First, {HEAD ~ a periodic array} of monoatomic surface steps are created on the surface of the substrate at an area to have {TAIL ~ the superlattice structure} grown thereon 
First , { HEAD ~ a periodic array } of monoatomic surface steps are created on the surface of the substrate at an area to have { TAIL ~ the superlattice structure } grown thereon
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH