92 research outputs found
Influence of random roughness on the Casimir force at small separations
The influence of random surface roughness of Au films on the Casimir force is
explored with atomic force microscopy in the plate-sphere geometry. The
experimental results are compared to theoretical predictions for separations
ranging between 20 and 200 nm. The optical response and roughness of the Au
films were measured and used as input in theoretical predictions. It is found
that at separations below 100 nm, the roughness effect is manifested through a
strong deviation from the normal scaling of the force with separation distance.
Moreover, deviations from theoretical predictions based on perturbation theory
can be larger than 100%.Comment: 18, 5 figure
Metastability and the Casimir Effect in Micromechanical Systems
Electrostatic and Casimir interactions limit the range of positional
stability of electrostatically-actuated or capacitively-coupled mechanical
devices. We investigate this range experimentally for a generic system
consisting of a doubly-clamped Au suspended beam, capacitively-coupled to an
adjacent stationary electrode. The mechanical properties of the beam, both in
the linear and nonlinear regimes, are monitored as the attractive forces are
increased to the point of instability. There "pull-in" occurs, resulting in
permanent adhesion between the electrodes. We investigate, experimentally and
theoretically, the position-dependent lifetimes of the free state (existing
prior to pull-in). We find that the data cannot be accounted for by simple
theory; the discrepancy may be reflective of internal structural instabilities
within the metal electrodes.Comment: RevTex, 4 pages, 4 figure
Facies analysis, glauconite distribution and sequence stratigraphy of the middle Eocene Qarara Formation, El-Minya area, Egypt
AbstractThe Qarara Formation consists mainly of shale at the base and overlain by limestone at the top. The formation is Middle Eocene (Lutetian) in age. Three sections located at the eastern bank of the Nile River in El-Minya Province have been measured, described, and sampled. These sections from north to south are: Gebel Qarara, El-Sheikh Fadl, and Gebel El-Ahmar.The main microfacies identified in the studied sections are: silty claystone, silty shale, fossiliferous glauconite, glauconitic (green) sand, glauconitic fossiliferous ironstone, glauconitic bioclastic wacke-packstone, glauconitic bioclastic lime-mudstone-wackestone. These microfacies have been deposited in shallow open marine environment.Collectively the studied rocks contain two principal facies: lower argillaceous facies and upper carbonate facies that separated by glauconitic fossiliferous ironstone bed. The lower argillaceous part represents highstand systems tract (HST), whereas the upper carbonate part represents transgressive systems tract (TST). The glauconitic fossiliferous ironstone bed is recognized as a sequence boundary (SB)
Stiction, Adhesion Energy and the Casimir Effect in Micromechanical Systems
We measure the adhesion energy of gold using a micromachined doubly-clamped
beam. The stress and stiffness of the beam are characterized by measuring the
spectrum of mechanical vibrations and the deflection due to an external force.
To determine the adhesion energy we induce stiction between the beam and a
nearby surface by capillary forces. Subsequent analysis yields a value J/m that is a factor of approximately six smaller than predicted
by idealized theory. This discrepancy may be resolved with revised models that
include surface roughness and the effect of adsorbed monolayers intervening
between the contacting surfaces in these mesoscopic structures.Comment: RevTex, 4 pages, 4 eps figure
Efficient out-coupling and beaming of Tamm optical states via surface plasmon polariton excitation
We present evidence of optical Tamm states to surface plasmon polariton (SPP) coupling. We experimentally demonstrate that for a Bragg stack with a thin metal layer on the surface, hybrid Tamm-SPP modes may be excited when a grating on the air-metal interface is introduced. Out-coupling via the grating to free space propagation is shown to enhance the transmission as well as the directionality and polarization selection for the transmitted beam. We suggest that this system will be useful on those devices, where a metallic electrical contact as well as beaming and polarization control is needed
Casimir forces on a silicon micromechanical chip
Quantum fluctuations give rise to van der Waals and Casimir forces that
dominate the interaction between electrically neutral objects at sub-micron
separations. Under the trend of miniaturization, such quantum electrodynamical
effects are expected to play an important role in micro- and nano-mechanical
devices. Nevertheless, utilization of Casimir forces on the chip level remains
a major challenge because all experiments so far require an external object to
be manually positioned close to the mechanical element. Here, by integrating a
force-sensing micromechanical beam and an electrostatic actuator on a single
chip, we demonstrate the Casimir effect between two micromachined silicon
components on the same substrate. A high degree of parallelism between the two
near-planar interacting surfaces can be achieved because they are defined in a
single lithographic step. Apart from providing a compact platform for Casimir
force measurements, this scheme also opens the possibility of tailoring the
Casimir force using lithographically defined components of non-conventional
shapes
Efficient out-coupling and beaming of Tamm optical states via surface plasmon polariton excitation
We present evidence of optical Tamm states to surface plasmon polariton (SPP) coupling. We experimentally demonstrate that for a Bragg stack with a thin metal layer on the surface, hybrid Tamm-SPP modes may be excited when a grating on the air-metal interface is introduced. Out-coupling via the grating to free space propagation is shown to enhance the transmission as well as the directionality and polarization selection for the transmitted beam. We suggest that this system will be useful on those devices, where a metallic electrical contact as well as beaming and polarization control is needed
Comment on the sign of the Casimir force
I show that reflection positivity implies that the force between any mirror
pair of charge-conjugate probes of the quantum vacuum is attractive. This
generalizes a recent theorem of Kenneth and Klich to interacting quantum
fields, to arbitrary semiclassical bodies, and to quantized probes with
non-overlapping wavefunctions. I also prove that the torques on
charge-conjugate probes tend always to rotate them into a mirror-symmetric
position.Comment: 13 pages, 1 figure, Latex file. Several points clarified and
expanded, two references added
Normal and Lateral Casimir Forces between Deformed Plates
The Casimir force between macroscopic bodies depends strongly on their shape
and orientation. To study this geometry dependence in the case of two deformed
metal plates, we use a path integral quantization of the electromagnetic field
which properly treats the many-body nature of the interaction, going beyond the
commonly used pairwise summation (PWS) of van der Waals forces. For arbitrary
deformations we provide an analytical result for the deformation induced change
in Casimir energy, which is exact to second order in the deformation amplitude.
For the specific case of sinusoidally corrugated plates, we calculate both the
normal and the lateral Casimir forces. The deformation induced change in the
Casimir interaction of a flat and a corrugated plate shows an interesting
crossover as a function of the ratio of the mean platedistance H to the
corrugation length \lambda: For \lambda \ll H we find a slower decay \sim
H^{-4}, compared to the H^{-5} behavior predicted by PWS which we show to be
valid only for \lambda \gg H. The amplitude of the lateral force between two
corrugated plates which are out of registry is shown to have a maximum at an
optimal wavelength of \lambda \approx 2.5 H. With increasing H/\lambda \gtrsim
0.3 the PWS approach becomes a progressively worse description of the lateral
force due to many-body effects. These results may be of relevance for the
design and operation of novel microelectromechanical systems (MEMS) and other
nanoscale devices.Comment: 20 pages, 5 figure
Finite temperature Casimir effect in piston geometry and its classical limit
We consider the Casimir force acting on a -dimensional rectangular piston
due to massless scalar field with periodic, Dirichlet and Neumann boundary
conditions and electromagnetic field with perfect electric conductor and
perfect magnetic conductor boundary conditions. It is verified analytically
that at any temperature, the Casimir force acting on the piston is always an
attractive force pulling the piston towards the interior region, and the
magnitude of the force gets larger as the separation gets smaller. Explicit
exact expressions for the Casimir force for small and large plate separations
and for low and high temperatures are computed. The limits of the Casimir force
acting on the piston when some pairs of transversal plates are large are also
derived. An interesting result regarding the influence of temperature is that
in contrast to the conventional result that the leading term of the Casimir
force acting on a wall of a rectangular cavity at high temperature is the
Stefan--Boltzmann (or black body radiation) term which is of order ,
it is found that the contributions of this term from the interior and exterior
regions cancel with each other in the case of piston. The high temperature
leading order term of the Casimir force acting on the piston is of order ,
which shows that the Casimir force has a nontrivial classical
limit
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