A solid material or {HEAD ~ combination} of {TAIL ~ materials} is evaporated in the chamber to form vapor 
A solid material or { HEAD ~ combination } of { TAIL ~ materials } is evaporated in the chamber to form vapor
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH