4. Structure, Stabilities, and Electronic Properties of Smart Ceramic Composites

Since the discovery of graphene sheet, researches on atomic-layered materials have been growing as new and active research fields in nanoscience and nanotechnology. Hexagonal boron-nitride (h-BN) monolayers have also received much interest due to the superior structural and mechanical properties similar to graphene. This chapter reviews the first-principles density functional study that reveals the strain-induced effects on atomic configurations and electronic properties of h-BN monolayers. The dispersion of the energy bands and the band gaps are examined under biaxial strains, and the band gaps are shown to be controllable by applying strains. The ionization energies and work functions for acceptor and donor states are also examined and they are shown to be tunable. The scanning tunneling microscopy (STM) images of carbon-doped h-BN monolayer are demonstrated for identifications of carbon impurities and the possibility to observe the carbon defects is exhibited. The relationship between the energy band structures and the applied strains is also shown to discuss the unique behaviors of the band gaps and the ionization energies induced by biaxial strains.