29,952 research outputs found
Carbon superatom thin films
Assembling clusters on surfaces has emerged as a novel way to grow thin films
with targeted properties. In particular, it has been proposed from experimental
findings that fullerenes deposited on surfaces could give rise to thin films
retaining the bonding properties of the incident clusters. However the
microscopic structure of such films is still unclear. By performing quantum
molecular dynamics simulations, we show that C_28 fullerenes can be deposited
on a surface to form a thin film of nearly defect free molecules, which act as
carbon superatoms. Our findings help clarify the structure of disordered small
fullerene films and also support the recently proposed hyperdiamond model for
solid C_28.Comment: 13 pages, RevTeX, 2 figures available as black and white PostScript
files; color PostScript and/or gif files available upon reques
Optical reconfiguration and polarization control in semi-continuous gold films close to the percolation threshold
Controlling and confining light by exciting plasmons in resonant metallic
nanostructures is an essential aspect of many new emerging optical
technologies. Here we explore the possibility of controllably reconfiguring the
intrinsic optical properties of semi-continuous gold films, by inducing
permanent morphological changes with a femtosecond (fs)-pulsed laser above a
critical power. Optical transmission spectroscopy measurements show a
correlation between the spectra of the morphologically modified films and the
wavelength, polarization, and the intensity of the laser used for alteration.
In order to understand the modifications induced by the laser writing, we
explore the near-field properties of these films with electron energy-loss
spectroscopy (EELS). A comparison between our experimental data and full-wave
simulations on the exact film morphologies hints toward a restructuring of the
intrinsic plasmonic eigenmodes of the metallic film by photothermal effects. We
explain these optical changes with a simple model and demonstrate
experimentally that laser writing can be used to controllably modify the
optical properties of these semi-continuous films. These metal films offer an
easy-to-fabricate and scalable platform for technological applications such as
molecular sensing and ultra-dense data storage.Comment: Supplementary materials available upon request ([email protected]
Evidence of thermal transport anisotropy in stable glasses of vapour deposited organic molecules
Vapour-deposited organic glasses are currently in use in many optoelectronic
devices. Their operation temperature is limited by the glass transition
temperature of the organic layers and thermal management strategies become
increasingly important to improve the lifetime of the device. Here we report
the unusual finding that molecular orientation heavily influences heat flow
propagation in glassy films of small molecule organic semiconductors. The
thermal conductivity of vapour-deposited thin-film semiconductor glasses is
anisotropic and controlled by the deposition temperature. We compare our data
with extensive molecular dynamics simulations to disentangle the role of
density and molecular orientation on heat propagation. Simulations do support
the view that thermal transport along the backbone of the organic molecule is
strongly preferred with respect to the perpendicular direction. This is due to
the anisotropy of the molecular interaction strength that limit the transport
of atomic vibrations. This approach could be used in future developments to
implement small molecule glassy films in thermoelectric or other organic
electronic devices.Comment: main manuscript: 17 pages and 7 figures; supplementary material: 6
pages and 7 figure
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