R. J. Baierle

Formation energy of native defects in BN nanotubes: an ab initio study

Electronic and structural properties of several charge states of vacancies, antisites and carbon substitutional impurities in a (10, 0) BN nanotube are investigated through density functional theory calculations. The formation energies indicate that neutral and simply charged states occur in the range of allowable electronic chemical potential. For carbon substitutional impurities, the most probable states are, besides the neutrals, the positively charged state for carbon at a boron site (CB+), and the negatively charged state for carbon at a nitrogen site (CN−). The charge compensation between neighbouring pairs of CB+ and CN− defects is suggested to explain the successful experimentally obtained boron carbonitride nanotubes. Vacancies always present high formation energies. The neutral and positively charged states of the nitrogen antisite show low formation energies. The calculated formation energies for all defects studied here can be interpreted as due to two main effects: a tendency to recover the number of electrons of the defect-free BN nanotube and the screening effects due to the perturbative potential of the defects.

Rationalizing the Hydrogen and Oxygen Evolution Reaction Activity of Two-Dimensional Hydrogenated Silicene and Germanene

We have undertaken first-principles electronic structure calculations to show that the chemical functionalization of two-dimensional hydrogenated silicene (silicane) and germanene (germanane) can become a powerful tool to increase the photocatalytic water-splitting activity. Spin-polarized density functional theory within the GGA-PBE and HSE06 types of exchange correlation functionals has been used to obtain the structural, electronic, and optical properties of silicane and germanane functionalized with a series of nonmetals (N, P, and S), alkali metals (Li, Na, and K) and alkaline-earth metals (Mg and Ca). The surface-adsorbate interaction between the functionalized systems with H2 and O2 molecules that leads to envisaged hydrogen and oxygen evolution reaction activity has been determined.

First principles study of Si-doped BC2N nanotubes

Spin polarized density functional theory is used to investigate the incorporation of substitutional Si atoms in the zigzag (5,0) and in the armchair (3,3) BC(2)N nanotubes (NTs). Our results show that the Si impurities in BC(2)N NTs have lower formation energy when compared to Si in carbon and boron nitride NTs. In neutral charge state, Si in the boron site (Si(B)) presents a spin split with two electronic levels within the NT band gap and it gives rise to a net spin magnetic moment net of 1mu(B). Si in the nitrogen site (Si(N)) introduces electronic levels near the top of the valence band that lead the system to exhibit acceptor properties, which suggest the formation of defect-induced type-p BC(2)N NTs. The defective levels for Si in the two nonequivalent carbon atom sites (Si(CI) and Si(CII)) are resonant with the valence and conduction bands, respectively. The calculations of formation energy in charge state show that for all the available values of the electronic chemical potential, Si(CI) and Si(CII) have lower formation energy in neutral charge state, while Si(B) and Si(N) present lower formation energy in neutral or single negative charge state depending on the position of the electronic chemical potential.

The effect of impurities in ultra-thin hydrogenated silicene and germanene: a first principles study.

Spin polarized density functional theory within the GGA-PBE and HSE06 approach for the exchange correlation term has been used to investigate the stability and electronic properties of nitrogen and boron impurities in single layers of silicane and germanane. We have observed that these impurities have lower formation energies in silicane and germanane when compared to their counterparts in graphane. We have also noticed that the adsorption of H atoms in the vicinity of defects stabilizes the system. In addition, we have shown that the electronic properties of silicane and germanane can be tuned when N and B are incorporated in the Si and Ge network. N-doping and B-doping give rise to n-type and p-type semiconductor properties. However, the adsorption of H atoms quenches the doping effects.

Segregation of phosphorus to SiO2/Si(001) interfaces

Abstract Dopant atoms segregate to SiO2/Si(001) interfaces. This causes problems during manufacture of submicron microelectronic devices. On the basis of ab initio calculations, we identify the physical mechanism by which P atoms are trapped and deactivated at SiO2/Si(001). We argue that segregation can occur to defected as well as to defect-free interfaces. In the latter case, the interfacial stress stabilizes pairs of threefold-coordinated phosphorus atoms. Implications for Complementary Metal-Oxide-Semiconductor (CMOS) process design are discussed.

Métodos de Cálculo de Estrutura Eletrônica de Materiais Nanoestruturados

Resumo Neste trabalho é apresentado uma descrição dos métodos de cálculo de estrutura eletrônica de materiais nanoestruturados. Inicialmente apresentamos as aproximações básicas para o cálculo quântico. Apresentamos os métodos de Hartree-Fock e da Teoria do Funcional da Densidade para a solução do problema eletrônico. Ao final, uma abordagem do problema nuclear através do método de dinâmica molecular clássico é apresentado.