Crystallographic defects play a crucial role in the properties of materials, with some being harmful while others are useful for specific applications, such as controlling electrical properties or creating artificial atoms for quantum technologies. Identifying these defects is essential but challenging. In collaboration of scientists from University of Montpelliers, Kansas State University and Polish Academy of Sciences in collaboration with Dr. Anton Pershin and Prof. Ádám Gali from Wigner Research Centre for Physics and Budapest University of Technology and Economics presented a novel methodology to identify point defects that combines isotope substitution and polytype control, along with a systematic comparison between experimental results and first-principles calculations. In particular, Dr. Anton Pershin and Prof. Ádám Gali brought insights on defect engineering of these defects from first-principles calculations that were verified in experiments.
They applied this methodology to hexagonal boron nitride (ℎ-BN) and its UV-emitting color center. By performing isotopic purification on the ℎ-BN matrix, they uncovered a local vibrational mode associated with the defect. Isotope-selective carbon doping confirms that this mode corresponds to a carbon-based defect. Further analysis, involving the variation of the stacking sequence of the ℎ-BN matrix, reveals different optical responses to hydrostatic pressure for nonequivalent defect configurations. Their results indicate that this UV color center is a carbon dimer within the ℎ-BN honeycomb lattice.
This work demonstrates that isotope substitution, both for the host matrix and its impurities, is a powerful tool for defect identification. Additionally, by tuning the stacking sequence in different polytypes of a material, unique signatures are created that aid in the identification of defects in two-dimensional materials.
