Quantitative Visualization of Topology and Morphing of Percolation Path in Nanoparticle Network Array Exhibiting Coulomb Blockade at Room Temperature

A network of one-dimensional (1D) necklaces of 10 nm Au nanoparticles was fabricated by a directed self-assembly to synthesize 1D necklaces followed by self-limiting monolayer deposition to form a two-dimensional (2D) network array. Scanning electron microscope (SEM) image analysis revealed a percolation threshold lower than random 2D arrays signifying the local 1D structure. The topology of (shortest) percolation paths (tortuosity) and the fraction of clusters isolated from the percolating array were quantified to relate the network morphology to the observed non-Ohmic (Coulomb blockade effect) behavior. Leveraging charge contrast in SEM, the morphing of the percolation path as a function of the kinetic energy of the conduction electron was visualized and quantified to understand the dynamic nature of the percolation behavior. The morphology can be systematically tailored by tuning the two self-assembly processes to obtain the same coverage of the array with significantly diverse non-Ohmic behavior. It was concluded that tortuosity and void fraction unify the Coulomb blockade behavior for a range of fabrication conditions leading to varying network morphologies with a threshold blockade bias ranging from 0.5 to 5.5 V at room temperature. This self-assembly avenue will allow the development of highly sensitive, all-metal electrochemical field effect transistors for applications in biology.