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The energetic stability, electronic and structural properties of MoS2 adsorbed on an amorphous a-HfO2 surface (MoS2/HfO2) are examined through ab initio theoretical investigations. Our total energy results indicate that the formation of MoS2/HfO2 is an exothermic process with an adsorption energy of 34 meV/Ų, which means that it is more stable than similar systems like graphene/HfO2 and MoS2/SiO2. There are no chemical bonds at the MoS2-HfO2 interface. Upon formation of MoS2/HfO2, the electronic charge distribution is mostly localized at the interface region with no net charge transfer between the adsorbed MoS2 sheet and -HfO2 surface. However, the MoS2 sheet becomes n-type doped when there are oxygen vacancies in the HfO2 surface. Further investigation of the electronic distribution reveals that there are no electron- and hole-rich regions (electron-hole puddles) on the MoS2 sheet, which makes this system promising for use in high-speed nanoelectronic devices. [ABSTRACT FROM AUTHOR]

GaP nanowire, a potential material for new devices where optical and electronic applications can be merged, suffers some limitations because it presents indirect band gap. Using first principles calculations we demonstrate that, due to confinement effects, the band gap not only is enlarged when in a nanowire form, but can be transformed to a direct band gap semiconductor nanowire, just by reducing the nanowire diameter to few nanometers. This transition to a direct band gap is obtained for [111] oriented GaP nanowires but not for [110] oriented nanowires. The effects of surface states which can alter the band gap have been studied with hydrogen saturation and an oxide cap layer on the surface of the GaP nanowire. The results show that, while the hydrogen is a perfect passivator, the GaP/Ga2O3 heterojunction presents a small conduction band offset but keeps direct band gap [111] oriented GaP nanowires. [ABSTRACT FROM AUTHOR]

Extended defects like stacking faults (SFs) can originate topologically protected metallic states in bulk topological insulators (TIs). These induced topological states are a response to the weakening of the inter-layer van der Waals interactions due to the SF defect. In TI thin films, the degeneracy of Dirac bands of opposite surfaces can be lifted upon the formation of SF defects. Such slab asymmetry can promote a net spin current, in the absence of backscattering processes, in thin film made of TIs. These results have been obtained by fully relativistic first principles calculations. [ABSTRACT FROM AUTHOR]

Extended defects like stacking faults (SFs) can originate topologically protected metallic states in bulk topological insulators (TIs). These induced topological states are a response to the weakening of the inter-layer van der Waals interactions due to the SF defect. In TI thin films, the degeneracy of Dirac bands of opposite surfaces can be lifted upon the formation of SF defects. Such slab asymmetry can promote a net spin current, in the absence of backscattering processes, in thin film made of TIs. These results have been obtained by fully relativistic first principles calculations. [ABSTRACT FROM AUTHOR]