Properties of magnetic thin film devices cannot be understood without detailed knowledge of their structure. For this purpose, a variety of thin film and multilayer systems have been studied. Both reciprocal space (low energy electron diffraction, reflection high energy electron diffraction, X-ray diffraction and reflectometry) and direct space (transmission electron microscopy) as well as Rutherford backscattering spectrometry have been applied. To gain understanding of an oxidation procedure for the growth of magnetite layers, thermal stability of iron layers on molybdenum seed layers has been investigated. Following the mosaicity and the out-of-plane coherence length over different ratios between the constituting layers allowed a deeper understanding of the limits of metallic superlattices. This, together with an approach to use hydrogen in the process gas during magnetron sputter epitaxy, opens routes for the growth of metallic superlattices of superior quality. A non-isostructural multilayer/superlattice system, Fe/MgO, has been investigated. In turn, this gave more understanding how superlattice diffraction patterns are suppressed by strain fields. As an alternative route to single-crystalline superlattices, amorphous multilayers present interesting opportunities. In this context, crystallization effects of iron/zirconium layers on alumiunium oxide were studied. Understanding these effects enables significant improvement in the quality of amorphous multilayers, and allows avoiding these, growing truly amorphous layers. Both the substantial improvement in quality of metallic superlattices, approaching true single-crystallinity, as well as the improvements in the growth of amorphous multilayers give rise to opportunities in the field of magnetic coupling and superconducting spin valves.

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In this thesis, carbon supported platinum nanoparticle catalysts were prepared using PtCl4 and H2PtCl6 as starting materials and 1-heptanethiol, tert-nonyl mercaptan, 1-hexadecanethiol, 1-octadecanethiol as surfactants. These new catalysts were employed for methanol oxidation reaction which are used for direct methanol fuel cells. Tert-nonyl mercaptane was used for the first time in this type of reaction and the other surfactants were used for comparison of the catalysts performance. Cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used in order to determine the nature of the catalysts. The average platinum crystallite particle sizes of all prepared catalysts were determined by both X-ray diffraction and transmission electron microscopy. It was found that platinum crystallizes in face-centered cubic structure and the surfactant play an important role on the size of platinum nanoparticles, branch surfactant, such as tert-nonyl mercaptane, causes an increase in the size of platinum nanoparticles, about 3 nm, compared to linear surfactant, such as 1-heptanethiol, about 2 nm. The oxidation states of platinum and their ratios were determined by XPS technique. These results indicated that platinum has two different oxidation states, zero and +4, and Pt(0) to Pt(IV) ratio is about 7.5 to 2.5. In addition to this, O 1s region of XPS was also examined and found that the surface of all of the catalysts covered by adsorbed hydroxide except the catalyst which was prepared by PtCl4 and tert-nonyl mercaptane (Catalyst IIa), where adsorption of water were observed and the catalyst which was prepared by H2PtCl6 and tert-nonyl mercaptane (Catalysts IIb), where adsorption of 65% of hydroxide and 35% of water were identified. Electrochemical studies indicated that Catalyst IIa has the maximum activity (&amp / #61566 / 342 A/gPt at 0.612 V) towards methanol oxidation reaction while Catalyst IIIb (H2PtCl6 and 1-hexanethiol were used to prepare this catalyst) has the minimum activity (&amp / #61566 / 91A/gPt at 0.580V). XRD, TEM and XPS results indicated that the optimum catalyst for methanol oxidation reaction contains about 3 nm of platinum nanoparticles, adsorbed hydroxide and water on the surface of catalyst, but sulphur. These results are in agreement with the proposed mechanism.

In this work, two groups of carbon supported Pt-Pd catalysts have been prepared in order to investigate the effect of Pd, as a second metal, and surfactants on the catalytic activity towards methanol and ethanol oxidation reactions used in the direct methanol and ethanol fuel cells. In the first group (group a), 1- hexanethiol was used as a stabilizing agent while in the second group (group b), 1,1 dimethyl hexanethiol was utilized. Cyclic voltammetry (CV), chronoamperometry (CA), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were used in order to determine the nature of the catalysts. The average crystalline size of the metal particles in the catalysts was explored by XRD and TEM. TEM results revealed the uniform distribution of the metal nanoparticles on carbon support with a narrow size distribution in the range of 3.0 to 3.7 nm and the average crystalline sizes of metal particles for group &ldquo / b&rdquo / catalysts were larger than that of group &ldquo / a&rdquo / catalysts which can be explained by the surfactant effect. These results were in good agreement with XRD data. The oxidation states of platinum (Pt(0) and Pt(IV)) and palladium (Pd(0) and Pd(II)) and their ratios were investigated by XPS and for the most active catalyst, catalyst Ib, these ratios were found to be as 6.94 and 13.7, respectively. Electrochemical activities of the catalysts towards methanol and ethanol oxidation reactions were recorded and compared with that of Pt/C and the commercial Pt (ETEK 20 %wt) catalysts. The results indicated that the group &lsquo / b&rsquo / catalyst has greater catalytic activities than that of group &lsquo / a&rsquo / catalysts. Catalyst Ib comes into prominence as the most active catalyst due to its superior characteristics that it possess such as highest extent of alloying with respect to the palladium amount used, active surface area, CO-tolerance, stability and Pt (0) to Pt (IV) and Pd (0) to Pd (II) ratios.

Structural characterization is essential for the understanding of the magnetic properties of thin films and multilayers. In this thesis, both crystalline and amorphous thin films and multilayers were analyzed utilizing transmission electron microscopy (TEM). High resolution TEM and electron diffraction studies emphasize on the growth of amorphous Fe91Zr9 and Co68Fe24Zr8 on both Al2O3 and Al70Zr30 in multilayer structures by magnetron sputtering. The properties of the growth surfaces were found to strongly influence the formation of nano-crystallites of the magnetic material at interfaces. Field induced uniaxial magnetic anisotropy was found to be possible to imprint into both fully amorphous and partially crystallized Co68Fe24Zr8 layers, yielding similar magnetic characteristics regardless of the structure. These findings are important for the understanding of both growth and magnetic properties of these amorphous thin films. As magnetic systems become smaller, new analysis techniques need to be developed. One such important step was the realization of electron energy-loss magnetic circular dichroism (EMCD) in the TEM, where information about the ratio of the orbital to spin magnetic moment (mL/mS) of a sample can be obtained. EMCD makes use of angular dependent inelastic scattering, which is characterized using electron energy-loss spectroscopy. The work of this thesis contributes to the development of EMCD by performing quantitative measurements of the mL/mS ratio. Especially, methods for obtaining energy filtered diffraction patterns in the TEM together with analysis tools of the data were developed. It was found that plural inelastic scattering events modify the determination of the mL/mS ratio, wherefore a procedure to compensate for it was derived. Additionally, utilizing special settings of the electron gun it was shown that EMCD measurements becomes feasible on the nanometer level through real space maps of the EMCD signal.

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Surface Plasmons (SP) are elementary excitations mixing electrons and photons at metal surfaces,which can be seen in a classical electrodynamics framework as electromagnetic surface eigenmodesof a metal-dielectric system. The present work bases on the ability of mapping SP eigenmodes withnanometric spatial resolution over a broad spectral range using spatially resolved fast electron basedspectroscopies in a Scanning Transmission Electron Microscope (STEM). Such an ability has beenseparately demonstrated during the last few years by many spatially resolved experiments of ElectronEnergy Loss Spectroscopy (EELS), which measures the energy lost by fast electrons interactingwith the sample, and CathodoLuminescence (CL), which measures the energy released by subsequentlyemitted photons. In the case of EELS, the experimental results are today well accountedfor by strong theory elements which tend to show that the quantity measured in an experiment canbe safely interpreted in terms of the surface eigenmodes of the sample. In order to broaden thisinterpretation to fast electron based spectroscopies in general, I have performed combined spatiallyresolved EELS and CL experiments on a simple single nanoparticle (a gold nanoprism). I have shownthat EELS and CL results bear strong similarities but also slight differences, which is confirmed bynumerical simulations. I have extended the theoretical analysis of EELS to CL to show that CLmaps equally well than EELS the radiative surface eigenmodes, yet with slightly different spectralfeatures. This work is a proof of principle clarifiying the quantities measured in EELS and CL,which are shown to be respectively some nanometric equivalent of extinction and scattering spectroscopieswhen applied to metal-dielectric systems. Based on this interpretation, I have applied EELSto reveal the SP eigenmodes of random metallic media (in our case, semicontinuous metal films beforethe percolation threshold). These SP eigenmodes constitute a long standing issue in nanooptics.I have directly identified the eigenmodes from measurements and data processing. I havefully characterized these eigenmodes experimentally through an electric field intensity pattern, aneigenenergy and a relaxation rate. Doing so, I have shown that the fractal geometry of the medium,which grows towards the percolation, induces random-like eigenmodes in the system at low energies.Keywords: Surface plasmons, fast electron based spectroscopies, scanning transmission electronmicroscopy, disordered media