Advances in Piezoresponse Force Microscopy

• Ferroelectric characterization using piezoresponse force microscopy (PFM), with a focus on quantitative measurements and resulting insight in the material properties.
  
• The role of switching spectroscopy (SS-PFM), contact Kelvin Probe Microscopy (cKPFM), contact resonance-based detection, nano-PUND, and Data Cube approaches in artifact avoidance and maximizing sensitivity on functional materials.
• PFM measurements in highly conducting liquids for life science and energy research.

Symposium Introduction by Session Chair | Dr. Thomas Mueller, Bruker

[00:02:30] PRESENTATION 1

Overview of AFM Electrical Modes for Ferroelectrics | Dr. Peter De Wolf, Bruker

Nanoscale characterization of ferroelectric materials is enabled by a wide variety of Scanning Probe Microscopy (SPM) based methods providing insight in morphological, electrical, and electromechanical information. In a short introductory talk, we will present an overview of the SPM modes relevant in this research field, with specific focus on the various implementations of Piezoresponse Force Microscopy (PFM).

A second part covers three recent implementations providing more detailed insight in ferroelectric material properties: (i) The application of PFM methods in liquid environments including highly conducting liquids for life science and energy research. (ii) The combination of PFM with a DataCube approach providing a resonance spectrum in each pixel, maximizing sensitivity and at the same time avoiding the limitations associated with contact mode (as used with conventional implementations for PFM). (iii) Focus on quantitative measurements by a switching spectroscopy (SS-PFM) or contact Kelvin Probe Microscopy (cKPFM) approach to avoid artifacts in PFM point spectroscopy. Two of these will be illustrated with a short live demonstration.

[00:19:00] PRESENTATION 2

The Opportunities of functional material property mapping using Piezoresponse Force Microscopy | Dr. Nina Balke, ORNL

Piezoresponse Force Microscopy (PFM) has become a powerful tool to study local electromechanical sample responses in ferroelectric materials. PFM is used to image and manipulate ferroelectric domains in ceramics, thin films, and polymers and contains information about local piezoelectric properties (PFM amplitude) as well as the direction of the polarization (PFM phase) in the probed volume. However, the measured properties are often reported in arbitrary units and internal phase offsets make it necessary to shift the measured PFM phase which can result in a loss of physical information. This presentation will go over the fundamentals of PFM and will address the issue of unwanted signal origins and PFM phase corrections towards more quantitative measurements. The goal is to be able to measure and calibrate functional material properties which can be compared with macroscopic measurements or theoretical predictions for more in-depth insight into physical processes in the material. The successful combination of PFM and theory is demonstrated in a 2D layered ferroelectric material, CuInP₂S₆, which allows to greatly enhance the information gain obtained by PFM.

[00:54:30] PRESENTATION 3

PFM and Nano-PUND: Complementary Techniques for Ferroelectrics | Dr. Brice Gautier, INSA Lyon

Piezoresponse Force Microscopy (PFM) has become a standard for ferroelectricity assessment at the nanoscale. This presentation will review PFM operating modes including DFRT and introduce nano-PUND, a complementary approach. PFM signals can have origins other than ferroelectricity, especially in the case of very thin films, leaky samples, or when ionic conduction is possible. In some cases, proving the ferroelectric nature of a sample is not possible by PFM alone, and the added information from a complementary approach is needed.

At the macroscopic scale, PUND (Positive Up Negative Down) is used to measure the remnant polarization in leaky ferroelectrics. However, the application of the PUND method is particularly tricky because of the unfavorable signal to noise ratio: capacitive current appears to be several orders of magnitude higher than the current to be measured, not to mention additional leakage currents.

In this presentation, we show how PUND method can be used with an AFM tip as a top electrode, especially by compensating the spurious contributions (capacitive, leakage current): we have called it the nano-PUND method. We show examples of the implementation of nano-PUND and the advantages compared to PFM. Lead Zirconium Tantalate (PZT) is first used as a test material, then Hafnium Zirconium oxide (Hf_0.5Zr_0.5O₂), extensively studied but particularly delicate when probed by PFM, illustrates the capabilities of the method.

[01:27:10] PRESENTATION 4

Recent Developments with Live Demonstration | Dr. Bede Pittenger and Dr. Mickael Febvre, Bruker

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This webinar was presented on: June 3, 2020