Ions with {HEAD ~ a specific mass} to charge ratio may selectively pass through the duct and {TAIL ~ impinge} on the substrate surface 
Ions with { HEAD ~ a specific mass } to charge ratio may selectively pass through the duct and { TAIL ~ impinge } on the substrate surface
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH