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Objective molecular dynamics simulations coupled with a density functional-based tight-binding model indicated that a stress-free single-walled (14,6) MoS 2 nanotube exhibits a torsional deformation of 0.87 deg/nm. Simulated electron diffraction patterns and atomic-resolution annular dark field scanning transmission electron microscopy (ADF-STEM) images of(More)
We examined the structure, morphology, and orientation of catalyst nanoparticles used for seeding and growing multiwall carbon nanotubes (MWCNTs) by plasma enhanced chemical vapor deposition in CH4/H2 gas mixtures. Iron catalyst nanocrystals are converted to Fe3C in CH4/H2 plasmas and the MWCNTs grow from Fe3C nanocrystals. Initially faceted and equiaxed(More)
The mineralogical constitution of the Earth's mantle dictates the geophysical and geochemical properties of this region. Previous models of a perovskite-dominant lower mantle have been built on the assumption that the entire lower mantle down to the top of the D″ layer contains ferromagnesian silicate [(Mg,Fe)SiO3] with nominally 10 mole percent Fe. On the(More)
The electronic structure of wurtzite InN has been investigated by electron energy loss spectroscopy ͑EELS͒. Spectra of the nitrogen K edge and the indium M 4,5 edge have been measured and were compared with calculated partial, N 2p and In 5p conduction band density of states in InN. Excellent agreement on the relative positions of the characteristic peaks(More)
Internal crystalline structure of cementite catalyst particles located inside the base of mul-tiwall carbon nanotubes was studied using nanoprobe convergent-beam electron diffrac-tion. The catalyst particles are single crystalline but exhibit combinations of small-angle ($1°–3°) rotations, twists, and bends along their axial length between adjacent(More)
Nanometer-scale semiconductors that contain a few intentionally added impurity atoms can provide new opportunities for controlling electronic properties. However, since the physics of these materials depends strongly on the exact arrangement of the impurities, or dopants, inside the structure, and many impurities of interest cannot be observed with(More)
The structures of carbon nanotubes grown from catalytic nanoparticles via plasma-enhanced chemical vapor deposition in CH 4 / H 2 mixtures show a strong dependence on the H 2-to-CH 4 ratio in the feed gas. A suite of characterization techniques, including optical emission, infrared, and Raman spectroscopies combined with convergent-beam and selected-area(More)
A study of high-resolution ADF imaging in uncorrected and aberration-corrected STEMs was carried out by multislice simulation. The presence of amorphous layers at the surface of a crystalline specimen is shown to significantly alter the visibility of the atomic columns. After propagating through an amorphous layer a portion of the beam passes without any(More)
With current advances in sub-angstrom resolution scanning transmission electron microscopy (STEM), it is now possible to image directly local crystal structures of materials where dramatically different atoms are separated from each other at distances about or less than 1 angstrom. We achieved direct imaging of atomic columns of nitrogen in close proximity(More)