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