Laser-Assisted Catalytic Growth (LCG) of Nanowires

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

Papers Reviewed 1. Alfredo M. Morales and Charles M. Lieber; A Laser Ablation Method for the Synthesis of Crystalline Semiconductor Nanowires; Science279, 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)

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.

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

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

Experimental Results TEM results

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.

Thank you! Any questions?

Laser-Assisted Catalytic Growth (LCG) of Nanowires