Manipulating metal-insulator transitions of VO_(2) films via embedding Ag nanonet arrays

Manipulating metal-insulator transitions in strongly correlated materials is of great importance in condensed matter physics,with implications for both fundamental science and technology.Vanadium dioxide(VO_(2)),as an ideal model system,is metallic at high temperatures and shown a typical metal-insulator structural phase transition at 341 K from rutile structure to monoclinic structure.This behavior has been absorbed tons of attention for years.However,how to control this phase transition is still challenging and little studied.Here we demonstrated that to control the Ag nanonet arrays(NAs)in monoclinic VO_(2)(M)could be effective to adjust this metal-insulator transition.With the increase of Ag NAs volume fraction by reducing the template spheres size,the transition temperature(Tc)decreased from 68°C to 51°C.The mechanism of Tc decrease was revealed as:the carrier density increases through the increase of Ag NAs volume fraction,and more free electrons injected into the VO_(2)films induced greater absorption energy at the internal nanometal-semiconductor junction.These results supply a new strategy to control the metal-insulator transitions in VO_(2),which must be instructive for the other strongly correlated materials and important for applications.

Morphological effect on electrochemical performance of nanostructural CrN

Size and morphology are critical factors in determining the electrochemical performance of the supercapacitor materials,due to the manifestation of the nanosize effect.Herein,different nanostructures of the CrN material are prepared by the combination of a thermal-nitridation process and a template technique.High-temperature nitridation could not only transform the hexagonal Cr_(2)O_(3)into cubic CrN,but also keep the template morphology barely unchanged.The obtained CrN nanostructures,including(i)hierarchical microspheres assembled by nanoparticles,(ii)microlayers,and(iii)nanoparticles,are studied for the electrochemical supercapacitor.The CrN microspheres show the best specific capacitance(213.2 F/g),cyclic stability(capacitance retention rate of 96%after 5000 cycles in 1-mol/L KOH solution),high energy density(28.9 Wh/kg),and power density(443.4 W/kg),comparing with the other two nanostructures.Based on the impedance spectroscopy and nitrogen adsorption analysis,it is revealed that the enhancement arised mainly from a high-conductance and specific surface area of CrN microspheres.This work presents a general strategy of fabricating controllable CrN nanostructures to achieve the enhanced supercapacitor performance.

Controllable Growth of Ni Nanocrystals Embedded in BaTiO₃/SrTiO₃Superlattices

BaTiO3/SrTiO3 superlattices with embedded Ni nanocrystals (NCs) have been grown on SrTiO3 (001) substrate using laser molecular beam epitaxy (L-MBE). In situ reflection high-energy electron diffraction (RHEED) was employed to investigate the process of lattice strain in the self-organization of Ni NCs and the epitaxial growth of BaTiO3/SrTiO3 superlattices. The results indicated that the strain from large lattice mismatch drove the self-organization of Ni NCs. Also, the layer-by-layer growth of BaTiO3/SrTiO3 superlattices Keywords: Nanocrystal;Superlattices;Self-organization 1. Introduction Oxide artificial superlattices, especially (001) oriented BaTiOsuperlattices and the island growth of Ni NCs were controllable ac-curately. The fine alternation of the two processes would provide a possible route to engineer controllably the nano-composite microstructure.