Direct Selective Epitaxy of 2D Sb2Te3 onto Monolayer WS2 for Vertical p-n Heterojunction Photodetectors.

Two-dimensional transition metal dichalcogenides (2D-TMDs) possess appropriate bandgaps and interact via van der Waals (vdW) forces between layers, effectively overcoming lattice compatibility challenges inherent in traditional heterojunctions. This property facilitates the creation of heterojunctions with customizable bandgap alignments. However, the prevailing method for creating heterojunctions with 2D-TMDs relies on the low-efficiency technique of mechanical exfoliation. Sb2Te3, recognized as a notable p-type semiconductor, emerges as a versatile component for constructing diverse vertical p-n heterostructures with 2D-TMDs. This study presents the successful large-scale deposition of 2D Sb2Te3 onto inert mica substrates, providing valuable insights into the integration of Sb2Te3 with 2D-TMDs to form heterostructures. Building upon this initial advancement, a precise epitaxial growth method for Sb2Te3 on pre-existing WS2 surfaces on SiO2/Si substrates is achieved through a two-step chemical vapor deposition process, resulting in the formation of Sb2Te3/WS2 heterojunctions. Finally, the development of 2D Sb2Te3/WS2 optoelectronic devices is accomplished, showing rapid response times, with a rise/decay time of 305 µs/503 µs, respectively.

Strategies for Controlled Growth of Transition Metal Dichalcogenides by Chemical Vapor Deposition for Integrated Electronics.

In recent years, transition metal dichalcogenide (TMD)-based electronics have experienced a prosperous stage of development, and some considerable applications include field-effect transistors, photodetectors, and light-emitting diodes. Chemical vapor deposition (CVD), a typical bottom-up approach for preparing 2D materials, is widely used to synthesize large-area 2D TMD films and is a promising method for mass production to implement them for practical applications. In this review, we investigate recent progress in controlled CVD growth of 2D TMDs, aiming for controlled nucleation and orientation, using various CVD strategies such as choice of precursors or substrates, process optimization, and system engineering. We then survey different patterning methods, such as surface patterning, metal precursor patterning, and postgrowth sulfurization/selenization/tellurization, to mass produce heterostructures for device applications. With these strategies, various well-designed architectures, such as wafer-scale single crystals, vertical and lateral heterostructures, patterned structures, and arrays, are achieved. In addition, we further discuss various electronics made from CVD-grown TMDs to demonstrate the diverse application scenarios. Finally, perspectives regarding the current challenges of controlled CVD growth of 2D TMDs are also suggested.

Visualizing Van der Waals Epitaxial Growth of 2D Heterostructures.

Understanding the growth mechanisms of 2D van der Waals (vdW) heterostructures is of great importance in exploring their functionalities and device applications. A custom-built system integrating physical vapor deposition and optical microscopy/Raman spectroscopy is employed to study the dynamic growth processes of 2D vdW heterostructures in situ. This allows the identification of a new growth mode with a distinctly different growth rate and morphology from those of the conventional linear growth mode. A model that explains the difference in morphologies and quantifies the growth rates of the two modes by taking the role of surface diffusion into account is proposed. A range of material combinations including CdI2 /WS2 , CdI2 /MoS2 , CdI2 /WSe2 , PbI2 /WS2 , PbI2 /MoS2 , PbI2 /WSe2 , and Bi2 Se3 /WS2 is systematically investigated. These findings may be generalized to the synthesis of many other 2D heterostructures with controlled morphologies and physical properties, benefiting future device applications.

Universal Precise Growth of 2D Transition-Metal Dichalcogenides in Vertical Direction.

Two-dimensional transition-metal dichalcogenides (TMDs) have been one of the hottest focus of materials due to the most beneficial electronic and optoelectronic properties. Up to now, one of the big challenges is the synthesis of large-area layer-number-controlled single-crystal films. However, the poor understanding of the growth mechanism seriously hampers the progress of the scalable production of TMDs with precisely tunable thickness at an atomic scale. Here, the growth mechanisms in the vertical direction were systemically studied based on the density functional theory (DFT) calculation and an advanced chemical vapor deposition (CVD) growth. As a result, the U-type relation of the TMD layer number to the ratio of metal/chalcogenide is confirmed by the capability of ultrafine tuning of the experimental conditions in the CVD growth. In addition, high-quality uniform monolayer, bilayer, trilayer, and multilayer TMDs in a large area (8 cm2) were efficiently synthesized by applying this modified CVD. Although bilayer TMDs can be obtained at both high and low ratios of metal/chalcogenide based on the suggested mechanism, they demonstrate significantly different optical and electronic transport properties. The modified CVD strategy and the proposed mechanism should be helpful for synthesizing and large-area thickness-controlled TMDs and understanding their growth mechanism and could be used in integrated electronics and optoelectronics.

CuFe2O4/MoS2 Mixed-Dimensional Heterostructures with Improved Gas Sensing Response.

Mixed-dimensional (2D + nD, n = 0, 1, and 3) heterostructures opened up a new avenue for fundamental physics studies and applied nanodevice designs. Herein, a novel type-II staggered band alignment CuFe2O4/MoS2 mixed-dimensional heterostructures (MHs) that present a distinct enhanced (20-28%) acetone gas sensing response compared with pure CuFe2O4 nanotubes are reported. Based on the structural characterizations and DFT calculation results, the tentative mechanism for the improvement of gas sensing performance of the CuFe2O4/MoS2 MHs can be attributed to the synergic effect of type-II band alignment and the MoS2 active sites.

[The effect of cadmium pollution on reproductive health in females].

OBJECTIVE: To study the relationship between cadmium pollution and its adverse effects on female reproductive health status in people living in cadmium polluted area in Zhenghe, Fujian provinces. METHODS: Data through laboratory studies on reproductive health of female residents in Cd-pollution area were studied and compared with those in control areas in Zhenghe. RESULTS: Both prevalence rates of abnormal menstrual cycle and dysmenorrhea in unmarried women in Cd-pollution area (19.1% vs. 42.6%) were significantly higher than those in control area (5.7% vs. 18.9%) and the rates of sterility in married women in Cd-pollution area (6.3%) were significantly higher than those in control area (1.1%). During the first two pregnancies, rates of queasiness, disgorgement, spontaneous abortion and stillbirth in married women in polluted area were 44.7%, 31.7%, 10.27% and 4.23%, significantly higher than those 26.5%, 17.8%, 2.85% and 1.05% in control area, with significant differences (P < 0.05). Results from cumulative odds model analysis showed that: living in Cd-pollution area was a possible risk factor related to female reproductive health (OR = 2.072), after the other risk factors being under control. CONCLUSION: The female reproductive health status of people residing in the cadmium polluted area had already been deteriorated.