Paper NS-ThP1
Aligned Growth of Carbon Nanotube using Protein Supramolecule

Thursday, October 18, 2007, 5:30 pm, Room 4C

Carbon nanotubes (CNTs) have remarkable electrical, mechanical and chemical properties and are expected for broad applications in nanoelectronics. For practical applications, it is desirable to be able to synthesize a CNT in a particular location. In this study, we present novel catalytic nanoparticle (NP) positioning technique for CNT growth, which is one application of the Bio Nano Processs (BNP)¹. We used cage-shaped protein, apoferritin (φ12nm) to synthesize homogenous catalytic φ7nm Co NPs within the cavity and the negatively charged outer surface of the apoferritin was used for electrostatic placement of the inner Co NP on Si substrate. We modified Si substrate with positively charged aminosilane molecule (3-amimopropyltriethoxysilane: APTES) and made electrostatic interaction between the ferritin and a surface-modified Si substrate place the ferritins with Co core on a Si substrate. Under appropriate ionic strength around neutral pH, negatively charged ferritins were adsorbed selectively on positively charged APTES-modified area that was fabricated on negatively charged SiO2 surface. This electrostatic adsorption method successfully worked to place the ferritins on the APTES patterns. Heat treatment under O2 gas removed outer protein shells selectively and left only Co NPs on the substrate. The substrate with NPs placed at the designed positions was set in a DC plasma chamber and heated. Firstly, the substrate was treated by H2 plasma to reduce the NPs. After the treatment, CNT growth was conducted under C2H2/H2 plasma. The SEM observation revealed that CNTs grew not on the Si substrate surface but on the NP patterned area. This indicated that the patterned Co NPs, which were synthesized through the BNP, worked as catalyst and determined CNT growth position. Here, we demonstrated novel technique for the CNT growth at the designed positions. We also have succeeded in the single NP placement by analyzing the electrostatic interaction precisely. Individual CNT growth from arranged single NPs will be realized for nanoelectronic devices such as field emission and vertical FET. Part of the experiment was done in Micro/Nanomachining Research and Education Center, Tohoku University. This study is partially supported by Leading Project of MEXT, Japan.

¹I. Yamashita, "Bio Nano Process: Fabrication of Nanoelectronic Devices Using Protein Supramolecules" Tech. Dig. 2006 International Electron Devices Meeting p.447.