Submonolayer nucleation and growth of copper on Ni(100)

Island densities and island sizes can be varied or even tailored by choice of external parameters in molecular beam epitaxy, i.e.: by the choice of substrate temperature. deposition rate, and coverage. We present a comprehensive study of the nucleation kinetics of Cu on Ni(100) using variable temperature scanning tunneling microscopy. The analysis of the saturation island density as a function of substrate temperature and deposition rate reveals that the smallest stable island abruptly changes from a dimer to a tetramer. The sizes of the critical nuclei are determined from the rate dependence of the saturation island density using mean-field nucleation theory consistent with results from the island size distribution using scaling theory. From the Arrhenius-plot, the microscopic quantities (migration barrier and dimer bond energy) have been deduced

Island shape transition in heteroepitaxial metal growth on square lattices

A novel mechanism for ramified island growth in the initial stages of metal heteroepitaxy is reported. Scanning tunneling microscopy measurements reveal that copper islands on Ni(100), as they grow in size, undergo a shape transition. Below a critical size of approximate to 480 atoms, compact islands form, while above this size they develop a ramified shape. This effect is not of kinetic origin and has been observed in an extended range of growth temperature (250-370 K) and deposition Aux (10(-5)-10(-2) monolayer/s). The shape transition is ascribed to the island size dependent strain relaxation

Power, norms and institutional change in the European Union: the protection of the free movement of goods

How do institutions of the European Union change? Using an institutionalist approach, this article highlights the interplay between power, cognitive limits, and the normative order that underpins institutional settings and assesses their impact upon the process of institutional change. Empirical evidence from recent attempts to reinforce the protection of the free movement of goods in the EU suggests that, under conditions of uncertainty, actors with ambiguous preferences assess attempts at institutional change on the basis of the historically defined normative order which holds a given institutional structure together. Hence, path dependent and incremental change occurs even when more ambitious and functionally superior proposals are on offer

Decrease in shunt volume in patients with cryptogenic stroke and patent foramen ovale

<p>Abstract</p> <p>Background</p> <p>In patients with patent foramen ovale (PFO) there is evidence supporting the hypothesis of a change in right-to-left shunt (RLS) over time. Proven, this could have implications for the care of patients with PFO and a history of stroke. The following study addressed this hypothesis in a cohort of patients with stroke and PFO.</p> <p>Methods</p> <p>The RLS volume assessed during hospitalisation for stroke (index event/T0) was compared with the RLS volume on follow-up (T1) (median time between T0 and T1 was 10 months). In 102 patients with a history of stroke and PFO the RLS volume was re-assessed on follow-up using contrast-enhanced transcranial Doppler/duplex (ce-TCD) ultrasound. A change in RLS volume was defined as a difference of ≥20 microembolic signals (MES) or no evidence of RLS during ce-TCD ultrasound on follow-up.</p> <p>Results</p> <p>There was evidence of a marked reduction in RLS volume in 31/102 patients; in 14/31 patients a PFO was no longer detectable. An index event classified as cryptogenic stroke (P < 0.001; OD = 39.2, 95% confidence interval 6.0 to 258.2) and the time interval to the follow-up visit (P = 0.03) were independently associated with a change in RLS volume over time.</p> <p>Conclusions</p> <p>RLS volume across a PFO decreases over time, especially in patients with cryptogenic stroke. These may determine the development of new strategies for the management in the secondary stroke prevention.</p