Study of Strain and Temperature Dependence of Metal Epitaxy

Metallic films are important in catalysis, magneto-optic storage media, and interconnects in microelectronics, and it is crucial to predict and control their morphologies. The evolution of a growing crystal is determined by the behavior of each individual atom, but technologically relevant structures have to be described on a time scale of the order of (at least) tenths of a second and on a length scale of nanometers. An adequate theory of growth should describe the atomistic level on very short time scales (femtoseconds), the formation of small islands (microseconds), as well as the evolution of mesoscopic and macroscopic structures (tenths of seconds). The development of efficient algorithms combined with the availability of cheaper and faster computers has turned density functional theory (DFT) into a reliable and feasible tool to study the microscopic aspects of growth phenomena (and many other complex processes in materials science, condensed matter physics, and chemistry). In this paper some DFT results for diffusion properties on metallic surfaces are presented. Particularly, we will discuss the current understanding of the influences of strain on the diffusion (energy barrier and prefactor) of a single adatom on a substrate. A DFT total energy calculation by its nature is primarily a static calculation. An accurate way to describe the spatial and temporal development of a growing crystal is given by kinetic Monte Carlo (KMC). We will describe the method and its combination with microscopic parameters obtained from ab initio calculations. It is shown that realistic ab initio kinetic Monte Carlo simulations are able to predict an evolving mesoscopic structure on the basis of microscopic details.Comment: 25 pages, 6 figures, In: ``Morphological Organisation during Epitaxial Growth and Removal'', Eds. Z. Zhang, M. Lagally. World Scientific, Singapore 1998. other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Density Functional Theory of Epitaxial Growth of Metals

This chapter starts with a summary of the atomistic processes that occur during epitaxy. We then introduce density functional theory (DFT) and describe its implementation into state-of-the-art computations of complex processes in condensed matter physics and materials science. In particular we discuss how DFT can be used to calculate parameters of microscopic processes such as adsorption and surface diffusion, and how they can be used to study the macroscopic time and length scales of realistic growth conditions. This meso- and macroscopic regime is described by the ab initio kinetic Monte Carlo approach. We discuss several specific theoretical studies that highlight the importance of the different diffusion mechanisms at step edges, the role of surfactants, and the influence of surface stress. The presented results are for specific materials (namely silver and aluminum), but they are explained in simple physical pictures suggesting that they also hold for other systems.Comment: 55 pages, 20 figures, to be published "Growth of Ultrathin Epitaxial Layers", The Chemical Physics of Soild Surfaces, Vol. 8, Eds D. A. King and D. P. Woodruff (Elsevier Science, Amsterdam, 1997

Hematologic and biochemical reference intervals in Shetland Sheepdogs

Background: Several breeds have physiological peculiarities that induce variations in reference intervals (RIs) compared with the general canine population. Shetland sheepdogs (SSs) are reported to be more predisposed to different diseases (eg, hyperlipidemia, gallbladder mucocele, and hypothyroidism). Consequently, a breed-specific approach is more often required. Objectives: The aim of this study was to determine whether the RIs of the general canine population could be applied to that of SSs, and to generate breed-specific RIs, where appropriate. Methods: Sixty\ua0clinically healthy and fasted SSs (36% of the population registered at the Italian Breed association) were examined. Routine hematology and biochemistry analyses were performed. The transference method was used to compare the results of SSs with the RIs of the general canine population. When these RIs were not validated, new RIs were generated according to the guidelines of the American Society of Veterinary Clinical Pathology. Differences associated with sex, age, coat color, and whether used as a pet, a herding dog, or an agility dog were also investigated. Results: The transference method validated for 30/38 SS RIs. For 6 of the remaining 8 variables, the difference with the claimed RIs could depend on preanalytical or analytical artifacts, whereas for glucose and total cholesterol, these differences could depend on breed peculiarities. However, in all SSs, the concentration of cholesterol was <12.95\ua0mmol/L. Relevant differences associated with sex, age, coat color, and use were not found. Conclusions: This study suggests that breed-specific RIs should be used for glucose and cholesterol in SSs

Comparison of protein carbonyl (Pco), paraoxonase-1 (pon1) and c-reactive protein (crp) as diagnostic and prognostic markers of septic inflammation in dogs

Reliable diagnostic and prognostic markers of sepsis are lacking, but essential in veterinary medicine. We aimed to assess the accuracy of C-Reactive Protein (CRP), protein carbonyls (PCO) and paraoxonase-1 (PON1) in differentiating dogs with sepsis from those with sterile inflammation and healthy ones, and predict the outcome in septic dogs. These analytes were retrospectively evaluated at admission in 92 dogs classified into healthy, septic and polytraumatized. Groups were compared using the Kruskal–Wallis test, followed by a Mann–Whitney U test to assess differences between survivors and non-survivors. Correlation between analytes was assessed using the Spearman’s test, and their discriminating power was assessed through a Receiver Operating Characteristic (ROC) curve. PON1 and CRP were, respectively, significantly lower and higher in dogs with sepsis compared with polytraumatized and clinically healthy dogs (p &lt; 0.001 for both the analytes), and also in dogs with trauma compared with healthy dogs (p = 0.011 and p = 0.017, respectively). PCO were significantly increased in septic (p &lt; 0.001) and polytraumatized (p &lt; 0.005) as compared with healthy dogs. PON1 and CRP were, respectively, significantly lower and higher in dogs that died compared with survivors (p &lt; 0.001 for both analytes). Ultimately, evaluation of CRP and PON1 at admission seems a reliable support to diagnose sepsis and predict outcomes

Scattering of rare-gas atoms at a metal surface: evidence of anticorrugation of the helium-atom potential-energy surface and the surface electron density

Recent measurements of the scattering of He and Ne atoms at Rh(110) suggest that these two rare-gas atoms measure a qualitatively different surface corrugation: While Ne atom scattering seemingly reflects the electron-density undulation of the substrate surface, the scattering potential of He atoms appears to be anticorrugated. An understanding of this perplexing result is lacking. In this paper we present density functional theory calculations of the interaction potentials of He and Ne with Rh(110). We find that, and explain why, the nature of the interaction of the two probe particles is qualitatively different, which implies that the topographies of their scattering potentials are indeed anticorrugated.Comment: RevTeX, 4 pages, 10 figure

A framework for dissecting affinities of multidrug efflux transporter AcrB to fluoroquinolones

Sufficient concentration of antibiotics close to their target is key for antimicrobial action. Among the tools exploited by bacteria to reduce the internal concentration of antibiotics, multidrug efflux pumps stand out for their ability to capture and expel many unrelated compounds out of the cell. Determining the specificities and efflux efficiency of these pumps towards their substrates would provide quantitative insights into the development of antibacterial strategies. In this light, we developed a competition efflux assay on whole cells, that allows measuring the efficacy of extrusion of clinically used quinolones in populations and individual bacteria. Experiments reveal the efficient competitive action of some quinolones that restore an active concentration of other fluoroquinolones. Computational methods show how quinolones interact with the multidrug efflux transporter AcrB. Combining experiments and computations unveils a key molecular mechanism acting in vivo to detoxify bacterial cells. The developed assay can be generalized to the study of other efflux pumps

Big endothelin-1 in cats with CKD : preliminary evaluation

In human medicine the concentration of serum endothelin-1 (ET-1)increases in hypertension and CKD. Also urinary ET-1 correlates withthe severity of renal disease and the magnitude of proteinuria. In dogs,increased concentration of ET-1, evaluated indirectly by the precursorBig Endothelin-1 (big-ET1), seems to be associated with the severityof CKD and hypertension.The aim of this study was to gain information about serum and urinarylevels of big-ET1 in cats with CKD, with and without hypertensionand proteinuria

First-principles kinetic Monte Carlo simulations for heterogeneous catalysis, applied to the CO oxidation at RuO2(110)

We describe a first-principles statistical mechanics approach enabling us to simulate the steady-state situation of heterogeneous catalysis. In a first step density-functional theory together with transition-state theory is employed to obtain the energetics of all relevant elementary processes. Subsequently the statistical mechanics problem is solved by the kinetic Monte Carlo method, which fully accounts for the correlations, fluctuations, and spatial distributions of the chemicals at the surface of the catalyst under steady-state conditions. Applying this approach to the catalytic oxidation of CO at RuO2(110), we determine the surface atomic structure and composition in reactive environments ranging from ultra-high vacuum (UHV) to technologically relevant conditions, i.e. up to pressures of several atmospheres and elevated temperatures. We also compute the CO2 formation rates (turnover frequencies). The results are in quantitative agreement with all existing experimental data. We find that the high catalytic activity of this system is intimately connected with a disordered, dynamic surface ``phase'' with significant compositional fluctuations. In this active state the catalytic function results from a self-regulating interplay of several elementary processes.Comment: 18 pages including 9 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Roughening of close-packed singular surfaces

An upper bound to the roughening temperature of a close-packed singular surface, fcc Al (111), is obtained via free energy calculations based on thermodynamic integration using the embedded-atom interaction model. Roughening of Al (111) is predicted to occur at around 890 K, well below bulk melting (933 K), and it should therefore be observable, save for possible kinetic hindering.Comment: RevTeX 4 pages, embedded figure