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