arXiv subjects

Woon Ih Choi

Publications and source records attributed to Woon Ih Choi.

4 recordsLinked to original sources

arXiv2010

Electrical transport in small bundles of single-walled carbon nanotubes: intertube interaction and effects of tube deformation

We report a combined electronic transport and structural characterization study of small carbon nanotube bundles in field-effect transistors (FET). The atomic structures of the bundles are determined by electron diffraction using an observation window built in the FET. The single-walled nanotube bundles exhibit electrical transport characteristics sensitively dependent on the structure of individual tubes, their arrangements in the bundle, deformation due to intertube interaction, and the orientation with respect to the gate electric field. Our ab-initio simulation shows that tube deformation in the bundle induces a bandgap opening in a metallic tube. These results show the importance of intertube interaction in electrical transport of bundled nanotubes.

cond-mat.mes-hall↗

arXiv2008

Modification of the electronic structure in a carbon nanotube with the charge dopant encapsulation

We present the first-principles study of effects of the charge dopants such as Cesium and Iodine encapsulated on the electronic structure of carbon nanotubes. An encapsulated cesium atom donates an electron to the nanotube and produces donor-like states below the conduction bands. In contrast, an iodine trimer (I$_{3}$) accepts an electron from the nanotube and produces an acceptor-like state above the valance band maximum. We find that a Cs atom inside a metallic armchair carbon nanotube gives rise to spatial oscillations of the density of states near the Fermi level.

cond-mat.mtrl-sci↗

arXiv2006

Combinatorial Search for Optimal Hydrogen-Storage Nanomaterials Based on Polymers

We perform an extensive combinatorial search for optimal nanostructured hydrogen storage materials among various metal-decorated polymers using first-principles density-functional calculations. We take into account the zero-point vibration as well as the pressure- and temperature-dependent adsorption-desorption probability of hydrogen molecules. An optimal material we identify is Ti-decorated cis-polyacetylene with reversibly usable gravimetric and volumetric density of 7.6 weight percent and 63 kg/m^3 respectively near ambient conditions. We also propose ``thermodynamically usable hydrogen capacity" as a criterion for comparing different storage materials.

cond-mat.mtrl-sci↗

arXiv2005

Reduction of Activation Energy Barrier of Stone-Wales Transformation in Endohedral Metallofullerenes

We examine effects of encapsulated metal atoms inside a C$_{60}$ molecule on the activation energy barrier to the Stone-Wales transformation using {\it ab initio} calculations. The encapsulated metal atoms we study are K, Ca and La which nominally donate one, two and three electrons to the C$_{60}$ cage, respectively. We find that isomerization of the endohedral metallofullerene via the Stone-Wales transformation can occur more easily than that of the empty fullerene owing to the charge transfer. When K, Ca and La atoms are encapsulated inside the fullerene, the activation energy barriers are lowered by 0.30, 0.55 and 0.80 eV, respectively compared with that of the empty C$_{60}$ (7.16 eV). The lower activation energy barrier of the Stone-Wales transformation implies the higher probability of isomerization and coalescence of metallofullerenes, which require a series of Stone-Wales transformations.

cond-mat.mes-hall↗