112 research outputs found
Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1-xKxFe2As2 superconductors
We report here an atomic resolution study of the structure and composition of
the grain boundaries in polycrystalline Sr0.6K0.4Fe2As2 superconductor. A large
fraction of grain boundaries contain amorphous layers larger than the coherence
length, while some others contain nanometer-scale particles sandwiched in
between amorphous layers. We also find that there is significant oxygen
enrichment at the grain boundaries. Such results explain the relatively low
transport critical current density (Jc) of polycrystalline samples with respect
to that of bicrystal films.Comment: 12 pages, 4 figure
Field-effect transistors made from solution-grown two-dimensional tellurene
The reliable production of two-dimensional crystals is essential for the
development of new technologies based on 2D materials. However, current
synthesis methods suffer from a variety of drawbacks, including limitations in
crystal size and stability. Here, we report the fabrication of large-area,
high-quality 2D tellurium (tellurene) using a substrate-free solution process.
Our approach can create crystals with a process-tunable thickness, from
monolayer to tens of nanometres, and with lateral sizes of up to 100 um. The
chiral-chain van der Waals structure of tellurene gives rise to strong in-plane
anisotropic properties and large thickness dependent shifts in Raman
vibrational modes, which is not observed in other 2D layered materials. We also
fabricate tellurene field-effect transistors, which exhibit air-stable
performance at room temperature for over two months, on off ratios on the order
of 106 and field-effect mobilities of around 700 cm2 per Vs. Furthermore, by
scaling down the channel length and integrating with high-k dielectrics,
transistors with a significant on-state current density of 1 A mm-1 are
demonstrated
One-pot synthesis of Pd-Pt@Pd core-shell nanocrystals with enhanced electrocatalytic activity for formic acid oxidation
NSFC [21361005, 21073152, 21373175]; Fujian Provincial Department of Science and Technology [2008F3099]; Foundation for the Talents by the Guizhou University [X060025]; Natural Science Foundation of Guizhou Province [20072013]Well-defined Pd-Pt@Pd core-shell nanocrystals with a Pd-Pt alloy core and a conformal Pd shell of similar to 2-3 nm were directly synthesized through a one-pot, aqueous solution approach without any preformed Pd or Pt seeds. These Pd-Pt@Pd core-shell nanocrystals show an enhanced electrocatalytic activity for formic acid oxidation compared with commercial Pd black
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