Overview of vertical nanostructures including (a) nanopillars,23 (b) nanowires,27 (c) nanoneedles,11 (d) nanotubes,55 (e) nanostraws,40 and (f) nanocones.57 The diameter, height, and aspect ratio of the vertical nanostructures are as follows: (a) 150 nm, 1.4 μm, 9; (b) 91 nm, 11 μm, 120; (c) 600 nm, 9 μm, 15; (d) 181 nm, 500 nm, 3; (e) 100 nm, 1.5 μm, 15; (f) 50 nm, 200 nm, 4. Scale bars are as follows: (a) 1 μm, (b) 500 nm, (c) 2 μm, (d) 200 nm. Reprinted with permission from the following: ref 23, Copyright 2015 Nature Publishing Group; ref 27, Copyright 2012 IOP Publishing Ltd.; ref 11, Copyright 2015 Nature Publishing Group; ref 55, Copyright 2014 Nature Publishing Group; ref 40, Copyright 2016 Royal Society of Chemistry; ref 57, Copyright 2014 Springer Nature.