a The sub-band structure of quantum-confined TI surface states described by Eq. (1) (left) and corresponding density of states (right). b SEM image of nanowires (and other nanostructures) grown on a substrate. c TEM image revealing the single-crystalline nanowire body, the remainder of the 20 nm Au-nanoparticle growth catalyst, and a 4-nm thick oxide layer at the nanowire surface. The inset shows the SAED pattern taken in the c-axis direction. TEM image and SAED pattern were taken from different nanowires and directions. d false-color SEM micrograph of device 5 with the schematics of electrical wiring. Pt/Au leads are colored yellow, the nanowire is shown in green. The inset shows a magnified view of the nanowire. e Schematic 3D image of the device construction. Pt/Au leads are illustrated in yellow. The blue and red arrow illustrate the angular momentum ℓ. f R(T) curves of devices 1, 2, 4, and 5. (c) Felix Münning, Oliver Breunig, Henry F. Legg et al./ Nature