416 research outputs found
The role of geometry on dispersive forces
The role of geometry on dispersive forces is investigated by calculating the
energy between different spheroidal particles and planar surfaces, both with
arbitrary dielectric properties. The energy is obtained in the non-retarded
limit using a spectral representation formalism and calculating the interaction
between the surface plasmons of the two macroscopic bodies. The energy is a
power-law function of the separation of the bodies, where the exponent value
depends on the geometrical parameters of the system, like the separation
distance between bodies, and the aspect ratio among minor and major axes of the
spheroid.Comment: Presneted at QFEXT05, Barcelona 2005. Submitted to J. Phys.
Controlled Anisotropic Deformation of Ag Nanoparticles by Si Ion Irradiation
The shape and alignment of silver nanoparticles embedded in a glass matrix is
controlled using silicon ion irradiation. Symmetric silver nanoparticles are
transformed into anisotropic particles whose larger axis is along the ion beam.
Upon irradiation, the surface plasmon resonance of symmetric particles splits
into two resonances whose separation depends on the fluence of the ion
irradiation. Simulations of the optical absorbance show that the anisotropy is
caused by the deformation and alignment of the nanoparticles, and that both
properties are controlled with the irradiation fluence.Comment: Submitted to Phys. Rev. Lett. (October 14, 2005
Casimir interactions in graphene systems
The non-retarded Casimir interaction (van der Waals interaction) between two
free standing graphene sheets as well as between a graphene sheet and a
substrate is determined. An exact analytical expression is given for the
dielectric function of graphene along the imaginary frequency axis within the
random phase approximation for arbitrary frequency, wave vector, and doping.Comment: 4 pages, 4 figure
Numerical study of the effect of structure and geometry on van der Waals forces
We use multipolar expansions to find the force on a gold coated sphere above
a gold substrate; we study both an empty gold shell and a gold coated
polystyrene sphere. We find four characteristic separation ranges. In the first
region, which for the empty gold shell occurs for distances, d, smaller than
the thickness of the coating, the result agrees with that on a solid gold
sphere and varies as d^(-2); for larger separations there is a region where the
force behaves as if the coating is strictly two dimensional and varies as
d^(-5/2); in the third region the dependence is more unspecific; in the forth
region when d is larger than the radius, the force varies as d^(-4). For
homogeneous objects of more general shapes we introduce a numerical method
based on the solution of an integral equation for the electric field over a
system of objects with arbitrary shapes. We study the effect of shape and
orientation on the van der Waals interaction between an object and a substrate
and between two objects.Comment: 8 pages, presented in the QFEXT07 conference, submitted to Journal of
Physics
First-Principles Studies of Hydrogenated Si(111)--77
The relaxed geometries and electronic properties of the hydrogenated phases
of the Si(111)-77 surface are studied using first-principles molecular
dynamics. A monohydride phase, with one H per dangling bond adsorbed on the
bare surface is found to be energetically favorable. Another phase where 43
hydrogens saturate the dangling bonds created by the removal of the adatoms
from the clean surface is found to be nearly equivalent energetically.
Experimental STM and differential reflectance characteristics of the
hydrogenated surfaces agree well with the calculated features.Comment: REVTEX manuscript with 3 postscript figures, all included in uu file.
Also available at http://www.phy.ohiou.edu/~ulloa/ulloa.htm
Spectral representation of the Casimir Force Between a Sphere and a Substrate
We calculate the Casimir force in the non-retarded limit between a spherical
nanoparticle and a substrate, and we found that high-multipolar contributions
are very important when the sphere is very close to the substrate. We show that
the highly inhomegenous electromagnetic field induced by the presence of the
substrate, can enhance the Casimir force by orders of magnitude, compared with
the classical dipolar approximation.Comment: 5 page + 4 figures. Submitted to Phys. Rev. Let
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