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