Being a flexible wide band gap semiconductor, hexagonal boron nitride (h-BN) has great potential for technological applications like efficient deep ultraviolet (DUV) light sources, building block for two-dimensional heterostructures and room temperature single photon emitters in the UV and visible spectral range. To enable such applications, it is mandatory to reach a better understanding of the electronic and optical properties of h-BN and the impact of various structural defects. Despite the large efforts in the last years, aspects such as the electronic band gap value, the exciton binding energy and the effect of point defects remained elusive, particularly when considering a single monolayer.Here, we directly measured the density of states of a single monolayer of h-BN epitaxially grown on highly oriented pyrolytic graphite, by performing low temperature scanning tunneling microscopy (LT-STM) and spectroscopy (STS). The observed h-BN electronic band gap on defect-free regions is (6.8 ± 0.2) eV. Using optical spectroscopy to obtain the h-BN optical band gap, the exciton binding energy is determined as being of (0.7 ± 0.2) eV. In addition, the locally excited cathodoluminescence and photoluminescence show complex spectra that are typically associated to intragap states related to carbon defects. Moreover, in some regions of the monolayer h-BN we identify, using STM, point defects which have intragap electronic levels around 2.0 eV below the Fermi level.

The electronic structure, lattice dynamics, and electron–phonon coupling of pure, boron and nitrogen-doped diamond carbon were investigated using first-principle calculations within the generalized-gradient and virtual crystal approximations. To examine the influence of the impurity content and pressure on the superconductivity of these systems, the electron–phonon coupling constant (λ) and the critical temperature (Tc) were calculated as a function of concentrations from 0 to 15% and pressures from 0 to 90 GPa. Regarding the boron-doped diamond, calculations indicated that its electron–phonon coupling strongly relates to the optical phonon modes, and the estimated critical temperatures matched previous theoretical and experimental results. Regarding the nitrogen-doped case, it was observed that both λ and Tc were larger than those obtained for the hole-doped case. The most distinguishing feature of this system was its rising acoustic contribution to the electron–phonon coupling, which led to significant values for λ and Tc. The majority of the scenarios investigated here presented a decreasing critical temperature with increasing pressure. In contrast to the other cases, C0.85N0.15 exhibited a positive dependence between Tc and pressure leading to a superconducting transition temperature of about 122 K at 20 GPa.

This study comprises an investigation of the superconductivity in highly doped diamond, comprising elements from groups III and V acting as acceptor and donor impurities, respectively, within the virtual crystal approximation. Calculations of the electron–phonon coupling were carried out for each case, enlightening the different aspects arising from different doping elements and their consequent impact on the superconducting critical temperature. These calculations indicated that among the hole-doped cases the electron–phonon coupling is strongly related to the optical phonons of the lattice. Regarding the electron-doped systems, it was observed that the coupling had contributions from both optical and acoustic vibrations, leading to high estimates for the critical temperature. Through the comparison between these opposing scenarios, several distinctions between the electron- and hole-doped cases became evident, implying that the mechanisms of superconductivity in doped diamond relate directly to the nature of the impurity added to the system. These results provide further evidence that the electronic and dynamic changes arising from the electron doping of a diamond may lead to superconductivity in high temperatures.

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