Scanning Tunneling Microscopy as a Method for Analyzing the Correlation of Local Resistive and Ferroelectric Properties in Memristive Compositions

The creation of multilayer resistive memory devices based on nanolayer memristive compositions with thin ferroelectric (FE) films, in which resistance switching is caused by a combination of effects related to the influence of interface regions, polarization states, charge transport mechanisms, and microscopic features of nanostructures, requires the development of new experimental approaches to the study of local electrophysical properties. One of the most common ways to investigate local electrophysical properties is the use of various atomic force microscopy (AFM) techniques, including the Kelvin probe microscopy, tunneling AFM, and piezoresponse AFM. The main reason for switching from AFM to scanning tunneling microscopy techniques when studying the local resistive properties of memristive compositions with FE films is the need to stabilize the probe-sample contact. The main obstacle to the effective use of AFM techniques to study the local ferroelectric properties in nanolayer memristive compositions with thin FE films is the occurrence of a strain gradient during scanning, which leads to the contribution of the flexoelectric effect and direct piezoelectric effect in the measurement results. In this work, we have developed a method of investigating the local FEproperties using scanning tunneling microscopy (STM) and spectroscopy (STS) techniques under ultra-high vacuum conditions. The essence of the proposed approach is to identify the contribution of polarization charges, as well as the features of their screening on the free surface of the FE film, to the results of STS measurements at different polarization orientations in the FE film. In combination with STM measurements of local morphological features, the analysis of experimental results makes it possible to identify the state of FE polarization, determine the contribution of the surface screening of polarization charges to the manifestation of memristive effects, and investigate the correlation between the local resistive and FE properties in nanolayer memristive compositions with thin FE films.