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Thin Bi films, especially noncentrosymmetric α-phase Bi films (α-Bi), have attracted considerable attention in recent years due to their intriguing physical properties such as ferroelectricity, nonlinear optical response, and coherent spin transport. However, the current experimental preparation of α-Bi films still presents substantial challenges, resulting in only isolated α-Bi islands being achieved. In this study, α-Bi/SrTiO3 (α-Bi/STO) was synthesized from a Bi2O2Se/STO (BOS/STO) heterostructure by depositing a Eu layer and reducing a BOS film. The so-formed α-Bi/STO interface features metallic conductivity with electron mobility of 7.7 × 104 cm2/V s and ultralow resistivity of 1 nΩ cm at 2 K, as well as high residual resistance ratios R300 K/R2 K up to 2353. Furthermore, we observed a complex weak antilocalization–weak localization–weak antilocalization crossover with increasing magnetic field at temperatures below 10 K. Our work presents the synthesis of α-Bi films, which could potentially serve as a valuable platform for experimental validation of diverse theoretical predictions associated with α-Bi heterostructures. Furthermore, this special synthesis method provides valuable insights into the preparation of other metastable films. [ABSTRACT FROM AUTHOR]

In this work, high-quality and centimeter-scale CsPbBr3 perovskite single-crystal thin films were grown using the metal-organic chemical vapor deposition method. Extremely flat surfaces without distinct grain boundaries were observed throughout the thin films. A high polarized degree of approximately 0.52 was measured from the single-crystal thin films by analyzing the polarization of the photoluminescence emission spectra. Low threshold amplified spontaneous emissions with an optical gain coefficient of 1215 cm−1 under the excitation energy of 301 μJ/cm2 and the highest value of 2857 cm−1 under the excitation energy of 1.08 mJ/cm2 were investigated under the excitation of a nanosecond laser at 266 nm. The CsPbBr3 single-crystal thin films showed excellent stability where the optical gain coefficient could be maintained over 1800 cm−1 after exposure to air for ten months. The results of this study not only provide high-quality single-crystal films for laser applications but also put forward a feasible scheme to improve the stability of the materials. [ABSTRACT FROM AUTHOR]

Optical analog computation is garnering increasing attention due to its innate parallel processing capabilities, swift computational speeds, and minimal energy requirements. However, traditional optical components employed for such computations are usually bulky. Recently, there has been a substantial shift toward utilizing nanophotonic structures to downsize these bulky optical elements. Nevertheless, these nanophotonic structures are typically realized in planar subwavelength nanostructures, demanding intricate fabrication processes and presenting limitations in their numerical apertures. In this study, we present a three-layer thin-film optical coating different from the conventional Fabry–Pérot nanocavity. Our design functions as a real-time Laplacian operator for spatial differentiation, and it remarkably boasts an ultrahigh numerical aperture of up to 0.7, enabling the detected edges to be sharper and have closely matched intensities. We also experimentally demonstrate its capacity for effective edge detection. This ultracompact and facile-to-fabricate thin-film spatial differentiator holds promising prospects for applications in ultrafast optical processing and biomedical imaging. [ABSTRACT FROM AUTHOR]

The interaction of domain structure and defects in ferroelectric thin films has been studied for decades. However, the role of dislocations and thermal stability of microstructures is still poorly studied. By combining transmission electron microscopy, x-ray diffraction experiments, and phase-field simulations, we show that dislocation pairs induced by post-annealing above 550 °C provide a stress field stabilizing a domains in 30 nm thick tetragonal PbTiO3 films on SrTiO3 substrate, initially exhibiting pure c domains. Based on phase-field simulations, we further discuss the effects of single dislocations and dislocation pairs on the nucleation of a-domains and the occurrence of non-ferroelastic 180° domains. Dislocations, and the possibility to tune them using an appropriate thermal annealing process, offer a path for modulating the domains and domain wall states and, thus, the physical properties of ferroelectric films. [ABSTRACT FROM AUTHOR]

Organic single crystals are highly promising for applications in optoelectronic devices because of their higher mobility and thermal stability than amorphous thin films. Although white organic single crystals have been fabricated by the double-doped method and applied to realize white organic light‐emitting devices (WOLEDs), the unbalanced carrier transport properties of the unipolar crystals severely limit the device performance. Here, ambipolar white organic single crystals are obtained by using mixed p- and n-type molecules as an ambipolar host for the red and green dopants. The white crystal with balanced carrier transport and balanced blue, green, and red emission intensity was applied to the single-crystal WOLEDs. The highest brightness of 1956 cd m−2 and the current efficiency of 1.31 cd A−1 are achieved, which are the best performance of the single-crystal WOLEDs reported to date. A high color rendering index is obtained, which varies between 82 and 87 with increasing driving current. It is expectable that this strategy would support the practical applications of organic single crystal-based OLEDs. [ABSTRACT FROM AUTHOR]

This study demonstrates superior electrical and electroluminescence performance of inverted quantum-dot light-emitting diodes (QD-LEDs) with a V2O5/poly(N-vinylcarbazole) (PVK) hole conduction layer. Hole- and electron-only device measurements reveal a more balanced charge carrier injection as well as the higher hole conduction capability in the inverted QD-LED than the standard one. Smooth stepwise hole conduction energy levels with a remarkably reduced hole barrier height (Δh) from 1.74 to 0.89 eV at QD/PVK are found to be responsible for high hole conduction and high luminous efficiency in the inverted QD-LED, which is validated by ultraviolet photoelectron spectroscopy measurements. The down-shifted electronic energy levels of PVK for reducing the Δh are discussed from the point of view of molecular orientation of PVK governed by interfacial atomic interaction with underlayers of V2O5 and QD for standard and inverted device structures, respectively. [ABSTRACT FROM AUTHOR]

An ultrathin, 5 nm, AlO film grown by atomic-layer deposition was used as a gate dielectric for amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The AlO layer showed a low surface roughness of 0.15 nm, a low leakage current, and a high breakdown voltage of 6V. In particular, a very high gate capacitance of 70 nF/cm was achieved, making it possible for the a-IGZO TFTs to not only operate at a low voltage of 1V but also exhibit desirable properties including a low threshold voltage of 0.3 V, a small subthreshold swing of 100 mV/decade, and a high on/off current ratio of 1.2χ107. Furthermore, even under an ultralow operation voltage of 0.6 V, well-behaved transistor characteristics were still observed with an on/off ratio as high as 3χ106.The electron transport through the Al2O3 layer has also been analyzed, indicating the Fowler-Nordheim tunneling mechanism. [ABSTRACT FROM AUTHOR]

Nd2Fe14B films with easy magnetization axis perpendicular to the film plane were grown onto Tabuffered piezoelectric (011)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) substrates using a magnetron sputtering technique. The film retains good permanent magnetic properties, with coercivities up to 1.4 T and spin reorientation near 150 K. Our investigations demonstrated that the converse piezoelectric effect generated by an electric field across the PMN-PT substrate can rotate the angle of spin reorientation of the Nd2Fe14B films, resulting in a considerable manipulation of magnetization by the electric field at temperatures below 150 K. The ratio of magnetization change reaches 30% in a magnetic field of 2 T when an electric field of 6 kV/cm is applied at 30 K. With increasing temperature, the electric field-induced tunability of magnetization decreases. These observations of permanent magnetic properties and electrically controlled magnetization effects make the Nd2Fe14B/PMN-PT heterostructure attractive for exploring multifunctional magnetic/electric devices. [ABSTRACT FROM AUTHOR]

Reliability and uniformity in resistance switching behaviours in top electrode Cu-sputtered TiO2-bottom electrode Pt memory structure were greatly improved by inserting an interface layer of 5nm-thick HfO2 between Cu and 50nm-thick TiO2. The thin HfO2 layer, with much smaller cluster size than TiO2, limited the Cu migration appropriately and induced more uniform Cu conducting filament distribution. The repeated rejuvenation and rupture of Cu filament was limited within the HfO2 layer, thereby improving the switching reliability and uniformity. This also greatly decreased operation power compared to a memory cell without the thin HfO2 layer. [ABSTRACT FROM AUTHOR]

Perovskite titanates such as SrTiO3 (STO) exhibit a wide range of important functional properties, including ferroelectricity and excellent photocatalytic performance. The wide optical band gap of titanates limits their use in these applications; however, making them ill-suited for integration into solar energy harvesting technologies. Our recent work has shown that by doping STO with equal concentrations of La and Cr, we can enhance visible light absorption in epitaxial thin films while avoiding any compensating defects. In this work, we explore the optical properties of photoexcited carriers in these films. Using spectroscopic ellipsometry, we show that the Cr3+ dopants, which produce electronic states immediately above the top of the O 2p valence band in STO reduce the direct band gap of the material from 3.75 eV to 2.4-2.7 eV depending on doping levels. Transient reflectance spectroscopy measurements are in agreement with the observations from ellipsometry and confirm that optically generated carriers are present for longer than 2 ns. Finally, through photoelectrochemical methylene blue degradation measurements, we show that these co-doped films exhibit enhanced visible light photocatalysis when compared to pure STO. [ABSTRACT FROM AUTHOR]

Thin Bi films, especially noncentrosymmetric α-phase Bi films (α-Bi), have attracted considerable attention in recent years due to their intriguing physical properties such as ferroelectricity, nonlinear optical response, and coherent spin transport. However, the current experimental preparation of α-Bi films still presents substantial challenges, resulting in only isolated α-Bi islands being achieved. In this study, α-Bi/SrTiO3 (α-Bi/STO) was synthesized from a Bi2O2Se/STO (BOS/STO) heterostructure by depositing a Eu layer and reducing a BOS film. The so-formed α-Bi/STO interface features metallic conductivity with electron mobility of 7.7 × 104 cm2/V s and ultralow resistivity of 1 nΩ cm at 2 K, as well as high residual resistance ratios R300 K/R2 K up to 2353. Furthermore, we observed a complex weak antilocalization–weak localization–weak antilocalization crossover with increasing magnetic field at temperatures below 10 K. Our work presents the synthesis of α-Bi films, which could potentially serve as a valuable platform for experimental validation of diverse theoretical predictions associated with α-Bi heterostructures. Furthermore, this special synthesis method provides valuable insights into the preparation of other metastable films. [ABSTRACT FROM AUTHOR]

The behavior of stress induced leakage current (SILC) in thin HfOxNy films is investigated. Except for the H dispersive transport process, the electron trapping process is responsible for the SILC generation in HfOxNy dielectric. This trapping process is severely modulated by temperature, thickness, and stress polarity. The recovery of SILC also proves the influence of trapping process to SILC. [ABSTRACT FROM AUTHOR]

Ge2Sb2Te5 (GST) films were deposited on TiN(50 nm)/SiO2/Si substrates and trench structures of TiAlN(100 nm)/Si with various deposition parameters by metal organic chemical vapor deposition (MOCVD). Hexagonal GST films were deposited at temperatures of 330–370 °C, deposition pressure of 40 Torr, bubbling temperatures of Ge(50 °C), Sb(10 °C), and Te(30 °C) precursors. Germanium incorporation into GST films by MOCVD is sensitively influenced by deposition parameters such as deposition pressure, deposition temperature, and bubbling temperatures of precursors. Trench structures with a diameter of 120 nm and a height of 200 nm are completely filled by GST MOCVD. [ABSTRACT FROM AUTHOR]

We grew fully strained epitaxial LaCrO3 (LCO) films on SrTiO3(001) under layer-by-layer control up to the film thickness of t = 130 nm using a pulsed laser deposition method. The spin axis of the antiferromagnetic LCO film was systematically examined as a function of t by using Cr L2,3-edge x-ray magnetic linear dichroism (XMLD). The XMLD results manifest a spin reorientation transition (SRT) across a transition thickness of tT ∼ 60 nm. This SRT is well explained in terms of two competing magnetic anisotropy energies of the surface/interface (KS) and the LCO film itself (KV). [ABSTRACT FROM AUTHOR]

We propose and demonstrate a selective lateral electrochemical etching using a superlattice as the etch-sacrificial layer. Differing from the previous methods that require a special etch-sacrificial layer and therefore deteriorate the epilayer grown atop, our method simplifies the epi-growth without compromising the epi-quality. At the reverse bias voltage of 20 V in 0.3 M oxalic acid electrolyte, a 50-nm-thick InGaN/AlGaN superlattice was etched laterally at the rate of ∼0.8 μm/min. Our method is efficient enough for the epitaxial lift-off process: an array of 80 μm × 80 μm square platelets is completely detached from substrate, with quantum-well emission properties preserved intact. [ABSTRACT FROM AUTHOR]