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Lecture 4Non-carbon nanotubes
1. BN nanotubes
B C N
Several features associated with BN-nanotubes
1. Interlayer-spacing = ?
0.33 nm
2. Can BN form pentagons or heptagons (五七連環 )? cannot
hexagon
B
N
o.kpentagon
not o.k
B-B bond
pentagon
not o.k
N-N bond
same as heptagon+ +
同電荷不會鍵結在一起
If BN cannot form pentagons how do they close BN-nanotubes,in other words, how BN nanotubes stop to grow?
4-member ring
BN-nanotubes made by arc discharge
How to make BN nanotubes?
1. Arc discharge.2. Substitution of carbon nanotubes
by BN using annealing process.
arc discharge using graphite rods
+ -
arc discharge using Ta-tube filled with BN powder as anodeand Cu rod as cathode
+ -
BN is insulator, cannot electrically conduct, so Ta-tubeis used for conduction purpose
Modified arc discharge
Carbon nanotubes, CNTs
CNTs + B2O5 heated in N2 (or NH3) flow at 1700 C for 40 mins
BN nanotubes
Substitution method
3B2O5
6NH3
+ 9H2O + 6CO
B N
Because C atoms are substituted by BN (not growth process), so BN nanotube tips are opened, i.e. substitution is difficultto proceed at tube tips.
Inorganic nanotubes MS2: M= Nb, W, Mo
Concertina-like structure, no M-M and S-S bonds only M-S bonds
M atoms situate at the central line
WS2-nanotube
6.2 Å inter-layer spacing
How to make MS2-nanotubes
W-wire
Heating in Air at 600-800 C
WO3 rod
Heating in H2S/H2 at 900 C
WS2-nanotubes
Template growth of MS2-nanotubes
3WO3 + 6H2S + 3H2 3WS2 + 9H2O
反應式
3MoO3 + 6H2S + 3H2 3MoS2 + 9H2O
Mixed phase of nanotubes
WxMoyCzS2-nanotubes, x + y + z = 1
WS2-nanotubes
Carbon nanotubes
WS2-nanotube
Carbon nanotubes
在 TEM下 , WS2比 carbon nanotubes 具更深之對比
0.62 nm0.34 nm
0.58 nm
NbS2-structure
S
Nb
C-tubes@WS2-nanotubes
NbS2-nanorodes