Effect of surface charges on the polarization of BaTiO₃ thin films investigated by UHV‐SPM

Abstract

Nanostructured BaTiO3 polar thin films are increasingly critical to the function of future multilayer ceramic capacitors and related oxide‐based electronic devices. The effect of surface charges on BaTiO3 polarization behavior is therefore investigated by ultra‐high vacuum scanning probe microscopy (UHV‐SPM) for 3 distinct morphologies—epitaxial, polycrystalline, and nanocrystalline films. Regardless of the film morphology, Kelvin probe force microscopy reveals that BaTiO3 thin film surfaces exhibit positive charging after contact scanning by various noble AFM probes due to the work function difference between tip and specimen. According to piezoresponse force microscopy, these positive charges uniformly stabilize downward polarized domains. However, the hysteresis and concomitant surface charging behavior are strongly sensitive to microstructure and defects. In particular, the stability and switching behavior are influenced by bulk and interfacial defect distributions and hence correlated to film deposition methods and grain size. Such morphology dependent properties for BaTiO3 films are revealed only through UHV measurements where screening charges from the ambient can be minimized, demonstrating the importance of UHV‐SPM for understanding ferroelectric thin films and nanostructures.

Hypothesis Learning in Automated Experiment: Application to Combinatorial Materials Libraries

“…The detection of the response as a function of slowly (Hz) varying large amplitude (3-10 V) waveforms allows measuring the local hysteresis loops. [67][68][69][70][71] The shape of the hysteresis loop is closely linked to tip-induced domain dynamics, [72,73] and thus represents local polarization switching mechanisms. [74,75] Here, we use the switching spectroscopy PFM approach, where hysteresis loops are measured over the rectangular grid of points, offering better statistics and information on the spatial variability of switching behavior.…”

Charge injection and decay of nanoscale dielectric films resolved via dynamic scanning probe microscopy

“…The "poly-film" sample (96 ± 78 nm grains) was prepared by chemical solution deposition via spin coating, and the "nano-film" sample (61 ± 55 nm) was prepared using microemulsion. 37,50 Grain sizes were determined based on the number of identifiable grains from AFM topography images over a known area. Both samples were annealed at 800°C in an oxygen atmosphere after each layer deposition, repeated a total of 20 times to reach the desired thickness.…”

“…Each BaTiO 3 dielectric thin film is 200 nm in thickness. The “poly‐film” sample (96 ± 78 nm grains) was prepared by chemical solution deposition via spin coating, and the “nano‐film” sample (61 ± 55 nm) was prepared using microemulsion 37, 50 . Grain sizes were determined based on the number of identifiable grains from AFM topography images over a known area.…”

“…Homogeneous epitaxial barium titanate specimens, nominally differing only by their grain size, provide a model system for assessing grain and grain‐boundary effects on charge injection and decay. To this end, the magnitude, distribution, and decay rates of injected charges are compared for two BaTiO 3 thin films, which are effectively identical except for their distinctly engineered nanostructuring and correspondingly macroscopically different dielectric constants 37, 38 . More broadly, our approach is especially applicable to the further development of nanocomposite dielectrics as well as multifunctional devices, such as grain‐boundary‐engineered ceramic dielectrics, 39 dielectric/ferroelectric multilayers, 40‐46 vertically aligned nanostructures, 47 and nanopatterned dielectrics 48, 49 …”

Effect of Humidity on the Writing Speed and Domain Wall Dynamics of Ferroelectric Domains

“…The interaction of adsorbed water with ferroelectric (FE) materials such as BaTiO 3 has been studied due to its dipolar character and the possibility to split into ionic species (i.e., OH − and H + ) (dissociation). [1][2][3][4][5][6][7][8] Consequentially, water plays a crucial role in the screening of the depolarization field and the stabilization of FE polarization in the absence of electrodes capable of supplying free charge. [9][10][11][12] This screening role is of particular importance in thin films studied by piezoresponse force microscopy (PFM), where the stability of patterned domain arrays (i.e., bits) is ruled by screening processes and is a prerequisite for information storage applications, where long-time data retention is needed.…”