Brain-like signal generating electric devices made of single-walled carbon nanotube and nanoparticle complex

For the future development of electronics in nanoscale, molecular nanodevices 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 utilized 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 electrical property of the complex was measured by using point-contact current imaging atomic force microscopy.[1,2] In the BPP-Zn case, 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. Cx-NDI nanoparticles also working as a rectifier on SWNT sidewall. PMo12 also has interesting electric properties. I-V curve obtained by PCI-AFM always show peaks called negative differential resistance (NDR). The NDR is considered that occurred by redox of PMo12. Because NDR is one of the components of noise generator, a random network of SWNT/PMo12 was fabricated and electrode which gap is about 1mm was put on the network. When bias was applied, amplitude of current, noise strength, was increased as bias increased from 0V to 125V. Further, current became unstable when 150 V was applied to the same device and then generated pulse current. The pulses were obtained as special case of the instability of a circuit. As the phenomena were expected to be utilized as neuron devices used in brain like computing, the behavior was chaotically analyzed. Each preparation condition had different #x201C;attractors#x201D; and the results might be the indexes for controlling the neuron behavior of the devices.