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