Development of Ionic Polymer-Functionalized Single Nanopipette Probes

Nanoprobes govern the spatiotemporal resolution of scanning probe microscopy techniques and are almost exclusively constructed with inorganic materials. Herein, we report the functionalization of single glass/quartz nanopipettes with lithium conducting polymers as conductive polymer nanoprobes. Lithium ion electrolytes with a reactive anion that can be covalently bonded (LiMTFSI) and a nonreactive anion (LiTFSI) are polymerized inside individual nanopipettes to develop single-ion conducting (p-SIC) and dual-ion conducting (p-DIC) nanoprobes, respectively. Customized tools and procedures are developed for handling delicate nanopipettes and for real-time monitoring of the polymerization reactions in an inert environment inside a glovebox. In situ monitoring of ionic conductivity changes characterizes the kinetics of polymerization in a single or bundle of nanopipettes. The room-temperature ionic conductivity and thermal activation energy of polymers inside nanopipettes are consistent with bulk values statistically, 10^–5 S/cm and 36 ± 7 kJ/mol for p-SIC and 10^–4 S/cm and 20 ± 4 kJ/mol for p-DIC, respectively. Heterogeneity among different polymer@nanopipettes is mitigated through an internal standardization method. Proof of principles for probing localized conductance, e.g., at the nanotip–substrate interface, are demonstrated using p-DIC@nanopipettes in repetitive approaching–landing–retrieval from a substrate immersed in lithium electrolyte solution. A common technical challenge with a risk of breaking the fragile nanotips is reduced by adopting a tilted nanotip─substrate alignment. The design also allows for closer proximity or surface contact theoretically limited by the quartz wall, which is critical for fundamental interfacial transport studies and for better imaging resolution. A capacitance term is found to be necessary in addition to the widely adopted tip─substrate distance-dependent resistance to quantitatively fit the approach curves. The polymer@nanotip platform provides a new capability to investigate ion transport across solid–electrolyte interfaces, which is vital for applications such as next-generation solid-state batteries, miniaturized memristors and transistors, and other energy and imaging systems.