First-Principles Study On The Functional Modulations Of Low-dimensional Boron Nitride Nanostructures

By performing First-Principles calculation methods, we studied and simulated thefunctional modulation of low-dimensional Boron Nitride (BN) nanostructures, such asthe formation mechanism and characterization of antisite atom segregation in porous BNnanotubes, and hydrogen adsorption induced metallization and transport properties ofgrain boundaries in BN nanosheet.First, from thermodynamics and chemical bonding dynamics, we studied antisiteatom segregation in porous boron nitride nanotubes (BNNTs), with respect to prefec-t counterparts, using density functional theory. Thermodynamic considerations showedthat the pores were able to overcome the barrier of antisite atom segregation; determin-ing the phenomenon is impossible or very difcult in the nanotube growth. A two-stepsynthesis approach was proposed for atom segregation or chemical doping. B and Natom segregations at the vacancy experienced quite diferent chemical bonding processes,which were ascribed to the nature of inserted B and N "clusters" and exhibited diferentredox properties. The B atoms prefered large-scale segregation, whereas the N atomstended to form some separate "segregated units". We proposed that diferent structuresand properties allow antisite atom segregation in BNNTs, either nonporous or porous, toofer many promising applications in new fields, such as biolabeling, purification, chem-ical, and biological separations.Second, from electronic structure calculation, we found that5-8-5line grain bound-aries greatly increased the hydrogen adsorption capability of BN sheets, meanwhile dis-tinctly modulated their bad gap, even led to insulator-metal translation, and induced mag-netism. From thermodynamics, the migration barrier of hydrogen adsorbed from intrin-sic sits to boundaries sites were general small, indicating that hydrogen atoms were aptto adsorb on BN boundaries rather than intrinsic site. Due to the diferent propertiesof Boron boundaries and Nitride boundaries, they experience diferent chemical bond-ing processes during hydrogen adsorption, which led to diferent electronic properties.Boron boundaries with hydrogen adsorption exhibit spin-semiconductor property, whichwas ascribed to Stoner Efect and made BN can be applied in spintronics switch de-vices; while hydrogen adsorption led Nitride boundaries to insulator-metal translationand induced magnetism, making them ideal one-dimensional metallic wires embedded in two-dimensional insulator, which had significant meaning in spintronics application.We also study the transport properties of Nitride boundaries with hydrogen adsorptionby using non-equilibrium electron transport method, and found that the system exhibitedNegative Diferential Resistance phenomena. This was ascribed to charge accumulationat the interface of electrodes and scattering area, which screened part of the applied elec-trical field with bias increasing. Negative Diferential Resistance phenomena proposedthis system as an ideal material of voltage regulator device.