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