Purely organic 4HCB single crystals show a capability of directly detecting 241Am 5.49 MeV α particles and X-ray imaging under low-dose rate (below 50 μGyair s−1) exposure conditions.
Bi Fe O 3 films have been grown on SrTiO3 (001) substrates by pulsed laser deposition. It was found that oxygen partial pressure is crucial to phase purity, surface morphology, and surface chemistry. Single-phase BFO films were obtained at 1Pa O2, while Bi2O3 appeared in the films deposited at 0.01Pa as confirmed by x-ray diffractions. It was revealed that Fe2+ and metallic Bi exist in the films fabricated at 0.01Pa by x-ray photoelectron spectroscopy investigation. Owing to Fe2+ in the samples deposited at 0.01Pa, the saturation magnetization is much larger than the ones fabricated at 1Pa. A well-saturated ferroelectric hysteresis loop with a polarization of 23.6μC∕cm2 was observed in the single-phase samples. In contrast, the films deposited at 0.01Pa exhibited poor ferroelectric properties.
The
ferroic domain, in metal halide perovskites (MHPs) at a low
symmetry phase, was reported to affect optoelectronic properties.
Building the relationship between ferroic domains and optoelectronic
properties of MHPs will be a non-trivial task for understanding the
charge transport mechanism. Here, high-quality CsPbBr3 single-crystal
films (SCFs) were successfully grown by a cast-capping method. Through
the phase transition process by heating and cooling the sample, dense
domains in CsPbBr3 SCFs were formed and observed by an in situ polarized optical microscope. These domains were
identified as 90° rotation twins by electron backscattered diffraction
and transmission electron microscopy. Interestingly, the photocurrent
response was dramatically enhanced after introducing ferroelastic
domains. The highest responsivity, external quantum efficiency, and
detectivity are 380 mA/W, 130%, and 12.9 × 1010 Jones,
respectively, which are surprisingly 25.03, 25, and 7.8 times higher
than those of the as-grown CsPbBr3 SCF, respectively, which
may be attributed to the function of the domain wall of separating
electrons and holes.
Ferroelectric (FE) materials, which typically adopt the perovskite structure with non-centrosymmetry and exhibit spontaneous polarization, are promising for applications in memory, electromechanical and energy storage devices. However, these advanced applications suffer from the intrinsic limitations of perovskite FEs, including poor complementary metal oxide semiconductor (CMOS) compatibility and environmental issues associated with lead. Hafnium oxide (HfO2), with stable bulk centrosymmetric phases, possesses robust ferroelectricity in nanoscale thin films due to the formation of non-centrosymmetric phases. Owing to its high CMOS compatibility and high scalability, HfO2 has attracted significant attention. In the last decade, significant efforts have been made to explore the origin of the ferroelectricity and factors that influence the FE properties in HfO2 films, particularly regarding the role of microstructure, which is vital in clarifying these issues. Although several comprehensive reviews of HfO2 films have been published, there is currently no review focused on the relationship between microstructure and FE properties. This review focuses on the microstructure-property relationships in FE polycrystalline and epitaxial HfO2 films. The crystallographic structures and characterization methods for HfO2 polymorphs are first discussed. For polycrystalline HfO2 films, the microstructure-FE properties relationships, driving force and kinetic pathway of phase transformations under growth parameters or external stimuli are reviewed. For epitaxial films, the lattice matching relations between HfO2 films and substrates and the corresponding impact on the FE properties are discussed. The FE properties between polycrystalline and epitaxial HfO2 films are compared based on their different microstructural characteristics. Finally, a future perspective is given for further investigating FE HfO2 films.
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