Dynamic hexagonal spreading patterns of small silicon droplets on the basal plane (001) of quartz were observed by video microscopy. A detailed analysis of the hexagonal triple line demonstrates that the patterns show slight chiral distortions that can be attributed to the screw axis of the substrate crystal. This article reveals the detailed influence of crystal symmetry on the anisotropy of reactive wetting. In this context, a first discussion about the interplay of wetting and etching of a crystal is provided.

Schematic representation of a semiconductor cluster isolated in the molecular beam during the flight though an electric Stern-Gerlach field. The cluster flies with a velocity v parallel to the cylindrical bent electrode surfaces, which can be seen in the cross section. The field induces a dipole moment in the cluster that is proportional to the polarizability. Owing to the well-defined inhomogeneity of the field a somewhat larger force is exerted on the negative partial charge than on the positive. The resulting force F and the polarizability can be determined in the molecular beam experiment from the deflection of the cluster from the linear flight path. REVIEWS Molecular Beam Studies on Semiconductor Clusters: Polarizabilities and Chemical BondingJorg August Becker* This article discusses experiments that measure polarizabilities, permanent dipole moments, and absorption spectra of semiconductor clusters such as Si,, Ga,As,w, and Ge,Te, isolated in a molecular beam. The experiments show that the transition from the typical optoelectronic properties of macroscopic semiconductor crystals to the molecular properties of small polyhedral semiconductor molecules occurs in several steps. The bonding in nanometer-sized semiconductor colloids with approximately 103-105 atoms is similar to that in the solid state. The bonding orbitals of the semiconductor crystals, which extend over a nanometer range, are, however, somewhat more strongly localized in these clusters and are therefore already slightly modified. Over the size range from lo3 to 10 atoms, a gradual transition occurs from localized solid-statelike bonds to molecule-like bonds. Interestingly, quantum size effects are found even in relatively small particles with about 10' atoms. These effects can be observed in the form of unusually small static polarizabilities of Si, clusters or in the absorption bands of Ga,As, clusters, which are strongly blue-shifted relative to those of the solid state. For smaller clusters, these effects disappear over the size range 10'-10 atoms, which is manifested by an increasing red-shift of the absorption bands with decreasing cluster size.

No abstract

No abstract

No abstract