 Figure 1(a) shows a schematic of the deposition in the "downhill" direction, that is, from an outer step edge to a lower terrace.The deposition angle "β" between the beam and surface is small (1°-3°) so that some areas of the terraces are exposed to the beam, and others are geometrically shadowed.The deposition angle "β" determines the width of the nanostructures, according to the following relation