Grain boundaries (GBs) of hexagonal
boron nitride (h-BN) grown on Cu(111) were investigated by scanning
tunneling microscopy/spectroscopy (STM/STS). The first experimental
evidence of the GBs composed of square-octagon pairs (4|8 GBs) was
given, together with those containing pentagon-heptagon pairs (5|7
GBs). Two types of GBs were found to exhibit significantly different
electronic properties, where the band gap of the 5|7 GB was dramatically
decreased as compared with that of the 4|8 GB, consistent with our
obtained result from density functional theory (DFT) calculations.
Moreover, the present work may provide a possibility of tuning the
inert electronic property of h-BN via grain boundary engineering