Band structure of the (19,0) carbon nanotube: (a) pristine and (b) interacting with a (001) surface of a quartz substrate with tube axis along (100). The Fermi level is set to zero. The insets show the respective atomic structures. The yellowish clouds in the inset (b) represent a plot of the electronic density for states within energies of up to 0.1 eV around the Fermi level (red rectangle in (b)). The bands responsible for the gap closure are localized spatially in the contact region along the flat surface of the nanotube (adapted from [30]).
