wherein {HEAD ~ a thickness} of the Mg Ag layer is in a range of 170 Å to {TAIL ~ 200 Å}, 
wherein { HEAD ~ a thickness } of the Mg Ag layer is in a range of 170 Å to { TAIL ~ 200 Å } ,
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH