First principles calculation on nitrogen effect on the growth of carbon nanotube Hyo-Shin Ahn 1,2, Seung-Cheol Lee 1, Seungwu Han 3, Kwang –Ryeol Lee 1 and Doh-Yeon Kim 2 1 Korea institute of science and technology 2 Department of materials science and engineering, Seoul national university 3 Department of physics, Ehwa womans university

CNT Growth by CVD Vertically aligned multi-wall CNT Chemical Physics Letters, Vol. 372, 603(2003)

Nitrogen effect in CNT fabrication Molecular nitrogen or without nitrogen Tangled CNT Atomic nitrogen Aligned CNT Process condition NH 3 decomposition N 2 decomposition in plasma H 2, Ar, N 2, NH 3 Ambient gas affects the growth of carbon nanotubes

Growth rate increases as the nitrogen concentration in microwave plasma J. Lee, and B. Lee, Thin Solid Films, 418, (2002) Vertically aligned multi-wall CNT due to high growth rate Chemical Physics Letters, Vol. 372, 603(2003) CNT growth in nitrogen atmosphere

Calculation of Growth Kinetics Kinetic barrier calculation by DMol 3 for each reaction step. Assumptions Flat graphitic plate represents the large radius (~over 10nm in radius) CNTs. Reduction of the kinetic barrier by the catalyst is not affected by the existence of nitrogen. reactant product

Zigzag EdgeArmchair Edge Growth kinetics of nanotube

Energy (arb. unit) 176 meV tetragonpentagon hexagon Growth reaction on zigzag edge Reaction Total energy for the zigzag edge growth is 176meV

Growth reaction on armchair edge pentagon hexagon 160 meV 64 meV Reaction Energy (arb. unit) The zigzag edge growth is rate determining in undoped CNT.

137meV 64meV Nitrogen incorporation ~70meV Pure C pentagon hexagon No significant change by nitrogen incorporation. 137meV 64meV 160meV Reaction Energy (arb. unit) 160meV Growth reaction incorporating nitrogen on armchair edge Growth reaction incorporating nitrogen on armchair edge

154meV ~26meV Pure C Nitrogen incorporation tetragon pentagon hexagon 150 meV 176 meV Nitrogen incorporation lowers kinetic barrier by ~26meV. Reaction Energy (arb. unit) 152meV No barrier Growth reaction incorporating nitrogen on zigzag edge Growth reaction incorporating nitrogen on zigzag edge No barrier

152meV 87meV 179meV96meV Nitrogen at top site Pure C pentagon hexagon Nitrogen at valley site No characteristic nitrogen effect on growth of armchair edge. 64meV 152meV 160meV 179meV 96meV 87meV Reaction Energy (arb. unit) Growth reaction on nitrogen incorporated armchair edge

No barrier Pure C Nitrogen in valley site tetragon pentagon hexagon 333meV Nitrogen in top site No barrier 176meV 333meV Nitrogen at valley site makes reaction difficult. However, nitrogen at top site eliminates the kinetic barrier for the growth. No barrier Reaction Energy (arb. unit) Growth reaction on nitrogen incorporated zigzag edge

Near the nitrogen incorporated region (top site), the activation energy for carbon growth disappears. No barrier Energy growth of C tetragon pentagon hexagon growth near the nitrogen incorporated region. No barrier 176 meV Growth reaction on nitrogen incorporated zigzag edge

electronic structure E b =176meV E b =0meV When nitrogen locates in the hexagon network, lone pair (localized) electrons around the nitrogen atom make weak bonds weaker bond

Conclusion In pure carbon system Armchair edge grows faster, then growth on zigzag edge is rate determining step. Nitrogen incorporation/Incorporated nitrogen effect on carbon attachment With nitrogen, the energy barrier for the zigzag edge growth becomes lower than that of armchair edge. - rate determining step is the growth of armchair edge. Nitrogen enhances the growth by lowering the kinetic barrier.

40 ㎚ CNT Growth by CVD H 2, Ar, N 2, NH 3