Chemical Vapor Deposition Synthesis of Intrinsic High-Temperature Ferroelectric 2D CuCrSe2.

Ultrathin 2D ferroelectrics with high Curie temperature are critical for multifunctional ferroelectric devices. However, the ferroelectric spontaneous polarization is consistently broken by the strong thermal fluctuations at high temperature, resulting in the rare discovery of high-temperature ferroelectricity in 2D materials. Here, a chemical vapor deposition method is reported to synthesize 2D CuCrSe2 nanosheets. The crystal structure is confirmed by scanning transmission electron microscopy characterization. The measured ferroelectric phase transition temperature of ultrathin CuCrSe2 is about ≈800 K. Significantly, the switchable ferroelectric polarization is observed in ≈5.2 nm nanosheet. Moreover, the in-plane and out-of-plane ferroelectric response are modulated by different maximum bias voltage. This work provides a new insight into the construction of 2D ferroelectrics with high Curie temperature.

A Universal Strategy for Synthesis of 2D Ternary Transition Metal Phosphorous Chalcogenides.

The 2D ternary transition metal phosphorous chalcogenides (TMPCs) have attracted extensive research interest due to their widely tunable band gap, rich electronic properties, inherent magnetic and ferroelectric properties. However, the synthesis of TMPCs via chemical vapor deposition (CVD) is still challenging since it is difficult to control reactions among multi-precursors. Here, a subtractive element growth mechanism is proposed to controllably synthesize the TMPCs. Based on the growth mechanism, the TMPCs including FePS3 , FePSe3 , MnPS3 , MnPSe3 , CdPS3 , CdPSe3 , In2 P3 S9 , and SnPS3 are achieved successfully and further confirmed by Raman, second-harmonic generation (SHG), and scanning transmission electron microscopy (STEM). The typical TMPCs-SnPS3 shows a strong SHG signal at 1064 nm, with an effective nonlinear susceptibility χ(2) of 8.41 × 10-11  m V-1 , which is about 8 times of that in MoS2 . And the photodetector based on CdPSe3 exhibits superior detection performances with responsivity of 582 mA W-1 , high detectivity of 3.19 × 1011  Jones, and fast rise time of 611 µs, which is better than most previously reported TMPCs-based photodetectors. These results demonstrate the high quality of TMPCs and promote the exploration of the optical properties of 2D TMPCs for their applications in optoelectronics.

Colorimetric and visual determination of iodide ions via morphology transition of gold nanobipyramids.

The gold nanobipyramids (Au NBPs) are widely used in the analytical detection of biochemistry due to their unique localized surface plasmon resonance (LSPR) properties. In our developed approach, I- in kelp was detected by etching Au NBPs in the presence of IO3-. Under acidic conditions, IO3- reacted rapidly with I- to form I2, subsequently I2 reacted with I- to form the intermediate I3-. In the presence of CTAB, Au NBPs were etched by I2 derived from I3-, resulting in a decrease in the aspect ratio of Au NBPs, to form a significant blue shift of LSPR longitudinal peak and color variation of colloid which changed from blue-green to magenta and could be employed to quantitatively detect the concentration of I- with the naked eye. A linear relationship can be found between the LSPR peak changes with the I- concentration in a wide range from 4.0 µM to 15.0 µM, and the sensitive limit of detection (LOD) was 0.2 µM for UV-vis spectroscopy and the obvious color changes with a visual LOD was 4.0 µM for the naked eye. Benefiting from the high specificity, the proposed colorimetric detection of I- in kelp samples was achieved, indicating the available potential of the colorimetric detection for the determination of I- in real samples. What's more, this detection procedure was time-saving and could avoid tedious procedures.

Strain forces tuned the electronic and optical properties in GaTe/MoS2 van der Waals heterostructures.

Two-dimensional (2D) van der Waals heterostructures (vdWHs) have attracted widespread attention in fundamental materials science and device physics. In this work, we report a novel GaTe/MoS2 vdWH and theoretically investigate the electronic and optical properties based on first-principles calculations. GaTe/MoS2 vdWH possesses an indirect band gap with type-II band alignment. Meanwhile, the interfacial charge transfer from MoS2 to GaTe can effectively separate electrons and holes. Also, this vdWH shows improved visible-ultraviolet optical absorption properties compared with those of the isolated GaTe or MoS2 monolayers. More remarkably, the biaxial strain can not only modulate the band gap but also enhance the optical performance in GaTe/MoS2 vdWH. In particular, the tensile strain is more effective for improving the optical absorption in the visible light region. These findings indicate that GaTe/MoS2 vdWH is a promising candidate for nanoelectronics and optoelectronic devices.