(d) to (f) High-magnification images of each point in (c) clearly showing the density difference.

We also demonstrated that this method could be applied to the growth of CNTs on a designated area of released micromechanical structures. Typically, released and movable microstructures fail by stiction when the structures are exposed to a liquid, and thus, this demonstration was only possible because no wet process was involved in our proposed method. Figure 5 shows the CNTs synthesized on the released comb structures formed on a device layer of a silicon-on-insulator (SOI) wafer. In Figure 5a, the CNTs were grown on a desired comb only, while the CNTs were grown in a band across multiple combs in Figure 5b. The insets in each figure are the close-up views of CNTs in red squares. Figure 5 CNTs on MEMS structure. The catalyst was deposited selectively on a comb structure parallel and perpendicular to the shadow mask. SEM images show AZD5582 manufacturer CNTs grown with the (a) parallel

and (b) perpendicular alignment between the shadow mask and the comb structure. The insets are the close-up views of the CNTs in red squares. Conclusions In conclusion, we demonstrated for the first time that the nanoparticles generated using the spark discharge method can be used successfully as catalysts for the growth of compound screening assay CNTs. The nanoparticles were transferred onto the desired area on a substrate by thermophoresis and were patterned using a shadow mask to realize patterned growth of CNTs. The nanoparticle deposition time determines the final density of the grown CNTs, and vertically aligned growth of CNTs was achieved after 10 min of

nanoparticle deposition in our experiment. An alternative approach to changing the density of CNTs was to change the gap between the shadow mask and the substrate, and a patterned line of CNTs with gradually varying density along the line could be formed by tilting the shadow mask. The proposed all-dry process could also be applied to completely fabricated micromechanical structures, as demonstrated by site-specifically growing the CNTs on the released high-aspect-ratio microstructures. Acknowledgements This work was supported by the National Research Foundation of Korea Grant BCKDHB funded by the Korean Government (MEST) (grant no. NRF-2011-0030206) and the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A2043661). References 1. Frank S, Poncharal P, Wang ZL, de Heer WA: Carbon nanotube quantum resistors. Science 1998, 280:1744.CrossRef 2. Tans SJ, Verschueren ARM, Dekker C: Room-temperature transistor based on a single carbon nanotube. Nature 1998, 393:49.CrossRef 3. Kong J, Franklin NR, Zhou C, Chapline MG, Peng S, Cho K, Dai H: Nanotube molecular wires as chemical sensors. Science 2000, 287:622.CrossRef 4. Murakami H, Hirakawa M, Tanaka C, Yamakawa H: Field emission from well-aligned, patterned, carbon nanotube emitters.