Current-Voltage Versus Time: How Metallic Coatings affect Conductive Atomic Force Microscopy Interpretation on Resistive-Switching Metal Halide Perovskites

Metal halide perovskites (MHPs) are commonly studied for their solar cell applications yet are a potentially effective switching medium in memristors. A memristor by design can remember its state after external excitation is removed. This function is helpful in reducing the von Neumann bottleneck in computing by creating more powerful and compact environments for the modern world. However, MHPs are limited by their lack of commercial scaling and puzzling material phenomena that are not easily understood by scientists. To address this, using techniques like atomic force microscopy (AFM) to study MHP thin film mechanisms can help understand, quantify, and optimize MHP efficiency.<br/><br/>When using AFM techniques like conductive AFM (c-AFM), valuable information such as photocurrent, dark current and I-V hysteresis can be uncovered in MHP films. Although, when measuring surface morphology with an AFM tip, many factors have been reported to influence the perception of its findings: surface charges, artifacts, charge injection, wearing of the tip, etc. The AFM tip metal coating can also create undesirable and unpredictable interactions with the sample surface, especially for volatile organics such as perovskites. Therefore, we measured how cyclic voltammetry changes over time as a function of AFM metallic tip coatings on resistive-switching FACsPbI₃ thin films. This approach of c-AFM coupled with heterodyne kelvin probe force microscopy (KPFM) and time-of-flight secondary ionization mass spectrometry (ToF-SIMS) reveals the local electrical, potential, and chemical changes in the film.<br/><br/>Common AFM metallic coatings for c-AFM applications like platinum, diamond, and iridium were used in this study. I-V maps showed changes in the Schottky barrier with each respective tip coating and alterations to resistive switching qualities over time. Disruptions during scanning shows the potential for dragging surface charges (e.g. I₂^-) and affecting the magnitude of current measured. KPFM was measured after c-AFM to demonstrate changes in local potential among different applied sample voltages and tip coatings. Lastly, ToF-SIMS revealed multi-dimensional chemistry at the film scanning sites. The use of tools such as AFM is vital for improving the future of MHP memristors, but understanding the limitations from data interpretation and application is important for comprehending what is found.