrystallization of the alloy and the formation of extended interfaces by intermixing at the Ag-Pd interfaces are responsible for a large enhancement of c₅₅. Using BLS for the Cu/Pd superlattices, I observed a 24% decrease of c₅₅ as Λ was decreased to ∼30-40 Å, followed by a rapid increase for smaller Λ. The observed homogeneous strain in the growth direction showed a strong relationship with c₅₅. The strain was localized at the interface and the Cu/Pd films were in compressive stress for Λ < 38 Å. In conclusion, a localized strain at the interfaces in Cu/Pd is related to the softening in c₅₅. The measurements of in-plane lattice spacing d[220] indicated a structural transformation of the films at Λ = 14 Å from an incoherent to a coherent structure. However, the in-plane strain did not show any relationship with the softening of c₅₅. For single crystalline Cu/Pd superlattices, well-defined RHEED streaks showed incommensurate growth of Cu(111) on Pd(111) layer. The measured shear elastic constant c₅₅ showed a 26% decrease with respect to the largest Λ film with a peak at Λ ≃ 40 Å. Unlike the sputtered films, while c₅₅ decreases by 26% with decreasing Λ, the Cu/Pd films show no change in d(avg)[111] for Λ > 40 Å. I observed no in-plane anisotropies in υ(R) as predicted from theory for single crystal films.
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England, Craig Dennis. "Properties of cobalt/copper and cobalt/palladium multilayers." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185707.
Full textAbstract:
The physical properties of Co/Cu and Co/Pd magnetic multilayers have been studied. The Co/Cu multilayers were prepared by sputtering, while the Co/Pd multilayers were made by sputtering and molecular beam epitaxy (MBE). Various x-ray diffraction techniques have been used to study the structure of the multilayers. Magnetometry techniques were used to study the magnetic properties. Various optical techniques have been used to investigate the magneto-optical properties. Brillouin light scattering spectroscopy was used to determine the effective elastic constants of the Co/Cu multilayers and the magnetic properties of the sputtered Co/Pd multilayers.