Ferroelectrics allow for a wide range of intriguing applications. However, maintaining ferroelectricity has been hampered by intrinsic depolarization effects. Here, by combining first-principles calculations and experimental studies, we report on the discovery of robust room-temperature out-of-plane ferroelectricity which is realized in the thinnest monolayer MoTe
2
with unexploited distorted 1T (
d
1T) phase. The origin of the ferroelectricity in
d
1T-MoTe
2
results from the spontaneous symmetry breaking due to the relative atomic displacements of Mo atoms and Te atoms. Furthermore, a large ON/OFF resistance ratio is achieved in ferroelectric devices composed of MoTe
2
-based van der Waals heterostructure. Our work demonstrates that ferroelectricity can exist in two-dimensional layered material down to the atomic monolayer limit, which can result in new functionalities and achieve unexpected applications in atomic-scale electronic devices.
Two-dimensional MXenes are promising
for various energy-related
applications such as energy storage devices and electrocatalysis of
water-splitting. MXenes prepared from hydrofluoric (HF) acid etching
have been widely reported. Nonetheless, the acute toxicity of HF acid
impedes the large-scale fabrication of MXenes and their wide utilization
in energy-related applications. It is thus greatly encouraging to
explore a more innocuous protocol for MXenes synthesis. Thereby, a
universal strategy based on thermal-assisted electrochemical etching
route is developed to synthesize MXenes (e.g., Ti2CT
x
, Cr2CT
x
, and V2CT
x
). Furthermore, the cobalt ion doped
MXenes show an exceptionally enhanced capability of hydrogen evolution
reaction (HER) and oxygen evolution reaction (OER) activity, demonstrating
their multifunctionalities, which is comparable to the commercialized
catalysts. Moreover, we successfully exploited our MXenes as cathodes
for the novel aqueous rechargeable battery, with proficient retention
and excellent electrical output performance. This work paves a nontoxic
and HF-free route to prepare various MXenes and demonstrates practical
applications of the materials.
Amorphous black phosphorus (a-BP) ultrathin films are deposited by pulsed laser deposition. a-BP field-effect trans-istors, exhibiting high carrier mobility and moderate on/off current ratio, are demonstrated. Thickness dependence of the bandgap, mobility, and on/off ratio are observed. These results offer not only a new nanoscale member in the BP family, but also a new opportunity to develop nano-electronic devices.
Molybdenum disulfide (MoS2) has been attracting much attentions due to its excellent electrical and optical properties. We report here the synthesis of large-scale and uniform MoS2 nanosheets with vertically standing morphology using chemical vapor deposition method. TEM observations clearly reveal the growth mechanism of these vertical structures. It is suggested that the vertical structures are caused by the compression and extrusion between MoS2 islands. More importantly, the vertical morphology of two dimensional (2D) materials hold many promising potential applications. We demonstrate here the as-synthesized vertically standing MoS2 nanosheets could be used for hydrogen evolution reaction, where the exchange current density is about 70 times of bulk MoS2. The field emission performance of vertically standing MoS2 were also improved due to the abundantly exposed edges.
A 2D system of Er-doped MoS2 layered nanosheets is developed. Structural studies indicate that the Er atoms can be substitutionally introduced into MoS2 to form stable doping. Density functional theory calculation implies that the system remains stable. Both NIR-to-NIR up-conversion and down-conversion light-emissions are observed in 2D transition metal dichalcogenides, ascribed to the energy transition from Er(3+) dopants.
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