Observation of Ultrathin Precursor Film Formation during Ge-Si Liquid-Phase Epitaxy from an Undersaturated Solution.

Our in situ X-ray study shows that a silicon substrate in contact with an undersaturated In(Ge) solution is wetted by an approximately 1 nm thin germanium film, which does not grow any thicker. The results can be understood by the use of thickness-dependent correlated interfacial energies. This near-equilibrium heterogeneous interface structure marks the initial stage of crystal growth before the formation of bulk material, which can only form under conditions of supersaturation. This finding uncovers a fundamental aspect of the thermodynamics at solid-liquid interfaces relevant for understanding the transition from equilibrium to supersaturation and is of importance for nanoscale solution growth methods.

Structure and activity of the anticaking agent iron(III) meso-tartrate.

Iron(III) meso-tartrate, a metal-organic complex, is a new anticaking agent for sodium chloride. A molecular structure in solution is proposed, based on a combination of experimental and molecular modelling results. We show that the active complex is a binuclear iron(iii) complex with two bridging meso-tartrate ligands. The iron atoms are antiferromagnetically coupled, resulting in a reduced paramagnetic nature of the solution. In solution, a water molecule coordinates to each iron atom as a sixth ligand, resulting in an octahedral symmetry around each iron atom. When the water molecule is removed, a flat and charged site is exposed, matching the charge distribution of the {100} sodium chloride crystal surface. This charge distribution is also found in the iron(iii) citrate complex, another anticaking agent. This gives a possible adsorption geometry on the crystal surface, which in turn explains the anticaking activity of the iron(III) meso-tartrate complex.

Formation of wurtzite InP nanowires explained by liquid-ordering.

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.

Complete chiral symmetry breaking of an amino acid derivative directed by circularly polarized light.

Circularly polarized light (CPL) emitted from star-forming regions is an attractive candidate as a cause of single chirality in nature. It has remained difficult, however, to translate the relatively small chemical effects observed on irradiation of molecular systems with CPL into high enantiomeric excesses. Here we demonstrate that irradiation of a racemic amino acid derivative with CPL leads to a small amount of chiral induction that can be amplified readily to give an enantiopure solid phase. A racemate composed of equal amounts of left- and right-handed crystals in contact with the irradiated solution is converted completely into crystals of single-handedness through abrasive grinding when racemization is effected in the solution. The rotation sense of the CPL fully determines the handedness of the final solid state. These findings illustrate the potential effectiveness of CPL in the control of molecular asymmetry, which is relevant for the origin of the single chirality inherent to many biological molecules.