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Lecture 17 - VLS - MSE 803 NANOMATERIALS AND NANOTECHNOLOGY...

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MSE 803: N ANOMATERIALS AND N ANOTECHNOLOGY Professor Xudong Wang 213 MSE Building Spring 2009 Class 17 Nanowire Synthesis II (Vapor-Liquid-Solid)
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What’s Vapor Liquid Solid (VLS) Process? 1. Source material sublimates forming a vapor phase 2. Upon the coming of source vapor, catalyst melts forming a liquid alloy droplet 3. The droplet saturates when source vapor keeps coming 4. Solute precipitates out from the droplet forming a solid 1D nanostructure Alloy droplet Source Vapor Metal catalyst Source Vapor Precipitate Grow Source Vapor A Au-Ge system
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Vapor Liquid Solid (VLS) Process Similar results obtained with: Pt, Ag, Pd, Cu and Ni (111) oriented Si “whiskers”: A small Au particle on a Si(111) surface heated at 950° exposed to a flow of SiCl 4 and H 2 Appl. Phys. Lett. 4, 89 (1964)
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Direct Observation of VLS Growth Ge particles+ Au nanoparticles on a TEM grid, heated in the TEM T= 500°C T=800°C J. Am. Chem. Soc., 123, 3165, (2001) Solid Au Alloying with Ge nucleation growth
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Size and Length Control Experiments: InP nanowires catalyzed by gold colloids from 10-30 nm Laser ablation assisted evaporation of InP solid precursor In a tube furnace at 650-700ºC InP target was ablated for several minutes with an ArF excimer laser Growth time: 3-15 mins Nanowire diameter Controlled by the size of catalyst Nanowire length Controlled by the growth time The ideal case J. Phys. Chem. B, 105, 4062, (2001)
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