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Point defects on a Si(001)-(2 x 1) surface were examined by scanning tunneling microscopy and ab initio pseudopotential calculations. The residual water molecules in the ultrahigh vacuum chamber are found to be the sole origin of the type-C defects. Most of the apparent dimer vacancies in the filled-state images were found to show a distinct U-shaped(More)
Silicon nanoclusters have become significant research interest due to their potential application to optoelectronic devices in visible range. We investigate the electronic and optical properties of hydrogenated and nitrogen-passivated silicon nanoclusters using density functional theory calculations. The energy gap between the highest occupied molecular(More)
We investigate the initial stage of the C incorporation into Si(001) using thermal dissociation of C2H2. The scanning tunneling microscopy shows that C-induced dimer vacancies (DVs) with depressed adjacent dimers are generated on the surface and aligned in the dimer direction, forming the 2xn structure. The ab initio pseudopotential calculations reveal(More)
An exchange of hydrogen-bond and coordinate covalent-bond (dative-bond) interactions is found to play a critical role in the self-assembly of NH3 molecules on the Si(001) surface. An NH3 molecule in the height of approximately 3-10 A above the surface is attracted toward the preadsorbed NH2 moiety through the long-range H-bond interaction. Within(More)
Adsorption states of the self-assembly of NH(3) molecules on the Si(001) surface are investigated using density-functional theory calculations. H-bond interactions between incoming and adsorbed NH(3) molecules produce a strong attractive potential field for the incoming molecules. Induced by the H bonds, physisorption states are formed on the adsorbed(More)
The C amount and the structure of the Si(001)-c(4 x 4) surface is studied using scanning tunneling microscopy (STM) and ab initio calculations. The c(4 x 4) phase is found to contain 1/8 monolayer C (1 C atom in each primitive unit cell). From the C amount and the symmetry of high-resolution STM images, it is inferred that the C atoms substitute the(More)
A simple procedure for the fabrication of sub-10 nm scale Si nanopillars in a 2-D array using reactive ion etching with 8 nm Co nanoparticles as etch masks is demonstrated. The obtained Si nanopillars are single crystalline tapered pillar structures of 5 nm (top) x 8 nm (bottom) with a density of approximately 4 x 10(10) pillars cm(-2) on the substrate,(More)
Understanding and effectively predicting the thermal stability of ternary transition metal oxides with heavy elements using first principle simulations are vital for understanding performance of advanced materials. In this work, we have investigated the thermal stability of mullite RMn2O5 (R  =  Bi, Pr, Sm, or Gd) structures by constructing temperature(More)
The recently developed spin-dependent pseudopotentials markedly improve the description of the energetics of isolated transition metal atoms ͓S.dependent pseudopotentials are obtained from a combination of spin-neutral and fully polarized atomic pseudo-potentials, employing the self-consistent local spin polarization to adapt to different environments.(More)
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