Browsing by Author "Krasheninnikov, Arkady V., Dr., Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Germany"

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    Structure and properties of two-dimensional BCN materials from first-principles calculations
    (Aalto University, 2021) Berseneva, Natalia; Krasheninnikov, Arkady V., Dr., Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Germany; Komsa, Hannu-Pekka, Dr., University of Oulu, Finland; Puska, Martti, Prof., Aalto University, Finland; Teknillisen fysiikan laitos; Department of Applied Physics; Computational Electronic Structure Theory (CEST) group; Perustieteiden korkeakoulu; School of Science; Rinke, Patrick, Assoc. Prof., Aalto University, Department of Applied Physics, Finland
    Hexagonal boron nitride (h-BN) and graphene are two prominent members of the two-dimensional (2D) materials family. Even though they are structurally similar, they possess contrasting electronic properties; graphene is a zero-bandgap semiconductor or semimetal, while h-BN is a wide band gap semiconductor. Therefore, combining them in one system—either as an alloy or as a heterostructure —can give rise to development of a new composite system with tuneable characteristics. The research presented in this thesis is focused on the properties of lateral BN-C heterostructures, as well as of BCN alloys where atoms are randomly distributed. The thesis illustrates that the mechanical and electronic properties of BCN alloys are governed by the concentrations and arrangements of the constituent elements. It is shown that the electron energy band gap of the BCN material can be continuously tuned from zero, as in graphene, to that of pristine h-BN (about 6 eV), what suggests the possibility to manufacture a 2D semiconductor with a controllable band gap. The energetics of BCN alloys on metal substrates was studied and it was shown that ruthenium substrate facilitates formation of a non-homogeneous BCN monolayer. The electronic properties of BN-C heterostructures with substitutional triangular carbon islands embedded into the h-BN host matrix were also investigated. Modern electronics demands not only materials with desired electronic properties, but also materials with specific magnetic characteristics. The thesis demonstrates that although h-BN is a non-magnetic material, it exhibits magnetic moments when B or N atoms are substituted by C. Furthermore, charging the system electrically affects the value of the possessed magnetic moment, which enhances usability of such h-BN systems. Commonly, materials used in electronics industry should be mechanically robust. This thesis reports mechanical properties of mixed BCN systems and shows that due to their excellent mechanical properties, h-BN structures can be used as reinforcing agents in bulk materials such as metals. This dissertation considers reinforcing of bulk aluminium by h-BN sheets and nanotubes. A proposed way to improve the strength of such a structure is through enhancing the adhesion at the interface between Al and h-BN by introducing point defects into the h-BN matrix. The results presented in this thesis support experimental phenomena. For example, they elucidate the mechanism of h-BN doping under electron beam irradiation. They also shed light on the growth of mixed BCN materials. The thesis further addresses computational challenges relevant to 2D materials, e.g., the problem of calculating accurate defect formation energies for charged systems. Consequently, the results of this thesis can support progress in both experimental work and simulations focused on 2D materials with defects.