Incident angle dependence of nanogap size in suspended carbon nanotube shadow lithography

Suspended nanotubes or nanowires can be used in line-of-sight depositions to produce nanometre-scale lines. Reported here is the experimental quantification of line-of-sight shadow widths for multiwalled carbon nanotubes that are suspended (400 nm) over a silicon nitride (Si₃N ₄) membrane (transmission electron microscopy) TEM grid by a lithographically defined resist line array. Aluminium evaporation was performed at incident angles of 0.7°-2.0° by use of the slit (0.81 mm diameter). Shadow widths and carbon nanotube diameters were directly observed by scanning transmission electron microscopy (STEM). Observed gaps were less (0-7 nm) than that predicted from simple line-of-sight geometry. Thus, surface migration assisted by the momentum of incident metal evaporant may be an important mechanism in nanoscale shadow lithography processes.