boron doping effect 1. effect on structure b a.c: 3 sp 2 (3 ) and 1 2p z (1 ) bonds b: 3 sp2 (3 )...

Boron doping effect 1. Effect on structure B a. C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å . Electrical ring current (resonance) disappears when B substitutes

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Boron doping effect

1. Effect on structure

a. C: 3 sp2 (3 ) and 1 2pz (1 ) bonds B: 3 sp2 (3 )

b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å

c. Electrical ring current (resonance) disappears when B substitutes C

2. Effect on electronic profile

CNT

metallic

Semiconductor

Page 3: Boron doping effect 1. Effect on structure B a.C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å c. Electrical

BC3 tubeFree electronic-like (metallic)

Page 4: Boron doping effect 1. Effect on structure B a.C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å c. Electrical

2. Effect on electronic profiles

Random doping of B in CNT

metallic

Semiconductor

EF depression to VB edge

more than 2 sub-bands crossing at EF

i.e. conductance increases

BC3 state (acceptor)

New Eg

Eg reduction by EF depression

Page 5: Boron doping effect 1. Effect on structure B a.C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å c. Electrical

B-doping

a. EF depression Eg reduction (semiconductor tube) and number of conduction channel increase (conductance > 4e2/h, metallic tube).

b. Creation of acceptor state near to VB edge and increase in hole carrier density (11016 spins/g for CNTs, 61016 spins/g for BCNTs).

c. Electron scattering density increase by B-doping centers (i.e. shorter mean free path and relaxation time compared with CNTs, = 0.4 ps and 4-10 ps for BCNTs and CNTs)

B+

scatteringd. The actual conductivity depends on competition between scattering density and increase in hole carrier (in practice, the latter > the former, so conductance )

Page 6: Boron doping effect 1. Effect on structure B a.C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å c. Electrical

e. Electron hopping magnitude in -band increase

B dopant

-band (VB)

-band (CB)e-

hopping

-band (CB)

Overlap of -electron wave function

BC3 state

Page 7: Boron doping effect 1. Effect on structure B a.C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å c. Electrical

f. Less influence on conductivity upon strain application

For CNT

Deflection angle

Page 8: Boron doping effect 1. Effect on structure B a.C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å c. Electrical

Temporary formation of sp3 character upon bending

Resistance reduction is due to (i) temporary formation of sp3 at bend regionand (ii) increasing hopping magnitude upon bending

bending

Planar sp2

Tetrahedral sp3

http://upload.wikimedia.org/wikipedia/commons/1/11/Sp2-Orbital.svg

http://upload.wikimedia.org/wikipedia/commons/9/9f/Sp3-Orbital.svg

Page 9: Boron doping effect 1. Effect on structure B a.C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å c. Electrical

e- hopping

bending

planar-band

-band

Page 10: Boron doping effect 1. Effect on structure B a.C: 3 sp 2 (3 ) and 1 2p z (1 ) bonds B: 3 sp2 (3 ) b. Bond length: C-C = 1.42 Å, B-C = 1.55 Å c. Electrical

For BCNTs

-band

BC3-state is less affected by bending, so channel remains openedfor conduction.

-band is blocked by bending

(note that tube bending induced distortion only occurs in -wave function and valence band essentially remains intact, if, only if, distortionalso takes place in valence band the tube fractureoccurs)

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