Confined step-flow growth of Cu intercalated between graphene and a Ru(0001) surface

By comparing the growth of Cu thin films on bare and graphene-covered Ru(0001) surfaces, we demonstrate the role of graphene as a surfactant allowing the formation of flat Cu films. Low-energy electron microscopy, X-ray photoemission electron microscopy and X-ray absorption spectroscopy reveal that depositing Cu at 580 K leads to distinct behaviors on both types of surfaces. On bare Ru, a Stranski-Krastanov growth is observed, with first the formation of an atomically flat and monolayer-thick wetting layer, followed by the nucleation of three-dimensional islands. In sharp contrast, when Cu is deposited on a graphene-covered Ru surface under the very same conditions, Cu intercalates below graphene and grows in a step-flow manner: atomically-high growth fronts of intercalated Cu form at the graphene edges, and extend towards the center of the flakes. Our findings suggest potential routes in metal heteroepitaxy for the control of thin film morphology.Comment: 9 pages, 4 figure

Reversible Graphene decoupling by NaCl photo-dissociation

We describe the reversible intercalation of Na under graphene on Ir(111) by photo-dissociation of a previously adsorbed NaCl overlayer. After room temperature evaporation, NaCl adsorbs on top of graphene forming a bilayer. With a combination of electron diffraction and photoemission techniques we demonstrate that the NaCl overlayer dissociates upon a short exposure to an X-ray beam. As a result, chlorine desorbs while sodium intercalates under the graphene, inducing an electronic decoupling from the underlying metal. Low energy electron diffraction shows the disappearance of the moir\'e pattern when Na intercalates between graphene and iridium. Analysis of the Na 2p core-level by X-ray photoelectron spectroscopy shows a chemical change from NaCl to metallic buried Na at the graphene/Ir interface. The intercalation-decoupling process leads to a n-doped graphene due to the charge transfer from the Na, as revealed by constant energy angle resolved X-ray photoemission maps. Moreover, the process is reversible by a mild annealing of the samples without damaging the graphene

Tomar o Pulso ao Tigre: Missões Militares Portuguesas em Espanha, entre a vigilância e a cooperação (1934 – 1939)

Dissertação apresentada para cumprimento dos requisitos necessários à obtenção do grau de Mestre em História ContemporâneaEste trabalho centra-se nas soluções de que o Exército Português lançou mão para melhorar o seu conhecimento do Exército espanhol, fazendo o estudo das missões militares de observação enviadas a Espanha de 1934 a 1939, numa fase crítica na história das relações entre os dois países ibéricos. Após as visitas realizadas antes da Guerra Civil espanhola, analisaremos o percurso da Missão Militar Portuguesa de Observação em Espanha (M.M.P.O.E.), e as principais linhas de força das suas actividades e os efeitos por elas produzidos em Lisboa. Assim que estalou a guerra em Espanha, o Exército Português agarrou a oportunidade para dissecar em detalhe o seu rival espanhol tão rapidamente quanto foi possível, tendo em conta o carácter excepcional da conjuntura. Aos primeiros contactos informais mantidos com os rebeldes espanhóis no Verão de 1936 por alguns oficiais portugueses seguiu-se uma diminuta mas motivada Missão Especial da Arma de Aeronáutica. Impressionados com a guerra aérea moderna, os seus membros sugeriam a criação de uma missão de observadores militares permanente, que viria a ser oficialmente criada em Março de 1937. Assim nasceu a M.M.P.O.E. O dispositivo assim criado servia na perfeição os objectivos do Governo, ao permitir o estabelecimento de um canal de comunicação directo com a Junta de Burgos. Paralelamente, constituía uma ferramenta preciosa para o Estado-Maior estudar o Exército Espanhol a partir de dentro e sopesar diversas implicações políticas e militares do conflito. Independentemente do custo económico e complexidade que um empreendimento desta natureza significou para um país pequeno e periférico como Portugal, os homens da M.M.P.O.E. deram boa conta de si, apesar de lhes faltar experiência de combate prévia

Telleiras de Pontevedra, patrimonio vernáculo industrial en Galicia

Para a protección do patrimonio vernáculo e industrial e a intentando contribuir para a valorización do extenso e xa tan deteriorado patrimonio en Galicia, desenvolveuse esta investigación sobre as telleiras existentes na provincia de Pontevedra. As telleiras son industrias vernáculas destinadas a producir tellas e ladrillos. Os cambios nas actividades industriais, provocadas polo desenvolvemento da industrialización e as diversas crises no sector, conduciron ó seu desuso e consecuente abandono, reaultando na súa case completa destrucción e no desaparecemento de unha parte importante da arquitectura vernácula e industrial da Galiza. O principal obxectivo da investigación é proporcionar coñecemento deste patrimonio vernáculo e industrial, a travé da catalogación, análise, definición de indicadores e valores, para futura intervención responsable do patrimonio cultural edificado, contribuíndo para a súa valorización e salvaguarda. No actual contexto arquitectónico non se encontran publicacións específicas referentes ás telleiras, as poucas referencias existentes son de índole histórica e etnográfica. Por este motivo, para a presente investigación foi realizada unha revisión da literatura do patrimonio vernáculo e industrial e, principalmente, foi definido o estado da arte no ámbito dos obxectivos establecidos e do obxecto en análise. Metodoloxicamente, esta é unha investigación documental de estudo comparativo de 11 casos de estudo, basada en métodos de análise cualitativa : é unha análise documental, con observación, fotografía, notas de campo e fichas de catalogación. A investigación desenvólvese en 7 capítulos, destacandose os referentes á fundamentación teórica (cap. 2 e 3), as fichas de catalogación (cap. 4), á análise dos resultados dos estudos de caso (cap. 5), permitindo unha coherente sistematización de resultados (cap. 6) e consecuente conclusión que responde os obxectivos principais (cap. 7). A investigación pretende ser un importante contributo para o coñecemento deste tipo de construción, fundamentándose na súa catalogación e a sua posterior análise para a estructuración dos seus indicadores formais, construtivos, tipolóxicos e de matriz espacial. En conclusión, contribue para a valorización e salvaguarda das telleiras da provincia de Pontevedra.Abstract: For the protection of industrial and vernacular heritage and to contribute to the significance of the extensive and deteriorated Galician heritage, this research addresses the still existing Telheiras, in the province of Pontevedra. Telheiras are industrial vernacular buildings, where bricks and tiles used to be produced. Changes in the industrial activity, caused by the advance of industrialization, and the various crises in the sector, led to its disuse and consequent abandonment, resulting in its almost complete destruction and the disappearance of a major part of the industrial and vernacular architecture of Galicia. The main objective of the research is to provide proper knowledge of this industrial vernacular heritage, through cataloguing, analysis, definition of indicators and values, for a responsible future intervention of the built cultural heritage, contributing to their significance and protection. In the current architectural context there isn’t specific publications regarding Telheiras, with the exception of a few existing historical and ethnographic references. Therefore, for the present investigation, it was addressed a literature review of the industrial and vernacular heritage and it was defined the state of the art, within the established aims and the object under examination. Methodologically, it concerns a documental research based on the comparative study of 11 case studies, through the application of qualitative methods of analysis: it is a documental analysis, with observation, photography, field notes and inquiries. The investigation is structured into seven chapters, related with theoretical approach (chs. 2 and 3), the inquiries (ch. 4), the analysis of case studies results (chapter 5), providing a coherent systematization of results (chapter 6) and consequent conclusion that addresses the main objectives (ch. 7). This research aims to be an important contribution to the knowledge of this type of heritage. It is based in cataloguing, and its subsequent analysis to structure indicators regarding formal, constructive, typological and spacial matrix parameters. In conclusion, it contributes to the promotion and safeguarding of Telheiras, in the province of Pontevedra

Strain relaxation in small adsorbate islands: O on W(110)

The stress-induced lattice changes in a p(1x2) ordered oxygen layer on W(110) are measured by low-energy electron diffraction. We have observed that small oxygen islands show a mismatch with the underlying lattice. Our results indicate that along [1-10] the average mismatch scales inversely with the island size as 1/L for all oxygen coverages up to 0.5 ML, while along [001] it is significant only for the smallest oxygen islands and scales as a higher power of the inverse island size. The behaviour along [1-10] is described by a one-dimensional finite-size Frenkel-Kontorova model. Using this model, together with calculated force constants, we make a quantitative estimate for the change of surface-stress upon oxygen adsorption. The result is consistent with our ab-initio calculations, which give a relative compressive stress of -4.72 N/m along [1-10] and a minute relative tensile stress of 0.15 N/m along [001]. The scaling along [001] is qualitatively explained as an effect induced by the lattice relaxation in the [1-10] direction.Comment: 22 pages, 5 figure

Stress engineering at the nanometer scale: Two-component adlayer stripes

Spontaneously formed equilibrium nanopatterns with long-range order are widely observed in a variety of systems, but their pronounced temperature dependence remains an impediment to maintain such patterns away from the temperature of formation. Here, we report on a highly ordered stress-induced stripe pattern in a two-component, Pd-O, adsorbate monolayer on W(110), produced at high temperature and identically preserved at lower temperatures. The pattern shows a tunable period (down to 16 nm) and orientation, as predicted by a continuum model theory along with the surface stress and its anisotropy found in our DFT calculations. The control over thermal fluctuations in the stripe formation process is based on the breaking/restoring of ergodicity in a high-density lattice gas with long-range interactions upon turning off/on particle exchange with a heat bath.Comment: 6 pages, 4 figure