Seung Yong Bae

Strained gallium nitride nanowires

Gallium nitride nanowires were synthesized on silicon substrates by chemical vapor deposition using the reaction of gallium and gallium nitride mixture with ammonia. Iron nanoparticles were used as catalysts. The diameter of nanowires is uniform as 25 nm and the lengths are 20–40 μm. The nanowires have single crystalline wurtzite structure with a few stacking faults. A careful examination into x-ray diffraction and Raman scattering data revealed that the separations of the neighboring lattice planes along the growth direction are shorter than those of bulk gallium nitride. The nanowires would experience biaxial compressive stresses in the inward radial direction and the induced tensile uniaxial stresses in the growth direction. The shifts of the band gap due to the stresses have been estimated using the experimental data, showing that the reduction of the band gap due to the tensile stresses can occur more significantly than the increase due to the compressive stresses. The temperature-dependent photolumi...

Single-crystalline gallium nitride nanobelts

Single-crystalline wurtzite gallium nitride nanobelts were synthesized by thermal reaction of gallium, gallium nitride, and ammonia using iron and boron oxide as catalysts. The structure of nanobelts was investigated by high-resolution transmission electron microscopy with electron energy-loss spectroscopy. They have a distinctive triangle tip and thick side edges. The widths are 200–300 nm, the thickness of belt plane is about 1/10 of the width, and the lengths are up to a few tens μm. The growth direction is uniformly perpendicular to the [010] direction.

Experimental and theoretical studies on the structure of N-doped carbon nanotubes: Possibility of intercalated molecular N2

The concentration distribution and electronic structure of N atoms doped in multiwalled banboo-like carbon nanotubes (CNTs) are examined by photon energy-dependent x-ray photoelectron spectroscopy and x-ray absorption near edge structure. The inner part of the nanotube wall has a higher N concentration and contains molecular N2 presumably intercalated between the graphite layers. These results are supported by the self-consistent charge-density-functional-based tight-binding calculation of double-walled CNTs, showing that the intercalation of N2 is energetically possible and the graphite-like N structure conformer becomes more stable when the inner wall is more heavily doped.

Triangular gallium nitride nanorods

Gallium nitride nanorods were synthesized by a chemical vapor deposition using the reaction of gallium/gallium nitride with ammonia. All nanorods have, exclusively, a triangle cross section with an average diameter of 50 nm. They consist of single-crystalline wurtzite structure crystal grown with the [010] direction. X-ray diffraction and Raman spectroscopy data suggest no shift of the lattice constants from those of the bulk. Temperature-dependent photoluminescence exhibits the I2 and free-to-bound emission peaks. The present triangular gallium nitride nanorods would be free from the stress, having the band-gap energy of the bulk.

Boron nitride nanotubes synthesized in the temperature range 1000-1200 °C

Abstract Boron nitride nanotubes were synthesized on the iron-deposited alumina substrates by a catalytic reaction of the ball-milled boron and boron nitride powder mixture with ammonia in the temperature range 1000–1200 °C. The diameter of nanotubes is in the range of 40–100 nm. The nanotubes grown below 1100 °C possess exclusively a bamboo-like structure. As the temperature increases to 1200 °C, almost all nanotubes show a cylindrical structure in which the boron nitride sheets are tilted to the tube axis by an angle of about 25°. Electron energy-loss spectroscopy identifies that the ratio of boron and nitrogen is almost one. The Raman scattering peak associated with the E 2g mode shifts to the higher frequency and narrows as the growth temperature increases. The results indicate that the growth temperature can be a crucial growth parameter in controlling the structure and crystallinity of boron nitride nanotubes. On the basis of the structural features, we suggest a base-growth mechanism for both bamboo-like and cylindrical boron nitride nanotubes.

Three-dimensional structure of helical and zigzagged nanowires using electron tomography.

Electron tomography and high-resolution transmission electron microscopy were used to characterize the unique three-dimensional structures of helical or zigzagged GaN, ZnGa2O4, and Zn2SnO4 nanowires. The GaN nanowires adopt a helical structure that consists of six equivalent <011> growth directions with the axial [0001] direction. We also confirmed that the ZnGa2O4 nanosprings have four equivalent <011> growth directions with the [001] axial direction. The zigzagged Zn2SnO4 nanowires consisted of linked rhombohedrons having the side edges matched to the <110> direction and the [111] axial direction.

Influence of In incorporation on the electronic structure of ZnO nanowires

High-density Zn0.85In0.15O and Zn0.75In0.25O nanowires were synthesized by thermal evaporation method. They consist of single-crystalline wurtzite ZnO structure with uniform [010] growth direction. X-ray diffraction (XRD) reveals the structural defects caused by the In incorporation. X-ray photoelectron spectrum (XPS) analysis suggests that In withdraw the electrons from Zn and increase the dangling-bond O2p states. The lower energy shift and green-band enhancement of photoluminescence are well correlated with the results of XRD and XPS.

Single-crystalline gallium-doped indium oxide nanowires

High-density gallium (Ga)-doped indium oxide (In2O3) nanowires whose Ga content [Ga∕(In+Ga) atomic ratio] is 0%, 7%, and 45%, were synthesized by thermal evaporation. They have an average diameter of 50nm and consist of nearly single-crystalline cubic In2O3 structure with the [010] growth direction. High-resolution x-ray diffraction analysis reveals that as the Ga content increases the position of In2O3 peaks shifts to the higher angle and a crystalline form (Ga,In)2O3 is produced. We estimated a 0.4% reduction of the lattice constant for 45% Ga-doped nanowires.

Fabrication of SiC-C coaxial nanocables: thickness control of C outer layers.

Aligned SiC-C coaxial nanocables were synthesized via the direct growth of SiC nanowires from silicon substrates and subsequent carbon deposition using pyrolysis of methane; the average diameter of the SiC nanowire cores is 20 nm; the thickness of the C outer layers is controlled in the range 3-50 nm; the degree of crystalline perfection of the graphitic sheets increases with the thickness.

Collisional quenching of vibrationally excited azabenzenes by unexcited azabenzenes

Abstract The collisional quenching of vibrationally excited methyl-substituted azabenzene series (pyrazine, pyridine, and pyrimidine), and deuterated species by unexcited parent molecules was studied with time-resolved C–H (or C–D) stretching infrared fluorescence spectroscopy. The collisional quenching rate and the average energy loss per collision were measured, showing an increase as the number of methyl groups and the dipole moment increase. The results indicate that the vibration-to-vibration energy transfer mediated through the dipole–dipole attractive force plays an important role in the collisional quenching of azabenzenes. The internal rotation of the methyl group facilitates the quenching of the methyl-substituted azabenzenes.