4,504 research outputs found
Synthesis of single-component metallic glasses by thermal spray of nanodroplets on amorphous substrates
We show that single component metallic glasses can be synthesized by thermal spray coating of nanodroplets onto an amorphous substrate. We demonstrate this using molecular dynamics simulations of nanodroplets up to 30 nm that the spreading of the nanodroplets during impact on a substrate leads to sufficiently rapid cooling (10^(12)â10^(13) K/s) sustained by the large temperature gradients between the thinned nanodroplets and the bulk substrate. However, even under these conditions, in order to ensure that the glass transition outruns crystal nucleation, it is essential that the substrate be amorphous (eliminating sites for heterogeneous nucleation of crystallization)
Desorption Dynamics of Heavy Alkali Metal Atoms (Rb, Cs) off the Surface of Helium Nanodroplets
We present a combined ion imaging and density functional theory study of the
dynamics of the desorption process of rubidium and cesium atoms off the surface
of helium nanodroplets upon excitation of the perturbed and states,
respectively. Both experimental and theoretical results are well represented by
the pseudodiatomic model for effective masses of the helium droplet in the
desorption reaction of m_eff/m_He~10 (Rb) and 13 (Cs). Deviations from this
model are found for Rb excited to the 6p state. Photoelectron spectra indicate
that the dopant-droplet interaction induces relaxation into low-lying
electronic states of the desorbed atoms in the course of the ejection process.Comment: in press, J. Phys. Chem. A (2014
Evolution of dopant-induced helium nanoplasmas
Two-component nanoplasmas generated by strong-field ionization of doped
helium nanodroplets are studied in a pump-probe experiment using few-cycle
laser pulses in combination with molecular dynamics simulations. High yields of
helium ions and a pronounced, droplet size-dependent resonance structure in the
pump-probe transients reveal the evolution of the dopant-induced helium
nanoplasma. The pump-probe dynamics is interpreted in terms of strong inner
ionization by the pump pulse and resonant heating by the probe pulse which
controls the final charge states detected via the frustration of electron-ion
recombination
Coalescence driven self-organization of growing nanodroplets around a microcap
The coalescence between growing droplets is important for the surface
coverage and spatial arrangements of droplets on surfaces. In this work, total
internal reflection fluorescence (TIRF) microscopy is utilized to in-situ
investigate the formation of nanodroplets around the rim of a polymer microcap,
with sub-micron spatial and millisecond temporal resolution. We observe that
the coalescence among droplets occurs frequently during their growth by solvent
exchange. Our experimental results show that the position of the droplet from
two merged droplets is related to the size of the parent droplets. The position
of the coalesced droplet and the ratio of parent droplet sizes obey a scaling
law, reflecting a coalescence preference based on the size inequality. As a
result of droplet coalescence, the angles between the centroids of two
neighbouring droplets increase with time, obeying a nearly symmetrical
arrangement of droplets at various time intervals. The evolution of the
position and number from coalescence of growing droplets is modelled. The
mechanism for coalescence driven self-organization of growing droplets is
general, applicable to microcaps of different sizes and droplets of different
liquids. The understanding from this work may be valuable for positioning
nanodroplets by nucleation and growth without using templates.Comment: 10 pages, 9 figure
Wave packet dynamics in triplet states of Na2 attached to helium nanodroplets
The dynamics of vibrational wave packets excited in Na2 dimers in the triplet
ground and excited states is investigated by means of helium nanodroplet
isolation (HENDI) combined with femtosecond pump-probe spectroscopy. Different
pathways in the employed resonant multi-photon ionization scheme are
identified. Within the precision of the method, the wave packet dynamics
appears to be unperturbed by the helium droplet environment
The structure and energetics of He and He nanodroplets doped with alkaline earth atoms
We present systematic results, based on density functional calculations, for
the structure and energetics of He and He nanodroplets doped with
alkaline earth atoms. We predict that alkaline earth atoms from Mg to Ba go to
the center of He drops, whereas Ca, Sr, and Ba reside in a deep dimple at
the surface of He drops, and Mg is at their center. For Ca and Sr, the
structure of the dimples is shown to be very sensitive to the He-alkaline earth
pair potentials used in the calculations. The transition
of strontium atoms attached to helium nanodroplets of either isotope has been
probed in absorption experiments. The spectra show that strontium is solvated
inside He nanodroplets, supporting the calculations. In the light of our
findings, we emphasize the relevance of the heavier alkaline earth atoms for
analyzing mixed He-He nanodroplets, and in particular, we suggest their
use to experimentally probe the He-He interface.Comment: Typeset using Revtex, 20 pages and 8 Postscript file
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