“…Catalyst-free methods are instead not mediated by any metal or intermediate phase, but rather employ crystal growth rate anisotropies to drive the preferential growth in one dimension [ 5 ]. This technique, often referred to as vapor-solid, has been demonstrated for the growth of Si nanowires [ 113 ], III-V semiconductor [ 109 , 114 , 115 ], and ZnO nanowires [ 116 ]. Catalyst-free growth can be performed, exploiting a self-assembled growth approach which typically relies on substrate-nanowire lattice mismatch, or exploiting a selective area approach, such as selective area growth (SAG) or selective area epitaxy (SAE).…”