Fe, Co, and Ni are catalytically effective for growing single-walled carbon nanotubes (SWNTs). On substrates, however, Ni tends to yield only multi-walled carbon nanotubes. Because enhanced surface diffusion at the elevated growth temperature required for deposition might cause coarsening of Ni catalyst nanoparticles, adjusting the nominal Ni thickness should be crucial for controlling the particle size. Using our previously developed combinatorial method, we prepared a thickness profile of Ni on a quartz glass (SiO2) substrate and found that Ni nanoparticles catalyzed the growth of SWNTs by chemical vapor deposition only when nominal Ni thickness was in the monolayer range.
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