Monoatomic and molecular reactions with defected hexagonal boron nitride monolayers- A density functional theory study

Nicholas Mondinos

Accurate density functional theory (DFT) computations are developed to predict the formation of structurally feasible monolayer pristine and defected hexagonal boron nitride (h-BN). Valuable chemical, geometric and key electronic properties are determined from adatom and molecular interactions with the created monolayers. The computations modelled the pristine and defected h-BN monolayer on a 128 atoms (8x4) supercell and utilised the Vienna ab-initio simulation package (VASP). DFT computations were chosen over molecular dynamic (MD) simulations as the main focus was the structural optimisation for the formation and reactions of the monolayers, compared to motional and kinetic energy outcomes from MD. The pristine h-BN was configured to contain mono-vacancies (N or B), consecutive B di-vacancies, and Stone-Wales (SW) geometric defect. The defect monolayers were then reacted with selected 1st, 2nd and 3rd row elements (H, Li, C, O, Al, Si, P, and S) of the periodic table, and selected molecules (O2, CO, phenol, and pyridine). The monoatomic reactions are all predicted to be thermodynamically feasible and highly exothermic. Assessment of valuable physiochemical properties, indicate substantial variations of the adatoms Bader charges (-5.00 to +3.24 |e-|), adatom magnetic moments (-0.12 to 0.38 μB), total surface magnetic moments (-0.97 to +1.61 μB), and electronic band gaps of (0.19 – 4.14 eV). Successful monoatomic reactions were also tested to determine if CO would chemically interact with the surfaces. Reaction outcomes included chemisorbed and physisorbed products while some were predicted to produce dissociation of molecules, atoms or formation of excited atomic or diatomic moieties. The molecular reaction outcomes predict CO and phenol are more reactive with vacancy defected h-BN than with the SW defect while dissociative adsorption of O2 molecules is highly exothermicover vacancy defected BN and SW defect surfaces. The large phenol and pyridine molecules adsorbvertically through interaction with B in most considered structures and with a potential of finetuning their band gaps. Assessment of physiochemical properties predict nonmagnetic propertiesfor all h-BN and SW products, while the magnetic properties of the monovacancy reacted layersare very similar and in the range of +0.49 to +0.80 μB. Bader charge of reactants vary between -1.18 to +2.90 |e-| indicating charge transfer to/from the BN surface. Most products show potential of band gap finetuning and possible applications in chemical synthesis. The results predicted promotes a promising use of BN-based materials in optoelectronic and photo-electrochemical applications, physical-chemical sensors, as an addition to the theoretical foundation of decorated and defected h-BN.

Monoatomic and molecular reactions with defected hexagonal boron nitride monolayers- A density functional theory study

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