Thomas Laude's pages - Science de la matière et de l'énergie

Synthesis methods

Note : These pages are in no way an exhaustive review of all the tremendous amount of work that as been published in the field. I welcome any remark or any proposal for links and bibliography.

Quick jumps :

Carbon nanostructures
BN nanostructures

Synthesis methods for carbon nanostructures:

Basically, there are 2 types of methods to get a carbon nanostructure. For those two methods, the morphologies obtained differ quite a lot.

The first is to grow slowly the structure from a surface by a soft chemicalgrowth.
The second is to submit the material to a quick heating over the sublimationpoint under low inert pressure.

Slow methods (The CVD techniques):

It is a chemical deposition (the deposition can be led for severaldays) through pyrolysis (the sample and the surrounding are heated, typicallyaround 700 C) of a hydrocarbide (acetylene, ethylene, benzene...) overa template substrate (for example, iron nano-particules embedded in silica).

See for instance : Z. W. Pan et al. - Very long carbon nanotube-nature, vol. 394, 13 aug. 1998

Violent methods

Krätschmer arc methods:

It is the most widely used method to synthesize carbon nanostructure because it is rather simple to undertake in laboratory. The principle is to submit 2 graphite electrodes to a high currentdischarge (typically 20V, 50A) inside an enclosure filled with inert gas(helium, argon...) at low pressure (between 50 and 700 mbar). Metallicparticles can be added in the initial electrodes to catalyse single wallnanotubes.

See W. Krätschmer, L.D. Lamb, K. Fostiropoulos, D.R. Huffman , Solid C60 : a new form of carbon - Nature 347, 354-358 (1990)
and C. Journet et al.- Large scale production of single-walled carbon nanotubes by the electric-arc technique - Nature 388 21 aug. 1997

The laser ablation methods:

It is rather similar to the arc method and was in fact the first one tobe developed. Studies (mainly in Rice university) have proved that it canlead to very similar structures to those obtained by the arc method : fullerenes, nanotube multi or mono-layered, onions...
The main differences are :

The material is submitted to a laser ablation instead of an arc discharge. (The laser is usually a pulsed YAG laser.)
No tube of reasonable length has ever been synthesized without some catalysing particles. This tends to say that a certain local anisotropy is necessaryto grow tube.
Particles are collected through a carrier gas on a cool plate far fromthe target. A secondary heating is usually added.

See A. Thess et al. - Crystalline ropes of metallic carbon nanotubes- science, vol. 273, 26 july 1996

Carbon's methods in brief	Slow methods (several days)	Fast methods (several minutes)
Techniques	CVD: (chemical vapour deposition) Pyrolysis (700 °C)of a hydrocarbon (acetylene, ethylene, benzene...) over a template substrate (iron nano-particles embedded in silica…)	Arc discharge: Electric arc discharge between graphite rods in inert atmosphere atlow pressure (Pulsed) laser ablation : Ablation of a graphite target in inert atmosphere at low pressure + oven heating + carrier gases to a cooled stage
Results	Large arrays of tubes long (up to 2 mm) but thick (diameter > 20 nm) No other morphology is obtained	All types of nanostructures (including Ropes of SWNT) Tubes are shorter (100 µm) but thin (> 1 nm)
Usually proposed Nucleation processes	Growth on surface through atoms of the gas phase captured on large catalyst particles.	Arc discharge : tubes -> growth on the electrodes tip spherical structures -> growth in plasma Ablation : growth by in plasma condensation

Synthesis methods for BN nanostructures:

For BN, many methods were inspired from carbon. But, to make an equivalent of carbon production (thin tubes over the micron scale, ropes, quantity higher that what is needed for electron microscopy observations...) remainded a challenge untill very recent days.

Non ablative laser heating method

Low power continuous CO2 laser on h-BN target in static N2 atmosphere
Thin BN tubes hundred micron long and nanopolyhedral BN/B particles. Macroscopic crown-like growth around impact.
T. laude, Y matsui, A. Marraud, B. jouffrey, Appl Phys Let 76, 22, p. 3239, (2000)

Arc discharge methods

Arc discharge on a hollow tungsten electrode filled with h-BN
Thin tubes < 200 nm + W particles
Chopra, N. G. et al. Boron nitride nanotubes. Science 269, 966-967(1995)

Arc discharge on a HfB2 electrode in N2
Thin tubes < 700 nm + Hf particles
A. Loiseau, F. Willaime, N. Demoncy, G. Hug, H. Pascard - Boron nitride nanotubes with reduced numbers of layers synthesized by arc-discharge -Phys. Rev. Lett. 76, 4737 (1996).

Arc discharge on a ZrB2 electrode in N2
Thin tubes < 100 nm + Zr particles
Y. saito, M. Maida,J. of Phys. Chem A 103, 10, 1291 (1999)

Arc discharge on B electrode in N2
BN bi-layered tubes several micron long and "nanococoons". Macroscopic quantities.
J. Cumings, A. Zettl, Chem. Phys. Let. 316, 211 (2000)

Laser ablation method

Excimer laser ablation of h-BN (in He)Yu
Thin tubes < 100 nm (+ Ni & Co)
D. P. Yu et al., Apl. Phys. Lett. 72, 16, 1966 (1998)
and G. W. Zhou, Z Zhang, Z. G. Bai, D. P. Yu, Sol. St. Com. 109,555 (1999)

H. P. compression (5-15 Gpa) of c-BN micro-crystals in a diamond anvil cell induced by laser heating
A few short tubes < 30 nm.
D. Golberg et al, Appl. Phys. Lett. 69 (14), 2045-2047 (1996)

Oven heating

Oven Heating (1200*C) of B and Li in a BN crucible in N2 atmosphere
A few short tubes < 30 nm + Li particles
M. Terauchi, M. Tanaka, H. Matsuda, M. Takeda & K. Kimura, Helical nanotubes of hexagonal boron nitride. Journ. of Elec. Micros. 46 (1), 75-78 (1997)

Oven heating (1000*C) of B previously ball milled in ammonia
Large filaments < 5 µm
Y. Chen, J.F. Gerald, J.S. Williams, S. Bulcock, Chem. Phys. Lett.299, 260 (1999)

Oven heating (1100 *C) of B2H6 + NH3 + ZrB2
Large filaments < 10 µm + ZrB2 particles
P. Gleize, M.C. Schouler, P. Gadelle, M. Caillet, J. of Mat. Science 29, 1575 (1994)

"Substitution" of C to BN in oxydizing atmosphere (Mechanism proposed by the authors of the papers)
Transformation of micrometer carbon multiwalled nanotube into BN nanotube.Or doping carbon SWNT ropes with some percentage of B/N
W. Han, Y. Bando, K. Kurashima, T. Sato, Appl. Phys. Let.73,21, 3085 (1998)
and D. Golberg, Y. Bando, W. Han, K. Kurashima, T. Sato, Chem. Phys.let. 308, 337 (1999)

To contact me: thomaslaudeABC@uminokai.net (Remove ABC, it is against spam.)
The material present here is copyrighted. Key-words: nanotechnology, science, nanotubes.