The enhancement of the functional properties of materials at reduced dimensions is crucial for continuous advancements in nanoelectronic applications. Here, we report that the scale reduction leads to the emergence of an important functional property, ferroelectricity, challenging the long-standing notion that ferroelectricity is inevitably suppressed at the scale of a few nanometers. A combination of theoretical calculations, electrical measurements, and structural analyses provides evidence of room-temperature ferroelectricity in strain-free epitaxial nanometer-thick films of otherwise nonferroelectric strontium titanate (SrTiO3). We show that electrically induced alignment of naturally existing polar nanoregions is responsible for the appearance of a stable net ferroelectric polarization in these films. This finding can be useful for the development of low-dimensional material systems with enhanced functional properties relevant to emerging nanoelectronic devices.

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO(3)) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO(3) matrix. Such correlation effects can lead to new functionalities in designed heterostructures.

Lithium iron phosphate olivine (LFP) and lithium manganese oxide spinel (LMO) are competitive and complementary to each other as cathode materials for lithium ion batteries, especially for use in hybrid electric vehicles and electric vehicles. Interest in these materials, due to their low cost and high safety, has pushed research and development forward and toward high performance in terms of rate capability and capacity retention or cyclability at a high temperature of around 60 °C. From the view point of basic properties, LFP shows a higher gravimetric capacity while LMO has better conductivities, both electrically and ionically. According to our comparison experiments, depending on the material properties and operational potential window, LFP was favored for fast charging while LMO led to better discharge performances. Capacity fading at high temperatures due to metal dissolution was revealed to be the most problematic issue of LFP and LMO-based cells for electric vehicles (EVs), with thicker electrodes, in the case of no additives in the electrolyte and no coating to prevent metal dissolution on cathode materials. Various strategies to enhance the properties of LFP and LMO are ready for the realization of EVs in the near future.

The enhancement of the functional properties of materials at reduced dimensions is crucial for continuous advancements in nanoelectronic applications. Here, we report that the scale reduction leads to the emergence of an important functional property, ferroelectricity, challenging the long-standing notion that ferroelectricity is inevitably suppressed at the scale of a few nanometers. A combination of theoretical calculations, electrical measurements, and structural analyses provides evidence of room-temperature ferroelectricity in strain-free epitaxial nanometer-thick films of otherwise nonferroelectric strontium titanate (SrTiO3). We show that electrically induced alignment of naturally existing polar nanoregions is responsible for the appearance of a stable net ferroelectric polarization in these films. This finding can be useful for the development of low-dimensional material systems with enhanced functional properties relevant to emerging nanoelectronic devices.

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO(3)) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO(3) matrix. Such correlation effects can lead to new functionalities in designed heterostructures.

Lithium iron phosphate olivine (LFP) and lithium manganese oxide spinel (LMO) are competitive and complementary to each other as cathode materials for lithium ion batteries, especially for use in hybrid electric vehicles and electric vehicles. Interest in these materials, due to their low cost and high safety, has pushed research and development forward and toward high performance in terms of rate capability and capacity retention or cyclability at a high temperature of around 60 °C. From the view point of basic properties, LFP shows a higher gravimetric capacity while LMO has better conductivities, both electrically and ionically. According to our comparison experiments, depending on the material properties and operational potential window, LFP was favored for fast charging while LMO led to better discharge performances. Capacity fading at high temperatures due to metal dissolution was revealed to be the most problematic issue of LFP and LMO-based cells for electric vehicles (EVs), with thicker electrodes, in the case of no additives in the electrolyte and no coating to prevent metal dissolution on cathode materials. Various strategies to enhance the properties of LFP and LMO are ready for the realization of EVs in the near future.

Epitaxial BiVO₄ photoanodes with precisely controlled crystallographic orientations were fabricated to elucidate the intrinsic influence of facet anisotropy on photoelectrochemical (PEC) glycerol oxidation. The <i>b</i>-axis-oriented (0<i>k</i>0) BiVO₄ film exhibited a 2.4-fold higher photocurrent density and a 2.6-fold greater charge-separation efficiency than the <i>c</i>-axis-oriented (00<i>l</i>) film, achieving a production rate of 81.4 mmol m^-2 h^-1 under AM 1.5 G illumination. PEC and charge-transfer analyses reveal that the enhanced activity of the (0<i>k</i>0) facet originates primarily from improved bulk charge separation and transport rather than surface catalytic effects. This work establishes crystallographic orientation control as an effective design strategy for developing energy-efficient oxide photoanodes for solar-driven glycerol oxidation beyond conventional water splitting.

• Ultra-thin (≈1 nm) MoS 2 capping layer enhanced polarization magnitude of HZO by threefold (from ≈14.8 to ≈42.2 μC cm−2). • This stems from ferroelectric o-phase stabilization through mechanical clamping enabled by strain sustainability of MoS 2 . • MoS 2 -capped HZO also demonstrated a reduction in defect concentration at the interface. • This is attributed to suppression of undesirable interfacial reactions due to dangling-bond-free nature of MoS 2 . Since the discovery of ferroelectric properties in HfO 2 -based thin films, capping effect has been extensively researched to induce ferroelectric orthorhombic phase through mechanical clamping. However, current research on capping materials has focused on oxide-based materials to address wake-up effect resulted from 3D metallic capping electrodes, yet the challenge of achieving a large double remnant polarization value remains unresolved. Here, ultra-thin (≈ 1 nm) MoS 2 , one of transition metal dichalcogenides, was employed as a novel capping layer on Hf 0.5 Zr 0.5 O 2 thin films. Notably, MoS 2 -capped Hf 0.5 Zr 0.5 O 2 films exhibited a higher orthorhombic phase fraction than uncapped films, resulting in an enhanced double remnant polarization value of ≈ 42.2 μC cm −2 . This represents approximately a three-fold increase compared to the uncapped Hf 0.5 Zr 0.5 O 2 films (≈ 14.8 μC cm −2 ), attributed to volumetric suppression via the clamping effect even with ultra-thin capping. Additionally, the MoS 2 -capped Hf 0.5 Zr 0.5 O 2 device exhibited enhanced cycling limits (>10 6 cycles), achieved by suppressed oxygen vacancies at the top electrode-Hf 0.5 Zr 0.5 O 2 film interface, thanks to the dangling bond-free nature of transition metal dichalcogenides. This study demonstrates that ultra-thin MoS 2 effectively functions as a capping layer, enhancing both remnant polarization and endurance for 1T-1C FeRAM applications while preserving the scalability of Hf 0.5 Zr 0.5 O 2 .