Theoretical Investigations of Boron Related Materials Using DFT

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: In the history of Chemistry, materials chemists have developed their ideas mainly by doing experiments in laboratories. The underlying motivation for this laboratory work has generally been pure curiosity or the ambition to find a solution to a specific problem. Minor changes in the composition or structure of a material can cause major changes in its properties. The development of powerful computers has now opened up the possibility to calculate properties of new materials using quantum mechanical methods.The Chemistry of different boron-related materials has been evaluated in this thesis by Density Functional Theory (DFT). Cubic boron nitride (c-BN) is a most interesting material for the microelectronics and tool industry. During thin film deposition of c-BN, several problems arise which most often result in unwanted BN isomorphs. Chemical processes at the (110) and (111) surface of c-BN have been investigated in order to shed light upon some of these complex processes. Typically adsorption energies and surface reconstruction were found to differ significantly between the two surfaces. Other materials investigated are layered transition-metal diborides (MeB2). Incorporation of transition-metal atoms into elemental boron in its most fundamental structure, ?-boron, has also been investigated. The calculations on MeB2 focused on the stability of the planar compared to the puckered structure of MeB2. Stability was investigated by calculating Density of States (DOS) and bond populations. Deviations in the cell parameters from their ideal values were also considered. A separate project concerned reactivity of the TiB2(001) surface. Molecular and dissociated adsorption energies and adsorption geometries were calculated for H2, H2O and O2. It was concluded that the titanium surface was more reactive than the boron surface and that the adsorption energies were comparable to or stronger than other well known surface-active compounds like TiO2.