1. Laser-Assisted Catalytic Growth (LCG) of Nanowires
EE 235 Paper 2 Review Presentation
Xiaojun Zhang

2. Papers Reviewed
1. Alfredo M. Morales and Charles M. Lieber; A Laser Ablation Method for the Synthesis of Crystalline Semiconductor Nanowires; Science 279, 208 (1998)
2. Xiangfeng Duan and Charles M. Lieber; Laser-Assisted Catalytic Growth of Single Crystal GaN Nanowires; J. Am. Chem. Soc. 122, 188 (2000)

3. Why LCG?
Template-mediated method: usually forms polycrystalline materials.
Conventional VLS method: the diameter of nanowires, which is determined by equilibrium cluster size, is generally too large.
Solution-liquid-solid synthesis: needs a catalyst that melts below the solvent boiling point.

4. Schematic of the Apparatus for Laser-Assisted Catalytic Growth
Furnace
Cold substrate to
collect nanowires
Focus lens
Laser
Laser: Nd–yttrium-aluminumgarnet
laser (wavelength, 532 nm)
Carrier gas inlet
Carrier gas exit
Target containing both nanowire
and catalyst materials

5. Proposed Nanowire Growth Model
Laser ablation creates vapor (B) Condenses into small clusters
(C) Growth continues by VLS mechanism (D) Growth terminates

6. Experimental Results
TEM results

7. Conclusions
It actually proceeds by the VLS mechanism. However, the clusters of catalyst are created by laser ablation. Therefore it is more versatile while selecting catalyst.
The nanowire diameter can be much smaller since it is not limited by the minimum diameter of the liquid catalyst under equilibrium.
Like the conventional VLS method, the catalyst should form a miscible liquid phase with the nanowire material, but not form a more stable solid phase under the nanowire growth conditions.
The nanowires generated by LCG normally lie on the substrate.

8. Thank you!
Any questions?