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