815 research outputs found
Time-resolved spectroscopy at surfaces and adsorbate dynamics: insights from a model-system approach
We introduce a model description of femtosecond laser induced desorption at
surfaces. The substrate part of the system is taken into account as a (possibly
semi-infinite) linear chain. Here, being especially interested in the early
stages of dissociation, we consider a finite-size implementation of the model
(i.e., a finite substrate), for which an exact numerical solution is possible.
By time-evolving the many-body wave function, and also using results from a
time-dependent density functional theory description for electron-nuclear
systems, we analyze the competition between several surface-response mechanisms
and electronic correlations in the transient and longer time dynamics under the
influence of dipole-coupled fields. Our model allows us to explore how coherent
multiple-pulse protocols can impact desorption in a variety of prototypical
experiments.Comment: replaces a shorter versio
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Experimental evidence for a partially dissociated water bilayer on Ru{0001}
Core-level photoelectron spectra, in excellent agreement with ab initio calculations, confirm that the stable wetting layer of water on Ru{0001} contains O-H and H2O in roughly 3:5 proportion, for OHx coverages between 0.25 and 0.7 ML, and T<170 K. Proton disorder explains why the wetting structure looks to low energy electron diffraction (LEED) to be an ordered p(root3xroot3)R30degrees adlayer, even though approximate to3/8 of its molecules are dissociated. Complete dissociation to atomic oxygen starts near 190 K. Low photon flux in the synchrotron experiments ensured that the diagnosis of the nature of the wetting structure quantified by LEED is free of beam-induced damage
Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths
We image the field enhancement at Ag nanostructures using femtosecond laser
pulses with a center wavelength of 1.55 micrometer. Imaging is based on
non-linear photoemission observed in a photoemission electron microscope
(PEEM). The images are directly compared to ultra violet PEEM and scanning
electron microscopy (SEM) imaging of the same structures. Further, we have
carried out atomic scale scanning tunneling microscopy (STM) on the same type
of Ag nanostructures and on the Au substrate. Measuring the photoelectron
spectrum from individual Ag particles shows a larger contribution from higher
order photoemission process above the work function threshold than would be
predicted by a fully perturbative model, consistent with recent results using
shorter wavelengths. Investigating a wide selection of both Ag nanoparticles
and nanowires, field enhancement is observed from 30% of the Ag nanoparticles
and from none of the nanowires. No laser-induced damage is observed of the
nanostructures neither during the PEEM experiments nor in subsequent SEM
analysis. By direct comparison of SEM and PEEM images of the same
nanostructures, we can conclude that the field enhancement is independent of
the average nanostructure size and shape. Instead, we propose that the
variations in observed field enhancement could originate from the wedge
interface between the substrate and particles electrically connected to the
substrate
Immutable Infrastructure Calls for Immutable Architecture
With the advent of cloud computing and the concept of immutable infrastructure, the scaling and deployment of applications has become significantly easier. This increases the possibility of “configuration drift” as an operations team manages this cluster of machines, both virtual and actual. In this paper we propose a revised view on configuration and architecture. We propose that software deployed on a public or private cloud should, to the furthest possible extent, be immutable and source controlled. This reduces configuration drift and ensures no configuration problems in production as a result of updates or changes. We will show an example of a software project deployed on Amazon Web Services with an immutable Jenkins setup which manages updating the whole cluster and is self-regenerating. We will also discuss how this lends itself naturally to interoperability between clouds, because of the infrastructure-agnostic nature of this approach
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