  We present experimental data and computational analysis of the formation of
GaN nanowires on graphene virtual substrates. We show that GaN nanowires on
graphene exhibit nitrogen polarity. We employ the DFT-based computational
analysis to demonstrate that among different possible configurations of Ga and
N atoms only the N-polar one is stable. We suggest that polarity discrimination
occurs due to the dipole interaction between the GaN nanocrystal and
$\pi$-orbitals of the graphene sheet.
