The spacer preferably comprises {TAIL ~ a material} selected from the group comprising refractory metal silicides and {HEAD ~ nitrides} 
The spacer preferably comprises { TAIL ~ a material } selected from the group comprising refractory metal silicides and { HEAD ~ nitrides }
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD