Electronic and transport properties of functionalized carbon nanotubes

Carbon nanotubes have received much attention in recent years due to their high structural stability and interesting electronic and transport properties. These novel properties can be utilized in many areas of applications. Many of these applications require modifications to pristine nanotubes. In particular, chemical functionalizations have been shown to be an attractive method to tailor some of electronic and mechanical properties. In this study, I present our computational study on electronic and transport properties of covalently side-wall functionalized carbon nanotubes. We found that functional-group-induced impurity states play important roles in modifying electronic and transport properties of nanotube near the Fermi level. A drastic difference has been found between monovalent and divalent functionalization cases. In monovalent functionalizations, the impurity states are located near the Fermi level and have strong effects on both electronic and transport properties. On the other hand, divalent functionalizations do not cause any significant disruption near the Fermi level due to rehybridization of two adjacent impurity states into bonding and antibonding states located relatively far away from the Fermi level. We believe that the covalent functionalization induced property changes provide a pathway for the band structure engineering, electronic, and chemical sensor applications of carbon nanotube

Relative stability of extended interstitial defects in silicon: First-principles calculations

Interstitials stored in {311} or {111} habit planes form rows of interstitial chains elongated in ⟨011⟩ direction. Exploiting the large aspect ratio to treat chains as infinite, first-principles calculations of large computation supercells reveal a unique formation energy trend for each defect, which is closely correlated with its distinct shape. The most energetically favorable structure changes from {311} rodlike defects to Frank loops as the number of interstitials in the defect increases. These results are consistent with transmission electron microscopy studies

Magnetic states and optical properties of single-layer carbon-doped hexagonal boron nitride

We show that carbon-doped hexagonal boron nitride (h-BN) has extraordinary properties with many possible applications. We demonstrate that the substitution-induced impurity states, associated with carbon atoms, and their interactions dictate the electronic structure and properties of C-doped h-BN. Furthermore, we show that stacking of localized impurity states in small C clusters embedded in h-BN forms a set of discrete energy levels in the wide gap of h-BN. The electronic structures of these C clusters have a plethora of applications in optics, magneto-optics, and opto-electronics

Force-matched embedded-atom method potential for niobium

Large-scale simulations of plastic deformation and phase transformations in alloys require reliable classical interatomic potentials. We construct an embedded-atom method potential for niobium as the first step in alloy potential development. Optimization of the potential parameters to a well-converged set of density-functional theory (DFT) forces, energies, and stresses produces a reliable and transferable potential for molecular dynamics simulations. The potential accurately describes properties related to the fitting data, and also produces excellent results for quantities outside the fitting range. Structural and elastic properties, defect energetics, and thermal behavior compare well with DFT results and experimental data, e.g., DFT surface energies are reproduced with less than 4% error, generalized stacking-fault energies differ from DFT values by less than 15%, and the melting temperature is within 2% of the experimental value.Comment: 17 pages, 13 figures, 7 table