Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. 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 to 33 m. The films at various thicknesses 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 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.

We study the Casimir-Lifshitz interaction out of thermal equilibrium, when the interacting objects are at different temperatures. The analysis is focused on the surface-surface, surface-rarefied body, and surface-atom configurations. A systematic investigation of the contributions to the force coming from the propagating and evanescent components of the electromagnetic radiation is performed. The large distance behaviors of such interactions is discussed, and both analytical and numerical results are compared with the equilibrium ones. A detailed analysis of the crossing between the surface-surface and the surface-rarefied body, and finally the surface-atom force is shown, and a complete derivation and discussion of the recently predicted nonadditivity effects and asymptotic behaviors is presented.

We demonstrate here a controllable variation in the Casimir force. Changes in the force of up to 20% at separations of ~100 nm between Au and AgInSbTe (AIST) surfaces were achieved upon crystallization of an amorphous sample of AIST. This material is well known for its structural transformation, which produces a significant change in the optical properties and is exploited in optical data storage systems. The finding paves the way to the control of forces in nanosystems, such as micro-or nanoswitches by stimulating the phase change transition via localized heat sources.Pacs numbers: 78.68.+m, 03.70.+k, 85.85.+j, 12.20.Fv 2 Casimir forces [1][2][3][4][5][6][7][8] arise between two surfaces due to the quantum zero-point energy of the electromagnetic field. The surfaces restrict the allowed wavelengths and thus the number of field modes within the cavity, which locally depresses the zero point energy of the electromagnetic field. The reduction depends on the separation between the plates thus there is a force between them, which for normal materials is always attractive [1].The zero point energy manifests itself as quantum fluctuations, which in the small separation limit give rise to the familiar van der Waals force. The original calculation of the Casimir force assumed two parallel plates with an infinite conductivity [1]. This was later modified to include the dielectric properties of real materials and the intervening medium [2,3], providing the first glimpse of possible methods to control the magnitude and even the direction of the force. This finding has motivated our attempts to manipulate the dielectric properties of a material and hence generate force contrast [9][10][11]. A particularly exciting possibility is to produce a 'switchable' force by employing materials whose optical properties can be changed in situ in response to a simple stimulus [9,10].So far the only significant contrast that has been demonstrated is only between different materials [11]. To obtain a large Casimir force contrast for a single material requires a large modification of its dielectric response, which has not been achieved in materials used up to now.Here we demonstrate that phase change materials (PCMs) [12][13][14][15][16][17][18][19][20][21], which are renowned to switch reporducibly between an amorphous and a crystalline phase, are very promising candidates to achieve a significant force contrast without a change of composition. These materials are already used in rewriteable optical data storage [13,14,[23][24][25], where the pronounced optical contrast between the amorphous and crystalline 3 state is employed to store information. This storage principle employs a focussed laser beam to locally heat a disk with a thin film of phase change material. Upon a variation of the power and length of the laser pulse the material can be reversibly switched between the amorphous and the crystalline phase many times. Here we will show that the pronounced contrast of optical properties enables a significant change of the Casimi...

An upper limit on the Casimir force is found using the dielectric functions of perfect crystalline materials which depend only on well-defined material constants. The force measured with the atomic force microscope is larger than this limit at small separations between bodies and the discrepancy is significant. The simplest modification of the experiment is proposed allowing one to make its results more reliable and answer the question if the discrepancy has any relation with the existence of a new force.The Casimir force 1 between closely spaced macroscopic bodies is an effect of quantum electrodynamics (QED) and for that reason could be predicted very accurately. In the rigorous Lifshitz theory 2,3 the force is defined by the optical properties of used materials. Knowledge of these properties is the weakest element in the theory restricting the accuracy that can be achieved. Though the measurement of the Casimir force is not the best way to test QED, such experiments are of great importance because they are sensitive to the presence of new fundamental forces 4 predicted in many modern theories (see, for example, Ref. 5 and references therein). To distinguish a new force from the background, we should be able to calculate the Casimir force with a precision better than the experimental one. In the series of recent experiments this force has been measured with the torsion pendulum (TP) 6 in the range of distances 0.6-6 µm and with the atomic force microscope (AFM) 7,8 in the range 0.1-0.9 µm. The corresponding precisions were 5% and 1%, respectively.The force per unit area between parallel plates arising as a result of electromagnetic fluctuations at nonzero temperature T is generalized by the Lifshitz theory, 3 where the plate material is taken into account by its dielectric function at imaginary frequencies ε(iζ):

The point at which two random rough surfaces make contact takes place at the contact of the highest asperities. The distance upon contact d 0 in the limit of zero load has crucial importance for determination of dispersive forces. Using gold films as an example we demonstrate that for two parallel plates d 0 is a function of the nominal size of the contact area L and give a simple expression for d 0 ͑L͒ via the surface roughness characteristics. In the case of a sphere of fixed radius R and a plate the scale dependence manifests itself as an additional uncertainty ␦d͑L͒ in the separation, where the scale L is related with the separation d via the effective area of interaction L 2 ϳ Rd. This uncertainty depends on the roughness of interacting bodies and disappears in the limit L → ϱ.