Post on 14-Dec-2015
First Principles Calculation of the Field Emission of Nitrogen/Boron Do
ped Carbon Nanotubes
Hyo-Shin Ahn§, Seungwu Han†, Kwang-Ryeol Lee,
Do Yeon Kim§
Future Technology Research Division, KIST, Seoul, Korea
§ also at the Division of Materials Science, Seoul National University, Seoul, Korea † at the Department of Physics, Ehwa Women’s University, Seoul, Korea
2005. 5. 3, ICMCTF 2005, San Diego, CA, USA
CNT is a strong candidate for field emission cathode materials
1. Structural advantage : Highly enhanced electric field
2. Materials property Low turn-on voltage
Field Emission from CNT
What’s the effect of doping?What’s the effect of doping?CNT-FED by Samsung
Tangled CNTC2H2+H2600~900
Tangled CNTC2H2+H2, C2H2+N2950
Tangled CNTC2H2+H2, C2H2+N2850
method
ferrocene+xylene
CH4+H2
CH4+N2
CH4+N2
C2H2+Ar
C2H2+NH3
C2H2+NH3
C2H2+NH3
C2H2+NH3
C2H2+NH3
C2H2+NH3
C2H2+NH3
C2H2+NH3
C2H2+NH3
C2H2+NH3
Reaction Gas CatalystTemperatue(oC)
APL 77 3764 (2000)Aligned CNTFe800 Thermal-CVD
APL 76 2367 (2000)Aligned CNTNi700 PE-CVD
JAP 89 5939 (2001)Aligned CNTFe550 PE-CVD
APL 75 3105 (1999)Aligned CNTFe, Ni500 PE-CVD
APL 75 1721 (1999)Tangled CNTNi, Co850~900Thermal-CVD
APL 80 4018 (2002)Aligned CNTNi660< PE-CVD
JAP 91 3847 (2002)Aligned CNT
Ni
800~900
Thermal-CVD
DRM 10 1235 (2001)Aligned CNT
Ni950
Thermal-CVD
TSF 398-399 150 (2001)Aligned CNT
Ni, Co950
Thermal-CVD
APL 78 901 (2001)Aligned CNTFe800 Thermal-CVD
APL 77 2767 (2000)Aligned CNTCo825 PE-CVD
APL 77 3397 (2000)Aligned CNTFe750~950Thermal-CVD
APL 77 830 (2000)Aligned CNTCo825 PE-CVD
APL 75 1086 (1999)Aligned CNTNi660 PE-CVD
Science 282, 1105 (1998)Aligned CNTNi666PE-CVD
CitationCNT MorphologySynthesis condition
Calculation Method
Plane wave
Localized basis
(5,5) Caped CNT, 250atoms
1. Ab initio tight binding calc.To obtain self-consistent potential and initial wave function with applied electric field
2. Relaxation of the wave functionBasis set is changed to plane wave to emit the electrons
• Time evolutionEvaluation of transition rate by time dependent Schrödinger equation
S. Han et al., PRB, 66, 241402 (2002).
Electronic Structure of Pure CNT
A State B State D stateC state
Localized states Due to the defective structure of CNT cap
and * bonds, Extended statesDue to the graphene structure of nanotube wall
S. Han et al., PRB, 66, 241402 (2002).
Emission from Pure CNT : 67.17A
Localized states
Extended states
EF
Cutoff radius 80Ry, Electric field: 1.0V/Å
Coupled states between localized and extended states signigicantly contribute to the field emssion.
B stateA state C state D state
π*+localized stateLocalized stateπ bond:Extended state
Electronic Structure of N doped CNT
Nitrogen Doping Effect
EF
- N-doped CNT
- Undoped CNTLocalized state
The nitrogen has lower on-site energy than that of carbon atom.
T. Yoshioka et al, J. Phys. Soc. Jpn., Vol. 72, No.10, 2656-2664 (2003).
The lower energy of the localized state makes it possible for more electrons to be filled in the localized states.
Doped Nitrogen Position
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
Ban
d sh
ift (
eV)
8
10
12
14
16
18
20
22
Em
ission current (A
)
Emission from B Doped CNT350atoms, (5,5) armchair-type, applied electric field: 0.5V/Å
0.0
0.2
1.0
1.2
1.4
1.6
1.8
Energ
y of l
oca
lized s
tate
s, E
-EF (eV) Boron doped CNT
Undoped CNT
3
4
5
6
7
8
9
10
Curre
nt(A
)
undoped CNT
Summary
• Emission of undoped carbon nanotube is mainly due to the localized states
• Nitrogen doping : – coupling of the extended and the localized states
– lowers the energy of the localized state
– emission current increased
• Boron doping : – no coupling of the states
– raises the energy of the localized state
– emission current decreased