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Dispersion Forces and Nano-Electro-Mechanical Systems |
keynote talks Monday, December 11, 2006 New developments in the Casimir effect C. Genet The Casimir force is an attractive
force arising between two mirrors in vacuum. It is named after the famous Dutch
physicist Hendrik Brugt
Gerhard Casimir who predicted its existence in 1948.
Compared with the ideal situation Casimir considered
at that time, a number of factors have to be taken into account when one wants
to describe correctly real Casimir force
measurements. I will review the influence of some main corrections coming from
material properties, finite temperature and surface roughness of the plates.
Furthermore, I will present some recent calculations on the Casimir
interaction between corrugated plates, which are not relying on the Proximity
Force Approximation. The plate corrugation leads to a lateral component of the Casimir force as well as to a Casimir
torque. A novel experimental approach for the
measure of the Casimir effect at large distances P. Antonini, G. Bressi, G. Carugno, G. Galeazzi, G.
Messineo, G. Ruoso We describe an experimental apparatus
and the measurement technique aimed to measure the Casimir
effect in the parallel plates configuration
in the 3-6 micrometer range. The apparatus is based on a mechanical resonator
and will use a homodyne detection technique to sense the Casimir force in the plane-parallel configuration. Calibrations show that a force of 5 x 10^{-11} N
can be measured with this set-up. This corresponds to the Casimir
force between the two 1 cm^{2} aluminium parallel plates at a distance of 5.5 micrometer.
It is possible to measure the built-in voltage and to control it with an accuracy of 1 mV,
that opens up the possibility to measure the Casimir
force at large distances. The minimum distance
between the surfaces so far obtained is 10 micrometer, limited by imperfect
parallelization, at level of 10^{-3} rad.
Improvement are in progress to increase the
parallelization at a level of 10^{-4} rad,
and to decrease other sources of systematic errors. Detectability
of dissipative motion in quantum vacuum through nanomechanical
structures and atomic physics detection schemes R. Onofrio I will discuss a feasibility study to detect the dynamical Casimir effect using nanomechanical
structures and cold atom systems. A high frequency mechanical resonator driven
in resonance is expected to create Casimir photons.
The photons are stored in a high quality electromagnetic cavity and detected through their interaction
with ultracold alkali atoms prepared in an inverted
population of hyperfine states, or with ultrasensitive
detection schemes based upon Rydberg states. A possible route to quantum control of
a nanomechanical resonator A. Cleland We are engaged in a project to investigate mechanical resonators
in the single-phonon quantum regime. The key to achieving quantum control of a
mechanical system is to use an extremely strong nonlinearity in either the
resonator or in its measurement system; we have chosen to use the latter. We
are coupling the highly nonlinear inductance of a Josephson phase qubit with a microwave frequency mechanical resonator,
which we hope will enable us to demonstrate the coherent creation and
manipulation of single phonons in the resonating element. The mechanical system
is a novel type of high quality factor, GHz frequency piezoelectric resonator,
which can have unprecedented quality factor in this frequency band. The quantum
mechanical properties of the resonators, especially in the single-phonon
regime, will be probed by the Josephson qubit, and we
plan to measure the single phonon T1 decay and T2 coherence times. I will
describe our progress to date in developing this unique system. Tuesday, December 12, 2006 Acoustic Casimir effect and its applications in MEMS R. Esquivel-Sirvent The most representative manifestation of the Casimir
effect is the attraction of two parallel neutral plates due to quantum vacuum
fluctuations. A classical analog of this effect was shown
experimentally by Larraza et al. [1], who placed two
parallel plates in the presence of acoustic white noise, showing that there was
a force between the plates similar to the Casimir
force. The theory of the acoustic Casimir effect for arbitrary materials was later presented
in [2]. Another important breakthrough
in acoustics has been achieved with MEM technologies giving rise to what is
known as nano phononics.
Examples include excitonic transport using surface
acoustic waves and more recently MEM resonators capable of generating sound at a frequency close to tera Hertz [3].
These examples are indicative of the possibility of rescaling acoustic
phenomena from the macroscopic to the micro and nano
scale. In this talk, the fundamentals of the experiment and theory of the
Acoustic Casimir effect are presented, showing the
differences and similarities with the quantum Casimir
effect. In particular, unlike the quantum effect, the acoustic case shows a
force that changes sign in a periodic way due to the finite bandwidth of the
noise. This allows the acoustic Casimir effect to be use as an actuating force in mems and nems, as will be
discussed in this talk. [1] A. Larraza, C.D. Holmes, R. T. Susbilla and B. Denardo, “An
acoustic Casimir Effect” ,
J. Acoust. Soc. Am. vol. 103 (1998) 276. [2] J.
Barcenas, L. Reyes and R. Esquivel-Sirvent, “ Acoustic Casimir
Pressure for Arbitrary Materials”, J. Acoust. Soc.
Am. vol. 116 (2004) 720. [3] A. Huynh, N. D. Lanzellotti-Kimura et al. “Subterahertz
Phonon Dynamics in Acoustic Nanocavities”, Phys. Rev.
Lett. vol. 97, (2006)
115502. Nanomechanical
sensing and metrology: Recent progress K. L. Ekinci Nanoelectromechanical systems (NEMS) have been at the center
of recent applied and fundamental research. This presentation will start with a
brief description of our recent work on nanomechanical
mass sensing. It will then outline some of the challenges involved in realizing
a practical NEMS mass sensor and focus on our efforts in addressing these
challenges. One of the challenges, namely the operation of a nanomechanical resonator in a rarefied gas atmosphere, has
led us to re-investigate a well-known fluid dynamics problem: Stokes’ second
problem of the oscillating plate in a fluid. At the frequencies of NEMS
motion, Stokes’ second problem needs to be reformulated in order to accurately
describe NEMS motion. On the other hand, our efforts to develop tunneling
displacement transducers have resulted in progress towards a functional
radiofrequency scanning tunneling microscope (STM). Dynamic Mode AFM
Measurements of the Casimir Force G. Torricelli and C. Binns We have used dynamic mode AFM to measure the Casimir
force between different geometric gold-coated shapes, including a 10µm diameter
Au-coated sphere, and Au surfaces. Due to the small size of the sphere we have
been able to demonstrate good agreement with the Lifshitz
model down to a separation of 55nm. For closer distances an increase in the
power-law of the force is observed due to surface roughness. Preliminary data
on the interaction between patterned surfaces will also be presented. Wednesday, December 13, 2006 Van der
Waals forces in dynamic fluctuation phenomena in double membrane films E. Kats We investigate eigen-modes of double
membrane films. The excitation spectrum includes overdamped
squeezing mode and elastic modes. We demonstrate that thermal fluctuations and
Van der Waals forces essentially modify the modes due
to non-linear coupling to the transverse shear viscous hydrodynamic mode. Casimir
forces and the thinning of superfluid Helium films J. Rudnick Recent experiments by Garcia, Chan and co-workers provide
striking evidence for Casimir forces mediated by both
critical fluctuations and Goldstone bosons. I will comment on three aspects of
their observations and the system they investigate: a) thinning of the film
well inside the superfluid phase, b) the relatively
substantial thinning of the film in the critical regime and c) the possible
influence of the Kosterlitz-Thouless transition on
the thinning of the Helium film Cluster-Formation in DNA-Coated
Colloidal Systems T. Schmatko,
B. Borzogui, N. Geerts, E.
Eiser, W.C.K. Poon, and
D. Frenkel Over the past ten years, researchers have focused on building
new types of nanomaterials based on DNA assemblies,
involving the specific recognition of two complementary strands. If at the
beginning the interest was essentially for the determination of mismatch between base pairs within the
structure of the genetic code^{1}, the attention moves to a more
material oriented goal, to promote for instance the creation of photonic
crystals. Indeed, such specific assemblies have the ability to form reversible
networks, (via the melting of the DNA double helix) with different degrees of
order, which can be tuned by the strength of the interactions involved in the
system. As far as we know, all groups have directed their efforts on short
single stranded (ss) DNA. However a recent
theoretical work predicts that very long flexible DNA, with a polymer like
behavior, would allow the formation of various phases (from an interesting
diamond crystal like to a 2D membrane like phase) that are forbidden for short
DNA-colloids systems^{2}. This paper directly inspires our
work. We present the first experimental results of aggregates of DNA coated
colloids made with l-phage DNA - a long double stranded DNA molecule of 16mm length. Confocal
imaging shows that the formation of a cluster phase is strongly temperature
dependent, with a very interesting reversible behavior around room temperature.
We find that the inter-colloidal distance within the cluster is much smaller
than the gyration radius of the DNA molecule. In order to understand better
these observations, we compare our results with molecular dynamic simulations:
we first focus on the attraction induced by bridging of polymers between
colloids and then we look at the temperature effect on flexible polyelectrolyte
in varying mono-valent salt concentrations. ^{1 }C.
A. Mirkin, R. L. Letsinger,
R. C. Mucic, et al., Nature 382, 607 (1996). ^{2 }A. V. Tkachenko,
Phys. Rev. Lett 89, 148303 (2002). Pull-in
and stability analyses of NEMS switches due to dispersion forces Ya-Pu Zhao It has been
recognized recently that vacuum induced forces played considerable roles in
micro-, nano- and quantum-electromechanical systems (MEMS,
NEMS and QEMS) with typical sizes in the micro- and nano-meter
ranges. Actuation, pull-in
and stiction are
the three major concerns for the application of Casimir
and van der Waals forces in MEMS, NEMS and QEMS. My
presentation will be in two major parts: First, a brief survey will be given
about the research in my group on MEMS, NEMS, surface-stress based biosensors
and molecular motors [1-7]. Second, a brief review will be presented about the
research of pull-in and stability analyses of MEMS/NEMS switches by Casimir and van der Waals forces
[8-13]. The dimensionless equilibrium
equations of electrostatic torsional actuators are
presented with the consideration of the vdW and Casimir torque. With the vdW and Casimir effects, the inherent instability of the actuators
is dependent on the scales of structures. The critical tilting angle keeps
constant approximately only in micron or larger scales, but it is not constant
when the gap between two plates is in nano-scales.
The pull-in voltage is also lower than that without consideration of vdW and Casimir torques. Without
the electrostatic torque, the pull-in instability can still occur with small
angle perturbation, and a critical gap is derived. Furthermore, the qualitative
analyses of the equations of motion show that the equilibrium points of the
corresponding autonomous system include stable focus point and center points,
as well as unstable saddle points. The Hopf
bifurcation points and fork bifurcation points also exist in the system. The
phase portraits show the periodic, heteroclinic and homoclinic orbits. Keywords: Pull-in
instability; NEMS switches; Casimir and van der Waals forces; Hopf
bifurcation; periodic, heteroclinic and homoclinic orbits. References
1.
Ren Q, Zhao YP, Han L and Zhao HB. A nanomechanical device based on light-driven proton pumps. Nanotechnology,
17: 1778–1785 (2006). 2.
Ren Q, Zhao YP, Yue
JC and Cui YB. Biological application of multi-component nanowires
in hybrid devices powered by F1-ATPase motors. Biomedical Microdevices, 8(3): 201-208 (2006). 3.
Zhang Y and Zhao YP. Applicability range of Stoney's
formula and modified formulae for a film/substrate bilayer.
Journal of Applied Physics, 99: 053513 (2006). 4.
He FQ and Zhao YP. Growth of ZnO nanotetrapods with hexagonal crown. Applied Physics
Letters, 88: 193113 (2006). 5.
Guo JG and Zhao YP. The size-dependent
elastic properties of nanocrystals with surface
effects. Journal of Applied Physics, 98: 074306 (2005). 6.
Yang CY and Zhao YP. Influences of hydration force and elastic
strain energy on stability of solid film in very thin solid-on-liquid
structure. Journal of Chemical Physics, 120(11): 5366-5376 (2004). 7.
Zhao YP, Wang LS and 8.
Lin WH and Zhao YP. Dynamics behavior of nanoscale
electrostatic actuators. Chinese Physics Letters, 20(11): 2070-2073
(2003). 9.
Wang GW, Zhang Y, Zhao YP and Yang GT. Pull-in stability study
of nanotubes under van der
Waals forces influence. Journal of Micromechanics and Microengineering,
14:1119-1125(2004). 10.
Lin WH and Zhao YP. Nonlinear behavior for nanoscales
electrostatic actuators with Casimir force. Chaos,
Solitons & Fractals, 23: 1777–1785 (2005). 11.
Lin WH and Zhao YP. Casimir effect on
the pull-in parameters of nanometer switches. Microsystem
Technologies, 11: 80-85 (2005). 12.
Guo JG and Zhao YP. Dynamic stability of
electrostatic torsional actuators with van der Waals effect. International Journal of Solids and
Structures, 43: 675-685 (2006). 13.
Guo JG and Zhao YP. Influence of van der Waals and Casimir forces on
electrostatic torsional actuators. Journal of Microelectromechanical Systems, 13(6): 1027-1035 (2004). The Shape Dependence of
Fluctuation-Induced Forces M. Kardar The Casimir force is an attraction
between parallel conducting plates due to quantum fluctuations of the
electromagnetic (EM) field. Thermal fluctuations of correlated fluids (such as
critical mixtures or superfluids) are also modified
by boundaries, resulting in similar interactions. A nice demonstration is
provided by the thinning of a wetting film of helium at and below the superfluid transition. Quantitative understanding of the
latter requires inclusion of surface undulations. The EM Casimir
force is also modified for corrugated surfaces in non-trivial fashion. I shall
also discuss other non-trivial geometries, in particular addressing the
possibility of a repulsive force for a piston, and the force between a plate
and a cylinder. Thursday, December 14, 2006 Measurements of static
and dynamic forces between nonpolar surfaces in
water: is the hydrophobic force a type of dispersion force? J. Israelachvili Recent improvements of direct force measuring techniques using
the Surface Forces Apparatus (SFA) have allowed for direct measurement of the
hydrophobic interaction potential between two surfaces in the distance regime
from 100 Ĺ down to contact. There appears to be a rapidly decaying short-range
force extending out to 10-20 Ĺ followed by a more slowly decaying interaction
to ~100 Ĺ. The unusual polarizability and dielectric
properties of water could be responsible for this interaction as a modified van
der Waals attraction with a short-range component
analogous to the non-retarded interaction and a longer ranged component
analogous to the retarded force. Non-equilibrium thermal
effects in the Van der Waals forces L. Pitaevskii Long distance behaviour of the thermal
Van-der Waals-Lifshitz
force between an atom and the surface of a substrate is investigated in the absence
of thermal equilibrium. When temperatures of the substrate and the environment
are different, the new decay law 1/z^{3} of the force on large
distances is discovered, which is slower than at thermal equilibrium. The force
is of a quantum nature and attractive or repulsive depending on whether the
temperature of the substrate is higher or smaller than the one of the
environment. An elementary derivation of this law is presented. It is based on
a picture of evanescent waves, created in vacuum by the black body radiation
impinging on the surface near the angle of total reflection. Experimental prove
of the theory by E. Cornell group in JILA is discussed. New effects in
interaction between macroscopic bodies are predicted. Casimir
energies, stresses, and forces: When are they well defined and how can they be
estimated? R. Jaffe Casimir pointed out
that the zero point energy of a quantum field changes when boundary
conditions are applied, and that the change gives rise to a force that can be calculated
for simple geometries. Modern experimental techniques enable precision
measurements of Casimir forces. However, attempts to
compute the Casimir energy for various geometries and
boundary conditions are both technically difficult and plagued with
divergences. Unlike the divergences of ordinary quantum field theory, that can
be rendered finite by a renormalization program, divergences in the Casimir energy indicate that it depends on the cutoffs that
distinguish real materials from idealized boundary conditions. I discuss where
the divergences come from and when finite Casimir
effects can be defined. Then I describe a semiclassical
approximation based on ray optics that enables one to estimate Casimir forces for a variety of experimentally interesting
geometries. Friday, December 15, 2006 Oscillating cantilever as probe of sphere/plane non contact interactions J. Chevrier, G.
Jourdan, M. Hrouzek, G. Torricelli, M. Rodrigučs^{,}, O. Dhez, F. Comin Measurements of non contact forces between interacting surfaces
meet nowadays a large interest due to the capability of MEMS and NEMS
preparation especially as resonant nano-oscillators.
Surfaces separated by vacuum gap of 100nm can strongly interact through both Casimir force and electrostatic interactions. As well known, the necessary quantitative measurements of non
contact interactions between surfaces face some severe difficulties: -
These forces can spatially vary over many orders of magnitude on
hundreds of nanometers. A consequence is
that a reasonable detection level at large distance is hardly compatible with
mechanical stability at short distances. -
Non linear effects are hardly avoidable. -
Important noises inherent to the coupling with the external
world (1/f, temperature, detection...) linked with dissipation. Thermally
induced Brownian motion is often the dominant source of noise at resonance and
is a limit at large distances. Measurements on real micro/nanosystems
at room temperature have led many groups to build dedicated force machines and
to apply specific measurement strategies. Here in introduction we shall first
describe based on a commercial Omicron AFM the measured interplay between Casimir force and Brownian motion, then the changes in the
lever damping induced by the Johnson noise in the electromechanical coupling.
Second, a “home made” force machine based on a Fabry Pérot cavity for detection of displacement will be
presented. It is designed for investigation of light mechanical effects from
visible to X ray: bolometric effect, Casimir force
and radiation pressure especially on structured surfaces at sub-micrometer
scale. With this machine, measurement of the Casimir
force gradient from 50nm up to about 500nm will be demonstrated and detailed
analysis of the lever Brownian vibrations with/without sphere will be
considered for the two first modes of vibration. Finally we shall describe a
measurement method that could be considered for spatially rapidly varying
forces based on cold damping techniques. As usual, cold damping here refers to
damping through an external feedback loop of the thermal fluctuations and it is
illustrated in the figure below: the spectral density of thermal displacement
is measured at a lever mechanical resonance. As the feedback loop gain is
increased, the temperature associated with this particular resonance mode
decreases from 300K down to 30K, the largest damping allowed by the noise of
optical detection. Figure caption: A fast capacitive actuation driven by a feedback loop based on the
cantilever speed progressively cancels the thermal fluctuations as the loop
gain is increased. Corresponding author contact
information: joel.chevrier@grenoble.cnrs.fr A theorem about the sign
of Casimir forces between dielectric bodies I. Klich It is well known that Casimir forces
between two flat mirrors are attractive. However, due to non-trivial dependence
on geometry, suggestions were raised in which such forces may be repulsive between
bodies of carefully chosen shape, such as two conducting hemispheres. Such
proposals might be of importance in nano-mechanical
applications as a solution to the stiction problem,
and raise fundamental questions regarding Casimir
forces. Therefore, it is of fundamental interest to understand the validity of
such proposals. In the talk I will discuss recent results dealing with this
problem. I will show that under symmetry conditions the Casimir
force between two dielectric bodies is always attractive, independent of the
exact form of the bodies or dielectric properties. Due to it's generality we expect the theorem
to play a role in other physical systems where fluctuating fields interact with
immersed bodies. Contributed
talks Monday, December 11, 2006 Dispersion
interaction between dielectrics with non-ideal geometries R. Golestanian In this talk, a formulation will be presented for the
calculation of theelectromagnetic--fluctuation forces
for dielectric objects of arbitrary geometry at small separations, as a perturbative expansion in the dielectric contrast. The
resulting Lifshitz energy automatically takes on the
form of a series expansion of the different many-body contributions. The formulation
has the advantage that the divergent contributions can be readily determined
and subtracted off, and thus makes a convenient scheme for realistic numerical
calculations, which could be useful in designing nano-scale
mechanical devices. Exploring the interactions of gold nanoparticles
with their near-field environment: plasmonic van der Waals-Casimir interactions U. Hakanson,
M. Agio, S. Kühn, L. Rogobete, V. Sandoghdar We present an
experiment in which the interaction between a single gold nanoparticles and another particle or a substrate
can be tuned by control of their separation using scanning probe technology. By
recording the plasmon resonance of the coupled system
as a function of the polarization of the incident field and the inter-particle
distance, we explore the Casimir-van der Waals type interaction between the two particles. The
distinct spectral changes of the scattered light from the particle pair are in
good agreement with the outcome of finite difference time-domain (FDTD) calculations.
We discuss the implications of our measurements and experimental technique for
precise measurements of the Casimir type interactions
and for studies of field enhancement in optical processes. Tuesday, December 12, 2006 Interacting surface plasmons
and the role of geometry on dispersive forces C.
E. Román-Velázquez and Cecilia Noguez The role of geometry on dispersive
forces is investigated by studying the force between different spheroidal particles and planar surfaces, due to the
interaction between surface plasmons. The force is
obtained, in the non-retarded limit, using a spectral
representation formalism and calculating the Coulomb interaction between the
surface plasmons of the macroscopic bodies with
arbitrary dielectric properties. When the particle is close to the substrate
the multipolar interactions induced by the substrate
modify the electromagnetic response of the system. It is found that the force
is a power-law function of the minimum separation between bodies, where the
exponent value depends on the geometrical parameters of the system, like the
aspect ratio among minor and major axes of the spheroid, as well as on the
separation itself. In this work, we study in detail the dispersive force for
particles with the same curvature but different aspect ratios that shows that
in this case the Derjaguin Approximation is not
applicable. We analyze in detail the interaction of oblate and prolate particles with a substrate. The influence of the
geometry on dispersive forces can be very important for experiments using
Atomic Force Microscopy. Casimir forces and geometry T. Emig According to quantum mechanics, all
space is filled with electromagnetic vibrations, even at ultracold
temperatures. Two parallel uncharged metal plates limit the number of
vibrations between them, creating an effective inward pressure that pushes the
plates together -- known as Casimir effect. But the
most challenging aspect of this effect is its dependence on geometry. Due to
its topological nature, Casimir forces can be
controlled by tailoring the shapes of the interacting bodies. However, due to
the diffraction of vibrations and the non-additivity
of fluctuation induced interactions, there is no intuitive way to tell how the
force will change with the object's shape. In this talk, I shall present a brief
introduction to Casimir forces, and a new approach to
study the geometry dependence of this interaction. An exact trace formula is
presented which yields the relevant information of the spectrum of the
Helmholtz wave equation in arbitrary geometries. Perturbative
and numerical implementations of this formula yield new and unexpected forms
for the Casimir interaction in rather simple
geometries. Implications on the non-linear dynamics of nanomechanical
systems and actuation schemes will be presented. Low-frequency response of
metals and related problems with the Casimir force V. B. Svetovoy Dependence of the Casimir force on the
dielectric function of materials is discussed. For metals the low-frequency
response is important for separations as small as 50 nm. Known data on gold
dielectric properties are reviewed and the methods to extract the Drude parameters from the data are discussed. Significant
dependence of the material response on the conditions of sample preparation is
reviled. Variation of the force due to this effect is estimated as large as
5-6%. Low-frequency behavior of metals gave rise to a principal problem with
the thermal Casimir force: there is no continuous
transition between real and ideal metals. Moreover, it seems like the Casimir entropy is not going to zero with the temperature.
Both of these problems are discussed in simple physical terms. It is
demonstrated that no contradictions with known physics exist. Wednesday, December 13, 2006 Thermal correction to the
Casimir force and radiative
heat transfer G. Bimonte We compare the theories of the thermal Casimir
force and of the radiative heat transfer through a
vacuum gap between real metal plates. It is shown that different models for the
reflection coefficients of the surfaces lead to largely different predictions
for the amount of heat transfer at submicron separations. A modification of the
impedance of infrared optics is suggested taking into account relaxation
processes. The power of radiative heat transfer
predicted from this impedance is several times less than previous predictions
due to different contributions from the transverse electric evanescent waves.
New measurements of the radiative heat transfer are
required to find out the adequate description of a metal in the theory of
electromagnetic fluctuations. Thermal effects of the Casimir force for
surface-atom and surface-surface configurations M. Antezza The Casimir-Polder force characterizes the surface-atom force
originating from the fluctuations of the electromagnetic field. Such a force
and its cousin, the van der Waals force, are not only
fascinating scientifically but also important technologically because of their
relevance for instance to atomic force microscopy and to MEMS. Our work [1] focused on the
theoretical study of the temperature dependence of the force both at
equilibrium and out of thermal equilibrium.
In particular, when the temperature of the surface is different from the
temperature of free space, the force is predicted to decay more slowly at large
distances and to exhibit a stronger dependence on the temperature. By positioning a Rb-87 Bose-Einstein
condensate a few microns from a dielectric surface and resonantly exciting it
into a mechanical dipole oscillation [2], the JILA team has recently observed
changes in the collective oscillation frequency that result from the spatial variations
in the force [3,4]. Clear evidence of non-equilibrium effects have been found.
Measurements agree with the theoretical predictions, marking the first
conclusive demonstration of the temperature dependence of the Casimir-Polder force. Future perspectives for accurate
measurements of the surface-atom force using Bloch oscillations [5] will be
also discussed. We will also show a recent
investigation [6] of
the force acting between two parallel plates held at different
temperatures. The force reproduces, as limiting cases, the well known Casimir-Lifshitz surface-surface force at thermal
equilibrium and the surface-atom force out of thermal equilibrium derived in
[1]. The asymptotic behavior of the force at large
distances is explicitly discussed. In particular when one of the two bodies is
a rarefied gas the force is not additive, being
proportional to the square root of the density. Nontrivial cross-over regions
at large distances are also identified [1] M. Antezza, L.P. Pitaevskii, and S. Stringari, Phys. Rev.
Lett. 95, 113202 (2005). [2]
M. Antezza, L.P. Pitaevskii,
and [3]
D.M. Harber, J.M. Obrecht,
J.M. McGuirk and E.A. Cornell, Phys. Rev. A 72, 033610 (2005). [4] J.M. Obrecht, R.J. Wild, M. Antezza, L.P. Pitaevskii, S. Stringari, and E.A. Cornell, submitted to Phys. Rev. Lett.
(2006), arXiv: physics/0608074. [5] I. Carusotto, L. Pitaevskii, S.
Stringari, G. Modugno, and M. Inguscio, Phys.
Rev. Lett. 95,
093202 (2005). [6] M. Antezza, L.P. Pitaevskii, S. Stringari, and V.B. Svetovoy,
accepted on Phys. Rev. Lett. (2006), arXiv: cond-mat/0607205. Casimir
force between planar mirrors in the real world F. Intravaia and C. Henkel In the field of nanotechnology, there is a considerable interest
in manipulating the Casimir force (both in magnitude
and sign) playing with geometry and material structure. The benefit one can
possibly achieve under realistic experimental conditions depends on properties
like microscopic surface roughness, finite conductivity, material temperature,
as shown by the comparison of accurate measurements with theory [1]. Regarding
the sign of the force, we have recently identified a parameter range for Casimir repulsion within a certain class of artificial (or
meta-) materials [2]. Our current activities aim at improving the understanding of dispersion forces between non-local
or dissipative media that pose intriguing theoretical challenges on their own.
Both aspects play a role for the finite-temperature correction to the Casimir force, for example, on which a consensus is
currently lacking. We investigate a particular non-local model that allows us
to perform calculations from first principles and to assess the limits and
scope of the widely used Lifshitz formula. [1] S.K. Lamoreaux. The casimir force: background, experiments, and applications.
Reports on Progress in Physics, 68(1):201–236, 2005. [2] C.Henkel and K. Joulain. Casimir force between
designed materials: What is possible and what not. Europhys. Lett.,
72:929–935, 2005. Thursday, December 14, 2006 Novel
quantitative measurements on the Casimir-Polder force M. F.M.
DeKieviet The Atomic
Beam Spin Echo (ABSE) method, originally developed in Stiction and friction in MEMS W. Merlijn
van Spengen, Micromachines
have a much larger surface over volume ratio than macroscopic systems and hence
are extremely sensitive to surface forces. Problems with stiction
(the unintentional sticking of microscopic surfaces) and friction make that
many MEMS (micro-electromechanical systems) designs cannot be realized or have
a lifetime that is too short to be interesting for commercial applications.
Although the detrimental effects caused by surface forces are a real
showstopper for MEMS technology, relatively little research is devoted to
investigating these effects on the scale of MEMS. Compared to AFM (atomic force
microscope) and SFA (surface forces apparatus) measurements, MEMS have the
added complication of a significant surface roughness on the scale of interest.
This roughness gives rise to multi-asperity contacts and relatively large
adhesive forces outside the real area of contact, with mixed plastic/elastic
contact mechanics to complicate matters even further. To study stiction
and friction on the MEMS scale, we have developed a MEMS device that can itself
be used to act as a stiction or friction sensor. With
a very sensitive electronic readout, it enables us to see normal (stiction) and friction forces with high accuracy in-situ,
on-chip. We can make force-distance curves and friction loops on the sidewalls
of a real MEMS device, with real MEMS surfaces, which gives us a unique
opportunity to study the effect of different surfaces and environmental
conditions on MEMS stiction and friction. Surface tension effects
in nanochannels: capillary filling and negative
pressure Niels Tas, Jeroen
Haneveld, Maryana Escalante, Henri Jansen, Miko Elwenspoek The capillary action in nanochannels
is very pronounced due to the large surface to volume ratio. For water in hydrophilic
channels with a hydrodynamic diameter of less than approx. 1 mm the absolute value of the Dynamic measurements of the capillary filling process in nanochannels show that the classical Washburn law is still
valid on the nanoscale, with small quantitative
deviations indicating an enhanced (apparent) viscosity. Depending on the
insulating properties of the channel wall this can be explained by the electroviscous effect or, for channels of around 10 nm in
height, most likely by a real increase in the liquid viscosity. For water in
hydrophilic silica channels the increased viscosity corresponds with a
stationary layer of 4 ± 2 monolayers next to the
channel walls. Friday, December 15, 2006 Experiments for the
detection of quantum electrodynamical torques and
repulsive forces Jeremy N. Munday, Davide Iannuzzi, Federico Capasso During the past decade, there have been
many experimental demonstrations of the attractive Casimir
force between two metal surfaces in vacuum. While high precision experiments
have been performed for this case, little work has been done between metalized objects in fluids, dielectric objects, or
optically anisotropic materials. For materials with suitably chosen dielectric
response functions, repulsive quantum electrodynamical
(QED) forces can arise. In addition, optically anisotropic materials can lead to
a QED toque resulting from the modification of the boundary conditions of the
electromagnetic fluctuations between the materials. We will discuss experiments
to detect these phenomena along with the technological implications of such
experiments. The
Casimir force between the silicon slabs A.Lambrecht, I.Pirozhenko,
L.Duraffourg, Ph.Andeucci We present calculations of the Casimir force between two Silicon slabs of variable thickness. The force is
found to depend strongly on this parameter and to decrease rapidly when the
slab separation exceeds the slab thickness. We also present a simple algebraic
approximation which allows to estimate qualitatively
the Casimir force over 5 orders of magnitude of slab
separation. The present results could be interesting for nanotechnologies to eliminate an
unwanted Casimir force. Casimir
curvature and edge effects The string-inspired worldline
formalism is employed to study the Casimir effect. In
this approach, the problem is mapped onto the path integral of a point
particle, which can be evaluated with The Aladin2 experiment:
expected signal and present sensitivity E. Calloni Aladin2 is a cryogenic experiment aimed at the first detection
of vacuum energy variation in a rigid body via the demonstration of the first
phase transition influenced by vacuum fluctuations. The origin of the
experiment stems from a possible future measurement of the "weight"
of vacuum energy, whose experimental feasibility passes through the possibility
of vacuum energy modulation in a rigid body. In Aladin2 experiment the rigid
body is a rigid Casimir
cavity and the vacuum energy modulation is obtained and measured via its
theoretically foreseen influence on the super-conducting phase transitions of a
cavity mirror. The Casimir cavity is a three-layer
system of thin films: the first layer is a normal metal, the second is a
dielectric layer, the third is a metal which can
undergo super-conducting transition. Following theoretical calculations (PRL,
94, 180402 (2005)) the change in Casimir free energy
due to transition from super-conducting to normal metal is found to be comparable with the
condensation energy. Therefore we expect a measurable shift of critical
magnetic field, with respect to a sample of the same material not included in the cavity. In this talk, after a brief
review of scientific motivations and theoretical calculations, the expected
signal will be presented and the reached experimental sensitivity discussed in
details. [Back] |