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