Autocatalytic MBE growth of GaAs nanowires on oxidized Si(100)
  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. 
Janusz Sadowski, Piotr Dluzewski, Janusz Kanski