Direct Imaging of the Relaxation of Individual Ferroelectric Interfaces in a Tensile‐Strained Film

Abstract

and due to slight difference in crystal structure, electronic structure, and strain states compared with the domains, are capable of exhibiting unique phenomena ranging from enhanced or suppressed conductivity, [4][5][6] to enhanced magnetoelectric coupling. [7,8] Given their energy cost, walls are typically unstable under applied fields [9] and will move, leading to marked enhancement of macroscopic material properties, such as dielectric, [10,11] piezoelectric, and electrooptic/electroacoustic coefficients. [6,[12][13][14][15][16] While much is known about domain wall contributions to macroscopic functionalities, the local dynamic behavior of domain walls at length scales approaching those of the distance between pinning centers (approximately nm length scales) remains difficult to access with experimental techniques, although recent advances in in situ transmission electron microscopy have greatly expanded the experimental capabilities. [17][18][19][20] The movement of domain walls is typically modeled as the motion of an elastic interface through a distribution of pinning centers, with such behavior implicated in observed phenomena such as creep, where walls are thermally activated across local energy barriers created through the pinning potential landscape, [21][22][23] domain wall roughening, [23,24] and faceting [25,26] (from changes to the shape of the domain wall from ideality), the dependence of the susceptibility on the driving field (Rayleigh behavior for the linear case, where Understanding the dynamic behavior of interfaces in ferroic materials is an important field of research with widespread practical implications, as the motion of domain walls and phase boundaries are associated with substantial increases in dielectric and piezoelectric effects. Although commonly studied in the macroscopic regime, the local dynamics of interfaces have received less attention, with most studies limited to domain growth and/or reversal by piezoresponse force microscopy (PFM). Here, spatial mapping of local domain wall-related relaxation in a tensile-strained PbTiO 3 thin film using time-resolved band-excitation PFM is demonstrated, which allows exploring of the field-induced strain (piezoresponse) as a function of applied voltage and time. Through multivariate statistical analysis on the resultant 4-dimensional dataset (x,y,V,t) with functional fitting, it is determined that the relaxation is strongly correleated with the distance to the domain walls, and varies based on the type of domain wall present in the probed volume. Phase-field modeling shows the relaxation behavior near and away from the interfaces, and confirms the modulation of the z-component of polarization by wall motion, yielding the observed piezoresponse relaxation. These studies shed light on the local dynamics of interfaces in ferroelectric thin films, and are therefore important for the design of ferroelectric-based components in microelectromechanical systems.

Tensor factorization for elucidating mechanisms of piezoresponse relaxation via dynamic Piezoresponse Force Spectroscopy

“…As a model system, we have chosen a 700 nm-thick PbTiO 3 thin film grown by chemical vapor deposition on (001) KTaO 3 substrates with an SrRuO 3 conducting buffer layer; this film displays a dense polydomain structure as previously reported 69,70 . The PFM was performed using a commercially available atomic force microscopy (Cypher, Oxford Instruments) fitted with an interferometric displacement sensor.…”

Autonomous Experiments in Scanning Probe Microscopy and Spectroscopy: Choosing Where to Explore Polarization Dynamics in Ferroelectrics

“…As a material system, we have chosen a 700 nm thick PbTiO 3 thin film grown by chemical vapor deposition on (001) KTaO 3 substrates with a SrRuO 3 conducting buffer layer, as reported by H. Morioka et al , The PFM was performed using an Oxford Instrument Asylum Research Cypher microscope with a National Instruments DAQ card and chassis and operated with a LabView framework. All experiments were performed using Budget Sensor Multi75E-G Cr/Pt coated AFM probes (∼3 N/m).…”

Toward Decoding the Relationship between Domain Structure and Functionality in Ferroelectrics via Hidden Latent Variables

“…An alternative approach for the analysis of switching behaviors can be based on the domain patterns and their evolution with time under bias, thermal, or pressure stimuli, i.e., feature extraction in the spatial domain. Here, chosen physical descriptors such as distance to the ferroelectric or ferroelastic wall or local curvature are selected and the correlations between the physical descriptors and switching behavior are explored . The drawback of such an approach is the large number of possible mechanisms and hence possible descriptors, giving rise to spurious correlations.…”

“…Here, chosen physical descriptors such as distance to the ferroelectric or ferroelastic wall or local curvature are selected and the correlations between the physical descriptors and switching behavior are explored. 48 The drawback of such an approach is the large number of possible mechanisms and hence possible descriptors, giving rise to spurious correlations. For completeness, it should be noted that the descriptors can be derived in an unsupervised fashion through specific machine learning algorithms, ranging from linear unmixing to autoencoders and variational autoencoders.…”