Two-dimensional (2D) magnets with intrinsic ferromagnetic/antiferromagnetic (FM/AFM) ordering are highly desirable for future spintronic devices. However, the direct growth of their crystals is in ...its infancy. Here we report a chemical vapor deposition approach to controllably grow layered tetragonal and non-layered hexagonal FeTe nanoplates with their thicknesses down to 3.6 and 2.8 nm, respectively. Moreover, transport measurements reveal these obtained FeTe nanoflakes show a thickness-dependent magnetic transition. Antiferromagnetic tetragonal FeTe with the Néel temperature (T
) gradually decreases from 70 to 45 K as the thickness declines from 32 to 5 nm. And ferromagnetic hexagonal FeTe is accompanied by a drop of the Curie temperature (T
) from 220 K (30 nm) to 170 K (4 nm). Theoretical calculations indicate that the ferromagnetic order in hexagonal FeTe is originated from its concomitant lattice distortion and Stoner instability. This study highlights its potential applications in future spintronic devices.
A facile electron-charging and reducing method was developed to prepare Au/＇VVO3 nanocomposites for plasmonic solar water splitting. The preparation method involved a charging step in which electrons ...were charged into WO3 under negative bias, and a subsequent reducing step in which the stored electrons were used to reductively deposit Au on the surface of WO3. The electron-charged WO3 （c-WO3） exhibited tunable reducibility that could be easily controlled by varying the charging parameters, and this property makes this method a universal strategy to prepare metalAVO3 composites. The obtained Au/VVO3 nanocomposite showed greatly improved photoactivity toward the oxygen evolution reaction （OER） when compared with WO3. After Au decoration, the OER photocurrent was improved by a percentage of over 80% at low potentials （〈0.6 V vs. SCE）, and by a percentage of over 30% at high potentials （〉1.0 V vs. SCE）. Oxygen evolution measurements were performed to quantitatively determine the Faraday efficiency for OER, which reflected the amount of photocurrent consumed by water splitting. The Faraday efficiency for OER was improved from 74% at the WO3 photoanode to 94% at the Au-8/＇vVO3 composite photoanode, and this is the first direct evidence that the Au decoration significantly restrained the anodic side reactions and enhanced the photoelectrochemical （PEC） OER efficiency. The high photoactivity of the composite photoanode toward OER was ascribed to the plasmon resonance energy transfer （PRET） enhancement and the catalytic enhancement of Au nanoparticles （NPs）.
Metastable 1T'-phase transition metal dichalcogenides (1T'-TMDs) with semi-metallic natures have attracted increasing interest owing to their uniquely distorted structures and fascinating ...phase-dependent physicochemical properties. However, the synthesis of high-quality metastable 1T'-TMD crystals, especially for the group VIB TMDs, remains a challenge. Here, we report a general synthetic method for the large-scale preparation of metastable 1T'-phase group VIB TMDs, including WS
, WSe
, MoS
, MoSe
, WS
Se
and MoS
Se
. We solve the crystal structures of 1T'-WS
, -WSe
, -MoS
and -MoSe
with single-crystal X-ray diffraction. The as-prepared 1T'-WS
exhibits thickness-dependent intrinsic superconductivity, showing critical transition temperatures of 8.6 K for the thickness of 90.1 nm and 5.7 K for the single layer, which we attribute to the high intrinsic carrier concentration and the semi-metallic nature of 1T'-WS
. This synthesis method will allow a more systematic investigation of the intrinsic properties of metastable TMDs.
Phase engineering of nanomaterials (PEN) offers a promising route to rationally tune the physicochemical properties of nanomaterials and further enhance their performance in various applications. ...However, it remains a great challenge to construct well‐defined crystalline@amorphous core–shell heterostructured nanomaterials with the same chemical components. Herein, the synthesis of binary (Pd‐P) crystalline@amorphous heterostructured nanoplates using Cu3−χP nanoplates as templates, via cation exchange, is reported. The obtained nanoplate possesses a crystalline core and an amorphous shell with the same elemental components, referred to as c‐Pd‐P@a‐Pd‐P. Moreover, the obtained c‐Pd‐P@a‐Pd‐P nanoplates can serve as templates to be further alloyed with Ni, forming ternary (Pd‐Ni‐P) crystalline@amorphous heterostructured nanoplates, referred to as c‐Pd‐Ni‐P@a‐Pd‐Ni‐P. The atomic content of Ni in the c‐Pd‐Ni‐P@a‐Pd‐Ni‐P nanoplates can be tuned in the range from 9.47 to 38.61 at%. When used as a catalyst, the c‐Pd‐Ni‐P@a‐Pd‐Ni‐P nanoplates with 9.47 at% Ni exhibit excellent electrocatalytic activity toward ethanol oxidation, showing a high mass current density up to 3.05 A mgPd−1, which is 4.5 times that of the commercial Pd/C catalyst (0.68 A mgPd−1).
Binary (Pd‐P) and ternary (Pd‐Ni‐P) nanoplates, both with crystalline@amorphous core–shell nanostructures, are synthesized using Cu3−χP nanoplates as templates. The obtained c‐Pd‐Ni‐P@a‐Pd‐Ni‐P heterostructured nanoplates exhibit superior electrocatalytic performance toward the ethanol oxidation reaction in alkaline media compared to c‐Pd‐P@a‐Pd‐P heterostructured nanoplates and commercial Pd/C catalysts.
Two‐dimensional (2D) magnetic crystals with intrinsic ferromagnetism are highly desirable for novel spin‐electronic devices. However, the controllable synthesis of 2D magnets, especially the direct ...growth of 2D magnets on substrate surfaces, is still a challenge. Here, we demonstrate the synthesis of ultrathin zinc‐blende phase manganese selenide (β‐MnSe) nanosheets using the chemical vapor deposition (CVD) technique. The 2D β‐MnSe crystals exhibit distinct ferromagnetic properties with a Curie temperature of 42.3 K. Density functional theory (DFT) calculations suggest that the ferromagnetic order in β‐MnSe originates from the exchange coupling between the unsaturated Se and Mn atoms. This study presents significant progress in the CVD growth of ultrathin 2D magnetic materials by thinning bulk magnets, and it will pave the way for the building of energy‐efficient spintronic devices in the future.
Two‐dimensional magnetic crystals with intrinsic ferromagnetism are highly desirable for novel spin‐electronic devices. Ultrathin zinc‐blende phase manganese selenide (β‐MnSe) nanosheets were synthesized using the chemical vapor deposition technique. The exchange coupling between the unsaturated Se and Mn atoms generates the ferromagnetic order in β‐MnSe, making it a ferromagnetic semiconductor with a Curie temperature of 42.3 K.
We report the preparation of CuWO4 nanoflake (NF) array films by using a solid phase reaction method in which WO3 NFs were employed as sacrificial templates. The SEM, TEM and XRD results demonstrated ...that the obtained CuWO4 films possessed a network structure that was composed of single crystalline NFs intersected with each other. The CuWO4 NF films showed superior photoelectrochemical (PEC) activity to other CuWO4 photoanodes reported recently for the oxygen evolution reaction (OER). We attributed the high activity to the unique morphological and crystalline structure of the CuWO4 film, which enhanced the photoactivity by providing a large specific area, a short hole transport distance from the inside of CuWO4 to the CuWO4/solution interface, and a low grain boundary density. Hydrogen treatment by annealing the CuWO4 NF film in mixed gases of H2 and Ar could further enhance the photoactivity, as hydrogen treatment significantly increased the electron density of CuWO4 by generating oxygen vacancy in the lattice. The photocurrent density for OER obtained on the hydrogen-treated (H-treated) CuWO4 NF film is the largest ever reported on CuWO4 photoanodes in the literature. Moreover, the CuWO4 photoanodes exhibit good stability in weak alkaline solution, while the H-treated CuWO4 photoanodes exhibit acceptable stability. This work not only reveals the potential of CuWO4 as a photoanode material for solar water splitting but also shows that the construction of nanostructured CuWO4 photoanodes is a promising method to achieve high PEC activity toward OER.
Crystal phases play a key role in determining the physicochemical properties of a material. To date, many phases of transition metal dichalcogenides have been discovered, such as octahedral (1T), ...distorted octahedral (1T′), and trigonal prismatic (2H) phases. Among these, the 1T′ phase offers unique properties and advantages in various applications. Moreover, the 1T′ phase consists of unique zigzag chains of the transition metals, giving rise to interesting in‐plane anisotropic properties. Herein, the in‐plane optical and electrical anisotropies of metastable 1T′‐MoS2 layers are investigated by the angle‐resolved Raman spectroscopy and electrical measurements, respectively. The deconvolution of J1 and J2 peaks in the angle‐resolved Raman spectra is a key characteristic of high‐quality 1T′‐MoS2 crystal. Moreover, it is found that its electrocatalytic performance may be affected by the crystal orientation of anisotropic material due to the anisotropic charge transport.
The distorted octahedral structure of 1T′‐MoS2
is confirmed, and the in‐plane optical and electrical anisotropies of metastable 1T′‐MoS2 layers are investigated. Importantly, the dependence of electrocatalytic activity on the anisotropic charge transport in 1T′‐MoS2 layers is demonstrated.
In recent years, two-dimensional (2D) magnetic transition metal chalcogenides (TMCs) have attracted tremendous research interests thanks to their intriguing properties that are essential in ...developing future electronic and spintronic devices in this modernizing era. This review aims to introduce recent developments in the preparation of 2D magnetic TMCs, especially chromium and iron-based chalcogenides, their structures, as well as the related intriguing magnetic phenomena. First, the common crystal structures of magnetic TMCs including both layered and nonlayered structures are introduced. Various chemical vapor deposition strategies for synthesizing 2D magnetic TMCs are then introduced with emphasis on the key synthesis parameters. Moreover, the intriguing physical properties associated with 2D TMCs such as magnetic anisotropy, thickness, and phase-dependent magnetic response as well as stability are summarized. Last but not least, challenges and future research directions are briefly discussed in light of recent advances in the field.
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