Exploring high-efficient catalysts for hydrogen evolution reaction (HER) has become very urgent for resolving the energy related issues. Recently, two-dimensional layered MoS
2
and its ...heterostructures with graphene or other traditional photocatalysts have presented great potentials for electrocatalytic and photocatalytic HER applications. On-site investigations of the atomic-scale structures and local electronic properties of the catalytically active sites are the key points for understanding the internal mechanisms, which however are hard to be achieved from the practical systems. Hereby, this review focuses on the recent progresses on the on-site scanning tunneling microscopy/spectroscopy investigations of the atomic structures and electronic properties of the ultrahigh-vacuum deposited and chemical vapor deposition (CVD) synthesized monolayer MoS
2
and MoS
2
/graphene vertical stacks on the electrodes of Au(111) and Au foils. The correlations between the respective HER activities, edge types and edge electronic states are comparatively introduced. Secondly, this review also introduces the photocatalytic HER applications of CVD-grown MoS
2
/WS
2
and WS
2
/MoS
2
vertical stacks on Au foils, mainly considering of their type-II band alignments and the novel interlayer charge transfer behaviors. Finally, future research directions are also proposed for in-depth understanding of the catalytic mechanism, as well as for exploring more efficient HER catalysts.
2D magnetic materials have attracted intense attention as ideal platforms for constructing multifunctional electronic and spintronic devices. However, most of the reported 2D magnetic materials are ...mainly achieved by the mechanical exfoliation route. The direct synthesis of such materials is still rarely reported, especially toward thickness‐controlled synthesis down to the 2D limit. Herein, the thickness‐tunable synthesis of nanothick rhombohedral Cr2S3 flakes (from ≈1.9 nm to tens of nanometers) on a chemically inert mica substrate via a facile chemical vapor deposition route is demonstrated. This is accomplished by an accurate control of the feeding rate of the Cr precursor and the growth temperature. Furthermore, it is revealed that the conduction behavior of the nanothick Cr2S3 is variable with increasing thickness (from 2.6 to 4.8 nm and >7 nm) from p‐type to ambipolar and then to n‐type. Hereby, this work can shed light on the scalable synthesis, transport, and magnetic properties explorations of 2D magnetic materials.
The thickness‐tunable synthesis of rhombohedral Cr2S3 flakes is first achieved via a facile chemical vapor deposition route by a unique design of the metal precursor and a precise control of the growth temperature. Particularly, the conduction behavior of the nanothick Cr2S3 is variable with increasing thickness, i.e., from p‐type to ambipolar, and then to n‐type.
Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) have emerged as attractive platforms in next-generation nanoelectronics and optoelectronics for reducing device sizes down ...to a 10 nm scale. To achieve this, the controlled synthesis of wafer-scale single-crystal TMDs with high crystallinity has been a continuous pursuit. However, previous efforts to epitaxially grow TMD films on insulating substrates (e.g., mica and sapphire) failed to eliminate the evolution of antiparallel domains and twin boundaries, leading to the formation of polycrystalline films. Herein, we report the epitaxial growth of wafer-scale single-crystal MoS2 monolayers on vicinal Au(111) thin films, as obtained by melting and resolidifying commercial Au foils. The unidirectional alignment and seamless stitching of the MoS2 domains were comprehensively demonstrated using atomic- to centimeter-scale characterization techniques. By utilizing onsite scanning tunneling microscope characterizations combined with first-principles calculations, it was revealed that the nucleation of MoS2 monolayer is dominantly guided by the steps on Au(111), which leads to highly oriented growth of MoS2 along the ⟨110⟩ step edges. This work, thereby, makes a significant step toward the practical applications of MoS2 monolayers and the large-scale integration of 2D electronics.
Monolayer transition metal dichalcogenides (TMDs) have become essential two-dimensional materials for their perspectives in engineering next-generation electronics. For related applications, the ...controlled growth of large-area uniform monolayer TMDs is crucial, while it remains challenging. Herein, we report the direct synthesis of 6-inch uniform monolayer molybdenum disulfide on the solid soda-lime glass, through a designed face-to-face metal-precursor supply route in a facile chemical vapor deposition process. We find that the highly uniform monolayer film, with the composite domains possessing an edge length larger than 400 µm, can be achieved within a quite short time of 8 min. This highly efficient growth is proven to be facilitated by sodium catalysts that are homogenously distributed in glass, according to our experimental facts and density functional theory calculations. This work provides insights into the batch production of highly uniform TMD films on the functional glass substrate with the advantages of low cost, easily transferrable, and compatible with direct applications.
Exploring new‐type 2D magnetic materials with high magnetic transition temperature and robust air stability has attracted wide attention for developing innovative spintronic devices. Recently, ...intercalation of native metal atoms into the van der Waals gaps of 2D layered transition metal dichalcogenides (TMDs) has been developed to form 2D non‐layered magnetic TMDs, while only succeeded in limited systems (e.g., Cr2S3, Cr5Te8). Herein, composition‐controllable syntheses of 2D non‐layered iron selenide nanosheets (25% Fe‐intercalated triclinic Fe5Se8 and 50% Fe‐intercalated monoclinic Fe3Se4) are firstly reported, via a robust chemical vapor deposition strategy. Specifically, the 2D Fe5Se8 exhibits intrinsic room‐temperature ferromagnetic property, which is explained by the change of electron spin states from layered 1T'‐FeSe2 to non‐layered Fe‐intercalated Fe5Se8 based on density functional theory calculations. In contrast, the ultrathin Fe3Se4 presents novel metallic features comparable with that of metallic TMDs. This work hereby sheds light on the composition‐controllable synthesis and fundamental property exploration of 2D self‐intercalation induced novel TMDs compounds, by propelling their application explorations in nanoelectronics and spintronics‐related fields.
In this work, the composition‐controllable syntheses of 2D non‐layered iron selenide nanosheets (25% Fe‐intercalated triclinic Fe5Se8 and 50% Fe‐intercalated monoclinic Fe3Se4), via a robust chemical vapor deposition strategy is presented. Intriguingly, it has been revealed that the 2D Fe5Se8 exhibits intrinsic room‐temperature ferromagnetic property, and the ultrathin Fe3Se4 presents a novel metallic feature.
Two-dimensional metallic transition metal dichalcogenides are emerging as prototypes for uncovering fundamental physical phenomena, such as superconductivity and charge-density waves, as well as for ...engineering-related applications. However, the batch production of such envisioned transition metal dichalcogenides remains challenging, which has hindered the aforementioned explorations. Herein, we fabricate thickness-tunable tantalum disulfide flakes and centimetre-sized ultrathin films on an electrode material of gold foil via a facile chemical vapour deposition route. Through temperature-dependent Raman characterization, we observe the transition from nearly commensurate to commensurate charge-density wave phases with our ultrathin tantalum disulfide flakes. We have obtained high hydrogen evolution reaction efficiency with the as-grown tantalum disulfide flakes directly synthesized on gold foils comparable to traditional platinum catalysts. This work could promote further efforts for exploring new efficient catalysts in the large materials family of metallic transition metal dichalcogenides, as well as exploiting their applications towards more versatile applications.Metallic transition metal dichalcogenides are important materials for catalysis, but scalable and controllable preparation methods are scarce. Here, the authors synthesize 2H-TaS
as centimetre-scale films of tunable thickness and show they are an efficient catalyst for hydrogen evolution.
Two-dimensional (2D) metallic transition-metal dichalcogenides (MTMDCs) are considered as ideal electrode materials for enhancing the device performances of 2D semiconducting transition-metal ...dichalcogenides, due to their similar atomic structures and complementary electronic properties. Vanadium ditelluride (VTe2) behaves as a fascinating material in MTMDCs family, presenting room-temperature ferromagnetism, charge density waves order, and topological property. However, its practical applications in universal electrode/energy-related fields remain unexplored. Herein, we achieved the direct synthesis of ultrathin, large-domain, and thickness-tunable 1T-VTe2 nanosheets on an easily available mica substrate by chemical vapor deposition (CVD). We further uncover that the CVD-derived 1T-VTe2 can serve as a high-performance electrode material thanks to its ultrahigh conductivity. Accordingly, a 6 times higher field-effect mobility (∼47.5 cm2 V–1 s–1) was achieved in 1T-VTe2-contacted monolayer MoS2 devices than that using a conventional Ti/Au electrode (∼8.1 cm2 V–1 s–1). Moreover, the CVD-synthesized 1T-VTe2 nanosheets are revealed to present excellent electrocatalytic activity for hydrogen evolution reaction. These results should propel the direct application of CVD-grown 2D MTMDCs as high-performance electrode materials in all 2D materials related devices.
For expanding the applications of 2D transition metal dichalcogenides (TMDCs), integrating functional devices with diverse conduction polarities in the same parent material is a very promising ...direction. Improving the contact issue at the metal‐semiconductor interface also holds fundamental significance. To achieve these concurrently, step‐like Cr2S3 vertical stacks with varied thicknesses are achieved via a one‐step chemical vapor deposition (CVD) method route. Various types of 2D Cr2S3 lateral homojunctions are thus naturally evolved, that is, pm‐ambipolar/n, p/ambipolar, ambipolar/n, and nm‐ambipolar/n junctions, allowing the integration of diverse conduction polarities in single Cr2S3 homojunctions. Significantly, on‐state current density and field‐effect mobility of the thinner 2D Cr2S3 flakes stacked below are detected to be ≈5 and ≈6 times increased in the lateral homojunctions, respectively. This work should hereby provide insights for designing 2D functional devices with simpler structures, for example, multipolar field‐effect transistors, photodetectors, and inverters, and provide fundamental references for optimizing the electrical performances of 2D materials related devices.
This work presents the direct synthesis of step‐like Cr2S3 lateral homojunctions via a one‐step chemical vapor deposition (CVD) route. The CVD derived Cr2S3 lateral homojunctions with thickness gradients allow the integration of diverse conduction polarities. Intriguingly, it is revealed that, the step‐like Cr2S3 homojunctions can be utilized to significantly ameliorate on‐state current density and field‐effect mobility of 2D Cr2S3 flakes.
2D metallic transition metal dichalcogenides (MTMDCs) are benchmark systems for uncovering the dimensionality effect on fascinating quantum physics, such as charge‐density‐wave (CDW) order, ...unconventional superconductivity, and magnetism, etc. However, the scalable and thickness‐tunable syntheses of such envisioned MTMDCs are still challenging. Meanwhile, the origin of CDW order at the 2D limit is controversial. Herein, the direct synthesis of wafer‐scale uniform monolayer 2H‐TaSe2 films and thickness‐tunable flakes on Au foils by chemical vapor deposition is accomplished. Based on the thickness‐tunable 2H‐TaSe2, the robust periodic lattice distortions that relate to CDW orders by low‐temperature transmission electron microscopy are directly visualized. Particularly, a phase diagram of the transition temperature from normal metallic to CDW phases with thickness by variable‐temperature Raman characterizations is established. Intriguingly, dramatically enhanced transition temperature from bulk value ≈90 to ≈125 K is observed from monolayer 2H‐TaSe2, which can be explained by the enhanced electron–phonon coupling mechanism. More importantly, an ultrahigh specific capacitance is also obtained for the as‐grown TaSe2 on carbon cloth as supercapacitor electrodes. The results hereby open up novel avenues toward the large‐scale preparation of high‐quality MTMDCs, and shed light on their applications in exploring some fundamental issues.
Wafer‐scale uniform monolayer 2H‐TaSe2 films and thickness‐tunable flakes are synthesized on Au foils by chemical vapor deposition (CVD) and a phase diagram of the CDW phase transition temperature with layer thickness is established. The enhanced transition temperature from bulk to monolayer is explained by the electron–phonon coupling mechanism. An ultrahigh specific capacitance is also obtained for as‐grown TaSe2 on carbon cloth as electrodes.
Two-dimensional (2D) semiconductors, especially transition metal dichalcogenides (TMDs), have been envisioned as promising candidates in extending Moore's law. To achieve this, the controllable ...growth of wafer-scale TMDs single crystals or periodic single-crystal patterns are fundamental issues. Herein, we present a universal route for synthesizing arrays of unidirectionally orientated monolayer TMDs ribbons (e.g., MoS
, WS
, MoSe
, WSe
, MoS
Se
), by using the step edges of high-miller-index Au facets as templates. Density functional theory calculations regarding the growth kinetics of specific edges have been performed to reveal the morphological transition from triangular domains to patterned ribbons. More intriguingly, we find that, the uniformly aligned TMDs ribbons can merge into single-crystal films through a one-dimensional edge epitaxial growth mode. This work hereby puts forward an alternative pathway for the direct synthesis of inch-scale uniform monolayer TMDs single-crystals or patterned ribbons, which should promote their applications as channel materials in high-performance electronics or other fields.
PDF
