An epitaxial route to strain: Strain can have a dramatic effect on the properties of materials. Zhanget al.introduced a large strain in the material PbTiO₃by growing it epitaxially in a composite with PbO. On the boundaries between the two materials, their normally different lattice constants were matched, giving rise to the strain. As a consequence, the films exhibited a very large electric polarization even in the absence of an electric field. The method may be applicable to generating other functional materials.Scence, this issue p.494

Atomic-scale ferroelectrics are of great interest for high-density electronics, particularly field-effect transistors, low-power logic, and nonvolatile memories. We devised a film with a layered structure of bismuth oxide that can stabilize the ferroelectric state down to 1 nanometer through samarium bondage. This film can be grown on a variety of substrates with a cost-effective chemical solution deposition. We observed a standard ferroelectric hysteresis loop down to a thickness of ~1 nanometer. The thin films with thicknesses that range from 1 to 4.56 nanometers possess a relatively large remanent polarization from 17 to 50 microcoulombs per square centimeter. We verified the structure with first-principles calculations, which also pointed to the material being a lone pair–driven ferroelectric material. The structure design of the ultrathin ferroelectric films has great potential for the manufacturing of atomic-scale electronic devices.

Ferroelectric tunnel junctions are promising towards high-reliability and low-power non-volatile memories and computing devices. Yet it is challenging to maintain a high tunnelling electroresistance when the ferroelectric layer is thinned down towards atomic scale because of the ferroelectric structural instability and large depolarization field. Here we report ferroelectric tunnel junctions based on samarium-substituted layered bismuth oxide, which can maintain tunnelling electroresistance of 7 × 10⁵with the samarium-substituted bismuth oxide film down to one nanometer, three orders of magnitude higher than previous reports with such thickness, owing to efficient barrier modulation by the large ferroelectric polarization. These ferroelectric tunnel junctions demonstrate up to 32 resistance states without any write-verify technique, high endurance (over 5 × 10⁹), high linearity of conductance modulation, and long retention time (10 years). Furthermore, tunnelling electroresistance over 10⁹is achieved in ferroelectric tunnel junctions with 4.6-nanometer samarium-substituted bismuth oxide layer, which is higher than commercial flash memories. The results show high potential towards multi-level and reliable non-volatile memories.

Reducing non-radiative recombination and decreasing the harmful defects are significant to achieve remarkable performance, and regarded as hallmarks of long photoluminescence (PL) lifetimes in inorganic halide perovskite films. Herein, we obtained an ultra-long PL lifetime of more than 2500 ns in inorganic halide perovskite films of polymer-cladding CsPbI₂Br (CPI2); this is the longest PL lifetime measured to date for inorganic halide perovskites. This enhanced lifetime was realized by introducing polyvinyl pyrrolidone (PVP) with two modifications: chemical passivation of trap states on the grain surface, mainly owing to the interactions of the O–Pb covalent-like bond, and improvement of crystallinity, resulting in the reduction of internal defects inside the grain. The PVP simultaneously caused a substantial enhancement in the steady-state PL intensity and quantum efficiency. The approach for chemical passivation would be utilized to enhance the physical properties of functional materials.