  Hexagonal boron nitride is widely used as a substrate for two-dimensional
materials in both electronic and photonic devices. Here, we demonstrate that
two-dimensional hexagonal boron nitride is also an ideal substrate for
one-dimensional single-walled carbon nanotubes. Nanotubes directly attached to
hexagonal boron nitride show bright photoluminescence with narrow linewidth at
room temperature, comparable to air-suspended nanotubes. Using
photoluminescence excitation spectroscopy, we unambiguously assign the
chiralities of nanotubes on boron nitride by tracking individual tubes before
and after contact with boron nitride. Although hexagonal boron nitride has a
low dielectric constant and is attached to only one side of the nanotubes, we
observe that optical transition energies are redshifted as much as ~50 meV from
the air-suspended nanotubes. We also perform statistical measurements on more
than 400 tubes, and the redshifts are found to be dependent on tube diameter.
This work opens up new possibilities for all-solid-state carbon nanotube
photonic devices by utilizing hexagonal boron nitride substrates.
