Switching Casimir forces with phase-change materials

Abstract

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...

Modifying the Casimir force between indium tin oxide film and Au sphere

“…[45][46][47][48]52 It was claimed that anomalous dependences of the residual potential difference and separation on contact on the separation distance observed in several experiments cast doubts on the measurements of the Casimir force performed to date. It was also suggested that inasmuch electrostatic calibrations are based on a fitting procedure there is no principal difference detween independent measurements of the Casimir force [20][21][22][23][24][25][26][27][28][29][30][35][36][37][39][40][41][42][43][44]71 and deriving the Casimir force by means of a fit from some much larger measured force of hypothetical origin. 31 In this respect we would like to note that the calibration consists in determination of the parameters of a setup using well established physical laws (in our case of electrostatics) and involves only well understood and precisely measured forces.…”

“…[20][21][22][23][24][25][26][27][28][40][41][42][43][44] The AFM system consists of a head, piezoelectric actuator, an AFM controller and computer. The head includes a diode laser which emits a collimated beam with a waist of tens of micrometers at the focus, an Au-coated cantilever with attached sphere that bends in response to the sphere-plate force, and photodetectors which measure the cantilever deflection through a differential measurement of the laser beam intensity.…”

“…For an indium tin oxide (ITO, In 2 O 3 :Sn) film interacting with an Au sphere the gradient of the Casimir force was measured 23,24 to be roughly 40%-50% smaller than between an Au sphere and an Au plate. In one more experiment 25 it was shown that for an Au sphere interacting with a plate made of AgInSbTe the gradient of the Casimir force decreases in magnitude by approximately 20% when the material of the plate in the crystalline phase is replaced with an amorphous one. For a semimetallic plate, the gradient of the Casimir force was reported to be 25%-35% smaller than for an Au plate.…”

Casimir force between a microfabricated elliptic cylinder and a plate

“…[36] discussed measurements of the gradient of the Casimir force in a linear regime (the same regime was employed in dynamic measurements by means of an atomic force microscope [49][50][51][52][53]). Here, we find the frequency shift of an oscillator, caused by the Casimir force between an elliptic cylinder and a plate, in the nonlinear regime.…”

Significance of the Casimir force and surface roughness for actuation dynamics of MEMS

“…In some cases tabulated optical data were taken into account. [27][28][29] In this paper, we will explore the actuation dynamics of microswitches made from real materials (with a definite measured optical response [41][42][43] and characterized by some degree of nanoscale roughness), accounting for both electrostatic and Casimir forces, which counteract an elastic restoring force [see Fig. 1(a)].…”