arXiv subjects

G. Palasantzas

Publications and source records attributed to G. Palasantzas.

27 records · Page 2Linked to original sources

arXiv2008

Transition from Casimir to van der Waals force between macroscopic bodies

The transition of van der Waals to Casimir forces between macroscopic gold surfaces is investigated by Atomic Force Microscopy in the plane-sphere geometry. It was found that the transition appears to take place at separations about 10 % the plasma wavelength for evaporated gold surfaces, which compares to theoretical predictions by incorporation of experimental optical data and roughness corrections. Moreover, the force data allow estimation of the Hamaker constant AH in the van der Waals regime, which is in good agreement with the Lifshitz theory predictions (even if roughness corrections are taken into account) and former surface force apparatus measurements.

cond-mat.mtrl-sci↗

arXiv2008

Influence of roughness on capillary forces between hydrophilic surfaces

Capillary forces have been measured by Atomic Force Microscopy in the plate-sphere setup between gold, borosilicate glass, GeSbTe, titanium, and UV irradiated amorphous titaniumdioxide surfaces. The force measurements were performed as a function contact time and surface roughness in the range 0.2 - 15 nm rms, and relative humidity ranging between 2 and 40 %. It is found that even for the lowest attainable relative humidity 2 % very large capillary forces are still present. The latter suggests the persistence of a nanometers thick adsorbed water layer that acts as a capillary bridge between contacting surfaces. Moreover, we found a significantly different scaling behavior of the force with rms roughness for materials with different hydrophilicity as compared to gold-gold surfaces.

cond-mat.mtrl-sci↗

arXiv2008

Quality factor due to roughness scattering of shear horizontal surface acoustic waves in nanoresonators

In this work we study the quality factor associated with dissipation due to scattering of shear horizontal surface acoustic waves by random self-affine roughness. It is shown the quality factor is strongly influenced by both the surface roughness exponent H, and the roughness amplitude w to lateral correlation length X ratio. Indeed, quality factors for roughness exponents H>0.5 are comparable to quality factors due to intrinsic dissipation mechanisms (e.g., thermoelastic losses and phonon-phonon scattering) especially for wave vectors <1/X. Our results indicate that this dissipation mechanism should be carefully considered in the design micro/nanoelectromechanical systems.

cond-mat.mtrl-sci↗

arXiv2008

Surface roughness influence on the quality factor of high frequency nanoresonators

Surface roughness influences significantly the quality factor of high frequency nanoresonators for large frequency - relaxation times within the non-Newtonian regime, where a purely elastic dynamics develops. It is shown that the influence of sort wavelength roughness, which is expressed by the roughness exponent H for the case of self-affine roughness, plays significant role in comparison with the effect of the long wavelength roughness parameters such as the rms roughness amplitude and the lateral roughness correlation length. Therefore, the surface morphology can play important role in designing high-frequency resonators operating within the non-Newtonian regime.

physics.flu-dyn↗

arXiv2008

Optical properties of gold films and the Casimir force

Precise optical properties of metals are very important for accurate prediction of the Casimir force acting between two metallic plates. Therefore we measured ellipsometrically the optical responses of Au films in a wide range of wavelengths from 0.14 mum to 33 mum. The films at various thickness were deposited at different conditions on silicon or mica substrates. Considerable variation of the frequency dependent dielectric function from sample to sample was found. Detailed analysis of the dielectric functions was performed to check the Kramers-Kronig consistency, and extract the Drude parameters of the films. It was found that the plasma frequency varies in the range from 6.8 eV to 8.4 eV. It is suggested that this variation is related with the film density. X-ray reflectivity measurements support qualitatively this conclusion. The Casimir force is evaluated for the dielectric functions corresponding to our samples, and for that typically used in the precise prediction of the force. The force for our films was found to be 5-14% smaller at a distance of 100 nm between the plates. Noise in the optical data is responsible for the force variation within 1%. It is concluded that prediction of the Casimir force between metals with a precision better than 10% must be based on the material optical response measured from visible to mid-infrared range.

cond-mat.other↗

arXiv2007

Measurement of dispersive forces between evaporated metal surfaces in the range below 100 nm

In this work we describe dispersion force (van der Waals/Casimir) measurements between gold surfaces at separations as close as 12 nm. The force measurements were performed in the plane-sphere configuration by Atomic Force Microscopy at distances ranging between 12 and 200 nm. This was accomplished by using evaporated smooth metal surfaces for both sphere and plane, and stiff cantilevers to minimize jump-to-contact problems. Finally, it is shown that below separations of 100 nm experiment and theory are found in agreement within 10 % by including in the theory the measured optical properties of gold and contribution from surface roughness.

cond-mat.mtrl-sci↗

arXiv2007

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%.

cond-mat.other↗

arXiv2007

Roughness corrections to the Casimir force: The importance of local surface slope

This paper concentrates on a study where finite conductivity corrections are included in the theoretical description of the effects of roughness on the Casimir force. The roughness data were taken from gold films evaporated onto Silicon and polysterene spheres. We conclude that for a detailed comparison with experimental data, i.e. at the level of at least 5 % at short separations below 200 nm, the lateral dimensions of roughness for real films should be included in the theoretical considerations. Moreover, if the RMS roughness is considerable, high local surface slopes are shown to have a significant effect on the Casimir force.

cond-mat.other↗

arXiv2007

Influence of random roughness on the adhesion between metal surfaces due to capillary condensation

The capillary force was measured by atomic force microscopy between a gold coated sphere mounted on a cantilever and gold surfaces with different roughness. For smooth surfaces the capillary adhesive force surpasses in magnitude any dispersion, e.g. van der Waals/Casimir, and/or electrostatic forces. A substantial decrease in the capillary force was observed by increasing the roughness ampltitude a few nanometers between 1-10 nm. From these measurements two limits can be defined: a smooth limit where a closely macroscopic size contact surface interacts through the capillary force, and the rough limit where only a few asperities give a capillary contribution.

cond-mat.mtrl-sci↗