Abstract
Current rectification is well-known in ion transport through nanoscale pores and
channel devices. The measured current is affected by both the geometry and fixed interfacial
charges of the nanodevices. In this paper, an interesting trend is observed in steady-state
current-potential measurements using single conical nanopores. A threshold low conductivity
state is observed upon the dilution of electrolyte concentration. Correspondingly, the
normalized current at positive bias potentials drastically increases and contributes to different
degree of rectification. The novel opposite trend at opposite bias polarities is employed to
differentiate the ion flux affected by the fixed charges at the substrate-solution interface
(surface effect), with respect to the constant asymmetric geometry (volume effect). The
surface charge density (SCD) of individual nanopores, an important physical parameter that
is challenging to measure experimentally and is known to vary from one nanopore to another,
are directly quantified by solving Poisson and Nernst-Planck equations in the simulation of
the experimental results. Flux distribution inside the nanopore and SCD of individual
nanopores are reported. The respective diffusion and migration translocations are found to
vary at different positions inside the nanopore. The knowledge is believed important for
resistive pulse sensing applications, as the detection signal is determined by the perturbation
of ion current by the analytes.