Electromechanical Behavior of Carbon Nanohorns and the Conductance Responses to Light Irradiation
Inorganic neuromorphic systems can serve as a platform to have a better understanding of the biology and provide possibilities to develop intelligent devices to emulate nervous systems.  Carbon nanohorn (CNH) aggregates  are one kind of promising building blocks for neuromorphic networks. The peripheral nanohorns may be used as "synapses" to connect neighboring CNH aggregates (Figure 1). Furthermore, the conductivity of CNH networks is possible to change corresponding to different external stimuli, such as light, heat, electric current, chemical modifications and so forth, which simulates the biological synaptic plasticity in nervous systems.
In this work, we present our recent results obtained from the hybrid film of oxidized CNHs (CNHox) encapsulating silver compound (AgX) particles, showing its comprehensive responses to light irradiation. The film was formed by the electrophoresis deposition of AgX@CNHox between two electrodes. The conductance was monitored during the irradiation under a Deuterium light source (the power density is estimated to be around 4.9 W/m2 at 245 nm). Figure 2 shows the typical result. The initial decrease of the conductance may be attributed to oxidation of the surface of CNHs, resulting in the increase of the contact resistance among CNH aggregates in the film. The following increase of the conductance can be understood by the formation of Ag bridges among CNH aggregates. These Ag bridges were decomposed from AgX under UV, which were originally inside CNHox and driven outside by the heat generated from the absorbance of visible/IR light by CNHox.
These preliminary results demonstrated the potential of CNHs to act as neuromorphic systems, showing a conductance evolution related with outside stimuli to mimic some biological intelligent processes to some extent, such as learning and memory etc.