A dilution gas for {TAIL ~ use} at the time of forming the surface layer is made of hydrogen , argon or {HEAD ~ helium} or the like 
A dilution gas for { TAIL ~ use } at the time of forming the surface layer is made of hydrogen , argon or { HEAD ~ helium } or the like
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH