 starting {TAIL ~ the simultaneous depositing} of Al and {HEAD ~ Ga} atom to form adjacent Al and Ga monolayers 
starting { TAIL ~ the simultaneous depositing } of Al and { HEAD ~ Ga } atom to form adjacent Al and Ga monolayers
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH