46 research outputs found
Beyond the simple Proximity Force Approximation: geometrical effects on the non-retarded Casimir interaction
We study the geometrical corrections to the simple Proximity Force
Approximation for the non-retarded Casimir force. We present analytical results
for the force between objects of various shapes and substrates, and between
pairs of objects. We compare the results to those from more exact numerical
calculations. We treat spheres, spheroids, cylinders, cubes, cones, and wings;
the analytical PFA results together with the geometrical correction factors are
summarized in a table.Comment: 18 pages, 19 figures, 1 tabl
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.
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
High-multipolar effects on the Casimir force: the non-retarded limit
We calculate exactly the Casimir force or dispersive force, in the
non-retarded limit, between a spherical nanoparticle and a substrate beyond the
London's or dipolar approximation. We find that the force is a non-monotonic
function of the distance between the sphere and the substrate, such that, it is
enhanced by several orders of magnitude as the sphere approaches the substrate.
Our results do not agree with previous predictions like the Proximity theorem
approach.Comment: 7 pages including 2 figures. Submitted to Europjysics Letter
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
Dispersive force between dissimilar materials: geometrical effects
We calculate the Casimir force or dispersive van der Waals force between a
spherical nanoparticle and a planar substrate, both with arbitrary dielectric
properties. We show that the force between a sphere and a plane can be
calculated through the interacting surface plasmons of the bodies. Using a
Spectral Representation formalism, we show that the force of a sphere made of a
material A and a plane made of a material B, differ from the case when the
sphere is made of B, and the plane is made of A. We found that the difference
depends on the plasma frequency of the materials, the geometry, and the
distance of separation between sphere and plane. The differences show the
importance of the geometry, and make evident the necessity of realistic
descriptions of the sphere-plane system beyond the Derjaguin Approximation or
Proximity Theorem Approximation
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
Plasmonic nature of van der Waals forces between nanoparticles
We propose a new approach to calculate van der Waals forces between
nanoparticles where the van der Waals energy can be reduced to the energy of
elementary surface plasmon oscillations in nanoparticles. The general theory is
applied to describe the interaction between 2 metallic nanoparticles and
between a nanoparticle and a perfectly conducting plane. Our results could be
used to prove experimentally the existence of plasmonic molecules and to
elaborate new control mechanisms for the adherence of nanoparticles between
each other or onto surfaces.Comment: 4 pages 5 figure