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First principles calculation on field emission of boron/nitrogen doped carbon nanotube

First principles calculation on field emission of boron/nitrogen doped carbon nanotube. 2004.11.29 Hyo-Shin Ahn 1,2 , Seungwu Han 3 , Kwang –Ryeol Lee 1 and Doh-Yeon Kim 2 1 Korea institute of science and technology

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First principles calculation on field emission of boron/nitrogen doped carbon nanotube

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  1. First principles calculation on field emission of boron/nitrogen doped carbon nanotube 2004.11.29 Hyo-Shin Ahn1,2, Seungwu Han3, Kwang –Ryeol Lee1 and Doh-Yeon Kim2 1 Korea institute of science and technology 2 Department of materials science and engineering, Seoul national university 3 department of physics, Ehwa womans university

  2. CNT-FED by Samsung Field emission Definition: the emission of electrons stripped from parent atoms by a high electric field via quantum mechanical tunneling   • Carbon nanotube • for field emission device • Structural advantage • - Property modification by doping

  3. “Role of extrinsic atoms on the morphology and field-emission properties of carbon nanotubes” L.H.Chan et al., APL., Vol.82, 4334(2003) Experimental measurement N B B/N doping on multiwall Carbon nanotube Nitrogen doping on CNT enhances emission, while boron suppresses

  4. Plane wave Calculation method –fist step Information of wave function shapes and state energy under applied electric field (5,5) Caped CNT, 250atoms • Relaxation of the wave function • Basis set is changed to plane wave to emit the electrons • Time evolution • Evaluation of transition rate by time dependent Schrödinger equation • Ab initio tight binding calc. To obtain self-consistent potential and initial wave function Localized basis “First-principles study of field emission of carbon nanotubes”, S. Han et al., PRB, Vol.66, 241402 (2002)

  5. Localized state: Due to the defective structure of nanotube cap <No bias> <Under bias> Electronic states of Carbon nanotube p and p* bonds, Extended states Due to the graphene structure of nanotube wall Extended states Localized states Energy EF <shapes of orbital> S. Han et al., PRB, Vol.66, 241402 (2002)

  6. Calculation method – second step (5,5) Caped CNT, 250atoms • Relaxation of the wave function • Basis set is changed to plane wave to emit the electrons • Time evolution • Evaluation of transition rate by time dependent Schrödinger equation • Ab initio tight binding calc. To obtain self-consistent potential and initial wave function Localized basis Plane wave

  7. Localized states Extended states Emission current of undoped CNT Total current: 67.17mA Cutoff radius 80Ry, Electric field: 1.0V/Å, Energy selection : E-Ef= -1.5eV ~ 0.5V EF

  8. Emission current vs. Bias voltage

  9. Emission current of N doped CNT Cutoff radius 80, Applied field 1.0V/Å, Energy selection : E-Ef= -1.5eV ~ 0.5V Total current: 87.59μA Localized state Extended state

  10. π*+localized state Shape of wave functions in N-doped CNT Localized state π extended state mixing of localized and extended states; large contribution to electron emission

  11. Emission current vs. Bias voltage

  12. Increase of emission current Undoped CNT Total current: 67.17mA 23% increase by N doping N-doped CNT Total current: 87.59μA

  13. Nitrogen position vs. emission current Applied electric field : 0.7V/Å, Energy selection : E-Ef= -1.5eV ~ 0.5V undoped CNT

  14. Boron doping exactly opposite effect - raising the localized state energy 350atoms, (5,5) armchair-type, applied electric field: 0.5V/Å undoped CNT

  15. Conclusion • Emission of undoped carbon nanotube is mainly due to the localized states • Nitrogen doping : • mixing of the extended and localized states • lowers the energy of localized state • emission current increase • Boron doping : • no hybridization of states • raises localized state energy • emission current decrease

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