[pt] A pesquisa aponta para a possibilidade de realizar a reação de redução de CO2 (CO2RR) para a formação de nanomateriais de carbono por ablação a laser pulsado(PLA) de alvos magnéticos de Ferro(Fe) e Níquel(Ni) em água pura deionizada. Os materiais coloidais sintetizados foram caracterizados por diferentes técnicas de espectroscopias ópticas (UVVis, ICP-MS, FTIR e Raman) e microscopia eletrônica de transmissão (TEM), revelando a presença de nanopartículas de óxidos e hidróxidos de metais de transição, junto com nanomaterial orgânico. Esse último, é bem visível por TEM, espectroscopia de raio-X por dispersão em energia (EDS), espectroscopia por perda de energia de elétrons (EELS), e espectroscopia Raman, que indica a presença de carbono amorfo grafítico e vibrações CH. No caso do nanomaterial obtido do Níquel, os resultados FTIR confirmam a presença da fase do hidróxido beta-Ni(OH)2, enquanto as medidas Raman e TEM sugerem também a presença de nano-folhas de Ni(HCO3)2. Os resultados experimentais foram enfim discutidos no contexto da origem e da evolução de moléculas simples e complexas de interesse astroquímico, com foco especial nas espécies potencialmente formadas na superfície de pequenos corpos metálicos do Sistema Solar e grãos de poeira cósmica do meio interestelar. / [en] The proposed research points to the possibility to perform CO2 reduction reaction (CO2RR) to solid carbon nanomaterials by the pulsed laser ablation (PLA) of magnetic target of iron (Fe) and nickel (Ni) in pure deionized water. The synthesized colloidal dispersions were characterized by different optical spectroscopies (UV-Vis, ICP-MS, FTIR and Raman) and transmission electron microscopy (TEM), revealing the presence of nanosized transition metal oxide and hydroxide nanoparticles, together with organic nanomaterial. The latter is well visible by TEM, energy-dispersive X-Ray spectroscopy (EDS), electron energy-loss spectroscopy(EELS), and Raman spectroscopy, which indicates the presence of amorphous graphitic carbon and CH vibrations. In the case of Ni derived nanomaterial, FTIR results confirm the presence of a beta-Ni(OH)2 hydroxide phase, while Raman and TEM measurements suggest also the presence of Ni(HCO3)2 nanosheets. The experimental results were finally discussed in the frame of the origin and evolution of simple and complex molecules of astrochemical interest, with special focus on those species potentially formed on the surface of metallic minor bodies in the solar system and cosmic dust grains in the interstellar medium(ISM).

Physical vapor deposition (PVD) refers to the removal of atoms from a solid or a liquid by physical means, followed by deposition of those atoms on a nearby surface to form a thin film or coating. Various approaches and techniques are applied to release the atoms including thermal evaporation, electron beam evaporation, ion-driven sputtering, laser ablation, and cathodic arc-based emission. Some of the approaches are based on a plasma discharge, while in other cases the atoms composing the vapor are ionized either due to the release of the film-forming species or they are ionized intentionally afterward. Here, a brief overview of the various PVD techniques is given, while the emphasis is on sputtering, which is dominated by magnetron sputtering, the most widely used technique for deposition of both metallic and compound thin films. The advantages and drawbacks of the various techniques are discussed and compared.

The discovery of high temperature superconductors led to a tremendous boom in the development of new applications based on this material. Due to the significant anisotropy and the dependence of the critical current density on the misorientation of grains, the so-called coated conductor technology was developed for these materials to realize long wires. These conductors are applied at liquid nitrogen temperature for cables or motors as well as in liquid helium for high-field applications, such as in magnets for particle accelerators or future fusion reactors. One of the main aspects of using superconducting materials in the above-mentioned areas is their high current-carrying capacity, which decreases for a number of reasons. Therefore, studying the superconducting current flow in such conductors remains a priority to understand the main mechanisms and to increase the critical current density in a wide range of temperatures and magnetic fields. The major goal of this thesis was to study the correlation between the local microstructure and the superconducting properties for Ag-doped YBa2Cu3O7−δ (YBCO), (Nd1/3Eu1/3Gd1/3)Ba2Cu3O7−δ (NEG) and the iron-based superconductor Ba(Fe1−xNix)2As2 (Ba122:Ni). Therefore, epitaxial films were grown of these materials by pulsed laser deposition on single crystals and two different commercial coated conductor templates having a different degree of granularity. Experimental techniques such as electron backscattering diffraction (EBSD) and scanning Hall probe microscopy (SHPM) allow to investigate both the local microstructure and local distribution of superconducting current in these films. Ag-doped YBCO films with different thickness were deposited on single crystalline SrTiO3 substrates as well as on RABiTS and IBAD-MgO-based templates. It is expected, that silver as dopant improves the growth of the films, and has a beneficial influence on the current transport across grain boundaries, which is of considerable interest for metal-based templates due to their granular structure. EBSD studies on the local microstructure revealed only minor changes with silver concentration. Nevertheless, an improvement in transport properties was observed for thicker YBCO:Ag layers on SrTiO3 and thin films on both metal-based templates. SHPM measurements show an improvement of the local current distribution, which is probably due to the improvement of the current transport between the grains. NEG films were grown with different thicknesses on RABiTS and IBAD-MgO-based templates for the first time. Structural studies revealed an epitaxial growth of all samples on both metal-based templates. Whereas NEG layers on SrTiO3 showed broad superconducting transitions due to film inhomogeneities, a narrow transition at about 89 K was measured for films grown on the metal templates. However, the critical current density is still inferior to YBCO films of similar thickness. This might be improved by further optimization of the growth and oxygen loading conditions. Finally, the Ba122:Ni films were studied on single crystalline CaF2 substrates and commercial metal-based templates. This material might be interesting for applications due to a low anisotropy, high upper critical fields and critical currents as well as a reduced sensitivity to grain boundaries. Structural studies showed an epitaxial growth on RABiTS templates, whereas no epitaxy was found on IBAD-MgO based tapes. Simultaneously, a broad superconducting transition was observed on the metallic templates, which requires a further optimization of the growth process. Detailed studies of the superconducting and electronic properties for Ba122:Ni films on CaF2 substrates revealed similar properties as for single crystals, which opens the prospects to use such films for different applied and fundamental tasks.

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This project revolves around a monostatic time of flight LiDAR, monostatic meaning that the emitted light and the incoming light are collocated and LiDAR being an acronym for light detection and ranging. The goal here is to explore and understand the principles of the LiDAR whilst also finding its advantages and shortcomings. One expected shortcoming is that of the effects of light scattering of the laser. To mitigate these effects a short laser pulse is desired without compromising on the power output. In order to reduce the pulse width the electronics of the LiDAR needed to be understood and two approaches emerged. The first revolved around simplifying the electronic schematics of the LiDAR to the point it could be described as a simple RLC-circuit and solving for the current analytically. The other approach was to simulate it using the simulation software LTspice. The results from the analytical approach and the LTspice simulation showed clear ways of how the pulse width could be decreased by altering the onboard resistance, inductance and capacitance. The easiest alternative was to simply reduce the capacitance, however this resulted in a lower power output. But these effects could be mitigated by simply increasing the applied voltage. However it was also discovered that the analytical and LTspice simulations were not entirely correct in their attempts to simulate the real behavior of the laser drive boards within the LiDAR. To study the effects of the scattering two theories were studied, namely Rayleigh and Mie scattering. The influence of Rayleigh scattering was quickly determined to be negligible but the Mie scattering results showed that it will definitely affect the LiDAR, even though the Mie scattering influence was extremely over exaggerated.

<p dir="ltr">Thin film materials are used in many areas of our daily lives. From memory storage chips to optical coatings, these thin films are essential to the technologies on which we rely. Multiferroic thin films, a group of materials that simultaneously exhibit ferromagnetism and ferroelectricity, are of particular interest because of the new opportunities that they enable in memory storage and sensors. Bismuth-based oxide materials have proven to be excellent candidates for these applications, with multiferroic properties and anisotropic structures. This novel self-assembled structure found in layered supercell systems has applications in optical devices, such as isolators and beamsplitters. Throughout this study, thin film strain and epitaxy must be tended to as the fundamentals of film growth, adding to the complexity of these challenges.</p><p dir="ltr">In this dissertation, bismuth-based oxides, and more specifically the Bi₃Fe₂Mn₂O_x (BFMO) layered supercell phase, are studied from three perspectives. First, BFMO is integrated onto silicon substrates for commercialization using a complex buffer layer stack to mediate the differences in the crystal lattice. This allows for a demonstration of device fabrication with this film. Second, the growth and impact of strain are examined through geometric phase analysis, discovering that strain is essential for the growth of the supercell phase in BFMO. This strain can be tuned through buffer layer addition to optimize the growth of this phase. Third, two methods are demonstrated to free the BFMO material from the typical film-substrate lattice matching requirements. The process of transferring the film from the original substrate onto a different substrate removes these restrictions, allowing virtually unlimited access to applications that were previously not possible. The two methods demonstrate different solutions to the specific challenges of transferring the highly strained BFMO thin film. These findings pave a practical way to integrate multiferroic layered oxide thin films onto chips for the next generation of devices.</p>

The use of ultracold neutrons (UCN) to study fundamental parameters such as the neutron lifetime and decay correlations in polarized neutron beta decay are poised to make significant contributions to our understand of the Standard Model and its extensions. To this end, the UCNA experiment is pursuing a precision measurement (0.2%) of the angular correlation between the neutron spin and the direction of emission of the electron in polarized neutron decay (the ``A'' asymmetry). The UCNA experiment makes use of the spallation-driven solid deuterium (SD2) UCN source at the Los Alamos Neutron Science Center (LANSCE). The UCN leave the source and are 100% polarized by passing through a strong magnetic field before their decay is observed by a very sensitive electron spectrometer. UCN guides facilitate the transfer of UCN from the source to the spectrometer. Common guide materials include stainless steel, copper, aluminum, and quartz. Often a thin film is applied to these components to increase their ability to transport/bottle and preserve the polarization of UCN. In the region of the SD2 UCN source, nickel-58 films are applied, whereas once the UCN are polarized, diamond-like carbon (DLC) films are employed. This dissertation covers the application, process developments, and characterization of these coatings. In addition a study concerning the surface finish resulting from the mechanical polishing and electropolishing of the guides that make up the UCNA beamline is presented. / Ph. D.

Magnetoelectricity (ME) is a physical property that results from an exchange between polar (electric dipole) and spin (magnetic dipole) subsystem: i.e., a change in polarization (P) with application of magnetic field (H), or a change in magnetization (M) with applied electric field (E). Magnetoelectricity can be found both in single phase and composite materials. Compared with single phase multiferroic materials, composite multiferroics have higher ME effects. Through a strictive interaction between the piezoelectricity of the ferroelectric phase and the magnetostriction of the ferromagnetic phase, said multiferroic composites are capable of producing relatively large ME coefficients. This Dissertation focused on the deposition and characterization of two-phase composite magnetoelectric thin films. First, single phase ferroelectric thin films were studied to improve the multiferroic properties of the composite thin films. Then structural, ferroelectric, ferromagnetic, and magnetoelectric properties of composite thin films were researched. Finally, regular nano-array composite films were deposited and characterized. First, for single phase ferroelectric thin films, the phase stability was controlled by epitaxial engineering. Because ferroelectric properties are strongly related to their crystal structure, it is necessary to study the crystal structures in single phase ferroelectric thin films. Through constraint of the substrates, the phase stability of the ferroelectric thin films were able to be altered. Epitaxial thin-layers of Pb(Fe1/2Nb1/2)O3 (or PFN) grown on (001), (110), and (111) SrTiO3 substrates are tetragonal, orthorhombic, and rhombohedral respectively. The larger constraint stress induces higher piezoelectric constants in tetragonal PFN thin film. Epitaxial thin-layers of Pb(Zr0.52Ti0.48)O3 (or PZT) grown on (001), (110), and (111) SrTiO3 substrates are tetragonal, monoclinic C, and rhombohedral respectively. Enhanced ferroelectric properties were found in the low symmetry monoclinic phase. A triclinic phase in BFO was observed when it was deposited on tilted (001) STO substrates by selecting low symmetry (or interim) orientations of single crystal substrates. Then, in two phase composite magnetoelectric thin films, the morphology stability was controlled by epitaxial engineering. Because multiferroic properties are strongly related to the nano-structures of the composite thin films, it is necessary to research the nano-structures in composite thin films. Nano-belt structures were observed in both BaTiO3-CoFe2O4 and BiFeO3-CoFe2O4 systems: by changing the orientation of substrates or annealing condition, the nano-pillar structure could be changed into nano-belts structure. By doing so, the anisotropy of ferromagnetic properties changes accordingly. The multi-ferroic properties and magnetoelectric properties or (001), (110) and (111) self-assembled BiFeO3-CoFe2O4 nano-composite thin film were also measured. Finally, the regular CoFe2O4-BiFeO3 nano-array composite was deposited by pulsed laser deposition patterned using a focused ion beam. Top and cross-section views of the composite thin film showed an ordered CoFe2O4 nano-array embedded in a BiFeO3 matrix. Multiferroic and magnetoelectric properties were measured by piezoresponse force microscopy and magnetic force microscopy. Results show (i) switching of the magnetization in ferromagnetic CoFe2O4 and of the polarization in ferroelectric BiFeO3 phases under external magnetic and electric field respectively, and (ii) changes of the magnetization of CoFe2O4 by applying an electric field to the BiFeO3 phase. / Ph. D.