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