Hanchul Kim

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We present a dynamic pathway model for the formation of C(60) using the action-derived molecular dynamics simulations. We propose candidate precursors for dynamic pathway models in which carbons spontaneously aggregate due to favorable energetics and kinetics. Various planar polycyclic models are in a disadvantageous state where they cannot be trapped in(More)
Uranium dioxide (UO2) is an important fuel material in the nuclear industry, and the behavior of the 5f electrons of uranium is one of the most interesting subjects about actinide elements and their compounds. Uranium dioxide is known to be a good insulator[1], and it is also known that the magnetic moment on uranium ions orders antiferromagnetically at(More)
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)
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)
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)
Action-derived molecular dynamics for the simulation of rare event and slow mode systems is reviewed. Theoretical background, implementation details, and comparison with other methods are presented. Numerical examples demonstrated include the structural formation and transformation of carbon fullerenes, and molecular reconfiguration of alanine dipeptide and(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)
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)