J.P. van der Eerden

Thermodynamical stability conditions for the occurrence of hollow cores caused by stress of line and planar defects

Abstract A general stress function for screw or edge dislocations is presented and discussed. Upon introducing this stress function into a formalism to check the stability of hollow cores around dislocations, it turns out that several cases can be distinguished. If the stress field is strong enough there may or may not exist a thermodynamical stable hollow core, depending on the driving force. Above a critical super- or undersaturation Δμ∗1 the hollow core will be closed, below a critical undersaturation Δμ∗2 the hollow core is replaced by a steep etchpit. If, on the other hand, the stress field is too weak hollow cores do not occur. A few examples of observed hollow cores, demonstrating the theory will be presented.

The direct correlation function in hard sphere fluids

The pair correlation function in a homogeneous hard sphere fluid at various densities has been measured in a large system, using the Monte Carlo method. The corresponding direct correlation function C2(r) has been determined directly from these measurements, and will be given here in closed form. We conclude that density functional models that neglect the effect of C3 and higher order direct correlation functions, that are defined in bulk fluids, are not able to describe an inhomogeneous hard sphere fluid accurately.

On the observation of the roughening transition of organic crystals, growing from solution

Abstract In order to determine whether a face (hkl) of a crystal is growing above or below the roughening temperature the quantities αhkl and αRhkl will be used. A method to calculate αRhkl has been given before. A method to calculate αhkl of a case (hkl) of a crystal in equilibrium with a saturated solution is presented for the case of a regular solution. The morphology of crystals, growing with faces below and above the roughening temperature is investigated experimentally. The transition from faceted to non-faceted growth, caused by kinetical roughening, which depends on the supersaturation, is investigated for the {110}; and {201}; faces of napthalene growing from toluene. The experimental results are in satisfying agreement with the expectations resulting from the calculated values of αhkl and αRhkl.

Determination of the Ising critical-temperature of F slices with an application to garnet

In this paper a general and simple method to calculate exactly the critical temperature for Ising nets on periodic structures is introduced. The method can be used to predict the morphological importance of F slices for realistic crystals. As an illustration it is applied to several types of garnet. The results are confronted with morphological data.

Formation of macrosteps due to time dependent impurity adsorption

Abstract A new model for the influence of non-equilibrium impurity adsorption on the collective behaviour of growth steps is presented. It is shown to lead to a dynamical coupling of step motion. Under quite general condtions this leads to a macrostep height increasing proportional to In(time). Predictions for and comparisons with experiments are indicated.

Hard sphere fluids near a hard wall and a hard cylinder

The local structure of a hard sphere fluid near a hard wall and near a hard cylinder is investigated using the Monte Carlo method. Near the wall we find a reduction in the average fluid density, and in the normal diffusivity. The simulation results are compared with the predictions of a density functional model. In this model the local density profile of a hard sphere fluid can be calculated in d-dimensional symmetry for any real symmetry dimension.

Growth of gypsum. I, Kinetics

Abstract A suspension of gypsum (CaSO 4 ▿2H 2 O) crystals has been grown from electrolyte solutions using the constant composition technique. In pure water a parabolic rate law governs the growth kinetics, while in NaNO 3 solutions the order increases from 1 at low supersaturations up to 4 at higher supersaturations. In NaNO 3 platelike crystals with some roughened faces develop under the given growth conditions. The higher growth rate in electrolyte solutions is partly due to the higher impingement rate and partly to a higher incorporation rate at the surface. The growth rate increases with increasing temperature.

Orientational order in naphthalene crystal-solution interfaces

Abstract We present experimental studies of growth forms of naphthalene crystals growing from various solutions under the condition that the classical α-factor of Jackson (i.e. the ratio of the heat of dissolution to the temperature) is essentially constant for all cases studied. If the molecules of the solvent contain phenyl rings or similar rings (in particular: pyridine), the side faces of the crystals become round at moderate supersaturations, indicating small step free energies. If the molecules of the solvent do not contain phenyl rings, but are of elongated or roughy spherical shape, the crystals stay faceted at all accessible supersaturations, indicating a much higher step free energy on the side faces. The analysis shows that these results are not compatible with the Jackson interface model. We suggest that in the first case there exists orientational order (a quasi smectic layer) in the liquid adjacent to the crystal faces. In the latter case the order is disturbed by the molecules of spherical or elongated shape, penetrating the ordered layers.

On the influence of surface diffusion and step integration kinetics on spiral growth

Abstract The results of an analytical theory for the surface diffusion problem on a surface which contains a single growth spiral are discussed. Different regimes for the spiral growth mechanism are identified and the supersaturation dependence of the growth rate and of the slope of the spiral hillock are given for each of the regimes. An implicit equation for the slope is fiven which replaces the, partially ad hoc, estimations of the previous back force theories. The role of tapering of the spiral hillock is discussed and it is argued that its influence is probably negligible for most experimental situations.

Scanning tunneling microscopy in an electrochemical system

Abstract Crystal growth can be studied by the observation of growth phenomena on the surfaces of these crystals. Using optical microscopy these phenomena can be examined both ex situ and in situ. Despite the high vertical resolution (~10 A) of some of these techniques (e.g. differential interference contrast microscopy) their lateral resolution is still poor (~ 1 μ). As a consequence it is possible to detect rather low growth steps, but not their shape. In order to obtain also a higher lateral resolution scanning tunneling microscopy (STM) was used on electrolytically grown Ag(100) single crystals. First as-grown surfaces were studied with an STM operating at atmospheric conditions. Second a new STM is described with which it is possible to operate in an electrochemical system (in situ STM). Some first results of this microscope are shown and related to optical microscopical observations.