Porous Carbon Protected Magnetite and Silver Hybrid Nanoparticles: Morphological Control, Recyclable Catalysts, and Multicolor Cell Imaging

A simple and facile synthetic strategy is developed to prepare a new class of multifunctional hybrid nanoparticles (NPs) that can integrate a magnetic core with silver nanocrystals embedded in porous carbon shell. The method involves a one-step solvothermal synthesis of Fe₃O₄@C template NPs with Fe₃O₄nanocrystals in the core protected by a porous carbon shell, followed by loading and in situ reduction of silver ions in the carbon shell in water at room temperature. The core–satellite and dumbbell-like nanostructures of the resulted Fe₃O₄@C–Ag hybrid NPs can be readily controlled by loading amount of silver ions. The hybrid NPs can efficiently catalyze the reduction reaction of organic dyes in water. The easy magnetic separation and high stability of the catalytically active silver nanocrystals embedded in the carbon shell enable the hybrid NPs to be recycled for reuse as catalysts. The hybrid NPs can also overcome cellular barriers to enter the intracellular region and light up the mouse melanoma B16F10 cells in multicolor modal, with no cytotoxicity. Such porous carbon protected Fe₃O₄@C–Ag hybrid NPs with controllable nanostructures and a combination of magnetic and noble metallic components have great potential for a broad range of applications in the catalytic industry and biomedical field

Oxygen Control of Atomic Structure and Physical Properties of SrRuO₃ Surfaces

Complex oxide thin films and heterostructures have become one of the foci for condensed matter physics research due to a broad variety of properties they exhibit. Similar to the bulk, properties of oxide surfaces can be expected to be strongly affected by oxygen stoichiometry. Here we explore the coupling between atomic structure and physical properties of SrRuO₃ (SRO), one of the most well-studied oxide materials. We perform a detailed <i>in situ</i> and <i>ex situ</i> experimental investigation of the surfaces of SRO thin films using a combination of scanning tunneling microscopy (STM), X-ray and ultraviolet photoelectron spectroscopy, SQUID magnetometry, and magnetotransport measurements, as well as <i>ab initio</i> modeling. A number of remarkable linear surface reconstructions were observed by STM and interpreted as oxygen adatoms, favorably adsorbed in a regular rectangular or zigzag patterns. The degree of oxygen coverage and different surface patterns change the work function of the thin films, and modify local electronic and magnetic properties of the topmost atomic layer. The <i>ab initio</i> modeling reveals that oxygen adatoms possess frustrated local spin moments with possible spin-glass behavior of the surface covered by adsorbed oxygen. Additionally, the modeling indicates presence of a pseudo gap on the topmost SrO layer on pristine SrO-terminated surface, suggesting possibility for realization of a surface half-metallic film

Electrophoretic-like Gating Used To Control Metal–Insulator Transitions in Electronically Phase Separated Manganite Wires

Electronically phase separated manganite wires are found to exhibit controllable metal–insulator transitions under local electric fields. The switching characteristics are shown to be fully reversible, polarity independent, and highly resistant to thermal breakdown caused by repeated cycling. It is further demonstrated that multiple discrete resistive states can be accessed in a single wire. The results conform to a phenomenological model in which the inherent nanoscale insulating and metallic domains are rearranged through electrophoretic-like processes to open and close percolation channels

Size- and Shape-Controlled Synthesis and Properties of Magnetic–Plasmonic Core–Shell Nanoparticles

Magnetic–plasmonic core–shell nanomaterials offer a wide range of applications across science, engineering, and biomedical disciplines. However, the ability to synthesize and understand magnetic–plasmonic core–shell nanoparticles with tunable sizes and shapes remains very limited. This work reports experimental and computational studies on the synthesis and properties of iron oxide–gold core–shell nanoparticles of three different shapes (sphere, popcorn, and star) with controllable sizes (70 to 250 nm). The nanoparticles were synthesized via a seed-mediated growth method in which newly formed gold atoms were added onto gold-seeded iron oxide octahedrons to form a gold shell. The evolution of the shell into different shapes was found to occur after the coalescence of gold seeds, which was achieved by controlling the amount of additive (silver nitrate) and reducing agent (ascorbic acid) in the growth solution. First-principles calculation, together with experimental results, elucidated the intimate roles of thermodynamic and kinetic parameters in the shape-controlled synthesis. Both discrete dipole approximation calculation and experimental results showed that the nanopopcorns and nanostars exhibited red-shifted plasmon resonance compared with the nanospheres, with the nanostars giving multispectral feature. This research has made a great step further in manipulating and understanding magnetic–plasmonic hybrid nanostructures and will make an important impact in many different fields

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