Mesoscopic fluctuations of electronic structure properties of boron phosphide nanocrystals
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- Abdulsattar, M.A. Electron. Mater. Lett. (2010) 6: 97. doi:10.3365/eml.2010.09.097
The ab initio restricted Hartree-Fock method is used to simulate the electronic structure of relatively large boron phosphide nanocrystals (216–1000 atoms). The calculations are divided into two parts, surface and core. Nanocrystals are found to have smaller lattice constants and higher ionicity as they increase in size. The core calculations show increasing energy gap, cohesive energy, and valence bandwidth as well as highly degenerated states with increasing nanocrystal size. The energy gap, cohesive energy, and valence bandwidth have damping fluctuations as these quantities converge to constant bulk values as the nanocrystal reaches a high number of atoms. These fluctuations are similar to mesoscopic fluctuations that converge to bulk values and are related to the geometry and various surfaces of the core. Unlike the core part, the hydrogenated B-terminated (001)-(1×1) surface of these crystals has a smaller energy gap, and wider valence and conduction bands. Reduced symmetry caused less degenerate states to occur at the surface. Having slightly different lattice constants, both core and shell parts experience stresses to match each other dimensions. On the other hand, unlike the energy gap, the ionization potentials and affinity do not converge to a unique value as the core of nanocrystals increases in size because of the different surfaces that bound these nanocrystals.