Defects play a key role in determining the properties of most materials and, because they tend to be highly localized, characterizing them at the single-defect level is particularly important. Scanning tunneling microscopy (STM) has a history of imaging the electronic structure of individual point defects in conductors, semiconductors, and ultrathin films, but single-defect electronic characterization at the nanometer-scale remains an elusive goal for intrinsic bulk insulators. Here we report the characterization and manipulation of individual native defects in an intrinsic bulk hexagonal boron nitride (BN) insulator via STM. Normally, this would be impossible due to the lack of a conducting drain path for electrical current. We overcome this problem by employing a graphene/BN heterostructure, which exploits graphenes atomically thin nature to allow visualization of defect phenomena in the underlying bulk BN. We observe three different defect structures that we attribute to defects within the bulk insulating boron nitride. Using scanning tunneling spectroscopy (STS), we obtain charge and energy-level information for these BN defect structures. In addition to characterizing such defects, we find that it is also possible to manipulate them through voltage pulses applied to our STM tip.
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