500-kHz Bandwidth Feedback for Scanning Ion Conductance Microscopy With Nanoresolution

Scanning ion conductance microscopy (SICM) has been developing rapidly and has been a versatile tool for nanoscale imaging. However, the imaging quality and scanning speed of SICM have been significant restriction factors for its various applications. One of the main reasons is the mutual restriction of bandwidth and noise of the ion current feedback. In this article, a low-noise two-stage transimpedance amplifier (TIA) with 500-kHz bandwidth was proposed and a low-capacitance pipette was combined to depress the high-frequency ion current noise of SICM's feedback circuit. The effect of pipette capacitance, which is a major cause of high-frequency noise, was significantly reduced by covering a thin polydimethylsiloxane (PDMS) film on the outer wall of the pipette. Finite-element method (FEM) was employed for the first time to simulate the pipette capacitance model. Impedance spectroscopy experiments verified that this method can greatly reduce the pipette capacitance (about 0.7 times). Through the comparative analysis of ion current noise, as well as the scanning experiments of standard silicon material sample and PMDS sample, it was demonstrated that the proposed method has a significant effect in reducing the high-frequency noise of ion current measurement. Therefore, our method can provide an avenue to realize high-speed imaging with high positioning accuracy.