Stabilization of silicon honeycomb chains by trivalent adsorbates
  The atomic structure of self-assembled quasi-one-dimensional Gd chains on Si(111) has been investigated by low-energy electron diffraction and scanning tunneling microscopy. Based on comparison between Gd and Ca chains we show that this Gd induced surface reconstruction belongs to the class of honeycomb chain-channel structures. This clearly demonstrates that, besides monovalent and divalent adsorbates, also trivalent adsorbates such as Gd stabilize silicon honeycomb chains. Consequently silicon honeycomb chains emerge as an universal building block in adsorbate induced silicon surface reconstructions. 
C. Battaglia, H. Cercellier, C. Monney, M.G. Garnier, P. Aebi