Transcript 投影片 1
Boron doping effect 1. Effect on structure B 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 CB metallic EF VB CB EF CNT Eg VB Semiconductor CB * EF VB BC3 tube Free electronic-like (metallic) 2. Effect on electronic profiles CB metallic EF VB EF depression to VB edge more than 2 sub-bands crossing at EF i.e. conductance increases CB EF Random doping of B in CNT New Eg Eg BC3 state (acceptor) VB Semiconductor Eg reduction by EF depression 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) d. The actual conductivity depends on competition between scattering density scattering and increase in hole carrier (in practice, the latter > the former, so conductance ) B+ e- e. Electron hopping magnitude in -band increase Overlap of -electron wave function hopping e- -band (CB) -band (VB) -band (CB) B dopant BC3 state f. Less influence on conductivity upon strain application For CNT R Deflection angle Resistance reduction is due to (i) temporary formation of sp3 at bend region and (ii) increasing hopping magnitude upon bending Temporary formation of sp3 character upon bending bending Planar sp2 Tetrahedral sp3 -band -band planar -band e- hopping bending For BCNTs -band is blocked by bending -band BC3-state is less affected by bending, so channel remains opened for conduction. (note that tube bending induced distortion only occurs in -wave function and valence band essentially remains intact, if, only if, distortion also takes place in valence band the tube fracture occurs)