The ferroelectric properties in single-crystalline perovskite
oxide
can be engineered by strain, which is conventionally achieved via
interfacial lattice mismatch between a substrate and an epitaxial
ferroelectric overlayer. To realize the continuous tuning of strain
in ferroelectrics and explore its functionality in the morphology
of freestanding membranes, in this study, we have performed a comprehensive
investigation on flexible BaTiO3 (BTO) membranes with varied
wrinkle patterns. The freestanding BTO membranes can be obtained from
the rigid epitaxial heterostructures by water-dissolving the Sr3Al2O6 (SAO) sacrificial interlayer,
and the different varied wrinkle patterns are gained by tailoring
the mixing ratios of polydimethylsiloxane (PDMS) supporters following
the thermal strain and elastic theory. Then, we have found that the
spontaneous polarization switching behavior of freestanding wrinkled
BTO membranes is curvature-dependent, and the coercive field of BTO
can be reduced by 15.03% once it suffers ∼1.34% tensile and
compressive strain. Our study provides a convenient and robust approach
to morphological changes of ferroelectrics and holds great promising
potential for applications in flexible oxide electronics.
Stoichiometry offset provides a promising platform for achieving multifunctionality in perovskite transition metal oxide. In this work, the electric transport and magnetic properties of LaMnO 3 (LMO) films featured with varied stoichiometry offset are systematically investigated. By applying a postannealing process with various annealing oxygen pressures, the concentration ratio of the cation and anion can be tuned, and the magnetic ground states such as ferromagnetic (FM) metal and FM or antiferromagnetic (AFM) insulator of LMO can be obtained. Additionally, a large exchange bias was also observed by an appropriate stoichiometry control. These phenomena can be understood by the regulable magnetic coupling of the Mn 3+ /Mn 4+ and the magnetic phase separation. Our results provide a simple way for achieving stoichiometry offset and a reference for the fundamental understanding of the multiphase coexistence of manganese oxide thin films.
Low-energy switching of ferroelectrics has been intensively
studied
for energy-efficient nanoelectronics. Mechanical force is considered
as a low-energy consumption technique for switching the polarization
of ferroelectric films due to the flexoelectric effect. Reduced threshold
force is always desirable for the considerations of energy saving,
easy domain manipulation, and sample surface protection. In this work,
the mechanical switching behaviors of BaTiO3/SrRuO3 epitaxial heterostructure grown on Nb:SrTiO3 (001)
substrate are reported. Domain switching is found to be induced by
an extremely low tip force of 320 nN (estimated pressure ∼0.09
GPa), which is the lowest value ever reported. This low mechanical
threshold is attributed to the small compressive strain, the low oxygen
vacancy concentration in BaTiO3 film, and the high conductivity
of the SrRuO3 electrode. The flexoelectricity under both
perpendicular mechanical load (point measurement) and sliding load
(scanning measurement) are investigated. The sliding mode shows a
much stronger flexoelectric field for its strong trailing field. The
mechanical written domains show several advantages in comparison with
the electrically written ones: low charge injection, low energy consumption,
high density, and improved stability. The ultralow-pressure switching
in this work presents opportunities for next-generation low-energy
and high-density memory electronics.
Most recently, the freestanding of an epitaxial single-crystal oxide has been greatly developed to its fundamental concerns and the possibility of integration with metal, two-dimensional, and organic materials for more promising functionalities. In an artificial ferromagnetic oxide heterostructure and superlattice, the release of the substrate constraint can induce a reasonable transformation of the magnetic structure because the change of the lattice field occurs. In this study, we have comprehensively investigated the evolution of magnetic properties of (La 0.7 Ca 0.3 MnO 3 /SrRuO 3 ) n [(LCMO/SRO) n ] ferromagnetic superlattices while they are epitaxially on SrTiO 3 and freestanding. It is found that the Curie temperature and the perpendicular exchange bias of the freestanding superlattices exhibit extreme sensitivity to the interface number and the thickness of LCMO and SRO, which can maximumly reach ∼293 K and ∼1150 Oe. These enhanced and bulk-beyond magnetic behaviors originate from the interfacial magnetic transition from ferromagnetic to antiferromagnetic via the charge reconstruction with the assistance of strain. Our study provides not only a reference for designing a high-performance flexible ferromagnetic architectural superlattice but also a deep understanding of the interfacial effect in freestanding ferromagnetic heterostructures benefiting flexible spintronics.
2D hexagonal boron nitride, graphene, molybdenum disulphide and tungsten disulfide nanosheets were successfully prepared at mild temperature using a facile “recrystallization of NaCl” exfoliation method. The proposed method was simple, inexpensive and practical. The thicknesses of the h‐BN, graphene, MoS2 and WS2 nanosheets were approximately 1.5, 1.1, 1.2 and 1 nm, respectively. It was very interesting that the 2D nanosheets exhibited excellent thermal catalytic degradation performance during preparation of carbon quantum dots by using ethylene glycol. What's more, nitrobenzene (NB) was also degraded and the best degradation rate of NB was 71% at 6 h in the thermal catalytic system. This interesting discovery will lead to new research directions for two‐dimensional materials.
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