다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

The ability to tune material properties using gating by electric fields is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as the observation of gate electric-field-induced superconductivity and metal-insulator transitions. Here, we describe an ionic field-effect transistor (termed an iFET), in which gate-controlled Li ion intercalation modulates the material properties of layered crystals of 1T-TaS2. The strong charge doping induced by the tunable ion intercalation alters the energetics of various charge-ordered states in 1T-TaS2 and produces a series of phase transitions in thin-flake samples with reduced dimensionality. We find that the charge-density wave states in 1T-TaS2 collapse in the two-dimensional limit at critical thicknesses. Meanwhile, at low temperatures, the ionic gating induces multiple phase transitions from Mott-insulator to metal in 1T-TaS2 thin flakes, with five orders of magnitude modulation in resistance, and superconductivity emerges in a textured charge-density wave state induced by ionic gating. Our method of gate-controlled intercalation opens up possibilities in searching for novel states of matter in the extreme charge-carrier-concentration limit.

http://absimage.aps.org/image/MAR15/MWS_MAR15-2014-020259.pdf

Gate-tunable phase transitions in thin flakes of 1T-TaS$_{2}$

Transition temperature of strong-coupled superconductors.

Hydrogen produced via water electrolysis can act as an ideal clean chemical fuel with superb gravimetric energy density and high energy conversion efficiency, solving the problems of conventional fossil fuel exhaustion and environmental contamination. Transition metal sulfides (TMS) have been extensively explored as effective, widely available alternatives to precious metals in overall water splitting. Herein, recent advances, covering preparation methods, intrinsic electrocatalytic performance, and optimization strategies, relating to TMS-based bifunctional electrocatalysts have been summarized systematically and comprehensively. Firstly, a general introduction to the reaction mechanisms and key parameters of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is provided. Next, the physicochemical properties of TMS and typical synthesis methods are introduced to give guidance for fabricating TMS materials with well-defined structures, controllable compositions, and excellent performance. Importantly, the intrinsic activities of TMS-based electrocatalysts and several strategies for improving their bifunctional electrocatalytic performance during water electrolysis are discussed in detail. Finally, perspectives covering the challenges and opportunities related to the further development of TMS-based materials with high activity and long-term durability for overall water splitting are given. The aim herein is to provide guidelines for the design and fabrication of TMS-based bifunctional electrocatalysts with excellent performance and to accelerate their large-scale practical application in water electrolysis.

Recent advances in transition-metal-sulfide-based bifunctional electrocatalysts for overall water splitting

Photoemission established tantalum phosphide as a Weyl semimetal, which hosts exotic Weyl fermion quasiparticles and Fermi arcs. Weyl semimetals are expected to open up new horizons in physics and materials science because they provide the first realization of Weyl fermions and exhibit protected Fermi arc surface states. However, they had been found to be extremely rare in nature. Recently, a family of compounds, consisting of tantalum arsenide, tantalum phosphide (TaP), niobium arsenide, and niobium phosphide, was predicted as a Weyl semimetal candidates. We experimentally realize a Weyl semimetal state in TaP. Using photoemission spectroscopy, we directly observe the Weyl fermion cones and nodes in the bulk, and the Fermi arcs on the surface. Moreover, we find that the surface states show an unexpectedly rich structure, including both topological Fermi arcs and several topologically trivial closed contours in the vicinity of the Weyl points, which provides a promising platform to study the interplay between topological and trivial surface states on a Weyl semimetal’s surface. We directly demonstrate the bulk-boundary correspondence and establish the topologically nontrivial nature of the Weyl semimetal state in TaP, by resolving the net number of chiral edge modes on a closed path that encloses the Weyl node. This also provides, for the first time, an experimentally practical approach to demonstrating a bulk Weyl fermion from a surface state dispersion measured in photoemission.

Experimental discovery of a topological Weyl semimetal state in TaP

Layered transition-metal dichalcogenides based on VIB elements have attracted substantial attention for their applications in energy storage and conversion. However, few studies have concentrated on VB element dichalcogenides. Herein, we report that trifunctional 2H-TaS2 nanoflakes exhibit high performance when applied in supercapacitors, hydrogen evolution reactions (HER) and oxygen evolution reactions (OER). Notably, TaS2 nanoflakes delivered a large volumetric capacitance (502 F cm−3 at the scan rate of 10 mV s−1) and remarkable cycling stability (over 91% after 5000 cycles). TaS2 nanoflakes also exhibited remarkable catalytic performances in HER and OER processes, showing very small overpotentials and Tafel slopes, which are far better than those of the previously reported TaS2 electrocatalysts. Furthermore, TaS2 is highly stable in both alkaline and acidic electrolyte solutions. This work offers a new concept to design VB element-based electrodes for future energy storage and conversion applications.

Multifunctional 2H-TaS2 nanoflakes for efficient supercapacitors and electrocatalytic evolution of hydrogen and oxygen

Oxygen permeation, stability and chemical bonding characteristics of 40 wt% Nd0.6Sr0.4CoO3−δ–60 wt% Ce0.9Nd0.1O2−δ (40NSCO–60CNO) dual-phase composite membrane reactors were investigated. The 40NSCO–60CNO oxygen permeable membrane was prepared via an in situ one-pot one-step EDTA–citric acid method. The crystal structure of the 40NSCO–60CNO dual phase material was characterized by X-ray diffraction (XRD) and in situ XRD. The microstructure was investigated using transmission electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) combined with energy-dispersive X-ray spectroscopy (EDXS) and electron energy-loss spectroscopy (EELS). The results show that the 40NSCO–60CNO composite represents a micro-scale mixture of only the two pure phases NSCO and CNO. The oxygen permeation fluxes through the 40NSCO–60CNO dual phase membrane were measured at elevated temperatures (900–1000 °C) with one side of it exposed to synthetic air and the other side to a flowing He gas stream. A stable oxygen permeation rate of 0.90 mL cm−2 min−1 was obtained with a 0.4 mm thick membrane under an air/He oxygen partial pressure gradient at 1000 °C. The 40NSCO–60CNO dual phase membrane with a thickness of 0.6 mm showed a stable oxygen flux of 0.55 mL cm−2 min−1 at 950 °C for 100 h under pure CO2 sweeping.

A novel dual phase membrane 40 wt% Nd0.6Sr0.4CoO3−δ–60 wt% Ce0.9Nd0.1O2−δ: design, synthesis and properties

High CO2-tolerance oxygen permeation dual-phase membranes Ce0.9Pr0.1O2-δ-Pr0.6Sr0.4Fe0.8Al0.2O3-δ

A series of composites based on (100-x)wt.%Ce0.9Pr0.1O2-δ-xwt.%Pr0.6Ca0.4FeO3-δ (x = 25, 40 and 50) doped with the cheap and abundant alkaline earth metal Ca2+ at the A-site has been successfully designed and fabricated. The crystal structure, oxygen permeability, phase and CO2 stability were evaluated. The composition of 60wt.%Ce0.9Pr0.1O2-δ-40wt.%Pr0.6Ca0.4FeO3-δ(60CPO-40PCFO) possesses the highest oxygen permeability among three studied composites. At 1000 °C, the oxygen permeation fluxes through the 0.3 mm-thickness 60CPO-40PCFO membranes after porous La0.6Sr0.4CoO3-δ each to 1.00 mL cm−2 min−1 and 0.62 mL cm−2 min−1 under air/He and air/CO2 gradients, respectively. In situ XRD results demonstrated that the 60CPO-40PCFO sample displayed a perfect structural stability in air as well as CO2-containing atmosphere. Thus, low-cost, Co-free and Sr-free 60CPO-40PCFO has high CO2 stability and is economical and environmental friendly since the expensive and volatile element Co was replaced by Fe and Sr was waived since it easily forms carbonates.

Dong Yan

Papers

Multifunctional 2H-TaS2 nanoflakes for efficient supercapacitors and electrocatalytic evolution of hydrogen and oxygen

A novel dual phase membrane 40 wt% Nd0.6Sr0.4CoO3−δ–60 wt% Ce0.9Nd0.1O2−δ: design, synthesis and properties

High CO2-tolerance oxygen permeation dual-phase membranes Ce0.9Pr0.1O2-δ-Pr0.6Sr0.4Fe0.8Al0.2O3-δ

High-flux dual-phase percolation membrane for oxygen separation

Effects of Al content on the oxygen permeability through dual-phase membrane 60Ce0.9Pr0.1O2-δ-40Pr0.6Sr0.4Fe1-xAlxO3-δ