arXiv subjects

Keiji Morokuma

Publications and source records attributed to Keiji Morokuma.

4 recordsLinked to original sources

arXiv2014

Nearly Exclusive Growth of Small Diameter Semiconducting Single-Wall Carbon Nanotubes from Organic Chemistry Synthetic End-Cap Molecules

The inability to synthesize single-wall carbon nanotubes (SWCNTs) possessing uniform electronic properties and chirality represents the major impediment to their widespread applications. Recently, there is growing interest to explore and synthesize well-defined carbon nanostructures, including fullerenes, short nanotubes, and sidewalls of nanotubes, aiming for controlled synthesis of SWCNTs. One noticeable advantage of such processes is that no metal catalysts are used, and the produced nanotubes will be free of metal contamination. Many of these methods, however, suffer shortcomings of either low yield or poor controllability of nanotube uniformity. Here, we report a brand new approach to achieve high efficiency metal-free growth of nearly pure SWCNT semiconductors, as supported by extensive spectroscopic characterization, electrical transport measurements, and density functional theory calculations. Our strategy combines bottom-up organic chemistry synthesis with vapour phase epitaxy elongation. We identify a strong correlation between the electronic properties of SWCNTs and their diameters in nanotube growth. This study not only provides material platforms for electronic applications of semiconducting SWCNTs, but also contributes to fundamental understanding of the growth mechanism and controlled synthesis of SWCNTs.

cond-mat.mtrl-sci↗

arXiv2006

R-matrix calculation of integral and differential cross sections for low-energy electron impact excitations of N2 molecule

Low-energy electron impact excitations of N$_2$ molecules are studied using the fixed-bond R-matrix method based on state-averaged complete active space SCF orbitals. Thirteen target electronic states of N$_2$ are included in the model within a valence configuration interaction representations of the target states. Integrated as well as differential cross sections of the $A^{3} Σ_{u}^{+}$, $B^{3} Π_{g}$, $W^{3} Δ_{u}$, ${B'}^{3} Σ_{u}^{-}$, ${a'}^{1} Σ_{u}^{-}$, $a^{1} Π_{g}$, $w^{1} Δ_{u}$ and $C^{3} Π_{u}$ states are calculated and compared with the previous experimental measurements. These excitations, especially of the higher four states, have not been studied enough theoretically in the previous literature. In general, good agreements are observed both in the integrated and differential cross sections. However, some discrepancies are seen in the integrated cross sections of the $A^{3} Σ_{u}^{+}$ and $C^{3} Π_{u}$ states, especially around a peak structure.

physics.chem-ph↗

arXiv2006

R-matrix calculation of differential cross sections for low-energy electron collisions with ground and electronically excited state O2 molecules

Differential cross sections for electron collisions with the O$_2$ molecule in its ground ${X}^{3}Σ_g^-$ state, as well as excited ${a}^{1}Δ_g$ and ${b}^{1}Σ_g^+$ states are calculated. As previously, the fixed-bond R-matrix method based on state-averaged complete active space SCF orbitals is employed. In additions to elastic scattering of electron with the O$_2$ ${X}^{3}Σ_g^-$, ${a}^{1}Δ_g$ and ${b}^{1}Σ_g^+$ states, electron impact excitation from the ${X}^{3}Σ_g^-$ state to the ${a}^{1}Δ_g$ and ${b}^{1}Σ_g^+$ states as well as '6 eV states' of ${c}^{1}Σ_u^{-}$, ${A'}^{3}Δ_u$ and ${A}^{3}Σ_u^{+}$ states is studied. Differential cross sections for excitation to the '6 eV states' have not been calculated previously. Electron impact excitation to the ${b}^{1}Σ_g^+$ state from the metastable ${a}^{1}Δ_g$ state is also studied. For electron impact excitation from the O$_2$ ${X}^{3}Σ_g^-$ state to the ${b}^{1}Σ_g^+$ state, our results agree better with the experimental measurements than previous theoretical calculations. Our cross sections show angular behaviour similar to the experimental ones for transitions from the ${X}^{3}Σ_g^-$ state to the '6 eV states', although the calculated cross sections are up to a factor two larger at large scattering angles. For the excitation from the ${a}^{1}Δ_g$ state to the ${b}^{1}Σ_g^+$ state, our results marginally agree with the experimental data except for the forward scattering direction.

physics.chem-ph↗

arXiv2006

R-matrix calculation of electron collisions with electronically excited O2 molecules

Low-energy electron collisions with O$_2$ molecules are studied using the fixed-bond R-matrix method. In addition to the O$_2$ ${X}^3Σ_{g}^-$ ground state, integrated cross sections are calculated for elecron collisions with the ${a}^1Δ_{g}$ and ${b}^1Σ_{g}^+$ excited states of O$_2$ molecules. 13 target electronic states of O$_2$ are included in the model within a valence configuration interaction representations of the target states. Elastic cross sections for the ${a}^1Δ_{g}$ and ${b}^1Σ_{g}^+$ excited states are similar to the cross sections for the ${X}^3Σ_{g}^-$ ground state. As in case of excitation from the ${X}^3Σ_{g}^-$ state, the O$_2^-$ $Π_u$ resonance makes the dominant contribution to excitation cross sections from the ${a}^1Δ_{g}$ and ${b}^1Σ_{g}^+$ states. The magnitude of excitation cross sections from the ${a}^1Δ_{g}$ state to the ${b}^1Σ_{g}^+$ state is about 10 time larger than the corresponding cross sections from the ${X}^3Σ_{g}^-$ to the ${b}^1Σ_{g}^+$ state. For this ${a}^1Δ_{g}$ $\to$ ${b}^1Σ_{g}^+$ transition, our cross section at 4.5 eV agrees well with the available experimental value. These results should be important for models of plasma discharge chemistry which often requires cross sections between the excited electronic states of O$_2$.

physics.chem-ph↗