Kinetic modelling of epitaxial film growth with up- and downward step barriers

The formation of three-dimensional structures during the epitaxial growth of films is associated to the reflection of diffusing particles in descending terraces due to the presence of the so-called Ehrlich-Schwoebel (ES) barrier. We generalize this concept in a solid-on-solid growth model, in which a barrier dependent on the particle coordination (number of lateral bonds) exists whenever the particle performs an interlayer diffusion. The rules do not distinguish explicitly if the particle is executing a descending or an ascending interlayer diffusion. We show that the usual model, with a step barrier in descending steps, produces spurious, columnar, and highly unstable morphologies if the growth temperature is varied in a usual range of mound formation experiments. Our model generates well-behaved mounded morphologies for the same ES barriers that produce anomalous morphologies in the standard model. Moreover, mounds are also obtained when the step barrier has an equal value for all particles independently if they are free or bonded. Kinetic roughening is observed at long times, when the surface roughness w and the characteristic length $\xi$ scale as $w ~ t^\beta$ and $\xi ~ t^\zeta$ where $\beta \approx 0.31$ and $\zeta \approx 0.22$, independently of the growth temperature.Comment: 15 pages, 7 figure

Aspects of CPT-even Lorentz-symmetry violating physics in a supersymmetric scenario

Background fermion condensates in a landscape dominated by global SUSY are reassessed in connection with a scenario where Lorentz symmetry is violated in the bosonic sector (actually, the photon sector) by a $CPT$-even $k_F$-term. An effective photonic action is discussed that originates from the supersymmetric background fermion condensates. Also, the photino mass emerges in terms of a particular condensate contrary to what happens in the $k_{AF}$-violation. Finally, the interparticle potential induced by the effective photonic action is investigated and a confining profile is identified.Comment: 14 pages. arXiv admin note: text overlap with arXiv:1102.3777 by other author

Modelling of epitaxial film growth with a Ehrlich-Schwoebel barrier dependent on the step height

The formation of mounded surfaces in epitaxial growth is attributed to the presence of barriers against interlayer diffusion in the terrace edges, known as Ehrlich-Schwoebel (ES) barriers. We investigate a model for epitaxial growth using a ES barrier explicitly dependent on the step height. Our model has an intrinsic topological step barrier even in the absence of an explicit ES barrier. We show that mounded morphologies can be obtained even for a small barrier while a self-affine growth, consistent with the Villain-Lai-Das Sarma equation, is observed in absence of an explicit step barrier. The mounded surfaces are described by a super-roughness dynamical scaling characterized by locally smooth (faceted) surfaces and a global roughness exponent $\alpha>1$. The thin film limit is featured by surfaces with self-assembled three-dimensional structures having an aspect ratio (height/width) that may increase or decrease with temperature depending on the strength of step barrier.Comment: To appear in J. Phys. Cond. Matter; 3 movies as supplementary materia

Formation of Nanopillar Arrays in Ultrathin Viscous Films: The Critical Role of Thermocapillary Stresses

Experiments by several groups during the past decade have shown that a molten polymer nanofilm subject to a large transverse thermal gradient undergoes spontaneous formation of periodic nanopillar arrays. The prevailing explanation is that coherent reflections of acoustic phonons within the film cause a periodic modulation of the radiation pressure which enhances pillar growth. By exploring a deformational instability of particular relevance to nanofilms, we demonstrate that thermocapillary forces play a crucial role in the formation process. Analytic and numerical predictions show good agreement with the pillar spacings obtained in experiment. Simulations of the interface equation further determine the rate of pillar growth of importance to technological applications.Comment: 5 pages, 4 figure

Desorption Dynamics of Heavy Alkali Metal Atoms (Rb, Cs) off the Surface of Helium Nanodroplets

We present a combined ion imaging and density functional theory study of the dynamics of the desorption process of rubidium and cesium atoms off the surface of helium nanodroplets upon excitation of the perturbed $6s$ and $7s$ states, respectively. Both experimental and theoretical results are well represented by the pseudodiatomic model for effective masses of the helium droplet in the desorption reaction of m_eff/m_He~10 (Rb) and 13 (Cs). Deviations from this model are found for Rb excited to the 6p state. Photoelectron spectra indicate that the dopant-droplet interaction induces relaxation into low-lying electronic states of the desorbed atoms in the course of the ejection process.Comment: in press, J. Phys. Chem. A (2014

Nontyphoidal Salmonella Gastroenteritis in Children: a 10 Year Review

Introdução: A Salmonella não tifoide é o agente mais frequente das toxinfeções alimentares nos países desenvolvidos. Em Portugal, são notificados em média 450 casos por ano, 80% dos quais em crianças. Métodos: Revisão casuística dos casos confirmados por coprocultura, internados num hospital do grupo I, na região de Lisboa e Vale do Tejo, entre 1999 e 2008. Análise estatística no programa SPSS® v16.0, com aplicação do teste de Spearman e significância estatística para p< 0,05. Resultados: Identificaram-se 213 internamentos. A mediana anual foi de 21 internamentos, 39% ocorrendo no verão. A mediana das idades foi de 4,2 anos, com doze casos em lactentes até aos três meses. Houve um predomínio no sexo masculino (57%). A mediana do total de leucócitos foi de 9300/mL e da proteína C reativa de 8,8 mg/dL, não se relacionando com a ocorrência de bacteriemia. A duração média do internamento foi de 5,2 dias. As principais complicações foram desidratação (117/213), bacteriemia (8/213), convulsão febril (6/213), síndrome de Mallory-Weiss (5/213) e apendicite aguda (3/213). Os serotipos mais isolados foram: S. Enteritidis (76%), S. Typhimurium (19%), outros (S. O4,5:i-, S. Derby, S. Hayfa, S. Menden, S. Rissen) (5%). Encontraram-se 27% de resistências à ampicilina e 15% ao trimetoprim-sulfametoxazol, sem resistências ao ceftriaxone. Conclusões: Nos 10 anos estudados, o número de casos manteve-se elevado, com morbilidade relevante e resistências significativas aos antibióticos de primeira linha

An Investigation of the KFK_{F}-type Lorentz-Symmetry Breaking Gauge Models in N=1N=1-Supersymmetric Scenario

In this work, we present two possible venues to accomodate the $K_{F}$-type Lorentz-symmetry violating Electrodynamics in an $N=1$-supersymmetric framework. A chiral and a vector superfield are chosen to describe the background that signals Lorentz-symmetry breaking. In each case, the $\ K_{\mu \nu \kappa \lambda }$-tensor is expressed in terms of the components of the background superfield that we choose to describe the breaking. We also present in detail the actions with all fermionic partners of the background that determine $\ K_{\mu \nu \kappa \lambda }$.Comment: 10 page

TEM study of defects versus growth orientations in heavily boron-doped diamond

International audienceHeavy boron-doping layer in diamond can be responsible for the generation of extended defects during the growth processes (Blank et al., Diam. Relat. Mater. 17, 1840 (2008) [1]). As claimed recently (Alegre et al., Appl. Phys. Lett. 105, 173103 (2014) [2]), boron pair interactions rather than strain-related misfit seems to be responsible for such dislocation generation. In the present work, electron microscopy observations are used to study the defects induced by heavy boron doping in different growth plane orientations. Facets of pyramidal Hillocks (PHs) and pits provide access to non-conventional growth orientations where boron atoms incorporation is different during growth. TEM analysis on FIB prepared lamellas confirm that also for those growth orientations, the generation of dislocations occurs within the heavily boron-doped diamond layers. Stacking faults (SFs) have been also observed by high resolution transmission electron microscopy (HREM). From the invisibility criteria, using weak beam (WB) observation, ½ [1-10] and 1/6 [11-2], Burger vectors have been identified. Their generation behavior confirms the mechanism reported by Alegre et al. where local in-plane strain effects induced at the growing surface of the diamond lattice by the neighboring of several boron atoms cause the generation of such extended defects

Anatomia de algumas ocorrências de gemas e seu enquadramento em protocolos de ordenamento territorial – contributo para uma reflexão sobre o estatuto dos depósitos gemíferos portugueses

[Abstract] Anatomy and Classification of Portuguese Gemstone Deposits and their inclusion in Territorial Management Protocols - The concept of gemstone resources includes the consideration of aspects such as the genetic type of deposits, geographical location and geological characterization of the ores. Based on archeological evidences and assuming the geological potentiality it is possible to consider the existence of resources base with gem quality, in Portugal. The main deposits are related to residual granite systems. In order to ensure a sustainable use, economical or patrimonial, it is necessary to classify these occurrences in a context of land management. This paper presents the typology of the most interesting occurrences considering its economical and patrimonial potentiality

A Case of Central Nervous System Infection by Candida Famata in an Immunosuppressed Patient with HIV-1 Infection

Invasive fungal infections caused by Candida species are increasingly observed in immunosuppressed patients. Candida albicans is the more often identified species and neurocandidiasis is associated with high mortality rates. Diagnosis and treatment of these infections are frequently challenging. We report a case of central nervous system infection caused by Candida famata in an HIV-1 infected patient. To our best knowledge this is just the second published case of neural infection by this agent.info:eu-repo/semantics/publishedVersio