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Electric properties of single-walled carbon nanotube and nanoparticle complex for neuron-like signal generation

Prof Hirofumi Tanaka
Mon, 21/08/2017 - 2:00pm to 3:30pm
CA2DM Theory Common (S16-06)
Prof Andrew Wee
Event Type: 


Complex of single-walled carbon nanotube (SWNT) and nanoparticles (NP) has potential of innovative electric nanodevices. In the present work, we measured individual electric property of SWNT/NP complex and found material of NP differed electric property of the complex widely. We also found polyoxometalate complex might be used as neuron firing device in brain computing.


For the future development of molecular electronics, nanoscale molecular devices should be constructed using nanometer-sized electrical wiring. To obtain high-quality devices composed of a few molecules, the nanoscale wiring and the device should have a constant interface. For this purpose, single-walled nanotube (SWNT) has been synthesized with several nanoparticles like 5,15-Bispentyl-porphyrinato Zinc(II) (BPP-Zn), N,N’-bisalkyl-1,4,5,8-naphthalenediimide (Cx-NDI, where x is number of methylene units in the alkyl side-chain) and 1:12 phosphomolybdic acid (PMo12). Then, the electrical property of the complex was measured by using point-contact current imaging atomic force microscopy (PCI-AFM, Fig.1).[1,2] Each nanoparticle showed different electric properties on SWNT. Especially, POM generated pulse like neuron behavior, which might be used in brain-like computing in the future.

2. Experimental Method      

First of all, we prepared BPP-Zn which has two pentyl groups to increase a solubility of SWNT/porphyrin complex [2]. SWNT (0.5 mg) was added to a DMF solution of BPP-Zn (0.1 mM, 5 mL), and then sonicated for 30 min. The solution was centrifuged at 1000 G and the supernatant was collected. SWNT/BPP-Zn complex was collected by a filter (0.5 mm, MILIPORE) and excess BPP-Zn was removed by rinsing by with CHCl3 (100 mL). The SWNT/BPP-Zn was added to DMF (2 mL) and complex was sonicated for 30 min. The DMF solution of SWNT/BPP-Zn complex was casted to a mica substrate and the surface was observed by the tapping-mode AFM (Fig. 2(a)). On the half of the substrate, Au was deposited as electrode with 30 nm thick. After finding individual complex, some of them was dispersed on substrate and check electric properties of the random network.

3.Results and Discussion    

The complex having 2.5-4.5 nm heights was observed. Since a diameter of SWNT is about 1.1-1.5 nm, height of porphyrin-aggregate on SWNT is about 1-3 nm, corresponding 2-6 porphyrin monomers. We measured the conduction property of the complex using PCI-AFM successfully. The results reveal the conduction property of SWNT/porphyrin complex. I-V curve was symmetric where porphyrin aggregate was not absorbed on SWNT, while it was asymmetric where porphyrin was absorbed. This means porphyrin nanoparticles work as rectification devices on the SWNT wiring.

Figure 2(b) shows an AFM image of SWNT/C3-NDI complex. It shows nanoparticles about 3-5 nm diameter of NDI adsorbed on the sidewall of SWNT. By changing the number of methylene unit of NDI, the shape of I-V curve changed. The results show that the majority of SWNT was metallic using C3-NDI to make a complex, while semiconducting when C9-NDI. Besides, the rectification ratio increased and band gap decreased as the size of the molecular nanoparticles increased.   

The rectification properties of SWNT/PMo12 complex were strongly determined by the property of nanotubes. Rectification ratio decreased and band gap increased as particle size was larger if SWNT is semiconducting, while opposite in the case of metallic SWNT. PMo12 also has interesting electric properties. I-V curve obtained by PCI-AFM always show peaks. The peak called negative differential resistance (NDR). Because NDR is one of the components of noise generator, a network of SWNT/PMo12 was fabricated and bias was applied. Amplitude of current, noise strength, was increased as bias increased from 0V to 125V (Fig. 3). Further, current became unstable when 150 V was applied to the same device and then generated pulse current (Fig. 4). The pulses are obtained as special case of the instability. The phenomena are expected to be utilized as neuron devices used in brain computing.


All BPP-Zn, NDI and PMo12 molecules can behave as rectification device on SWNT. PCI-AFM is a useful technique to detect the electrical properties of such kinds of systems described above. It is important to control rectification properties of the complex to realize electronic nanodevices. PMo12/SWNT network generated pulse when 150V was applied. It is expected to be used as neuron firing devices in neuronal computing in the future.


[1] a) Y. Otsuka, Y. Naitoh, T. Matsumoto, T. Kawai, Jpn. J. Appl. Phys., Part 2 41 (2002) L742. b) A. Terawaki, Y. Otsuka, H. Y. Lee, T. Matsumoto et al., Appl. Phys. Lett. 86 (2005) 113 901. c) Y. Otsuka, Y. Naitoh, T. Matsumoto, T. Kawai, Appl. Phys. Lett. 82 (2003) 1944. d) T. Yajima, H. Tanaka, T. Matsumoto, Y. Otsuka et al., Nanotechnology, 18 (2007) 551.

[2] H. Tanaka, T. Yajima, T. Matsumoto, Y. Otsuka et al., Adv. Mater. 18 (2006) 1411.

About the Speaker

Prof. Dr. Hirofumi Tanaka

Department of Human Intelligent Systems,

Graduate School of Life Science and Systems Engineering,

Kyushu Institute of Technology (Kyutech),

2-4, Hibikino, Wakamatsu, Kitakyushu 808-0196, Japan.

Prof. Tanaka completed his doctorate in materials science studying the structural and magnetic properties of ferromagnetic nanoalloys at Osaka University in 1999. Next, he studied the conductivity of metallic nanowires with double-probe scanning tunneling microscopy as a special postdoctoral researcher at RIKEN under Prof. M. Aono. After that, he advanced the molecular-ruler method in which precise multilayers of self-assembled molecular monolayers are used as lithographic resists to yield nanostructures with precise nanometer-scale spacings as a postdoctoral researcher at the Pennsylvania State University under Prof. Paul Weiss (presently UCLA, chief editor of ACS Nano). He then joined the Research Center for Molecular-Scale Nanoscience at the Institute for Molecular Science in 2003 under Prof. T. Ogawa as an assistant professor, where he directed research in molecular electronics using carbon nanotube electrodes. He found that gold nanoparticles can switch to metallic conduction of SWNTs to semiconducting simply by nanoparticle adsorption. This work led to the development of molecular electronics to study electrical properties affected by interactions between molecular nanoparticles and SWNT or graphene nanoribbon. He has also focused on the development of atomic switches, exploring the ultimate miniaturization of electrical switches, and controlled by photo irradiation 2004-2008 in a key technology project of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) and receive an excellent journal award from Japan Society of Applied Physics in 2012. After moving to Osaka University in 2008, he focused on graphene nanoribbons as electrical wires. In 2012, he earned best paper award of Japanese Society of Applied Physics. He moved to department of Human Intelligence Systems, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology as a full professor in April 2014 and is focusing on bio-mimic and/or neuromorphic electric nanodevices. His wide knowledge of materials from metals and inorganic materials to organic materials, and techniques on measurement and fabrication help leading efforts molecular electronics and in combining nanocarbon and nanoparticles to realize a new world of electronic nanosystems.

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