Zinc Chalcogenide Seed-Mediated Synthesis of CdSe Nanocrystals: Nails, Chesses and Tetrahedrons

Systematically shape-controlled synthesis of colloidal semiconductor nanocrystals (NCs) has attracted increasing attention recently for both fundamental and technological interest. The study on the synthesis of colloidal CdSe NCs has given rise to well-developed methods for producing diverse shapes such as rods, wires, cubs and discs. In the current study, we demonstrate the shape evolution of CdSe NCs by using a seed-mediated approach by control reaction temperature and injection methods. The synthesis utilizes small (2.0–3.0 nm) zinc chalcogenide NCs with zincblende structure as seeds for subsequent growth, which results in distinct shapes of nail-shaped, tetrahedron-shaped, chess piece-shaped, and Y-shaped CdSe NCs with high yield and good uniformity. The morphologies and crystal structures of the prepared CdSe NCs were well characterized by transmission electron microscopy (TEM), high resolution TEM, and X-ray diffraction measurements. This wide variation of shapes provides important information on the growth of CdSe NCs and promotes the shape-controlled synthesis of other NCs by seed-mediated synthetic method

Promising Three-Dimensional Flowerlike CuWO₄ Photoanode Modified with CdS and FeOOH for Efficient Photoelectrochemical Water Splitting

This paper describes a novel promising film based on the flowerlike CuWO₄ structure, and applied to photoelectrochemical (PEC) water splitting as a photoanode first. The growth mechanism and microstructure of CuWO₄ are discussed in detail. The PEC measurements indicate that flowerlike CuWO₄ exhibited a photocurrent density of 0.58 mA/cm² at 0.8 V versus RHE. When coupled with CdS and FeOOH layers, the triple CuWO₄/CdS/FeOOH photoanode exhibited further improved PEC performance with a higher photocurrent density of about 2.05 mA/cm² at 0.8 V versus RHE and excellent operation stability. The remarkable PEC performance stems from several crucial factors: (i) ideal band gap; (ii) improved light absorption; (iii) efficient charge–hole pair separation and collection

Growth Intermediates for CVD Graphene on Cu(111): Carbon Clusters and Defective Graphene

Graphene growth on metal films via chemical vapor deposition (CVD) represents one of the most promising methods for graphene production. The realization of the wafer scale production of single crystalline graphene films requires an atomic scale understanding of the growth mechanism and the growth intermediates of CVD graphene on metal films. Here, we use <i>in situ</i> low-temperature scanning tunneling microscopy (LT-STM) to reveal the graphene growth intermediates at different stages via thermal decomposition of methane on Cu(111). We clearly demonstrate that various carbon clusters, including carbon dimers, carbon rectangles, and ‘zigzag’ and ‘armchair’-like carbon chains, are the actual growth intermediates prior to the graphene formation. Upon the saturation of these carbon clusters, they can transform into defective graphene possessing pseudoperiodic corrugations and vacancies. These vacancy-defects can only be effectively healed in the presence of methane via high temperature annealing at 800 °C and result in the formation of vacancy-free monolayer graphene on Cu(111)

Dipole Orientation Dependent Symmetry Reduction of Chloroaluminum Phthalocyanine on Cu(111)

We demonstrate a dipole orientation dependent symmetry reduction of 4-fold symmetric chloroaluminum phthalocyanine (ClAlPc) molecules on a Cu(111) surface by combined low temperature scanning tunneling microscopy (LT-STM) and density functional theory (DFT) calculations. Unexpected symmetry reduction from 4-fold (C4) to 2-fold (C2) was observed for Cl-down (dipole up) adsorbed ClAlPc, while molecules adopted Cl-up (dipole down) configuration reserved the C4 symmetry. DFT calculations indicated strong charge accumulation at the interface region between Cu surface and the Cl atom in Cl-down adsorbed ClAlPc due to the electron transfer from the bonded Cu atoms. This can result in charge redistribution within the phthalocyanine (Pc) macrocycle, and the formation of anionic Pc with an uptake of 1.3 e, which can be subjected to Jahn–Teller distortion. The inequivalent charge distribution onto the four lobes would be further enlarged due to the conformational distortion. The two down-bended lobes with more electrons interact stronger with the substrate and are much closer to the surface, leading to the C2 symmetry with one pair of up-bended lobes brighter and longer than their perpendicular counterparts for Cl-down adsorbed ClAlPc

Halogen-Adatom Mediated Phase Transition of Two-Dimensional Molecular Self-Assembly on a Metal Surface

Construction of tunable and robust two-dimensional (2D) molecular arrays with desirable lattices and functionalities over a macroscopic scale relies on spontaneous and reversible noncovalent interactions between suitable molecules as building blocks. Halogen bonding, with active tunability of direction, strength, and length, is ideal for tailoring supramolecular structures. Herein, by combining low-temperature scanning tunneling microscopy and systematic first-principles calculations, we demonstrate novel halogen bonding involving single halogen atoms and phase engineering in 2D molecular self-assembly. On the Au(111) surface, we observed catalyzed dehalogenation of hexabromobenzene (HBB) molecules, during which negatively charged bromine adatoms (Br^δ−) were generated and participated in assembly via unique C–Br^δ+···Br^δ− interaction, drastically different from HBB assembly on a chemically inert graphene substrate. We successfully mapped out different phases of the assembled superstructure, including densely packed hexagonal, tetragonal, dimer chain, and expanded hexagonal lattices at room temperature, 60 °C, 90 °C, and 110 °C, respectively, and the critical role of Br^δ− in regulating lattice characteristics was highlighted. Our results show promise for manipulating the interplay between noncovalent interactions and catalytic reactions for future development of molecular nanoelectronics and 2D crystal engineering

Anisotropic Strain-Mediated Growth of Monatomic Co Chains on Unreconstructed Regions of the Au(111) Surface

Single-metal-atom chains, the ultimate one-dimensional (1D) structure, have intriguing physical and chemical properties. However, their controllable and massive production remains challenging as it requires the positioning of individual atoms with atomic precision. Here, by using a two-step molecular beam epitaxy method, we successfully fabricate single-cobalt-atom chains on a metal surface, where organic molecules are first sublimated onto heated Au(111), followed by deposition of Co atoms. Adsorption of 8OH-TPB (octahydroxyl tetraphenylbenzene) on Au(111) induces surface reconstruction transition from a herringbone to a triangular pattern. Co deposition leads to the formation of 1D √3R30° chains with a cross section of only one atom propagating along the [11̅0] direction, which are separated from each other by a lateral spacing of 7–10 times the lattice constant of Au(111). The growth mechanism lies in the surface strain anisotropy induced by the strong Co–Au bonding, where the distance between the two Au atoms bridged via a Co adatom is significantly enlarged, while the Au–Au distance along the Co chain remains almost intact. The observed chain length distribution can be interpreted in terms of electronic scattering vectors at the Fermi surface of the Au(111) surface states

Tissue-Engineered Bone Immobilized with Human Adipose Stem Cells-Derived Exosomes Promotes Bone Regeneration

Exosomes, nanoscale extracellular vesicles functioning as cell-to-cell communicators, are an emerging promising therapeutic in the field of bone tissue engineering. Here, we report the construction and evaluation of a novel cell-free tissue-engineered bone that successfully accelerated the restoration of critical-sized mouse calvarial defects through combining exosomes derived from human adipose-derived stem cells (hASCs) with poly­(lactic-<i>co</i>-glycolic acid) (PLGA) scaffolds. The exosomes were immobilized on the polydopamine-coating PLGA (PLGA/pDA) scaffolds under mild chemical conditions. Specifically, we investigated the effects of hASC-derived exosomes on the osteogenic, proliferation, and migration capabilities of human bone marrow-derived mesenchymal stem cells in vitro and optimized their osteoinductive effects through osteogenic induction. Furthermore, an in vitro assay showed exosomes could release from PLGA/pDA scaffold slowly and consistently and in vivo results showed this cell-free system enhanced bone regeneration significantly, at least partially through its osteoinductive effects and capacities of promoting mesenchymal stem cells migration and homing in the newly formed bone tissue. Therefore, overall results demonstrated that our novel cell-free system comprised of hASC-derived exosomes and PLGA/pDA scaffold provides a new therapeutic paradigm for bone tissue engineering and showed promising potential in repairing bone defects

Mouse Bone Marrow Mesenchymal Stem Cells Inhibit Sepsis-Induced Lung Injury in Mice via Exosomal SAA1

Sepsis is a global disease burden, and approximately 40% of cases develop acute lung injury (ALI). Bone marrow mesenchymal stromal cells (BMSCs) and their exosomes are widely used in treating a variety of diseases including sepsis. As an acute phase protein, serum amyloid A1 (SAA1) regulates inflammation and immunity. However, the role of SAA1 in BMSCs-exosomes in septic lung injury remains to be elucidated. Exosomes derived from serum and BMSCs were isolated by ultracentrifugation. SAA1 was silenced or overexpressed in mouse BMSCs using lentiviral plasmids, containing either SAA1-targeting short interfering RNAs or SAA1 cDNA. Sepsis was induced by cecal ligation and puncture (CLP). LPS was used to induce ALI in mice. Mouse alveolar macrophages were isolated by flow cytometry. Levels of SAA1, endotoxin, TNF-α, and IL-6 were measured using commercial kits. LPS internalization was monitored by immunostaining. RT-qPCR or immunoblots were performed to test gene and protein expressions. Serum exosomes of patients with sepsis-induced lung injury had significantly higher levels of SAA1, endotoxin, TNF-α, and IL-6. Overexpression of SAA1 in BMSCs inhibited CLP- or LPS-induced lung injury and decreased CLP- or LPS-induced endotoxin, TNF-α, and IL-6 levels. Administration of the SAA1 blocking peptide was found to partially inhibit SAA1-induced LPS internalization by mouse alveolar macrophages and reverse the protective effect of SAA1. In conclusion, BMSCs inhibit sepsis-induced lung injury through exosomal SAA1. These results highlight the importance of BMSCs, exosomes, and SAA1, which may provide novel directions for the treatment of septic lung injury

Bifunctional Hybrid a‑SiO<i>_x</i>(Mo) Layer for Hole-Selective and Interface Passivation of Highly Efficient MoO<i>_x</i>/a-SiO<i>_x</i>(Mo)/n-Si Heterojunction Photovoltaic Device

The promising n-Si-based solar cell is constructed for the purpose of realizing hole- and electron-selective passivating contact, using a textured front indium tin oxide/MoO<i>_x</i> structure and a planar rear a-SiO<i>_x</i>/poly­(Si­(n⁺)) structure severally. The simple MoO<i>_x</i>/n-Si heterojunction device obtains an efficiency of 16.7%. It is found that the accompanying ternary hybrid SiO<i>_x</i>(Mo) interlayer (3.5–4.0 nm) is formed at the MoO<i>_x</i>/n-Si boundary zone without preoxidation and is of amorphous structure, which is determined by a high-resolution transmission electron microscope with energy-dispersive X-ray spectroscopy mapping. The creation of lower-oxidation states in MoO<i>_x</i> film indicates that the gradient distribution of SiO<i>_x</i> with Mo element occurs within the interlayer, acting as a passivation of silicon substrate, which is revealed by X-ray photoelectron spectroscopy with depth etching. Specifically, calculations by density functional theory manifest that there are two half-filled levels (localized states) and three unoccupied levels (extended states) relating to Mo component in the ternary hybrid a-SiO<i>_x</i>(Mo) interlayer, which play the roles of defect-assisted tunneling and direct tunneling for photogenerated holes, respectively. The transport process of photogenerated holes in the MoO<i>_x</i>/n-Si heterojunction device is well-described by the tunnel-recombination model. Meanwhile, the a-SiO<i>_x</i>/poly­(Si­(n⁺)) has been assembled on the rear of the device for direct tunneling of photoinduced electrons and blocking photoinduced holes