  The electronic structure of rhombohedral sp2 hybridized boron nitride (r-BN)
is characterized by X-ray absorption near-edge structure spectroscopy.
Measurements are performed at the boron and nitrogen K-edges (1s) and
interpreted with first-principles density functional theory calculations,
including final state effects by applying a core-hole. We show that it is
possible to distinguish between different 2D planar polytypes such as
rhombohedral, twinned rhombohedral, hexagonal and turbostratic BN by the
difference in chemical shifts. In particular, the chemical shift at the B
1s-edge is shown to be significant for the turbostratic polytype. This implies
that the band gap can be tuned by a superposition of different polytypes and
stacking of lattice planes.
