Ultrathin two-dimensional (2D) semiconducting layered materials offer great potential for extending Moore's law of the number of transistors in an integrated circuit
. One key challenge with 2D ...semiconductors is to avoid the formation of charge scattering and trap sites from adjacent dielectrics. An insulating van der Waals layer of hexagonal boron nitride (hBN) provides an excellent interface dielectric, efficiently reducing charge scattering
. Recent studies have shown the growth of single-crystal hBN films on molten gold surfaces
or bulk copper foils
. However, the use of molten gold is not favoured by industry, owing to its high cost, cross-contamination and potential issues of process control and scalability. Copper foils might be suitable for roll-to-roll processes, but are unlikely to be compatible with advanced microelectronic fabrication on wafers. Thus, a reliable way of growing single-crystal hBN films directly on wafers would contribute to the broad adoption of 2D layered materials in industry. Previous attempts to grow hBN monolayers on Cu (111) metals have failed to achieve mono-orientation, resulting in unwanted grain boundaries when the layers merge into films
. Growing single-crystal hBN on such high-symmetry surface planes as Cu (111)
is widely believed to be impossible, even in theory. Nonetheless, here we report the successful epitaxial growth of single-crystal hBN monolayers on a Cu (111) thin film across a two-inch c-plane sapphire wafer. This surprising result is corroborated by our first-principles calculations, suggesting that the epitaxial growth is enhanced by lateral docking of hBN to Cu (111) steps, ensuring the mono-orientation of hBN monolayers. The obtained single-crystal hBN, incorporated as an interface layer between molybdenum disulfide and hafnium dioxide in a bottom-gate configuration, enhanced the electrical performance of transistors. This reliable approach to producing wafer-scale single-crystal hBN paves the way to future 2D electronics.
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.
Uncovering the thickness‐dependent electronic property and environmental stability for 2D materials are crucial issues for promoting their applications in high‐performance electronic and ...optoelectronic devices. Herein, the extrahigh air stability and giant tunable electronic bandgap of chemical vapor deposition (CVD)–derived few‐layer PdSe2 on Au foils, by using scanning tunneling microscope/spectroscopy (STM/STS), are reported. The robust stability of 2D PdSe2 is uncovered by the observation of nearly defect/adsorption‐free atomic lattices on long‐time air‐exposed samples. A one‐to‐one correspondence between the electronic bandgap (from ≈1.15 to ≈0 eV) and thickness of PdSe2/Au (from bilayer to bulk) is established. It is also revealed that few‐layer semiconducting PdSe2 flakes present zero‐gap edges, induced by hybridization of Pd 4d and Se 4p orbitals. This work hereby provides straightforward evidence for the thickness‐tunable electronic property and air stability of 2D semiconductors, thus shedding light on their applications in next‐generation electronic devices.
The thickness‐dependent electronic property and environmental stability for 2D PdSe2/Au are unveiled by scanning tunneling microscope/spectroscopy. The robust stability of 2D PdSe2 is uncovered on long‐time air‐exposed samples. Particularly, a one‐to‐one correspondence between the electronic bandgap and thickness of PdSe2/Au is established. Besides, zero‐gap edges are observed in the PdSe2 flakes on Au foils.
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.
Palladium diselenide (PdSe2) is an emerging 2D layered material with anisotropic optical/electrical properties, extra‐high carrier mobility, excellent air stability, etc. So far, ultrathin PdSe2 is ...mainly achieved via mechanical exfoliation from its bulk counterpart, and the direct synthesis is still challenging. Herein, the synthesis of ultrathin 2D PdSe2 on conductive Au foil substrates via a facile chemical vapor deposition route is reported. Intriguingly, an anisotropic growth behavior is detected from the evolution of ribboned flakes with large length/width ratios, which is well explained from the orthorhombic symmetry of PdSe2. A unique even‐layered growth mode from 2 to 20 layers is also confirmed by the perfect combination of onsite scanning tunneling microscopy characterizations, through deliberately scratching the flake edge to expose both even and odd layers. This even‐layered, ribboned 2D material is expected to serve as a perfect platform for exploring unique physical properties, and for developing high‐performance electronic and optoelectronic devices.
Ultrathin 2D PdSe2 is synthesized on novel Au foil substrates via a facile chemical vapor deposition route. An anisotropic growth behavior is detected from the evolution of ribboned flakes, which arises from the orthorhombic symmetry of PdSe2 and the unique metallic substrate of Au. A unique even‐layered growth mode is also confirmed by onsite scanning tunneling microscopy characterizations.
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have emerged as perfect platforms for developing applications in nano-electronics, catalysis, energy storage and environmental-related ...fields due to their superior properties. However, the low-cost, batch production of high-quality 2D TMDCs remains a huge challenge with the existing synthetic strategies. Herein, we present a scalable chemical vapor deposition (CVD) approach for the batch production of high-quality MoS
2
nanosheet powders, by using naturally abundant, water-soluble and recyclable NaCl crystal powders as templates. The high-quality MoS
2
nanosheets powders are achieved by a facile water dissolution-filtration process, by virtue of the excellent dispersibility of the as-grown products in water. The internal mechanism for the scalable synthesis strategy is explored. The applications of the MoS
2
nanosheets powders are also demonstrated as catalysts or adsorbents in hydrogen evolution reaction (HER) and organic dyes adsorption, respectively. This work should hereby pave ways for the mass production and application of powdery TMDCs in energetic and environmental related fields.
Kagome materials have recently garnered substantial attention due to the intrinsic flat band feature and the stimulated magnetic and spin-related many-body physics. In contrast to their bulk ...counterparts, two-dimensional (2D) kagome materials feature more distinct kagome bands, beneficial for exploring novel quantum phenomena. Herein, we report the direct synthesis of an ultrathin kagome-structured Co-telluride (Co9Te16) via a molecular beam epitaxy (MBE) route and clarify its formation mechanism from the Co-intercalation in the 1T-CoTe2 layers. More significantly, we unveil the flat band states in the ultrathin Co9Te16 and identify the real-space localization of the flat band states by in situ scanning tunneling microscopy/spectroscopy (STM/STS) combined with first-principles calculations. A ferrimagnetic order is also predicted in kagome-Co9Te16. This work should provide a novel route for the direct synthesis of ultrathin kagome materials via a metal self-intercalation route, which should shed light on the exploration of the intriguing flat band physics in the related systems.
As an emerging class of semiconducting transition metal dichalcogenides (TMDCs), two-dimensional (2D) rhenium dichalcogenides (ReX
2
, X = S or Se) have recently aroused great research interest due ...to their unique anisotropic structure (1T’ phase), and the related novel properties and applications. Recently, many efforts have been devoted to the controllable syntheses of high-quality monolayer or few-layer ReX
2
flakes/films by chemical vapor deposition (CVD), wherein the metallic Au foil is found to be a unique substrate, due to the relatively strong interfacial coupling between monolayer ReX
2
and Au. And the conductive nature of Au enables
in situ
characterizations of the as-grown ReX
2
samples, which is essential for exploring the fundamental properties and internal growth mechanisms. Hereby, this review focuses on the recent progresses on the CVD syntheses and
in situ
characterizations of high-quality monolayer ReX
2
flakes/films and their heterostructures with graphene on Au foils. The effects of Au foils on improving the crystal quality and inducing the growth of monolayer ReX
2
single crystals are intensively addressed. The crystallinity, domain morphology, atomic and electronic structures, as well as the growth behaviors of monolayer ReX
2
flakes/films and graphene/ReX
2
heterostructures on Au revealed by
in situ
characterization techniques are also highlighted. As contrasts, the growth behaviors of monolayer or few-layer ReX
2
on insulating substrates are also discussed. Besides, the potential applications of 2D ReX
2
in new-generation electronic, optoelectronic devices, and energy-related fields are also introduced. Finally, future research directions are also prospected for propelling the practical applications of 2D ReX
2
materials in more versatile fields.
Epitaxial growth of wafer-scale monolayer semiconducting transition metal dichalcogenide single crystals is essential for advancing their applications in next-generation transistors and highly ...integrated circuits. Several efforts have been made for the growth of monolayer MoS2 single crystals on high-symmetry Au(111) and sapphire substrates, while more prototype growth systems still need to be discovered for clarifying the internal mechanisms. Herein, we report the epitaxial growth of unidirectionally aligned monolayer MoS2 domains and single-crystal films on low-symmetry Au(101) vicinal facets via a facile chemical vapor deposition method. On-site scanning tunneling microscopy observations reveal the formation of a specific rectangular Moiré pattern along the 101̅ step edge of Au(101) and along its perpendicular direction. The perfect lattice constant matching of MoS2/Au(101) along the substrate high-symmetry directions (i.e., Au101̅, Au 010) as well as the step-edge-guiding effect are proposed to facilitate the robust epitaxy. Multiscale characterizations further confirm the domain-boundary-free feature of the monolayer MoS2 films merged by unidirectionally aligned monolayer domains. This work hereby puts forward a symmetry mismatched epitaxial system for the direct synthesis of monolayer MoS2 single crystals, which should deepen our understanding about the epitaxy of 2D layered materials and propel their applications in various fields.
PDF
