Projecto e construção de um aparelho para a medição da taxa de emissão de electrões secundários

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia FísicaA formação de uma nuvem de electrões no interior dos aceleradores de partículas leva à deterioração da qualidade do feixe de partículas. Esta nuvem é o resultado da ionização do gás residual pelo feixe de partículas e pelos electrões resultantes da colisão do feixe com as paredes internas do acelerador. Os electrões da nuvem electrónica, ao colidirem com as paredes do sistema de vácuo, são multiplicados de acordo com a taxa de produção de electrões secundários da superfície (SEY) e interagem com o feixe de alta energia, reduzindo desta forma a sua qualidade. Uma forma de prevenir a deterioração do feixe é empregar materiais que sejam emissores pobres de electrões secundários. De entre as várias soluções até ao momento conhecidas, os revestimentos de carbono depositados por cátodo magnetrão parecem ser a solução mais promissora [1, 2]. Contudo, mais tarde detectou-se um aumento da SEY destes materiais em função da exposição prolongada ao ar, não tendo por isso sido encontrada a solução ideal. Nesse sentido o trabalho aqui desenvolvido pretende ser uma contribuição, que se espera significativa, para o estudo e compreensão destes processos. Nesta óptica foi projectado, construído e implementado um aparelho para medição da SEY de diversos materiais. Foram ainda realizados testes de funcionamento do aparelho e da sua aptidão para os estudos previstos, tendo sido comprovada a sua fiabilidade. As experiências foram realizadas a uma pressão de 10-6 mbar em duas amostras de grafite. As medidas efectuadas permitiram o estudo da influência de parâmetros cruciais na taxa de emissão de electrões secundários, nomeadamente o ângulo de incidência do feixe de electrões e a rugosidade da superfície da amostra. Estudou-se ainda a percentagem relativa de electrões reflectidos presentes na taxa de emissão de electrões secundários. O aparelho desenvolvido foi acoplado ao aparelho multitécnicas da linha de Investigação “Ciência e Engenharia de Superfícies e Tecnologia de Vácuo” do CEFITEC, proporcionando ao sistema mais uma forma de análise

Fabrication of Isolated Iron Nanowires

Nanoscale interconnects are an important component of molecular electronics. Here we use X-ray spectromicroscopy techniques as well as scanning probe methods to explore the self-assembled growth of insulated iron nanowires as a potential means of supplying an earth abundant solution. The intrinsic anisotropy of a TiO2(110) substrate directs the growth of micron length iron wires at elevated temperatures, with a strong metal-support interaction giving rise to ilmenite (FeTiO3) encapsulation. Iron nanoparticles that decorate the nanowires display magnetic properties that suggest other possible applications

Fabrication of isolated iron nanowires

Nanoscale interconnects are an important component of molecular electronics. Here we use X-ray spectromicroscopy techniques as well as scanning probe methods to explore the self-assembled growth of insulated iron nanowires as a potential means of supplying an earth abundant solution. The intrinsic anisotropy of a TiO2(110) substrate directs the growth of micron length iron wires at elevated temperatures, with a strong metal–support interaction giving rise to ilmenite (FeTiO3) encapsulation. Iron nanoparticles that decorate the nanowires display magnetic properties that suggest other possible applications

Spectromicroscopy of a Model Water–Gas Shift Catalyst: Gold Nanoparticles Supported on Ceria

Nanometer-sized gold particles supported on ceria are an important catalyst for the low-temperature water–gas shift reaction. In this work, we prepared a model system of epitaxial, ultrathin (1–2 nm thick) CeO_2–<i>x</i>(111) crystallites on a Rh(111) substrate. Low-energy electron microscopy (LEEM) and X-ray photoemission electron microscopy (XPEEM) were employed to characterize the in situ growth and morphology of these films, employing Ce 4f resonant photoemission to probe the oxidation state of the ceria. The deposition of submonolayer amounts of gold at room temperature was studied with scanning tunneling microscopy (STM) and XPEEM. Spatially resolved, energy-selected XPEEM at the Au 4f core level after gold adsorption indicated small shifts to higher binding energy for the nanoparticles, with the magnitude of the shift inversely related to the particle size. Slight reduction of the ceria support was also observed upon increasing Au coverage. The initial oxidation state of the ceria film was shown to influence the Au 4f binding energy; more heavily reduced ceria promoted a larger shift to higher binding energy. Understanding the redox behavior of the gold/ceria system is an important step in elucidating the mechanisms behind its catalytic activity

Visualization of Water-Induced Surface Segregation of Polarons on Rutile TiO2(110)

Water-oxide surfaces are ubiquitous in nature and of widespread importance to phenomena like corrosion as well as contemporary industrial challenges such as energy production through water splitting. So far, a reasonably robust understanding of the structure of such interfaces under certain conditions has been obtained. Considerably less is known about how overlayer water modifies the inherent reactivity of oxide surfaces. Here we address this issue experimentally for rutile TiO2(110) using scanning tunneling microscopy and photoemission, with complementary density functional theory calculations. Through detailed studies of adsorbed water nanoclusters and continuous water overlayers, we determine that excess electrons in TiO2 are attracted to the top surface layer by water molecules. Measurements on methanol show similar behavior. Our results suggest that adsorbate-induced surface segregation of polarons could be a general phenomenon for technologically relevant oxide materials, with consequences for surface chemistry and the associated catalytic activity

Ce=O Terminated CeO2

Multiply bonded lanthanide oxo groups are rare in coordination compounds and have not previously been reported for a surface termination of a lanthanide oxide. Here we report the observation of a Ce=O terminated ceria surface in a CeO2(111)-((Formula presented.) × (Formula presented.))R30° reconstruction of ≈3 nm thick ceria islands prepared on Pt(111). This is evidenced by scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS) measurements in conjunction with density functional theory (DFT) calculations. A Ce=O stretching frequency of 775 cm−1 is observed in HREELS, compared with 766 cm−1 calculated by DFT. The calculations also predict that the Ce=O bond is weak, with an oxygen vacancy formation energy of 0.85 eV. This could play an important role in the facile removal of lattice oxygen from CeO2, accompanied by the reduction of CeIV to CeIII, which is a key attribute of ceria-based systems in connection with their unique catalytic properties.Fil: Grinter, David C.. Colegio Universitario de Londres; Reino UnidoFil: Allan, Michael. Colegio Universitario de Londres; Reino UnidoFil: Yang, Hyun Jin. Colegio Universitario de Londres; Reino UnidoFil: Salcedo, Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Química; ArgentinaFil: Murgida, Gustavo Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes; ArgentinaFil: Shaw, Bobbie Jean. Colegio Universitario de Londres; Reino UnidoFil: Pang, Chi L.. Colegio Universitario de Londres; Reino UnidoFil: Idriss, Hicham. Colegio Universitario de Londres; Reino UnidoFil: Ganduglia Pirovano, M. Verónica. Consejo Superior de Investigaciones Científicas. Instituto de Catálisis y Petroleoquímica; EspañaFil: Thornton, Geoff. Colegio Universitario de Londres; Reino Unid

Ce=O Terminated CeO 2

Multiply bonded lanthanide oxo groups are rare in coordination compounds and have not previously been reported for a surface termination of a lanthanide oxide. Here we report the observation of a Ce=O terminated ceria surface in a CeO(2)(111)‐([Formula: see text] × [Formula: see text] )R30° reconstruction of ≈3 nm thick ceria islands prepared on Pt(111). This is evidenced by scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and high‐resolution electron energy loss spectroscopy (HREELS) measurements in conjunction with density functional theory (DFT) calculations. A Ce=O stretching frequency of 775 cm(−1) is observed in HREELS, compared with 766 cm(−1) calculated by DFT. The calculations also predict that the Ce=O bond is weak, with an oxygen vacancy formation energy of 0.85 eV. This could play an important role in the facile removal of lattice oxygen from CeO(2), accompanied by the reduction of Ce(IV) to Ce(III), which is a key attribute of ceria‐based systems in connection with their unique catalytic properties

Integrated genomic characterization of endometrial carcinoma

We performed an integrated genomic, transcriptomic and proteomic characterization of 373 endometrial carcinomas using array- and sequencing-based technologies. Uterine serous tumours and ~25% of high-grade endometrioid tumours had extensive copy number alterations, few DNA methylation changes, low oestrogen receptor/progesterone receptor levels, and frequent TP53 mutations. Most endometrioid tumours had few copy number alterations or TP53 mutations, but frequent mutations in PTEN, CTNNB1, PIK3CA, ARID1A and KRAS and novel mutations in the SWI/SNF chromatin remodelling complex gene ARID5B. A subset of endometrioid tumours that we identified had a markedly increased transversion mutation frequency and newly identified hotspot mutations in POLE. Our results classified endometrial cancers into four categories: POLE ultramutated, microsatellite instability hypermutated, copy-number low, and copy-number high. Uterine serous carcinomas share genomic features with ovarian serous and basal-like breast carcinomas. We demonstrated that the genomic features of endometrial carcinomas permit a reclassification that may affect post-surgical adjuvant treatment for women with aggressive tumours.National Institutes of Health (U.S.) (Grant 5U24CA143799-04)National Institutes of Health (U.S.) (Grant 5U24CA143835-04)National Institutes of Health (U.S.) (Grant 5U24CA143840-04)National Institutes of Health (U.S.) (Grant 5U24CA143843-04)National Institutes of Health (U.S.) (Grant 5U24CA143845-04)National Institutes of Health (U.S.) (Grant 5U24CA143848-04)National Institutes of Health (U.S.) (Grant 5U24CA143858-04)National Institutes of Health (U.S.) (Grant 5U24CA143866-04)National Institutes of Health (U.S.) (Grant 5U24CA143867-04)National Institutes of Health (U.S.) (Grant 5U24CA143882-04)National Institutes of Health (U.S.) (Grant 5U24CA143883-04)National Institutes of Health (U.S.) (Grant 5U24CA144025-04)National Institutes of Health (U.S.) (Grant U54HG003067-11)National Institutes of Health (U.S.) (Grant U54HG003079-10)National Institutes of Health (U.S.) (Grant U54HG003273-10