Specialized lecture by Principal Researcher Alexander Tselev, University of Aveiro, Portugal

Scanning Probe Microscopy of Functional Materials

In this lecture, I will present a few insightful applications of advanced and novel Scanning Probe Microscopy (SPM) techniques to nanoscale characterization of functional materials.

In the first part, the highlight will be on epitaxial growth of complex metal oxides with perovskite structure in the Pulsed Laser Deposition (PLD). After a short introduction into this class of materials, the focus will be placed on signatures of film growth modes revealed with atomically-resolved in-situ Scanning Tunneling Microscopy (STM) [1].

As the second example, I will spotlight an approach for measuring thermal resistance of individual grain boundaries in polycrystals [2]. Material thermal conductivity is crucial in applications ranging from thermal management to energy harvesting. Understanding and controlling the impact of extended phonon-scattering defects, like grain boundaries, on thermal conductivity is essential for efficient material design, yet systematic studies are limited by the lack of adequate tools. We employed thermal waves propagating across grain boundaries to quantify their thermal resistance by assessing changes in thermal wave amplitude and phase across grain boundaries. In our technique, thermal waves are generated by a lithographically defined microheater, and the resulting thermal wave field is mapped with a temperature-sensitive scanning probe. We quantified grain boundary thermal resistance in SrTiO₃ ceramic with an average grain size of approximately 5 μm.

The concluding example will be the near-field microwave microscopy (SMM), a scanning probe technique exploiting electric fields formed at a sharp scanning probe and oscillating at a GHz frequency. The technique allows localized quantitative characterization and mapping material dielectric permittivity and conductivity. I will discuss its application to quantitative characterization of AC conductivity of ferroelectric domain walls in epitaxial thin films of Pb(Zr_0.2Ti_0.8)O₃ (PZT). The domain walls show a large conductance at GHz frequencies while the conduction at DC is undetectable [3]. The technique has opened the door to the use of noninvasive, small electric fields for probing the ferroelectric domain structure and walls in ambient [4]. It also allowed near-field imaging of objects in liquids through ultrathin membranes [5].

[1] A. Tselev, et al., ACS Nano 2015, 9, 4316.

[2] D. Alikin, et al., ACS Appl. Mater. Interfaces 2024, 16, 42917.

[3] A. Tselev, et al., Nat. Commun. 2016, 7, 11630.

[4] S. M. Neumayer, et.al., NCE 2023, 3, 014005.

[5] A. Tselev, et al., ACS Nano 2016, 10, 3562.