Lecture 4 Non-carbon nanotubes

1. BN nanotubes BC 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.k pentagon 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 anode and Cu rod as cathode + - BN is insulator, cannot electrically conduct, so Ta-tube is used for conduction purpose Modified arc discharge

Carbon nanotubes, CNTs CNTs + B 2 O 5 heated in N 2 (or NH 3 ) flow at 1700  C for 40 mins BN nanotubes Substitution method

3B 2 O 5 6NH 3 + 9H 2 O + 6CO BN

Because C atoms are substituted by BN (not growth process), so BN nanotube tips are opened, i.e. substitution is difficult to proceed at tube tips.

Inorganic nanotubes MS 2 : 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

WS 2 -nanotube 6.2 Å inter-layer spacing

How to make MS 2 -nanotubes W-wire Heating in Air at  C WO 3 rod Heating in H 2 S/H 2 at 900  C WS 2 -nanotubes Template growth of MS 2 -nanotubes

3WO 3 + 6H 2 S + 3H 2  3WS 2 + 9H 2 O 反應式 3MoO 3 + 6H 2 S + 3H 2  3MoS 2 + 9H 2 O

Mixed phase of nanotubes

W x Mo y C z S 2 -nanotubes, x + y + z = 1

WS 2 -nanotubes Carbon nanotubes

WS 2 -nanotube Carbon nanotubes 在 TEM 下, WS 2 比 carbon nanotubes 具更深之對比

0.62 nm 0.34 nm

0.58 nm NbS 2 -structure S Nb

2 -nanotubes

NbS 2 -nanorodes