•Mica surface ions were exchanged for Ag, Ca, Mn, Fe, Ni, Cu, Zn, Co, and Cd.•The metal ions remain at the surface after washing with water.•No counter ions are present after metal ion exchange.The surface potassium ions of muscovite mica were exchanged for several different metal ions from aqueous solution (Ag, Ca, V, Mn, Fe, Ni, Cu, Zn, Co, and Cd). The surfaces were rinsed in water, dried under nitrogen atmosphere, and subsequently analysed using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and, for half the systems, surface X-ray diffraction (SXRD). XPS and SXRD confirmed the presence of the different metal ions at the muscovite mica surface, with a partial monolayer of the monovalent and divalent ions present on the surface. No counter ions from the used salts were detected. AFM revealed that Ni-, and Fe-terminated muscovite mica surfaces were partially covered by nanoparticles, most likely consisting of metal (hydr)oxide. The exchanged ions remained on the surface after rinsing with ultra pure water three times. SXRD showed that Cd and Ag have a lower affinity for the muscovite mica surface than Cu, Ca, and Mn.Download high-res image (118KB)Download full-size image

•Au, Ag, and Cu surfaces reacted with different organothiols to give a new compound.•A carboxylic acid and thiol functional group are vital for a reaction to take place.•Organothiol chain length influences the speed of the reaction.Copper, silver and gold layers evaporated on the muscovite mica (001) surface were exposed to a series of molecules containing an organothiol and/or a carboxylic acid chemical functional group to investigate the potential of these compounds to modify the surfaces. The surfaces were investigated using optical microscopy, atomic force microscopy, scanning electron microscopy, energy dispersive analysis of X-rays, and X-ray diffraction. Organothiols containing a carboxylic acid group were found to change the surface morphology drastically over a period of days, while molecules containing only one of these functional groups were usually not able to do so. The mechanism is most likely a reaction between the organothiol and the metal surface, forming a thermodynamically stable new compound. This finding could be of importance in the many applications where organothiols are used to functionalize noble metal surfaces.Download high-res image (437KB)Download full-size image

Crystal growth occurs at the interface of a crystal and its growth medium. Due to the abrupt termination at the surface, at the interface the properties of the crystal will typically deviate from the bulk and this can affect the growth behaviour. Also the properties of the growth medium at the interface will typically differ from the bulk. In growth from solution, for example, the liquid will show ordering induced by the crystal surface or have a different composition. Here techniques to study such growth interfaces will be discussed together with examples of the effect that the properties of the interface can have on the growth.

The solid–liquid interface formed by single terminated muscovite mica in contact with two different ionic solutions is analyzed using surface X-ray diffraction. Specular and nonspecular crystal truncation rods of freshly cleaved mica immersed in CsCl or RbBr aqueous solution were measured. The half monolayer of the surface potassium ions present after the cleavage is completely replaced by the positive ions (Cs+ or Rb+) from the solution. These ions are located in the ditrigonal surface cavities with small outward relaxations with respect to the bulk potassium position. We find evidence for the presence of a partly ordered hydration shell around the surface Cs+ or Rb+ ions and partly ordered negative ions in the solution. The lateral liquid ordering induced by the crystalline surface vanishes at distances larger than 5 Å from the surface.

Viedma ripening was recently applied to a reaction enabling the conversion of achiral reactants in solution into enantiopure product crystals. Here we show that the configuration of the final product and the rate of deracemization are highly dependent on the initial crystal nucleation process or, if applied, seed crystals. Depending on the nucleation process, the transformation proceeds through total spontaneous resolution or Viedma ripening. Swift solid state deracemization can also be achieved using heating–cooling cycles as an alternative to Viedma ripening, provided that crystal nucleation results in a sufficiently high initial enantiomeric excess to trigger the deracemization process.

Chiral purification is a very important step in the production of many products such as active pharmaceutical ingredients (API). These procedures are typically limited to a maximum yield of 50%. Methods that include a racemization method, such as Viedma ripening, offer a theoretical yield of 100%. Racemic conglomerate formation is a necessary condition for chiral purification processes that exploit crystallization, such as Viedma ripening. This condition forms a limiting factor because only 10% of the chiral organic molecules crystallize in this way; the other 90% form racemic compounds. For two compounds that crystallize as racemic compounds we demonstrate that salt formation can transform these into racemic conglomerates and show that these can subsequently be fully deracemized using Viedma ripening. Salt formation thus promises to be a crystal engineering tool to significantly extend the applicability of Viedma ripening.

•One out of 2500 AFM measurements detected a step on muscovite surfaces.•Phase contrast microscopy detected a step-free area of 1 mm2 on muscovite.•Phase sensitive interferometry also did not find steps on this square millimetre.•Surface X-ray diffraction showed that 13 × 10 mm of muscovite is atomically flat.•The flatness of the muscovite is quality dependent.Muscovite mica is a widely used material because of its transparency, heat resistance and especially its flatness. This study investigates how flat muscovite mica really is. The surface of cleaved muscovite mica was studied with the help of several optical techniques, surface X-ray diffraction and with atomic force microscopy. The results show that for high-quality muscovite mica, large (> 1 cm2) step-free surface areas exist, which makes it one of the flattest materials around. Several reasons are given to explain why this crystal is so incredibly flat. The flatness of muscovite mica can be exploited in applications such as the surface force apparatus and creating a flat interface for organic solar cells.

Stable layers of crown ethers were grown on muscovite mica using the potassium–crown ether interaction. The multilayers were grown from solution and from the vapor phase and were analyzed with atomic force microscopy (AFM), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, and surface X-ray diffraction (SXRD). The results show that the first molecular layer of the three investigated dibenzo crown ethers is more rigid than the second because of the strong interaction of the first molecular layer with the potassium ions on the surface of muscovite mica. SXRD measurements revealed that for all of the investigated dibenzo crown ethers the first molecule lies relatively flat whereas the second lies more upright. The SXRD measurements further revealed that the molecules of the first layer of dibenzo-15-crown-5 are on top of a potassium atom, showing that the binding mechanism of this layer is indeed of the coordination complex form. The AFM and SXRD data are in good agreement, and the combination of these techniques is therefore a powerful way to determine the molecular orientation at surfaces.

Macromolecular crystallography is the most direct and accurate approach to determine the three-dimensional structure of biological macromolecules. The growth of high quality single crystals, yielding diffraction to the highest X-ray resolution, remains a bottleneck in this methodology. Here we show that through a modification of the batch crystallization method, an entirely convection-free crystallization environment is achieved, which enhances the purity and crystallinity of protein crystals. This is accomplished by using an upside-down geometry, where crystals grow at the “ceiling” of a growth-cell completely filled with the crystallization solution. The “ceiling crystals” experience the same diffusion-limited conditions as in space microgravity experiments. The new method was tested on bovine insulin and two hen egg-white lysozyme polymorphs. In all cases, ceiling crystals diffracted X-rays to resolution limits beyond that for other methods using similar crystallization conditions without further optimization. In addition, we demonstrate that the ceiling crystallization method leads to crystals with much lower impurity incorporation.

Viedma ripening is a process in which a compound that forms a stable racemic conglomerate can be converted to an enantiomerically pure solid state. Combining this deracemization process with Ostwald’s rule of stages, allows Viedma ripening to be extended to a racemic compound for which the conglomerate exists only in a metastable form. This is demonstrated for glutamic acid, a proteinogenic amino acid. Since Ostwald ripening is one of the processes occurring during Viedma ripening, we thus make use of Ostwald twice.

We report an in situ surface X-ray diffraction study of liquid AuIn metal alloys in contact with zinc-blende InP (111)B substrates at elevated temperatures. We observe strong layering of the liquid metal alloy in the first three atomic layers in contact with the substrate. The first atomic layer of the alloy has a higher indium concentration than in bulk. In addition, in this first layer we find evidence for in-plane ordering at hollow sites, which could sterically hinder nucleation of zinc-blende InP. This can explain the typical formation of the wurtzite crystal structure in InP nanowires grown from AuIn metal particles.

The recently discovered technique of deracemization by means of grinding a racemic conglomerate in contact with a solution wherein racemization occurs has been scaled up using an industrial bead mill to demonstrate the practical applicability. The time needed to reach the enantiopure end state is drastically reduced as a result of the efficient grinding that can be achieved using bead mills.

A new upside-down geometry is proposed to achieve the beneficial effects of microgravity crystal growth by making use of buoyant forces instead of compensating for them. We show by growth experiments on sodium chlorate and lysozyme that crystal growth in an upside-down geometry leads to the formation of a buoyancy assisted depletion zone where convection is suppressed. The effects on growth rate and morphology that are observed are all indicative of diffusion limited growth, just as would happen in the absence of gravity. The optical quality of the lysozyme crystals clearly improved, but no effects of the growth method on X-ray diffraction quality could be observed. The simplicity of the growth geometry offers the possibility to perform large scale protein crystal growth experiments under microgravity-like conditions, without the requirement of compensating for gravity.

If crystal growth from solution takes place in a closed container, a critical Rayleigh number can be defined, below which buoyancy driven convection is suppressed and mass transport is completely determined by diffusion at gravitational accelerations higher than 0g. Using finite element simulations and an analytical model, we show that it is possible to predict the critical value of the Rayleigh number. This result can be used to optimize growth conditions for microgravity protein crystal growth, if the gravitational acceleration cannot be canceled completely, like in space, or is canceled inhomogeneously, like in gradient magnetic fields.

Experiments on microgravity crystal growth in gradient magnetic fields for nickel sulfate and lysozyme are compared with finite element simulations. These simulations include the inhomogeneous effective gravity that accompanied the magnet experiments. An excellent agreement between the simulations and the experiments was found. Methods to reduce the adverse effects of the inhomogeneous effective gravity and to optimize the growth conditions are discussed.

Wurtzite ScAlN nanowires, grown on a scandium nitride (ScN) thin film by hydride vapor phase epitaxy (HVPE), were analyzed by energy dispersive analysis of X-rays (EDX), CL, high resolution transmission electron spectroscopy (HRTEM), and scanning electron microscopy (SEM). The wires were grown along the [0 0 0 1] axis, had an average length of 1μm, a diameter between 50 and 150 nm, and a ScAlN composition with a 95:5 Al:Sc ratio. Cathodoluminescence studies on the individual wires showed a sharp emission near 2.4 eV, originating from the Sc atoms in the aluminum nitride (AlN) matrix. The formation of such a semiconducting ScAlN alloy could present a new alternative to InAlN for optoelectronic applications operating in the 200–550 nm range.

Highlights•We introduce a new furnace for in situ surface X-ray diffraction experiments.•The furnace is designed to withstand corrosive environments.•Experiments can be performed up to 50 bar of pressure and 800° centigrade.•The growth of gallium nitride at 50 bar and 800° proves its validity.We introduce a high pressure high temperature chamber for in situ synchrotron X-ray studies. The chamber design allows for in situ studies of thin film growth from solution at deeply buried interfaces in harsh environments. The temperature can be controlled between room temperature and 1073 K while the pressure can be set as high as 50 bar using a variety of gases including N2 and NH3. The formation of GaN on the surface of a Ga13Na7 melt at 1073 K and 50 bar of N2 is presented as a performance test.