412
14 Nanostructures
Fig. 14.20 Density of
states for a (9, 0) metallic
and (10, 0) semiconducting
zig-zag carbon nanotube
within the tight-binding
approximation (13.2). The
energy scale is given in
units of the tight-binding
parameter T ≈ 3 eV. The
dashed lines are the DOS
of graphene. Adapted
from [1367]
Fig. 14.21 Calculated
absorption spectra for a
(semiconducting) (10, 0)
carbon nanotube for
parallel (solid line) and
perpendicular (dotted line)
polarization. The thick
(thin) lines are calculated
with (without) the matrix
element included. Adapted
from [1374]
14.3.4 Other Anorganic Nanotubes
Structures similar to carbon nanotubes have been reported for BN [1378, 1379]. A boron nitride
nanotube is a cylindrically rolled part of a BN sheet. BN tubes are always semiconducting (Fig. 14.23)
and have a band gap beyond 5 eV similar to hexagonal BN which is mostly independent on chirality
and diameter [1380]. Thus, while carbon nanotubes appear black since they absorb within 0–4 eV,
BN is transparent (or white if scattering). For high energies larger than 10 eV C and BN tubes are
quite similar since they are isoelectronic and the high-lying unoccupied states are less sensitive to the
difference in the nuclear charges than the states at and below the Fermi energy [1381].
14 Nanostructures
Fig. 14.20 Density of
states for a (9, 0) metallic
and (10, 0) semiconducting
zig-zag carbon nanotube
within the tight-binding
approximation (13.2). The
energy scale is given in
units of the tight-binding
parameter T ≈ 3 eV. The
dashed lines are the DOS
of graphene. Adapted
from [1367]
Fig. 14.21 Calculated
absorption spectra for a
(semiconducting) (10, 0)
carbon nanotube for
parallel (solid line) and
perpendicular (dotted line)
polarization. The thick
(thin) lines are calculated
with (without) the matrix
element included. Adapted
from [1374]
14.3.4 Other Anorganic Nanotubes
Structures similar to carbon nanotubes have been reported for BN [1378, 1379]. A boron nitride
nanotube is a cylindrically rolled part of a BN sheet. BN tubes are always semiconducting (Fig. 14.23)
and have a band gap beyond 5 eV similar to hexagonal BN which is mostly independent on chirality
and diameter [1380]. Thus, while carbon nanotubes appear black since they absorb within 0–4 eV,
BN is transparent (or white if scattering). For high energies larger than 10 eV C and BN tubes are
quite similar since they are isoelectronic and the high-lying unoccupied states are less sensitive to the
difference in the nuclear charges than the states at and below the Fermi energy [1381].