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The Au-assisted molecular beam epitaxial growth of InAs nanowires is discussed. In situ reflection high-energy electron diffraction observations of phase transitions of the catalyst particles indicate that they can be liquid below the eutectic point of the Au-In alloy. The temperature range where the catalyst can be liquid covers the range where we observed nanowire formation (380–430 °C). The variation of nanowire growth rate with temperature is investigated. Pure axial nanowire growth is observed at high temperature while mixed axial/lateral growth occurs at low temperature. The change of the InAs nanowire shape with growth duration is studied. It is shown that significant lateral growth of the lower part of the nanowire starts when its length exceeds a critical value, so that their shape presents a steplike profile along their axis. A theoretical model is proposed to explain the nanowire morphology as a result of the axial and lateral contributions of the nanowire growth. [ABSTRACT FROM AUTHOR]

The polarity of GaN nanowires grown on Si(111) by molecularbeamepitaxy is determined by convergent beam electron diffraction. Thickspecimens lead to unambiguous results showing their N-polarity. Complementarysample etching indicates that all the nanowires have the same N-polarityand are surrounded by a Ga-polar two-dimensional layer. A correlationwith the initial growth stage which uses consecutive exposures ofthe Si substrate to Al and N is established. Al–Si liquid dropletsare formed and produce AlN columnar pedestals playing the role ofseeds for the GaN nanowires. On the surrounding Si surface, the GaNlayer nucleates with the opposite Ga-polarity. [ABSTRACT FROM AUTHOR]