69 research outputs found
Wetting Phase Transition at the Surface of Liquid Ga-Bi alloys: An X-ray Reflectivity Study
X-ray reflectivity measurements of the binary liquid Ga-Bi alloy reveal a
dramatically different surface structure above and below the monotectic
temperature C.
A Gibbs-adsorbed Bi monolayer resides at the surface at both regimes.
However, a 30 {\AA} thick, Bi-rich wetting film intrudes between the Bi
monolayer and the Ga-rich bulk for .
The internal structure of the wetting film is determined with {\AA}
resolution, showing a theoretically unexpected concentration gradient and a
highly diffuse interface with the bulk phase.Comment: 5 RevTex pages, 3 figures, Phys. Rev. Let
X-ray study of the liquid potassium surface: structure and capillary wave excitations
We present x-ray reflectivity and diffuse scattering measurements from the
liquid surface of pure potassium. They strongly suggest the existence of atomic
layering at the free surface of a pure liquid metal with low surface tension.
Prior to this study, layering was observed only for metals like Ga, In and Hg,
the surface tensions of which are 5-7 fold higher than that of potassium, and
hence closer to inducing an ideal "hard wall" boundary condition. The
experimental result requires quantitative analysis of the contribution to the
surface scattering from thermally excited capillary waves. Our measurements
confirm the predicted form for the differential cross section for diffuse
scattering, where , over a range of and that is larger than
any previous measurement. The partial measure of the surface structure factor
that we obtained agrees with computer simulations and theoretical predictions.Comment: 7 pages, 7 figures; published in Phys. Rev.
Antiferromagnetic Domain Wall Engineering in Chromium Films
We have engineered an antiferromagnetic domain wall by utilizing a magnetic
frustration effect of a thin iron cap layer deposited on a chromium film.
Through lithography and wet etching we selectively remove areas of the Fe cap
layer to form a patterned ferromagnetic mask over the Cr film. Removing the Fe
locally removes magnetic frustration in user-defined regions of the Cr film. We
present x-ray microdiffraction microscopy results confirming the formation of a
90{\deg} spin-density wave propagation domain wall in Cr. This domain wall
nucleates at the boundary defined by our Fe mask.Comment: submitted to AP
Surface oxidation of liquid Sn
We report the results of an x-ray scattering study that reveals oxidation
kinetics and formation of a previously unreported crystalline phase of SnO at
the liquid-vapour interface of Sn. Our experiments reveal that the pure liquid
Sn surface does not react with molecular oxygen below an activation pressure of
\~5.0*10-6 Torr. Above that pressure a rough solid Sn oxide grows over the
liquid metal surface. Once the activation pressure has been exceeded the
oxidation proceeds at pressures below the oxidation pressure threshold. The
observed diffraction pattern associated with the surface oxidation does not
match any of the known Sn oxide phases. The data have an explicit signature of
the face-centred cubic structure, however it requires lattice parameters that
are about 9% smaller than those reported for cubic structures of high-pressure
phases of Sn oxides.
Keywords: X-ray scattering, diffraction, and reflection; Oxidation; Surface
chemical reaction; Surface structure, morphology, roughness, and topography;
Tin; Tin oxides; Liquid surfaces; Polycrystalline thin filmsComment: 18 pages, 6 figures, 1 table; Submitted to Surface Scienc
Solvent Mediated Assembly of Nanoparticles Confined in Mesoporous Alumina
The controlled self-assembly of thiol stabilized gold nanocrystals in a
mediating solvent and confined within mesoporous alumina was probed in situ
with small angle x-ray scattering. The evolution of the self-assembly process
was controlled reversibly via regulated changes in the amount of solvent
condensed from an undersaturated vapor. Analysis indicated that the
nanoparticles self-assembled into cylindrical monolayers within the porous
template. Nanoparticle nearest-neighbor separation within the monolayer
increased and the ordering decreased with the controlled addition of solvent.
The process was reversible with the removal of solvent. Isotropic clusters of
nanoparticles were also observed to form temporarily during desorption of the
liquid solvent and disappeared upon complete removal of liquid. Measurements of
the absorption and desorption of the solvent showed strong hysteresis upon
thermal cycling. In addition, the capillary filling transition for the solvent
in the nanoparticle-doped pores was shifted to larger chemical potential,
relative to the liquid/vapor coexistence, by a factor of 4 as compared to the
expected value for the same system without nanoparticles.Comment: 9 pages, 9 figures, appeared in Phys. Rev.
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