Shorena Dekanosidze

Ionic-covalent chemical or covalent-ionic chemical bonds usually occur in crystalline compounds. Therefore, for them, the polarity of the bond is an important characteristic, the magnitude of which affects the electronic structure and, through it, the properties of the substance. A good example of this is boron nitride.

Boron nitrides (BN) are compounds with bonds of covalent- ionic type. Therefore, binding polarity is an important characteristic affecting their physical properties. Dependencies of measurable parameters on static effective charges of constituent atoms are so complex that, these are virtually undetectable experimentally. As for the theoretically obtained atomic charges in boron nitrides, they are characterized by a significant scatter making them almost unreliable. The general reason for this lies in the impossibility of unambiguous division of the electron density between atoms of elements. It pushes the search for a semiempirical solution of the problem. We have derived the expression for the effective charge number q in a binary compound (effective charges of B and N atoms should be +qe and -qe, respectively) depending on number of molecules N in primitive parallelogram, its sectional area S transverse to the external electric field direction, Young's modulus Y and permittivity ε in same direction. Semiempirically estimated values of q (in a- and c-directions) are physically reasonable: hexagonal h-BN - 0.35 and 0.09, cubic c-BN - 0.49, and wurtzite-like w-BN boron nitrides - 0.76 and 0.50. Also quite natural are qualitative conclusions: in h-BN intralayer bonds polarity is much stronger than that between hexagonal layers; bonds are stronger polarized in denser modifications c-BN and w-BN, which are characterized by higher coordination numbers as well; bonds polarities in c-BN and along c-axis in w-BN are almost indistinguishable; and bonds polarities in a- and c-directions in w- BN are different. Obtained static charges can be used in the refinement of the BN electron structure calculations.

Influence of boron impurities on electron-transport in crystalline silicon is well known because p-Si – basic semiconducting material of the modern microelectronics – usually is obtained by doping with B. It is too important to understand the mechanism interaction of B dopants with radiation defects in silicon to (i) develop effective radiation treatment technologies for electronic devices and integrated circuits, (ii) improve their radiation resistance, and (iii) design effective solid-state radiation sensors and detectors.Based on authors' previous works the role of B-impurities in formation of secondary radiation defects in Si crystals is investigated. Dependences of these processes on isochronous annealing temperature (80–600 °C) are studied by using the Hall measurements of temperature-dependencies (100–300 K) of holes' concentration and mobility in silicon before and after irradiation with 8 MeV electrons at the dose of 5∙1015 cm–2. Two main conclusions are made: boron atoms in silicon crystals (i) serve as extremely active sinks of radiation defects, and (ii) participate in space-charge-screening of the relatively high-conductive inclusions in form of clusters of radiation defects.

In the frames of simple Drude model, there are analytically treated the general features of electron transport in 2D metals. It is demonstrated that depending on the Fermi level position such materials can reveal a nonstandard current–voltage characteristic opening wide perspectives of creating the novel functional 2D materials for superfast nanoelectronics

There are a number of experimental and many theoretical papers that support nanotubular forms of elemental boron.

Nanotubular boron is quite promising with significant technical applications. As is known, carbon nanotubes, which are semiconductors or semimetals, are widely used in practice. At the same time, structural defects are easily formed in them, which practically change the electrical conductivity without changing the radius. The advantage of boron is based on the fact that boron nanotubes are metallic conductors.