201 research outputs found
Electronic Cooling via Interlayer Coulomb Coupling in Multilayer Epitaxial Graphene
In van der Waals bonded or rotationally disordered multilayer stacks of
two-dimensional (2D) materials, the electronic states remain tightly confined
within individual 2D layers. As a result, electron-phonon interactions occur
primarily within layers and interlayer electrical conductivities are low. In
addition, strong covalent in-plane intralayer bonding combined with weak van
der Waals interlayer bonding results in weak phonon-mediated thermal coupling
between the layers. We demonstrate here, however, that Coulomb interactions
between electrons in different layers of multilayer epitaxial graphene provide
an important mechanism for interlayer thermal transport even though all
electronic states are strongly confined within individual 2D layers. This
effect is manifested in the relaxation dynamics of hot carriers in ultrafast
time-resolved terahertz spectroscopy. We develop a theory of interlayer Coulomb
coupling containing no free parameters that accounts for the experimentally
observed trends in hot-carrier dynamics as temperature and the number of layers
is varied.Comment: 54 pages, 15 figures, uses documentclass{achemso}, M.T.M. and J.R.T.
contributed equally to this wor
Participatie en draagvlak voor hernieuwbare energieprojecten
Er is consensus over het belang van proces- en financiële participatie van de omgeving (burgers en bedrijven) bij de besluitvorming over hernieuwbare energieprojecten. In deze bijdrage constateren wij echter dat er sprake lijkt van een mismatch tussen, enerzijds, de wens om (initiatiefnemers voor te schrijven) voldoende participatiemogelijkheden te bieden en draagvlak te realiseren en, anderzijds, de juridische normen die gelden voor rechtmatige besluitvorming. De toekomstige Omgevingswet biedt op dat punt slechts weinig verandering. Is participatie gebaat bij verdere regulering? Of volstaat een goede toepassing in de praktijk op basis van beleid, gedragscodes en richtlijnen
One- and two-photon ionization cross sections of the laser excited 6s6p^1P_1 state of barium
Stimulated by a recent measurement of coherent control in photoionization of
atomic barium, we have calculated one- and two-photon ionization cross sections
of the aligned 6s6p^1P_1 state of barium in the energy range between the
5d_{3/2} and 5d_{5/2} states of Ba^+. We have also measured these
photionization spectra in the same energy region, driving the one- or
two-photon processes with the second or first harmonic of a tunable dye laser,
respectively. Our calculations employ the eigenchannel R-matrix method and
multichannel quantum defect theory to calculate the rich array of autoionizing
resonances in this energy range. The non-resonant two-photon process is
described using lowest-order perturbation theory for the photon-atom
interactions, with a discretized intermediate state one-electron continuum. The
calculations provide an absolute normalization for the experiment, and they
accurately reproduce the rich resonance structures in both the one and
two-photon cross sections, and confirm other aspects of experimental
observations. These results demonstrate the ability of these computationally
inexpensive methods to reproduce the experimental observables in one- and
two-photon ionization of heavy alkaline earths, and they lay the groundwork for
future studies of the phase-controlled interference between one-photon and
two-photon ionization processes.Comment: 10 pages, 9 figures, submitted to Phys.Rev.
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