Showing papers by "Umar Mohideen published in 2012"
TL;DR: In this article, the authors present measurement results for the gradient of the Casimir force between an Au-coated sphere and an Aucoated plate obtained by means of an atomic force microscope operated in a frequency-shift technique.
Abstract: 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 $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ Torr with a hollow glass sphere of 41.3 $\ensuremath{\mu}$m 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 plasmalike 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.
130 citations
TL;DR: In this paper, the authors measured the gradient of the Casimir force between an Au sphere and a plate made of ferromagnetic metal (Ni), and demonstrated that the magnetic properties influence the force magnitude.
Abstract: 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.
71 citations
TL;DR: In this paper, the experimental data for the Casimir force between an Au-coated sphere and an untreated or, alternatively, UV-treated indium tin oxide (ITO) film deposited on a quartz substrate were presented.
Abstract: 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 (ITO) 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 random, systematic, and total experimental errors are determined at a 95$%$ confidence level. It is demonstrated that the UV treatment of an ITO 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 very good agreement with computations disregarding the contribution of free carriers in the dielectric permittivity. According to the hypothetical 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.
63 citations
TL;DR: In this article, the displacement of Ni ions from the cantilever by EDTA, followed by water flow removes the tensile stress and restores the canticlever deflection to its original value.
Abstract: A microcantilever sensor based on a reversible displacement reaction was developed. The demonstration was performed with the Ni–NTA–EDTA sample system. Ni ions, a typical heavy metal, were injected and adsorbed onto a NTA-functionalized AFM cantilever in a fluid cell. This adsorption resulted in tensile stress which was detected by monitoring the corresponding deflection of the microcantilever. In the next step, EDTA was injected into the cell to release the adsorbed Ni ions from the surface of the cantilever. Since EDTA molecules have a stronger affinity for Ni ions compared to NTA, they compete with and eventually replace the NTA molecules and take over the binding positions on Ni. The displacement of Ni ions from the cantilever by EDTA, followed by water flow removes the tensile stress and restores the cantilever deflection to its original value. In this way, both heavy metal ions and EDTA can be specifically recognized. From the cantilever deflection, the concentration of Ni ions and EDTA can be quantified. The detection limits are presently at the micromolar level. Another weaker Ni ion binder, imidazole, was unable to dissociate Ni ions from NTA and produce similar effects. The demonstrated principle can be used for microcantilever sensors which are capable of regeneration for multiple uses. The method presented can be generalized to detect other reactants.
22 citations
TL;DR: It is demonstrated that for the special selection of semiconductor materials the calculation results using the standard Lifshitz theory and the phenomenological approach differ significantly and the predicted effects are easily detectable using the existing laboratory setups.
Abstract: We propose a new experiment on the measurement of the Casimir force and its gradient between a Au-coated sphere and two different plates made of doped semiconductors. The concentrations of charge carriers in the plates are chosen slightly below and above the critical density at which the Mott–Anderson insulator–metal transition occurs. We calculate changes in the Casimir force and the Casimir pressure due to the insulator–metal transition using the standard Lifshitz theory and the phenomenological approach neglecting the contribution of free charge carriers in the dielectric permittivity of insulator materials (this approach was recently supported by the measurement data of several experiments). It is demonstrated that for the special selection of semiconductor materials (S- or Se-doped Si, B-doped diamond) the calculation results using the two theoretical approaches differ significantly and the predicted effects are easily detectable using the existing laboratory setups. In the case that the prediction of the phenomenological approach is confirmed, this would open opportunities to modify the van der Waals and Casimir forces with almost no change of room temperature dielectric permittivity.
10 citations
TL;DR: In this paper, the authors derived constraints on corrections to Newtonian gravity of the Yukawa type and light elementary particles from two recently performed measurements of the gradient of the Casimir force.
Abstract: We derive constraints on corrections to Newtonian gravity of the Yukawa type and light elementary particles from two recently performed measurements of the gradient of the Casimir force. In the first measurement the configuration of two Au surfaces has been used, whereas in the second a nonmagnetic metal Au interacted with a magnetic metal Ni. In these configurations one arrives at different and similar, respectively, theoretical predictions for the Casimir force when the competing theoretical approaches are employed. Nevertheless, we demonstrate that the constraints following from both experiments are in mutual agreement and in line with constraints obtained from earlier measurements. This confirms the reliability of constraints on non-Newtonian gravity obtained from measurements of the Casimir force.
10 citations
TL;DR: In this paper, the Casimir interaction between two parallel metallic cylinders and between a metallic cylinder and a plate was investigated numerically at all separation distances and analytically at large separations.
Abstract: We investigate the Casimir interaction between two parallel metallic cylinders and between a metallic cylinder and plate. The material properties of the metallic objects are implemented by the plasma, Drude and perfect metal model dielectric functions. We calculate the Casimir interaction numerically at all separation distances and analytically at large separations. The large-distance asymptotic interaction between one plasma cylinder parallel to another plasma cylinder or plate does not depend on the material properties, but for a Drude cylinder it depends on the dc conductivity . At intermediate separations, for plasma cylinders the asymptotic interaction depends on the plasma wave length p while for Drude cylinders the Casimir interaction can become independent of the material properties. We conrm the analytical results by the numerics and show that at short separations, the numerical results approach the proximity force approximation.
9 citations
TL;DR: In this article, the effect of the reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film was observed after UV treatment of the latter.
Abstract: Additional information is provided on the effect of the significant (up to 35%) reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film which was observed after UV treatment of the latter. A striking feature of this effect is that the reduction is not accompanied with a corresponding variation of the dielectric permittivity, as confirmed by direct ellipsometry measurements. The measurement data are compared with computations using the Lifshitz theory. It is shown that the data for the untreated sample are in a very good agreement with theory taking into account the free charge carriers in the indium tin oxide. The data for the UV-treated sample exclude the theoretical results obtained with account of free charge carriers. These data are found to be in a very good agreement with theory disregarding the free charge carriers in an indium tin oxide film. A possible theoretical explanation of our observations as a result of phase transition of indium tin oxide from metallic to dielectric state is discussed in comparison with other related experiments.
8 citations
TL;DR: In this article, the authors measured the Casimir force and its gradient between an Au-coated sphere and two different plates made of doped semiconductors, where the concentrations of charge carriers in the plates were chosen slightly below and above the critical density at which the Mott-Anderson insulator-metal transition occurs.
Abstract: We propose a new experiment on measuring the Casimir force and its gradient between an Au-coated sphere and two different plates made of doped semiconductors. The concentrations of charge carriers in the plates are chosen slightly below and above the critical density at which the Mott-Anderson insulator-metal transition occurs. We calculate changes in the Casimir force and the Casimir pressure due to the insulator-metal transition using the standard Lifshitz theory and the phenomenological approach neglecting the contribution of free charge carriers in the dielectric permittivity of insulator materials (this approach was recently supported by the measurement data of several experiments). It is demonstrated that for the special selection of semiconductor materials (S- or Se-doped Si, B-doped diamond) calculation results using both theoretical approaches differ significantly and the predicted effects are easily detectable using the existing laboratory setups. In the case that the prediction of the phenomenological approach is confirmed, this would open opportunities to modify the van der Waals and Casimir forces with almost no change of room-temperature dielectric permittivity.
8 citations
TL;DR: In this article, the cancellation and dynamic modulation of the Casimir force between two transparent electrodes and radiation pressure was demonstrated by using transparent electrodes, where the attractive Casimir forces between the two surfaces were balanced by radiation pressure on the first surface from light transmitted through the second transparent surface.
Abstract: We demonstrate the cancellation and dynamic modulation of the Casimir force by using transparent electrodes and radiation pressure. The attractive Casimir force between the two surfaces is balanced by radiation pressure on the first surface from light transmitted through the second transparent surface. The cancellation and dynamic modulation of dispersion forces will find applications in the design and enhanced performance of micro- and nanoelectro mechanical systems.
7 citations
TL;DR: In this article, the effect of the reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film was observed after UV treatment of the latter.
Abstract: Additional information is provided on the effect of the significant (up to 35%) reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film which was observed after UV treatment of the latter. A striking feature of this effect is that the reduction is not accompanied with a corresponding variation of the dielectric permittivity, as confirmed by direct ellipsometry measurements. The measurement data are compared with computations using the Lifshitz theory. It is shown that the data for the untreated sample are in a very good agreement with theory taking into account the free charge carriers in the indium tin oxide. The data for the UV-treated sample exclude the theoretical results obtained with account of free charge carriers. These data are found to be in a very good agreement with theory disregarding the free charge carriers in an indium tin oxide film. A possible theoretical explanation of our observations as a result of phase transition of indium tin oxide from metallic to dielectric state is discussed in comparison with other related experiments.
26 Jul 2012
TL;DR: In this article, the authors measured the Casimir force between carefully cleaned Au surfaces of a sphere and a plate using a dynamic atomic force microscope in the frequency modulation regime in high vacuum.
Abstract: The gradient of the Casimir force between carefully cleaned Au surfaces of a sphere and a plate is measured using a dynamic atomic force microscope in the frequency modulation regime in high vacuum. The electrostatic calibration of the setup did not reveal any effect of patches or surface contaminants. The experimental data for the force gradient are found to be consistent with theory using the plasma model approach over the entire measurement range. The Drude model approach is excluded by the data at separations from 235 to 400 nm at a 67% confidence level.
Posted Content•
TL;DR: Berman et al. as discussed by the authors developed a discrete two-dimensional model of a cantilever which incorporates the effects of inhomogeneity, the geometry of an attached particle, and the influence of external time-dependent forces.
Abstract: Author(s): Berman, Gennady P; Gorshkov, Vyacheslav N; Kuzmenko, Vasily V; Mohideen, Umar | Abstract: We developed a discrete two-dimensional model of a cantilever which incorporates the effects of inhomogeneity, the geometry of an attached particle, and the influence of external time-dependent forces. We provide a comparison between the solutions for our discrete model and its continuous limit. The rotational-vibrational mode is studied in detail. The results of numerical simulations demonstrate usefulness of our model for many applications when a cantilever has a complicated geometry and is affected by time-depended and distributed external forces.
26 Jul 2012
TL;DR: In this article, the effect of the reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film was observed after UV treatment of the latter.
Abstract: Additional information is provided on the effect of the significant (up to 35%) reduction in the magnitude of the Casimir force between an Au-coated sphere and an indium tin oxide film which was observed after UV treatment of the latter. A striking feature of this effect is that the reduction is not accompanied with a corresponding variation of the dielectric permittivity, as confirmed by direct ellipsometry measurements. The measurement data are compared with computations using the Lifshitz theory. It is shown that the data for the untreated sample are in a very good agreement with theory taking into account the free charge carriers in the indium tin oxide. The data for the UV-treated sample exclude the theoretical results obtained with account of free charge carriers. These data are found to be in a very good agreement with theory disregarding the free charge carriers in an indium tin oxide film. A possible theoretical explanation of our observations as a result of phase transition of indium tin oxide from metallic to dielectric state is discussed in comparison with other related experiments.