47 research outputs found
Laser Fluorescence Spectroscopy: Application in Determining the Individual Photophysical Parameters of Proteins
Experimental and theoretical investigation of angular dependence of the Casimir force between sinusoidally corrugated surfaces
In the current work we present the complete results for the measurement of
normal Casimir force between shallow and smooth sinusoidally corrugated gold
coated sphere and a plate at various angles between the corrugations using an
atomic force microscope. All measured data were compared with the theoretical
approach using the proximity force approximation and theory based on derivative
expansion. In both cases real material properties of the surfaces and non-zero
temperature were taken into account. Special attention is paid to the
description of electrostatic interactions between corrugated surfaces at
different angels between corrugations and samples reparation and
characterization. The measured forces are found to be in good agreement with
the theory including correlation effects of geometry and material properties
and deviate significantly from the predictions of the proximity force
approximation approach. This provides the quantitative confirmation for the
observation of diffraction-type effects that are disregarded within the PFA
approach. The obtained results open new opportunities for control of the
Casimir effect in micromechanical systems
Comparison between experiment and theory for the thermal Casimir force
We analyze recent experiments on measuring the thermal Casimir force with
account of possible background effects. Special attention is paid to the
validity of the proximity force approximation (PFA) used in the comparison
between the experimental data and computational results in experiments
employing a sphere-plate geometry. The PFA results are compared with the exact
results where they are available. The possibility to use fitting procedures in
theory-experiment comparison is discussed. On this basis we reconsider
experiments exploiting spherical lenses of centimeter-size radii.Comment: Plenary talk at the 10th International Conference "Quantum Field
Theory Under the Influence of External Conditions" (Benasque, Spain, 2011);
16 pages, 5 figure
Modifying the Casimir force between indium tin oxide film and Au sphere
We present complete results of the experiment on measuring the Casimir force
between an Au-coated sphere and an untreated or, alternatively, UV-treated
indium tin oxide film deposited on a quartz substrate. Measurements were
performed using an atomic force microscope in a high vacuum chamber. The
measurement system was calibrated electrostatically. Special analysis of the
systematic deviations is performed, and respective corrections in the
calibration parameters are introduced. The corrected parameters are free from
anomalies discussed in the literature. The experimental data for the Casimir
force from two measurement sets for both untreated and UV-treated samples are
presented. The experimental errors are determined at a 95% confidence level. It
is demonstrated that the UV treatment of an I TO plate results in a significant
decrease in the magnitude of the Casimir force (from 21% to 35% depending on
separation). However, ellipsometry measurements of the imaginary parts of
dielectric permittivities of the untreated and UV-treated samples did not
reveal any significant differences. The experimental data are compared with
computations in the framework of the Lifshitz theory. It is found that the data
for the untreated sample are in a very good agreement with theoretical results
taking into account the free charge carriers in an ITO film. For the UV-treated
sample the data exclude the theoretical results obtained with account of free
charge carriers. These data are in a very good agreement with computations
disregarding the contribution of free carriers. According to the explanation
provided, this is caused by the phase transition of the ITO film from metallic
to dielectric state caused by the UV treatment. Possible applications of the
discovered phenomenon in nanotechnology are discussed.Comment: 30 pages, 19 figures, 1 tabl
Gradient of the Casimir force between Au surfaces of a sphere and a plate measured using atomic force microscope in a frequency shift technique
We present measurement results for the gradient of the Casimir force between
an Au-coated sphere and an Au-coated plate obtained by means of an atomic force
microscope operated in a frequency shift technique. This experiment was
performed at a pressure of 3x10^{-8} Torr with hollow glass sphere of 41.3 mcm
radius. Special attention is paid to electrostatic calibrations including the
problem of electrostatic patches. All calibration parameters are shown to be
separation-independent after the corrections for mechanical drift are included.
The gradient of the Casimir force was measured in two ways with applied
compensating voltage to the plate and with different applied voltages and
subsequent subtraction of electric forces. The obtained mean gradients are
shown to be in mutual agreement and in agreement with previous experiments
performed using a micromachined oscillator. The obtained data are compared with
theoretical predictions of the Lifshitz theory including corrections beyond the
proximity force approximation. An independent comparison with no fitting
parameters demonstrated that the Drude model approach is excluded by the data
at a 67% confidence level over the separation region from 235 to 420 nm. The
theoretical approach using the generalized plasma-like model is shown to be
consistent with the data over the entire measurement range. Corrections due to
the nonlinearity of oscillator are calculated and the application region of the
linear regime is determined. A conclusion is made that the results of several
performed experiments call for a thorough analysis of the basics of the theory
of dispersion forces.Comment: 35 pages, 14 figures, 1 table; to appear in Phys. Rev.
Measurement of the gradient of the Casimir force between a nonmagnetic sphere and a magnetic plate
We measured the gradient of the Casimir force between an Au sphere and a
plate made of ferromagnetic metal (Ni). It is demonstrated that the magnetic
properties influence the force magnitude. This opens prospective opportunities
for the control of the Casimir force in nanotechnology and for obtaining
Casimir repulsion by using ferromagnetic dielectrics.Comment: 15 pages, 4 figures, to appear in Phys. Rev.