In situ X-ray diffraction and the evolution of polarization during the growth of ferroelectric superlattices

Bein, Benjamin; Hsing, Hsiang-Chun; Callori, Sara J.; Sinsheimer, John; Chinta, Priya V.; Headrick, Randall L.; Dawber, Matthew

doi:10.1038/ncomms10136

Cited by 40 publications

(47 citation statements)

References 49 publications

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“…For example, uncompensated bound surface charges at epitaxial ferroelectric interfaces result in a depolarizing field, which can trigger a drop of the ferroelectric Curie temperature (T c ) or nanoscale domain splitting [13][14][15][16][17]. Furthermore, ferroelectric layers are usually grown below T c [18][19][20][21], so that their polarization state is set during the heterostructure growth [22][23][24]. Here the deposition process and the accompanying transient electrostatic effects at the metal-ferroelectric interface govern the resulting polarization state.…”

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confidence: 99%

Depolarizing-Field Effects in Epitaxial Capacitor Heterostructures

et al. 2019

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We identify a transient enhancement of the depolarizing field, leading to an unexpected quench of net polarization, during the growth of a prototypical metal-ferroelectric-metal epitaxial system made of BaTiO 3 and SrRuO 3 . Reduced conductivity and, hence, charge screening efficiency in the early growth stage of the SrRuO 3 top electrode promotes a breakdown of ferroelectric BaTiO 3 into domains. We demonstrate how a thermal annealing procedure can recover the single-domain state. By tracking the polarization state in situ, using optical second harmonic generation, we bring new understanding to interface-related electrostatic effects in ferroelectric capacitors.

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confidence: 99%

Depolarizing-Field Effects in Epitaxial Capacitor Heterostructures

et al. 2019

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“…X-rays have the potential to overcome these challenges owing to their highly penetrating nature and sensitivity to nanometrescale features. Observation of subsurface structures in real time during film growth appears to be even more challenging, and has rarely been attempted 7 . Bulk signals are sometimes observed as unwanted background in grazing-incidence surface X-ray scattering experiments, but there have been few attempts to quantitatively understand the features responsible for such signals 8,9 .…”

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confidence: 99%

Direct measurement of the propagation velocity of defects using coherent X-rays

et al. 2016

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The properties of artificially grown thin films are often strongly a ected by the dynamic relationships between surface growth processes and subsurface structure. Coherent mixing of X-ray signals promises to provide an approach to better understand such processes. Here, we demonstrate the continuously variable mixing of surface and bulk scattering signals during realtime studies of sputter deposition of a-Si and a-WSi2 films by controlling the X-ray penetration and escape depths in coherent grazing-incidence small-angle X-ray scattering. Under conditions where the X-ray signal comes from both the growth surface and the thin film bulk, oscillations in temporal correlations arise from coherent interference between scattering from stationary bulk features and from the advancing surface. We also observe evidence that elongated bulk features propagate upwards at the same velocity as the surface. Furthermore, a highly surface-sensitive mode is demonstrated that can access the surface dynamics independently of the subsurface structure.A key objective for understanding surface dynamics during thin film growth is the ability to monitor nanometre-scale surface fluctuation dynamics in real time 1-3 . These fluctuations of roughness and density occur on timescales that rarely exceed a few seconds, and take place in environments that are inaccessible to most high spatial resolution probes. For example, scanning probe microscopy is widely used to study interfacial reactivity in non-vacuum environments 4 , but is limited by its inability to probe surfaces in real time during deposition; electron microscopy is mainly limited to high-vacuum environments and low magnetic fields 5,6 . X-rays have the potential to overcome these challenges owing to their highly penetrating nature and sensitivity to nanometrescale features. Observation of subsurface structures in real time during film growth appears to be even more challenging, and has rarely been attempted 7 . Bulk signals are sometimes observed as unwanted background in grazing-incidence surface X-ray scattering experiments, but there have been few attempts to quantitatively understand the features responsible for such signals 8,9 .The interaction of surfaces with nanometre-scale buried defects and the formation of bulk defects at a growing surface are integral to many industrial processes. For example, misfit dislocations nucleate at free surfaces and buried interfaces in strained-layer epitaxial growth of layers for photonic devices 10 ; motion and ordering of oxygen vacancies in complex oxide materials for ferroelectric memory depend on the surface conditions during growth 11-13 ; and voids in electrochemically deposited layers used for interconnects in electronic circuits are introduced by surface processes during deposition 14 .The use of X-ray scattering techniques to probe in situ realtime processes has largely been restricted to well-ordered crystalline structures and to statistical averages of disorder, owing to limitations in the spectral brightness of X-ray sources. A fu...

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“…While tremendous advances have been made in understanding ferroelectrics on their own, fundamental aspects of their behavior in the ultrathin regime or once inserted in multilayers or superlattice architectures are still under intense investigation [19][20][21]. The buildup of a ferroelectric polarization P in a material is accompanied by the accumulation of bound charges at its surfaces.…”

Section: Ferroelectric Thin Filmsmentioning

confidence: 99%

“…This depolarizing field D depends on the thickness of the ferroelectric layer and its electrostatic environment, such as the presence of metallic electrodes or the surrounding gas partial pressure and their respective charge screening efficiencies [22][23][24]. The role of the depolarizing field becomes critical in ultrathin ferroelectric single layers and in superlattices, where interface effects may become predominant [19,21,25,26]. As illustrated in Figure 1, a small change in film thickness and charge environment will have a drastic influence on the manifestation of a ferroelectric state and its domain configuration.…”

Section: Ferroelectric Thin Filmsmentioning

confidence: 99%

Probing Ferroic States in Oxide Thin Films Using Optical Second Harmonic Generation

et al. 2018

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Forthcoming low-energy consumption oxide electronics rely on the deterministic control of ferroelectric and multiferroic domain states at the nanoscale. In this review, we address the recent progress in the field of investigation of ferroic order in thin films and heterostructures, with a focus on non-invasive optical second harmonic generation (SHG). For more than 50 years, SHG has served as an established technique for probing ferroic order in bulk materials. Here, we will survey the specific new aspects introduced to SHG investigation of ferroelectrics and multiferroics by working with thin film structures. We show how SHG can probe complex ferroic domain patterns non-invasively and even if the lateral domain size is below the optical resolution limit or buried beneath an otherwise impenetrable cap layer. We emphasize the potential of SHG to distinguish contributions from individual (multi-) ferroic films or interfaces buried in a device or multilayer architecture. Special attention is given to monitoring switching events in buried ferroic domain-and domain-wall distributions by SHG, thus opening new avenues towards the determination of the domain dynamics. Another aspect studied by SHG is the role of strain. We will finally show that by integrating SHG into the ongoing thin film deposition process, we can monitor the emergence of ferroic order and properties in situ, while they emerge during growth. Our review closes with an outlook, emphasizing the present underrepresentation of ferroic switching dynamics in the study of ferroic oxide heterostructures.

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In situ X-ray diffraction and the evolution of polarization during the growth of ferroelectric superlattices

Cited by 40 publications

References 49 publications

Depolarizing-Field Effects in Epitaxial Capacitor Heterostructures

Depolarizing-Field Effects in Epitaxial Capacitor Heterostructures

Direct measurement of the propagation velocity of defects using coherent X-rays

Probing Ferroic States in Oxide Thin Films Using Optical Second Harmonic Generation

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