{TAIL ~ the first element} and the second element are substantially perpendicular to {HEAD ~ the substrate surface}, wherein 
{ TAIL ~ the first element } and the second element are substantially perpendicular to { HEAD ~ the substrate surface } , wherein
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH