Integration of One-Dimensional (1D) Lead-Free Perovskite Microbelts onto Silicon for Ultraviolet–Visible–Near-Infrared (UV-vis-NIR) Heterojunction Photodetectors

Lead-free perovskites are considered to be candidates for next-generation photodetectors, because of their excellent charge carrier transport properties and low toxicity. However, their application in integrated circuits is hindered by their inadequate performance and size restrictions. To aim at the development of lead-free perovskite-integrated optoelectronic devices, a CsAg2I3/silicon (CAI/Si) heterojunction is presented in this work by using a spatial confinement growth method, where the in-plane growth of CAI microbelts with high-quality single-crystal characteristics is primarily dependent on the concentration of surrounding precursor solution. The fabricated photodetectors based on the CAI/Si heterojunctions exhibit a broad-spectrum detection capability in the ultraviolet–visible–near-infrared (UV-vis-NIR) range. In addition, the photodetectors show good photoelectric detection performance, including a maximum responsivity of 48.5 mA/W and detectivity of 1.13 × 1011 Jones, respectively. Besides, the photodetectors have a rapid response of 6.5/224 μs and good air stability for over 2 months. This work contributes a new idea to design next-generation optoelectronic devices with high integration density

Continuous Production of Graphite Nanosheets by Bubbling Chemical Vapor Deposition Using Molten Copper

We report a bubbling chemical vapor deposition method for mass production of high-quality graphite nanosheets using molten copper as the catalyst for continuous growth. Bubbles containing precursor gas (CH₄ or natural gas) are produced by inserting an aerator into molten copper. High-quality graphite nanosheets with a thickness ranging from a few to 40 graphitic layers are grown on bubble surfaces and carried to the copper surface. The production rate can be as high as 9.4 g/h using a crucible with a volume of 3 L. The high quality of the graphite nanosheets is demonstrated by composites with very high conductivity. The highly conductive composite shows excellent performance in an electromagnetic interference (EMI) shielding application with an EMI effectiveness of >70 dB at X band. Moreover, except for precursor gases, the lack of other chemicals in the growth process makes it an environmentally friendly approach. Natural gas can also be used as the precursor, making it a low-cost production. In addition, the naturally crumpled feature of the graphite nanosheets should allow them to ber used in multiple applications, because restacking can be prevented

Electron-Rich Driven Electrochemical Solid-State Amorphization in Li–Si Alloys

The physical and chemical behaviors of materials used in energy storage devices, such as lithium-ion batteries (LIBs), are mainly controlled by an electrochemical process, which normally involves insertion/extraction of ions into/from a host lattice with a concurrent flow of electrons to compensate charge balance. The fundamental physics and chemistry governing the behavior of materials in response to the ions insertion/extraction is not known. Herein, a combination of in situ lithiation experiments and large-scale ab initio molecular dynamics simulations are performed to explore the mechanisms of the electrochemically driven solid-state amorphization in Li–Si systems. We find that local electron-rich condition governs the electrochemically driven solid-state amorphization of Li–Si alloys. This discovery provides the fundamental explanation of why lithium insertion in semiconductor and insulators leads to amorphization, whereas in metals, it leads to a crystalline alloy. The present work correlates electrochemically driven reactions with ion insertion, electron transfer, lattice stability, and phase equilibrium

Electron-Rich Driven Electrochemical Solid-State Amorphization in Li–Si Alloys

The physical and chemical behaviors of materials used in energy storage devices, such as lithium-ion batteries (LIBs), are mainly controlled by an electrochemical process, which normally involves insertion/extraction of ions into/from a host lattice with a concurrent flow of electrons to compensate charge balance. The fundamental physics and chemistry governing the behavior of materials in response to the ions insertion/extraction is not known. Herein, a combination of in situ lithiation experiments and large-scale ab initio molecular dynamics simulations are performed to explore the mechanisms of the electrochemically driven solid-state amorphization in Li–Si systems. We find that local electron-rich condition governs the electrochemically driven solid-state amorphization of Li–Si alloys. This discovery provides the fundamental explanation of why lithium insertion in semiconductor and insulators leads to amorphization, whereas in metals, it leads to a crystalline alloy. The present work correlates electrochemically driven reactions with ion insertion, electron transfer, lattice stability, and phase equilibrium

Evolution of Lattice Structure and Chemical Composition of the Surface Reconstruction Layer in Li_1.2Ni_0.2Mn_0.6O₂ Cathode Material for Lithium Ion Batteries

Voltage and capacity fading of layer structured lithium and manganese rich (LMR) transition metal oxide is directly related to the structural and composition evolution of the material during the cycling of the battery. However, understanding such evolution at atomic level remains elusive. On the basis of atomic level structural imaging, elemental mapping of the pristine and cycled samples, and density functional theory calculations, it is found that accompanying the hoping of Li ions is the simultaneous migration of Ni ions toward the surface from the bulk lattice, leading to the gradual depletion of Ni in the bulk lattice and thickening of a Ni enriched surface reconstruction layer (SRL). Furthermore, Ni and Mn also exhibit concentration partitions within the thin layer of SRL in the cycled samples where Ni is almost depleted at the very surface of the SRL, indicating the preferential dissolution of Ni ions in the electrolyte. Accompanying the elemental composition evolution, significant structural evolution is also observed and identified as a sequential phase transition of <i>C</i>2/<i>m</i> →<i>I</i>41 → Spinel. For the first time, it is found that the surface facet terminated with pure cation/anion is more stable than that with a mixture of cation and anion. These findings firmly established how the elemental species in the lattice of LMR cathode transfer from the bulk lattice to surface layer and further into the electrolyte, clarifying the long-standing confusion and debate on the structure and chemistry of the surface layer and their correlation with the voltage fading and capacity decaying of LMR cathode. Therefore, this work provides critical insights for design of cathode materials with both high capacity and voltage stability during cycling

Dimensionality Controlled Octahedral Symmetry-Mismatch and Functionalities in Epitaxial LaCoO₃/SrTiO₃ Heterostructures

Epitaxial strain provides a powerful approach to manipulate physical properties of materials through rigid compression or extension of their chemical bonds via lattice-mismatch. Although symmetry-mismatch can lead to new physics by stabilizing novel interfacial structures, challenges in obtaining atomic-level structural information as well as lack of a suitable approach to separate it from the parasitical lattice-mismatch have limited the development of this field. Here, we present unambiguous experimental evidence that the symmetry-mismatch can be strongly controlled by dimensionality and significantly impact the collective electronic and magnetic functionalities in ultrathin perovskite LaCoO₃/SrTiO₃ heterojunctions. State-of-art diffraction and microscopy reveal that symmetry breaking dramatically modifies the interfacial structure of CoO₆ octahedral building-blocks, resulting in expanded octahedron volume, reduced covalent screening, and stronger electron correlations. Such phenomena fundamentally alter the electronic and magnetic behaviors of LaCoO₃ thin-films. We conclude that for epitaxial systems, correlation strength can be tuned by changing orbital hybridization, thus affecting the Coulomb repulsion, U, instead of by changing the band structure as the common paradigm in bulks. These results clarify the origin of magnetic ordering for epitaxial LaCoO₃ and provide a route to manipulate electron correlation and magnetic functionality by orbital engineering at oxide heterojunctions