  GaAs nanowires were grown by molecular beam epitaxy on Si(100) substrates
covered with 5 nm SiO2. The growth was performed with As4 at low, close to
stoichiometric, As4/Ga flux ratio, using Ga nanodroplets as catalyst. The
nanowires are found to be in epitaxial relation to the Si substrate due to
contact via pinholes through the SiO2 layer. The nanowires are up to 15
micrometers long and have diameters of about 100 nm, the catalyzing Ga
nanodroplets are observed at their tops.
