Understanding the Verwey transition in magnetite (Fe3O4), a strongly correlated magnetic oxide, is a one‐century‐old topic that recaptures great attention because of the recent spectroscopy studies ...revealing its orbital details. Here, the modulation of the Verwey transition by tuning the orbital configurations with ionic gating is reported. In epitaxial magnetite thin films, the insulating Verwey state can be tuned continuously to be metallic showing that the low‐temperature trimeron states can be controllably metalized by both the gate‐induced oxygen vacancies and proton doping. The ionic gating can also reverse the sign of the anomalous Hall coefficient, indicating that the metallization is associated with the presence of a new type of carrier with competing spin. The variable spin orientation associated with the sign reversal is originated from the structural distortions driven by the gate‐induced oxygen vacancies.
Ionic gating can suppress the Verwey state in magnetite (Fe3O4) by metalizing the trimeron insulating state with gated‐induced proton addition and oxygen vacancy. Tuning the trimeron state also causes the sign reversal in the anomalous Hall effect, indicating that the ionic gating can create a new type of carrier carrying competing spins.
We present a comparative investigation of the morphological, structural, and optical properties of vertically aligned ZnO nanowires (NWs) before and after high energy argon ion (Ar+) milling. It is ...found that the outer regions of the as-grown sample change from crystalline to amorphous, and ZnO core–shell NWs with ZnO nanocrystals embedded are formed after Ar+ milling. Optical properties of the ZnO NWs have been investigated systematically through power and temperature dependent photoluminescence measurements, and the phenomenon of exciton localization as well as the relevant favorable photoluminescence characteristics is elucidated. Interestingly, under high density optical pumping at room temperature, coherent random lasing action is observed, which is ascribed to exciton localization and strong scattering. Our results on the unique optical properties of localized exciton in ZnO core–shell nanostructures shed light on developing stable and high-efficiency excitonic optoelectronic devices such as light-emitting diodes and lasers.
We have developed a facile method to synthesize upconversion YF3:Yb,Tm nanocrystals in ethylene glycol. These nanocrystals exhibit an assembly structure with a peanut-like appearance. A layer of TiO2 ...shell can be facilely coated on the YF3:Yb,Tm nanocrystals via a sol–gel process and crystallized through annealing. The developed YF3:Tb,Tm@TiO2 particles show good photocatalytic activity under the UV band and work better in the UV/NIR band of a Xe lamp, as the core particles can efficiently upconvert NIR light into UV one.
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•We developed a facile route to synthesize upconversion YF3:Yb,Tm nanocrystals.•The nanocrystals exhibit an assembly structure with a peanut-like appearance.•Core/shell particles of YF3:Tb,Tm@TiO2 were obtained via a sol–gel process.•The YF3:Tb,Tm@TiO2 particles show good photocatalytic activity under the UV/NIR band.•The core particles of YF3:Yb,Tm can efficiently upconvert NIR light into UV one.
Controlled wrinkled surface is useful for a wide range of applications, including flexible electronics, smart adhesion, wettability, stamping, sensoring, coating, and measuring. In this work, ...thickness-gradient-guided spontaneous formation of ordered wrinkling patterns in metal films deposited on soft elastic substrates is revealed by atomic force microscopy, theoretic analysis, and simulation. It is observed that in the thicker film region, broad cracks form, and the film surface remains flat. In the thinner film region, the cracks attenuate along the direction of the thickness decrease, and various wrinkle patterns including branched stripes, herringbones, and labyrinths can coexist. The interplay between the residual compression and the thickness gradient leading to the formation of such wrinkling patterns is discussed based on a nonlinear wrinkling model. The simulated wrinkling patterns as well as the variation trends of the wrinkle wavelength and amplitude along the gradient direction are in good agreement with the experimental observations. The report in this work could promote better understanding and fabrication of such ordered wrinkling patterns by tunable thickness gradient.
The anomalous Hall effect (AHE) and magneto-crystalline anisotropy (MCA) are investigated in epitaxial NixFe1−x thin films grown on MgO (001) substrates. The scattering independent term b of ...anomalous Hall conductivity shows obvious correlation with cubic magneto-crystalline anisotropy K1. When nickel content x decreasing, both b and K1 vary continuously from negative to positive, changing sign at about x = 0.85. Ab initio calculations indicate NixFe1−x has more abundant band structures than pure Ni due to the tuning of valence electrons (band fillings), resulting in the increased b and K1. This remarkable correlation between b and K1 can be attributed to the effect of band filling near the Fermi surface.
Magnetic hollow spheres with a controlled diameter and shell thickness have emerged as an important class of magnetic nanomaterials. The confined hollow geometry and pronouncedly curved surfaces ...induce unique physical properties different from those of flat thin films and solid counterparts. In this paper, we focus on recent progress on submicron-size spherical hollow magnets (e.g., cobalt- and iron-based materials), and discuss the effects of the hollow shape and the submicron size on magnetic and optical properties.
Metal molybdenum (Mo) films have been deposited on viscoelastic gel (for comparison also on elastic PDMS) substrates by magnetron sputtering technique and the wrinkling patterns are investigated by ...using optical microscopy, atomic force microscopy and scanning electron microscopy. For elastic PDMS substrates, the Mo films can spontaneously form labyrinth wrinkles, whose sizes increase linearly with the film thickness. For viscoelastic gel substrates, two wrinkle patterns with different wavelengths, namely 1st (with small wavelength) and 2nd (with large wavelength) wrinkling, can be observed in the films. They are originated from the surface instability of gel during sputtering and the thermal compression after deposition, respectively. The 2nd wrinkle wavelength increases with the film thickness whereas the 1st wrinkle wavelength is thickness independent. The structural characteristics, morphological evolutions and physical mechanisms of these wrinkling patterns have been discussed and analyzed based on the stress theory.
•Metal Mo films were deposited on elastic PDMS and viscoelastic gel substrates by sputtering.•The surface patterns on gel are quite different from those on PDMS.•Two levels of wrinkles (1st and 2nd) coexist in the films on viscoelastic substrates.•The 1st wrinkles form during sputtering and are insensitive to the film thickness.•The 2nd wrinkles form after deposition and increase with the film thickness.
•Orthorhombic BN thin film was prepared on graphite by magnetron sputtering method.•The film showed an island-in-honeycomb morphology and a honeycomb-like structure.•Field emission properties of the ...film were improved compared to cubic BN film.
Nanocrystalline orthorhombic boron nitride (oBN) thin films with an island-in-honeycomb morphology were prepared on graphite substrate by radio frequency (r.f.) magnetron sputtering. The Field emission (FE) measurement results indicated that the FE properties are significantly enhanced in oBN films compared to high quality cBN films, the turn-on electric field of oBN films is decreased from 17.0 V/μm to 6 V/μm, and the highest emission current density is increased from 2.8 × 10−5 to 3 × 10−4 A/cm2. The enhanced FE properties of the oBN films can be attributed to significant reduction in effective potential barrier caused by both protruded island-in-honeycomb morphology and honeycomb-like interconnected internal structure.
Phase diagrams and glass transition behaviors of poly(l-lactic acid)/polyoxymethylene (PLLA/POM) blends have been investigated in our previous work (Macromolecules 2013, 46, 5806–5814). In this work, ...the crystallization behaviors and physical properties of the PLLA/POM blends with the PLLA as the major component have been systematically studied. POM was crystallized into the fragment crystals that were finely dispersed in the PLLA matrix when cooling down from the melt of the blends. It was found that the POM fragment crystals accelerated the crystallization process of PLLA matrix and increased the final crystallinity of PLLA significantly in the blends. At the same time, the PLLA spherulites nucleated by POM fragment crystals were much smaller than those obtained from neat PLLA. It was further found that the crystallization rate of PLLA was quite dependent upon the POM loadings and the highest crystallization rate was observed at POM loadings of 7 wt %. It is considered that the POM fragment crystals take the nuclei role to initiate the crystallization of PLLA at low POM loadings, while a high content of POM in the blends leads to the large POM spherulites that cannot nucleate PLLA crystallization effectively. The obtained PLLA/POM blends at low POM loadings with small PLLA spherulites exhibited excellent optical transmittance and good mechanical performance.
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