Symmetry lowering phase transitions in ferroelectrics, magnets, and materials with various other forms of inherent order lead to the formation of topological defects. Their non-trivial real-space ...topology is characterized by a topological charge, which represents the topological invariant. The study of topological defects in such materials has seen increased interest over the last decade. Among the methods used for their study, scanning probe microscopy (SPM) with its many variants has provided valuable new insight into these structures at the nanoscale. In this perspective, various approaches are discussed, and different techniques are compared with regard to their ability to investigate topological defect properties.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Structurally different from conventional oxide ferroelectrics with rigid lattices, van der Waals (vdW) ferroelectrics have stable layered structures with a combination of strong intralayer and weak ...interlayer forces. These special atomic arrangements, in combination with the ferroelectric order, give rise to fundamentally new phenomena and functionalities, including downscaling limits, origin of the polarization and switching mechanisms. Furthermore, their easily stackable nature means that vdW ferroelectrics are readily integrable with highly dissimilar materials, such as industrial silicon substrates, without interfacial issues, and are thus regarded as attractive building blocks for post-Moore’s law electronics. In this Review, we consider the experimentally verified vdW ferroelectric systems by discussing their unique characteristics, such as quadruple-well potentials, metallic ferroelectricity and dipole-locking effects. We highlight the emerging field of engineered vdW ferroelectricity, created by artificially breaking centrosymmetry in stacks of otherwise nonpolar parent materials. Additionally, innovative device applications harnessing vdW ferroelectricity are showcased, including transistors able to beat the Boltzmann tyranny, nonvolatile memories and optoelectronic and flexible devices. Recent progress and existing challenges provide a perspective on future research directions and applications.van der Waals ferroelectrics are different from conventional oxide or polymer-based ferroelectrics in terms of both crystal structure and functionality. This Review discusses the experimentally verified van der Waals ferroelectrics, their unique characteristics and their potential applications in post-Moore’s law electronics.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Ferroelectric domain walls naturally form at nanoscale interfaces of polar order leading to electronic properties distinct from the bulk that can also be electrically programmed. These nanoscale ...features currently are being actively explored for the development of agile, low‐energy electronics for applications in memory, logic, and brain‐inspired neuromorphic computing. In this article, the authors review the state of the art, the latest developments, and outline key device and material challenges, emerging opportunities, and new directions for the accelerated engineering and commercialization of domain wall technology.
Ferroelectric domain walls are electrically programmable nanoscale interfaces that are highly promising for the development of low‐energy electronics for applications in memory, logic, and brain‐inspired computing. In this article, the authors review the latest developments and outline key device issues, material challenges, and opportunities for the accelerated engineering and commercialization of domain wall technology.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A prominent challenge towards novel nanoelectronic technologies is to understand and control materials functionalities down to the smallest scale. Topological defects in ordered solid-state ...(multi-)ferroic materials, e.g., domain walls, are a promising gateway towards alternative sustainable technologies. In this article, we review advances in the field of domain walls in ferroic materials with a focus on ferroelectric and multiferroic systems and recent developments in prototype nanoelectronic devices.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The sensitivity of organic–inorganic perovskites to environmental factors remains a major barrier for these materials to become commercially viable for photovoltaic applications. In this work, the ...degradation of formamidinium lead iodide (FAPbI3) perovskite in a moist environment is systematically investigated. It is shown that the level of relative humidity (RH) is important for the onset of degradation processes. Below 30% RH, the black phase of the FAPbI3 perovskite shows excellent phase stability over 90 d. Once the RH reaches 50%, degradation of the FAPbI3 perovskite occurs rapidly. Results from a Kelvin probe force microscopy study reveal that the formation of nonperovskite phases initiates at the grain boundaries and the phase transition proceeds toward the grain interiors. Also, ion migration along the grain boundaries is greatly enhanced upon degradation. A post‐thermal treatment (PTT) that removes chemical residues at the grain boundaries which effectively slows the degradation process is developed. Finally, it is demonstrated that the PTT process improves the performance and stability of the final device.
Moisture‐induced degradation of FAPbI3 perovskite is systematically investigated. A Kelvin probe force microscopy study reveals that the formation of nonperovskite phases initiates at the grain boundaries and the phase transition proceeds toward the grain interiors. A post‐thermal treatment that removes chemical residues at the grain boundaries which effectively slows the degradation process is developed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
BiFeO
3
is one of the most studied multiferroic materials. Both its magnetic and ferroelectric properties can be influenced by doping. A large body of work on the doped material has been presented in ...the past couple of years. In this paper we provide a perspective on general doping concepts and their impact on the material's functionality.
This paper provides a perspective on general doping concepts of multiferroic BiFeO
3
and their impact on the material's functionality.
The critical role of grain boundaries for (CH(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 perovskite solar cells studied by Kelvin probe force microscopy under bias voltage and illumination is reported. Ion ...migration is enhanced at the grain boundaries. Under illumination, the light‐induced potential causes ion migration leading to a rearranged ion distribution. Such a distribution favors photogenerated charge‐carrier collection at the grain boundaries.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Developing nano‐ferroelectric materials with excellent piezoelectric performance for piezocatalysts used in water splitting is highly desired but also challenging, especially with respect to reaching ...large piezo‐potentials that fully align with required redox levels. Herein, heteroepitaxial strain in BaTiO3 nanoparticles with a designed porous structure is successfully induced by engineering their surface reconstruction to dramatically enhance their piezoelectricity. The strain coherence can be maintained throughout the nanoparticle bulk, resulting in a significant increase of the BaTiO3 tetragonality and thus its piezoelectricity. Benefiting from high piezoelectricity, the as‐synthesized blue‐colored BaTiO3 nanoparticles possess a superb overall water‐splitting activity, with H2 production rates of 159 μmol g−1 h−1, which is almost 130 times higher than that of the pristine BaTiO3 nanoparticles. Thus, this work provides a generic approach for designing highly efficient piezoelectric nanomaterials by strain engineering that can be further extended to various other perovskite oxides, including SrTiO3, thereby enhancing their potential for piezoelectric catalysis.
Heteroepitaxial strain in BaTiO3 nanoparticles with a designed porous structure is induced by engineering the surface reconstruction, resulting in a significant increase of the BaTiO3 tetragonality and thus its piezoelectricity. Benefiting from high piezoelectricity, the as‐synthesized BaTiO3 nanoparticles possess a superb piezocatalytic overall water‐splitting activity.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Layered low‐dimensional perovskite structures employing bulky organic ammonium cations have shown significant improvement on stability but poorer performance generally compared to their 3D ...counterparts. Here, a mixed passivation (MP) treatment is reported that uses a mixture of bulky organic ammonium iodide (iso‐butylammonium iodide, iBAI) and formammidinium iodide (FAI), enhancing both power conversion efficiency and stability. Through a combination of inactivation of the interfacial trap sites, characterized by photoluminescence measurement, and formation of an interfacial energetic barrier by which ionic transport is reduced, demonstrated by Kelvin probe force microscopy, MP treatment of the perovskite/hole transport layer interface significantly suppresses photocurrent hysteresis. Using this MP treatment, the champion mixed‐halide perovskite cell achieves a reverse scan and stabilized power conversion efficiency of 21.7%. Without encapsulation, the devices show excellent moisture stability, sustaining over 87% of the original performance after 38 d storage in ambient environment under 75 ± 20% relative humidity. This work shows that FAI/iBAI, is a new and promising material combination for passivating perovskite/selective‐contact interfaces.
Mixed passivation treatment using iso‐butylammonium iodide and formammidinium iodide applied on the surface of perovskite is shown to reduce defects and ion migration. This results in enhancement in both stability and power conversion efficiency reaching 21.7%.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Topological structures have considerable potential in nanoelectronics and new device concepts. They are key to the design and understanding of novel functionalities in ferroic materials — that is, ...materials that have one or more types of built-in order such as magnetic, ferroelectric, ferroelastic and multiferroic materials.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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