This keeps the modified regions from reaching {HEAD ~ the outer face} of {TAIL ~ the substrate}, thus making it possible to prevent particles from occurring when forming the modified regions 
of
This keeps the modified regions from reaching { HEAD ~ the outer face } of { TAIL ~ the substrate } , thus making it possible to prevent particles from occurring when forming the modified regions
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD 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