Multiple-beam interferometry with thin metal films and unsymmetrical systems

Clarkson, M T

doi:10.1088/0022-3727/22/4/001

Cited by 54 publications

(46 citation statements)

References 11 publications

(17 reference statements)

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“…The resulting interference spectrum is collected with an objective lens and directed to a CCD camera (c) and a spectrometer (s). This interferometry technique is employed to determine the optical distance between the silver mirrors, which can be used to determine the mica thickness and the film thickness D of the confined liquid (Born and Wolf 1980, Clarkson 1989, Heuberger 2001. The optical zero D = 0, when the mica sheets are in contact, has to be determined before filling with liquid.…”

Section: Measurement Of Normal Forcementioning

confidence: 99%

Molecular liquid under nanometre confinement: density profiles underlying oscillatory forces

Perret¹,

Nygård²,

Satapathy³

et al. 2010

J. Phys.: Condens. Matter

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Ultrathin (<12 nm) films of tetrakis(trimethyl)siloxysilane (TTMSS) have been confined by atomically flat mica membranes in the presence and absence of applied normal forces. When applying normal forces, discrete film thickness transitions occur, each involving the expulsion of TTMSS molecules. Using optical interferometry we have measured the step size associated with a film thickness transition (7.5Å for compressed, 8.4Å for equilibrated films) to be smaller than the molecular diameter of 9.0Å. Layering transitions with a discrete step size are commonly regarded as evidence for strong layering of the liquid's molecules in planes parallel to the confining surfaces and it is assumed that the layer spacing equals the measured periodicity of the oscillatory force profile. Using x-ray reflectivity (XRR), which directly yields the liquid's density profile along the confinement direction, we show that the layer spacing (10-11Å) proves to be on average significantly larger than both the step size of a layering transition and the molecular diameter. We observe at least one boundary layer of different electron density and periodicity than the layers away from the surfaces.

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Section: Measurement Of Normal Forcementioning

confidence: 99%

Molecular liquid under nanometre confinement: density profiles underlying oscillatory forces

Perret¹,

Nygård²,

Satapathy³

et al. 2010

J. Phys.: Condens. Matter

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“…Upon fast approach, A is used to control the gap width. White light is sent through the low-finesse interferometer and analyzed with a spectrometer (s) in order to calculate the gap width with a typical resolution of 20 pm [19][20][21]. Simultaneously the light is directed into a CCD camera (c) to image the film in real time.…”

mentioning

confidence: 99%

X-ray reflectivity reveals equilibrium density profile of molecular liquid under nanometre confinement

Perret¹,

Nygård²,

Satapathy³

et al. 2009

Europhys. Lett.

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-A silane (tetrakis(trimethylsiloxy)silane) has been confined within a space of a few molecular diameters (9Å) between two atomically flat opposing mica membranes. The liquid's electron density profile along the confinement direction has been determined by synchrotron X-ray reflectivity for film thicknesses of 8.58 and 11.22 nm. We find the liquid's molecules to be strongly layered at layer distances significantly larger than the effective molecular diameter. The considerable free volume enables the confined liquid to retain its liquid properties.A liquid which is confined within a slit or pore exhibits properties markedly different from the bulk liquid if it is confined within a space of only a few molecular diameters in size [1]. Such "extreme confinement" imposes a structural ordering to the liquid, which in turn will affect many of the liquid's properties. A considerable part of confined-fluids research has been concerned with measurements of the normal and lateral forces acting between two approaching surfaces in a liquid medium. Typically, oscillatory forces are observed having a periodicity of just below one molecular diameter and an exponential decay of comparable length scale [2][3][4][5]. Discrete steps in film thickness are observed, which are commonly interpreted as layering transitions through expulsions of single molecular layers. However, unambiguous electrondensity profiles providing proof of such liquid layering have not yet been experimentally determined. More recently, synchrotron X-ray diffraction from various single solid-liquid interfaces and free surfaces revealed structural ordering [6][7][8][9][10][11]. A recent structural investigation of liquid within a nanometre-sized gap reported thickness quantization between silicon surfaces at externally forced surface separations [12].(a) E-mail: friso.vanderveen@psi.ch Using X-ray reflectivity (XRR) [13] as a function of perpendicular momentum transfer q ⊥ we have determined the electron density profile along the confinement direction of the spherical, non-polar liquid tetrakis(trimethylsiloxy)silane (TTMSS) having a molecular diameter of 9.0Å [8]. The liquid was confined between flat surfaces and the gap width between the surfaces was allowed to equilibrate in the absence of external forces. The confining walls were formed by a pair of (001)-oriented single-crystal surfaces of muscovite mica. The confinement configuration can be regarded as a free-standing single crystal which is interrupted by an ultrathin film of fluid. The advantage of using a crystal lies in its known structure and in its smooth surface provided it is free of atomic steps. The latter is a prerequisite for resolving distinct electron density peaks in the confined liquid. Figure 1 shows a schematic of the confinement geometry and the molecular structure of the mica crystal and TTMSS. Muscovite mica H 2 KAl 3 (SiO 4 ) 3 is a stack of aluminum silicate sheets separated by sheets of potassium ions. The muscovite (001) planes are easily cleaved due to the absence of cova...

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“…Each acquired transmission spectrum results from a single spot within the contact area. The local distance between the mica membranes is determined from the transmission spectrum using the fast spectral correlation method (Heuberger, 2001;Israelachvili, 1973) and multilayer matrix method (Born & Wolf, 1980;Clarkson, 1989). The spectrometer is mounted on an xy-stage.…”

Section: Methodsmentioning

confidence: 99%

X-ray reflectivity theory for determining the density profile of a liquid under nanometre confinement

Perret

Nygård

Satapathy

et al. 2010

J Synchrotron Radiat

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An X-ray reflectivity theory on the determination of the density profile of a molecular liquid under nanometre confinement is presented. The confinement geometry acts like an X-ray interferometer, which consists of two opposing atomically flat single-crystal mica membranes with an intervening thin liquid film of variable thickness. The X-rays reflected from the parallel crystal planes (of known structure) and the layered liquid in between them (of unknown structure) interfere with one another, making X-ray reflectivity highly sensitive to the liquid's density profile along the confinement direction. An expression for the reflected intensity as a function of momentum transfer is given. The total structure factor intensity for the liquid-filled confinement device is derived as a sum of contributions from the inner and outer crystal terminations. The method presented readily distinguishes the confined liquid from the liquid adsorbed on the outer mica surfaces. It is illustrated for the molecular liquid tetrakis-(trimethyl)siloxysilane, confined by two mica surfaces at a distance of 8.6 nm.

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Multiple-beam interferometry with thin metal films and unsymmetrical systems

Cited by 54 publications

References 11 publications

Molecular liquid under nanometre confinement: density profiles underlying oscillatory forces

Molecular liquid under nanometre confinement: density profiles underlying oscillatory forces

X-ray reflectivity reveals equilibrium density profile of molecular liquid under nanometre confinement

X-ray reflectivity theory for determining the density profile of a liquid under nanometre confinement

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