Neuromorphic networks are formed by random self-assembly of silver nanowires. Silver nanowires are coated with a polymer layer after synthesis in which junctions between two nanowires act as resistive switches, often compared with neurosynapses. We analyze the role of single junction switching in the dynamical properties of the neuromorphic network. Network transitions to a high-conductance state under the application of a voltage bias higher than a threshold value. The stability and permanence of this state is studied by shifting the voltage bias in order to activate or deactivate the network. A model of the electrical network with atomic switches reproduces the relation between individual nanowire junctions switching events with current pathway formation or destruction. This relation is further manifested in changes in 1/f power-law scaling of the spectral distribution of current. The current fluctuations involved in this scaling shift are considered to arise from an essential equilibrium between formation, stochastic-mediated breakdown of individual nanowire-nanowire junctions and the onset of different current pathways that optimize power dissipation. This emergent dynamics shown by polymer-coated Ag nanowire networks places this system in the class of optimal transport networks, from which new fundamental parallels with neural dynamics and natural computing problem-solving can be drawn.

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In the research of advanced materials based on nanoscience and nanotechnology, it is often desirable to measure nanoscale local electrical conductivity at a designated position of a given sample. For this purpose, multiple-probe scanning probe microscopes (MP-SPMs), in which two, three or four scanning tunneling microscope (STM) or atomic force microscope (AFM) probes are operated independently, have been developed. Each probe in an MP-SPM is used not only for observing high-resolution STM or AFM images but also for forming an electrical contact enabling nanoscale local electrical conductivity measurement. The world's first double-probe STM (DP-STM) developed by the authors, which was subsequently modified to a triple-probe STM (TP-STM), has been used to measure the conductivities of one-dimensional metal nanowires and carbon nanotubes and also two-dimensional molecular films. A quadruple-probe STM (QP-STM) has also been developed and used to measure the conductivity of two-dimensional molecular films without the ambiguity of contact resistance between the probe and sample. Moreover, a quadruple-probe AFM (QP-AFM) with four conductive tuning-fork-type self-detection force sensing probes has been developed to measure the conductivity of a nanostructure on an insulating substrate. A general-purpose computer software to control four probes at the same time has also been developed and used in the operation of the QP-AFM. These developments and applications of MP-SPMs are reviewed in this paper.

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