Biomedical subjects

E Vlieg

Publications and source records attributed to E Vlieg.

At least 19 recordsLinked to original sources

PubMed2006

Observation of a liquid phase with an orthorhombic orientational order.

Using surface x-ray diffraction, we have determined the structure of liquid Bi monolayers on Cu(111) for a range of coverages. By combining diffuse scattering data from the liquid with information from the substrate scattering, the ordering properties of Bi have been fully determined. Even though the substrate is hexagonal, we find that the liquid does not show hexatic order but has an orthorhombic orientational order that occurs in three domains. Simultaneously, Bi has partial solidlike properties, even well above its melting point.

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PubMed2005

Epitaxial 2D nucleation of the stable polymorphic form of the steroid 7alphaMNa on the metastable form: implications for Ostwald's rule of stages.

This paper presents in situ observations of the epitaxial nucleation and growth of the stable polymorph of a steroid, 7alphaMna, on a specific face of the metastable form at low supersaturation, using optical microscopy and in situ Raman spectroscopy. The presence of the metastable polymorph is essential for the nucleation and growth of the stable one. The order of the metastable zones of the stable and metastable polymorphs is reversed for the epitaxial growth process as compared to the case of 3D nucleation. The rate of transformation of the metastable polymorph to the stable one can be controlled by the supersaturation.

Acetone↗

PubMed2005

Experimental and computational growth morphology of two polymorphs of a yellow isoxazolone dye.

We report on the crystal structures and the experimentally found and the computationally predicted growth morphologies of two polymorphs of a yellow isoxazolone dye. The stable polymorph I has a blocklike habit, and the metastable polymorph II grows as fine needles, nucleating only by heterogeneous or contact nucleation. The habits of both polymorphs depend on the supersaturation during growth. The experimental observations are compared with predictions of the attachment energy model and kinetic Monte Carlo lattice simulations in which the growth is modeled as an "atomistic process", governed by surface energetics. These Monte Carlo simulations correctly predict the shape and the dependence on supersaturation of the crystal morphology for both polymorphs: for polymorph I, a strong dependence on supersaturation is found from the simulations. For polymorph II, the order of morphological importance is reproduced correctly, as well as the needlelike morphology.

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PubMed2004

Thickness-dependent ordering of water layers at the NaCl(100) surface.

We have determined the ordering properties of water adsorbed at room temperature on the rock salt (100) surface under four different conditions: ultrahigh vacuum, dry nitrogen atmosphere, 45% and 75% relative humidity. Details of the atomic structure are determined for both sides of the solid-liquid interface. The top most layer of NaCl shows a small relaxation that changes from an expansion to a contraction with increasing humidity. Under all measured conditions water monolayers with different ordering properties are present at the interface. Surprisingly, we find that the amount of ordering in the first layer is increasing with increasing thickness of the water film. At a solid-liquid interface, the ordering appears to be correlated with the solubility.

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PubMed2003

Liquid order at the interface of KDP crystals with water: evidence for icelike layers.

We present a surface x-ray diffraction study on the KDP-water interface in which the structure of both the crystalline and liquid part of the interface has been measured. We have been able to determine the ordering components in the liquid in both the perpendicular and parallel directions. We find interface-induced ordering in the first four layers of water molecules. The first two layers behave icelike and are strongly bound to the surface. The next two layers are more diffuse and show only minor lateral and perpendicular ordering. Subsequent layers are found to behave similar to a bulk liquid.

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PubMed2003

New (sqrt3 xsqrt 3)R30 degrees phase of Pb on Ge(111) and its consequence for the melting transition.

Depending on the preparation method, we find two different structures of the Pb/Ge(111) system at a nominal coverage of 4 / 3 monolayer that exhibit different melting points. One is the well studied beta phase that melts at 270 degrees C, but the other is a new and metastable phase that melts at 330 degrees C. Using surface x-ray diffraction the atomic structure of both phases is found to be surprisingly similar. The difference in melting points can be explained by the distribution of the excess Pb present on the surface, which has a direct effect on the vacancy density. We propose a modified phase diagram, in which the melting temperature of the beta phase depends strongly on coverage.

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PubMed2001

Controlling crystal surface termination by cleavage direction.

We have investigated the cleaving behavior of potassium bichromate (K(2)Cr(2)O(7)) crystals using atomic force microscopy. This crystal has a double layered AB structure along [001]. We find that, upon cleavage along the [001] plane in the <100> directions, one side is completely A terminated, while the other is B terminated. Moreover, the cleavage plane (between an A and a B layer, or between B and A) depends on the imposed direction of cleavage, i.e., [100] or [*100]. This means that the molecular layer that terminates the crystal surface can be controlled by choosing the macroscopic direction of the cleavage force. One of the two terminations is metastable and partly reconstructs to the stable termination.

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PubMed1998

The Dutch-Belgian beamline at the ESRF.

A brief description is given of the design principles and layout of the Dutch-Belgian beamline at the ESRF. This beamline optimizes the use of the available bending-magnet radiation fan by splitting the beam into two branches, each accommodating two experimental techniques.

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PubMed1997

Slits as adjustable pinholes for coherent X-ray scattering experiments.

The combination of accurate translation stages with carefully polished slit blades leads to slits that have many advantages as pinholes for coherent X-ray scattering experiments. The size is adjustable and can be made as small as 0.5 mum. Setting up is easy, while the blade thickness (1 mm tungsten) also makes the slits useful for hard X-rays. A relation between the slit-sample distance and the minimum beam size, together with the corresponding slit size, is derived. This shows that a micrometer-sized beam can be achieved with this type of slits.

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PubMed1996