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