[16p-424-1~8] CS.4 7. Code-sharing Session: Beam Technology and Nanofabrication

▲ [16p-424-2] Fabrication of Tunnel Barriers in Suspended Multiwall Carbon Nanotube Using Focused Ion Beam Technique

〇(D)Norizzawati Mohd Ghazali^1,2, Hiroshi Tomizawa^1,3, Noriyuki Hagiwara^1,4, Katsuya Suzuki^1,4, Abdul Manaf Hashim^1,2, Tomohiro Yamaguchi¹, Seiji Akita⁵, Koji Ishibashi^1,6 (1.RIKEN, 2.Malaysia-Japan Int.l Inst. of Tech., UTM, 3.Tokyo Univ. of Sci, 4.Chiba Univ., 5.Osaka Pref. Univ., 6.RIKEN CEMS)

Keywords:Focused Ion Beam, Carbon Nanotube

This work demonstrates a reliable process to fabricate tunnel barriers in the suspended multi-wall carbon nanotubes (MWCNT) by the mechanical transfer technique. We get information on the effects of backscattering ions from a substrate, which may be one of the problems in the barrier formation in the MWCNT on the substrate. It may also open a way to fabricate nanotube based mechanical functional devices. To fabricate the suspended MWCNTs, first, palladium (Pd) metal is deposited for source and drain electrodes with thickness of 100nm and a gap between the electrodes is 500nm. The nanotubes are dispersed on the polymethyl methacrylate (PMMA) film on the substrate. Then, the PMMA film is peeled off and it is transferred to the desired position between the electrodes under an optical microscope. After transfer, the PMMA film is dissolved in acetone at room temperature. Fig. 1 shows scanning electron microscope (SEM) images of the fabricated suspended MWCNTs. Figure 2 shows the ion dose dependence of the resistance change by the irradiation. The resistance before irradiation is ranging in 10-30kW for all samples. From this result, it is shown that the resistance increases with increasing Ga ion dose for both nanotubes on a substrate [1] and the suspended nanotubes. Interestingly, for the case of the suspended nanotubes higher dose is needed to increase the resistance as compared to the nanotube on a substrate. This result seems to show that the effect of the underneath substrate and reflected ions from the substrate during FIB process is important. However, some of the suspended CNT samples show only a small resistance change after irradiation although high ion dose was irradiated on the nanotube. This is possibly due to the PMMA residue remaining after the transfer process which could affect the irradiation process. The work to obtain suspended nanotube devices with less residue is on the way in order to achieve small resistance variation of the fabricated devices.
[1] H. Tomizawa, The 76th JSAP Autumn Meeting 2015.