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M. Lippmann, A. Ehnes , O. H. Seeck

A cell for confined liquids investigated with x-rays. M. Lippmann, A. Ehnes , O. H. Seeck Deutsches Elektronen -Synchrotron DESY, Notkestr . 85, 20607, Hamburg , Germany. The new experimental cell: Substrates are two diamonds. Previous experiments.

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M. Lippmann, A. Ehnes , O. H. Seeck

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  1. A cell for confined liquids investigated with x-rays. M. Lippmann, A. Ehnes, O. H. Seeck DeutschesElektronen-Synchrotron DESY, Notkestr. 85, 20607, Hamburg , Germany The new experimental cell: Substrates are two diamonds Previous experiments Confined liquid in slit geometry: Properties of the liquid are modified ! Surface force apparatus. 150 mm Substrate Thickness less than 100 Å First X-ray data at colloids and real liquids. Substrate Zwanenburg et al, Phys Rev Lett85, 2000 Seeck et al, Eur Phys Lett60, 2002 Layering of the liquid molecules in the gapalso visible, no in-plane information Thin film of a liquid confined between two substrates. The gap has a thickness of a few molecular diameters. The goal of the investigation is to study the molecular structure of the liquid film under confined conditions by means of reflectivity and especially out-of-plane x-ray measurements. Normal force vs. the gap size. Klein&Kumacheva, Science 269, 1995 • Layering of the liquid molecules in the gap. • Solidification of the liquid film. The confined effects show up at film thickness as large as ten times molecular diameter. P08 Beamline, PETRA III, DESY Substrates and preparation The working principle of the cell is similar to that of a diamond anvil cell (DAC) setup: Two well aligned diamonds are moved towards, at the DAC to apply pressure, here set the gap. For well defined gaps the alignment proce-dure is critical. It is done by a piezo stage which has a trans-lation in vertical direction with max. 100 µm ± 1 nm and tilting angles in x, y direc-tion: 0.5 mrad ± 0.05 µrad. The cell has been assembled and pre-aligned in a Class 2 (ISO 4) clean room. Diamond substrates (a) diameter 4 mm, height 3 mm. (b) The confinement region (the culet in the center): 200 µmdiameter(c) Optical fringes at a misaligned gap of approx. 1µm size, looking from top. (d) ) Side view of the gap with a small droplet of OMCTS: The liquid is injected in bottom part of the sample cell and heated by means of a heater. The liquid evaporates and condenses on the surface of the diamonds. (e) An AFM image from the central part of the confined surface. The scratches are approx. 1.4 nm deep (top to bottom). • Confined liquid cell as it fits into the P08 6-circle diffractometer. • The photon energy was 12.38 keV or 18 keV. • The beam size was (30 x200) µm or (3x20) µm (vertical x horizontal). • Vacuum was not applied. Experimental Data: Reflectivities of a confined benzene films:. Beam size: (3x20)µm(vxh) the culet with diameter 200µm The gap size changes of 200 Å to 160 Å with increasing of Pz of 67.5 to 74. (c) (a) (b) Beam size: (3x20)µm(vxh) the culet with diameter 400µm The curves are measured at different sample position. The films have a thickness of ca. 30 Å, comparable to the size of the films studied with SFA. The molecular diameter of CCl4 is approx. 5 Å. (c) Beam size: (3x20)µm(vxh) Fullreflectivity. The large q-range allows for analysis with atomic precision. (b) Structure factor of confined benzene film in out-off-plane direction (right):In the confined date is observed increase of the intensity at smaller q regions. It could be explain with creation of small clusters in the plane of the substrate surface. The curves is possible to be measure only with the beam size of (3x20)µm(vxh). Reflectivities of a confined OMCTS film Beam size: (30x200) µm(vxh) , the culet with diameter 200 µm The film has a thickness of 150 Å and decrease with increasing the pressure. The molecular diameter of OMCTS is approx. 7.8 Å . The confined film is ca. 20 times larger than the molecular size. Conclusion: The setup can be used to confine liquids to molecular levels. In-plane and out-off-plane x-ray measurements are possible. For gaps on atomic levels, the quality of the diamond surfaces needs to be improved. The application of the micro focused beam is essential.

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