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Filmes finos de LaNiO3 depositados sobre substratos monocristalinos pelo método dos precursores poliméricos
(Universidade Federal de São Carlos, 2004-08-06) Mambrini, Giovanni Pimenta; Varela, José Arana; https://lattes.cnpq.br/1807399214239200; https://lattes.cnpq.br/7723027354150918
This work reports a systematic study on the deposition and characterization of LaNiO3 thin films. This material is a ceramic conductor and presents a near metallic behavior, and is interesting for capacitor electrodes application in memories systems, because of the reduction of fatigue behavior. The synthesis of the precursor resin was realized by the polymeric precursor method. The films were deposited with the spin-coating technique on five different substrates: Si(100), Safire(0001), MgO(100), LaAlO3(100) and SrTiO3(100), and after they were crystallized at 700ºC for two hours in a conventional furnace or at 700ºC for ten minutes in a microwave oven. After that, the films were characterized by X ray diffraction, scanning electron microscopy, atomic force microscopy and measurements of electrical resistivity as a function of temperature. The films deposited on Si(100) were tested as electrodes for SrTiO3 capacitors, deposited with the same method. Polycrystalline and single phase LaNiO3 thin films were obtained on Si(100), Safire(0001) and MgO(100) substrates, whereas the films deposited on LaAlO3(100) and SrTiO3(100) substrates were epitaxial. The method enable a good thickness control and allows the deposition of films without cracks and very homogeneous. Electrical measurements shown a metallic behavior between 20 and 300K, and the epitaxial films have a smaller electrical resistivity, in comparison with the polycrystalline ones. The best result was obtained with the deposition on strontium titanate substrate and the measured resistivity was 250µΩcm, lower than that obtained with others methods reported in the literature. The crystallization in a microwave oven was not so satisfactory, since films with higher resistivity than that crystallized in conventional furnaces were obtained, because their morphology. However, these films are still good for an application in capacitors systems. The system Au/SrTiO3/LaNiO3/Si(100) was also studied being the lanthanum nickelate a good electrode for this system. Dielectric constant of 250 at 10 kHz was obtained which is about the same reported in the literature for this system with Pt electrodes. Dielectric constant measurements as a function of the applied potential of work shown an asymmetric behavior because the difference between the two electrodes of the capacitor. The charge imprisonment in the ceramic/electrode interface causes a reduction in the capacitance with applied potential. In this manner, a simple methodology for preparation of thin films was used resulting in good characteristics and promising for application in DRAM systems. THIN FILMS DEPOSITED ON SINGLE CRYSTAL SUBSTRATES BY THE POLIMERIC PRECURSOR METHOD: This work reports a systematic study on the deposition and characterization of LaNiO3 thin films. This material is a ceramic conductor and presents a near metallic behavior, and is interesting for capacitor electrodes application in memories systems, because of the reduction of fatigue behavior. The synthesis of the precursor resin was realized by the polymeric precursor method. The films were deposited with the spin-coating technique on five different substrates: Si(100), Safire(0001), MgO(100), LaAlO3(100) and SrTiO3(100), and after they were crystallized at 700ºC for two hours in a conventional furnace or at 700ºC for ten minutes in a microwave oven. After that, the films were characterized by X ray diffraction, scanning electron microscopy, atomic force microscopy and measurements of electrical resistivity as a function of temperature. The films deposited on Si(100) were tested as electrodes for SrTiO3 capacitors, deposited with the same method. Polycrystalline and single phase LaNiO3 thin films were obtained on Si(100), Safire(0001) and MgO(100) substrates, whereas the films deposited on LaAlO3(100) and SrTiO3(100) substrates were epitaxial. The method enable a good thickness control and allows the deposition of films without cracks and very homogeneous. Electrical measurements shown a metallic behavior between 20 and 300K, and the epitaxial films have a smaller electrical resistivity, in comparison with the polycrystalline ones. The best result was obtained with the deposition on strontium titanate substrate and the measured resistivity was 250µΩcm, lower than that obtained with others methods reported in the literature. The crystallization in a microwave oven was not so satisfactory, since films with higher resistivity than that crystallized in conventional furnaces were obtained, because their morphology. However, these films are still good for an application in capacitors systems. The system Au/SrTiO3/LaNiO3/Si(100) was also studied being the lanthanum nickelate a good electrode for this system. Dielectric constant of 250 at 10 kHz was obtained which is about the same reported in the literature for this system with Pt electrodes. Dielectric constant measurements as a function of the applied potential of work shown an asymmetric behavior because the difference between the two electrodes of the capacitor. The charge imprisonment in the ceramic/electrode interface causes a reduction in the capacitance with applied potential. In this manner, a simple methodology for preparation of thin films was used resulting in good characteristics and promising for application in DRAM systems.
Estudo da influência da adição de compostos de boro na resistência à oxidação de refratários a base de carbeto de silício-liga de nitreto.
(Universidade Federal de São Carlos, 2004-08-06) Rodrigues, Cesar Augusto Frasson; Morelli, Márcio Raymundo; https://lattes.cnpq.br/0172837599844991
In this work, boron was added in a commercial silicon carbide bonded silicon nitride refractory and its influence has been evaluated. These materials have been used as high temperature structural ceramic due to their properties combination, as the hot modulus of rupture, abrasion resistance, excellent thermal conductivity, good thermal shock resistance and good corrosion resistance. To prepare the studied compositions, boron compounds were added during mixing stage and sintered at 1450o C in a nitrogen atmosphere. Some compositions were tested on a first stage using hot modulus of rupture tests and X ray diffractions. On a second stage, modulus of rupture at room temperature, scanning electronic microscopy and mainly oxidation tests (980 and 1230o C / 200 hours) were performed and valued. The obtained results were compared with the commercial refractory. As the weight gain is an oxidation indicative, samples made with boron nitride have indicated trends to be a good alternative to increase the oxidation resistance. Besides, boron additives contributed to crystallize the silica film in the samples and contributed to getting a better oxidation resistance. The oxygen diffusivity is bigger in the vitreous silica than in the crystalline, and due to this crystallization, boron additives have shown a good opportunity to decrease the oxidation rate. The results obtained by SEM showed silicon nitride fibers, mainly inside the porous. Moreover, as informed on the paper references, boron has contributed to form air bubbles in the silica film, but without bubbles rupture. These ruptures could be responsible to increase the oxidation rate in the silicon carbide surfaces. Also, spherulits were not observed in the oxidized film.