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