In certain embodiments, {HEAD ~ multiple portions} of surface 501 are sequentially exposed to {TAIL ~ electromagnetic radiation} 
are sequentially exposed to
In certain embodiments , { HEAD ~ multiple portions } of surface 501 are sequentially exposed to { TAIL ~ electromagnetic radiation }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL