Shaolong Jiang

Batch production of 6-inch uniform monolayer molybdenum disulfide catalyzed by sodium in glass

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.Growth of large-area monolayer transition metal dichalcogenides is critical for their application but remains challenging. Here Yang et al. report rapid chemical vapor deposition of 6-inch monolayer molybdenum disulfide by sufficiently uniformly supplying the precursors and catalysts.

Application of chemical vapor–deposited monolayer ReSe2 in the electrocatalytic hydrogen evolution reaction

Controlled synthesis of structurally anisotropic rhenium diselenide (ReSe2) with macroscopically uniform and strictly monolayer thickness as well as tunable domain shape/size is of great interest for electronics-, optoelectronics-, and electrocatalysis-related applications. Herein, we describe the controlled synthesis of uniform monolayer ReSe2 flakes with variable morphology (sunflower- or truncated-triangle-shaped) on SiO2/Si substrates using different ambient-pressure chemical vapor deposition (CVD) setups. The prepared polycrystalline ReSe2 flakes were transferred intact onto Au foil electrodes and tested for activity in the hydrogen evolution reaction (HER). Interestingly, compared to the compact truncated-triangle-shaped ReSe2 flakes, their edge-abundant sunflower-shaped counterparts exhibited superior electrocatalytic HER activity, featuring a relatively low Tafel slope of ∼76 mV/dec and an exchange current density of 10.5 μA/cm2. Thus, our work demonstrates that CVD-grown ReSe2 is a promising two-dimensional anisotropic material for applications in the electrocatalytic HER.

Structure-dependent electrical conductivity of protein: its differences between alpha-domain and beta-domain structures

Electron transports in the α-domain and β-domain of proteins have been comprehensively investigated. The structure-dependent electron transport of proteins has been experimentally measured and theoretically simulated, and both the theoretical and experimental results demonstrate significant differences in electrical conductivity between the α-domain and β-domain. By controlling the feedback system of the scanning tunneling microscope (STM), the conductance of a single α-domain protein hemoglobin (Hgb) and a β-domain protein superoxide dismutase enzyme (SOD) were measured, respectively. The current signal of Hgb is obviously stronger, indicating that the α-domain is more conductive. To confirm our finding, molecular orbitals of both the β-domain in SOD and α-domain in Hgb have been analyzed based on first-principles calculations. As expected, tunneling transport and hopping in the α-domain are both more efficient, indicating that it is easier for electrons to transport through the α-domain, which are in great agreement with our experimental data. In order to explain our results, molecular structures of α- and β-domains have been carefully analyzed and show that the explanation should lie in the differences in packing mode between the α-domain and β-domain. This research should be very important to application prospects in molecular electronics.

Direct synthesis and in situ characterization of monolayer parallelogrammic rhenium diselenide on gold foil

Rhenium diselenide (ReSe2) has recently garnered great research interest due to its distorted 1T structure, anisotropic physical properties, and applications in polarization-sensitive photodetectors. However, ReSe2 synthesized by chemical vapor deposition (CVD) is usually a multilayer/polycrystalline material containing numerous grain boundaries, thereby hindering its further applications. Here we describe the direct CVD growth of high-quality monolayer ReSe2 single crystals with a parallelogram shape arising from its anisotropic structure on a gold foil substrate. In particular, we use low-energy electron microscopy/diffraction combined with scanning tunneling microscopy/spectroscopy to determine the atomic-scale structure, domain orientation/boundaries, and band features of monolayer ReSe2 flakes grown directly on gold foils. This work may open new opportunities for the direct synthesis and in situ characterization of CVD-grown monolayer ReSe2.Improving the synthesis of crystalline monolayer transition metal dichalcogenides requires insight into domain and boundary structures. Here, the authors produce monolayer rhenium diselenide by chemical vapour deposition onto gold foil, allowing in situ analysis of domain and defect structure.

Temperature-dependent Raman spectroscopy studies of the interface coupling effect of monolayer ReSe2 single crystals on Au foils

Rhenium diselenide (ReSe2), which bears in-plane anisotropic optical and electrical properties, is of considerable interest for its excellent applications in novel devices, such as polarization-sensitive photodetectors and integrated polarization-controllers. However, great challenges to date in the controllable synthesis of high-quality ReSe2 have hindered its in-depth investigations and practical applications. Herein, we report a feasible synthesis of monolayer single-crystal ReSe2 flakes on the Au foil substrate by using a chemical vapor deposition route. Particularly, we focus on the temperature-dependent Raman spectroscopy investigations of monolayer ReSe2 grown on Au foils, which present concurrent red shifts of Eg-like and Ag-like modes with increasing measurement temperature from 77-290 K. Linear temperature dependences of both modes are revealed and explained from the anharmonic vibration of the ReSe2 lattice. More importantly, the strong interaction of ReSe2 with Au, with respect to that with SiO2/Si, is further confirmed by temperature-dependent Raman characterization. This work is thus proposed to shed light on the optical and thermal properties of such anisotropic two-dimensional three-atom-thick materials.

Vertical 1T-TaS2 Synthesis on Nanoporous Gold for High-Performance Electrocatalytic Applications

2D metallic TaS2 is acting as an ideal platform for exploring fundamental physical issues (superconductivity, charge-density wave, etc.) and for engineering novel applications in energy-related fields. The batch synthesis of high-quality TaS2 nanosheets with a specific phase is crucial for such issues. Herein, the successful synthesis of novel vertically oriented 1T-TaS2 nanosheets on nanoporous gold substrates is reported, via a facile chemical vapor deposition route. By virtue of the abundant edge sites and excellent electrical transport property, such vertical 1T-TaS2 is employed as high-efficiency electrocatalysts in the hydrogen evolution reaction, featured with rather low Tafel slopes ≈67-82 mV dec-1 and an ultrahigh exchange current density ≈67.61 µA cm-2 . The influence of phase states of 1T- and 2H-TaS2 on the catalytic activity is also discussed with the combination of density functional theory calculations. This work hereby provides fundamental insights into the controllable syntheses and electrocatalytic applications of vertical 1T-TaS2 nanosheets achieved through the substrate engineering.

Na-assisted fast growth of large single-crystal MoS 2 on sapphire

Monolayer molybdenum sulfide (MoS2), a typical semiconducting transition metal dichalcogenide, has emerged as a perfect platform for next-generation electronics and optoelectronics due to its sizeable band gap and strong light-matter interactions. Nevertheless, the controlled growth of a monolayer MoS2 single-crystal with a large-domain size and high crystal quality still faces great challenges. Herein, we demonstrate the fast growth of a large-domain monolayer MoS2 on the c-plane sapphire substrate with the assistance of sodium chloride (NaCl) crystals as the intermediate promoter. Particularly, the volatilization temperature of the NaCl crystal and the growth temperature of MoS2 are established to be the key parameters that influence the growth efficiency of MoS2 at an optimized growth condition. Monolayer triangular MoS2 domain with an edge length ∼300 μm is obtained within 1 min, featured with a growth rate ∼5 μm s-1. The Na element from the NaCl crystal is found to be able to facilitate the two dimensional growth of monolayer MoS2. This work thus offers novel insights into the high-efficiency production of large-domain monolayer MoS2 on insulating growth substrates.

Space-confined growth of monolayer ReSe2 under a graphene layer on Au foils

Vertical heterostructures based on two-dimensional (2D) materials have attracted widespread interest for their numerous applications in electronic and optoelectronic devices. Herein, we report the direct construction of an abnormal graphene/ReSe2 stack on Au foils by a two-step chemical vapor deposition (CVD) strategy. During the second growth stage, monolayer ReSe2 is found to preferentially evolve at the interface between the first-grown graphene layer and the Au substrate. The unusual stacking behavior is unraveled by in-situ “cutting open” the upper graphene from the defects to expose the lower ReSe2 using scanning tunneling microscopy (STM). From combination of these results with density functional theory calculations, the domain boundaries and edge sites of graphene are proposed to be adsorption sites for Re and Se precursors, further facilitating the growth of ReSe2 at the van der Waals gap of graphene/Au. This work hereby offers an intriguing strategy for obtaining vertical 2D heterostructures featured with an ultra-clean interface and a designed stacking geometry.

Identifying the Non-Identical Outermost Selenium Atoms and Invariable Band Gaps across the Grain Boundary of Anisotropic Rhenium Diselenide

Rhenium diselenide (ReSe2) is a unique transition-metal dichalcogenide (TMDC) possessing distorted 1T structure with a triclinic symmetry, strong in-plane anisotropy, and promising applications in optoelectronics and energy-related fields. So far, the structural and physical properties of ReSe2 are mainly uncovered by transmission electron microscopy and spectroscopy characterizations. Herein, by combining scanning tunneling microscopy and spectroscopy (STM and STS) with first-principles calculations, we accomplish the on-site atomic-scale identification of the top four non-identical Se atoms in a unit cell of the anisotropic monolayer ReSe2 on the Au substrate. According to STS and photoluminescence results, we also determine the quasiparticle and optical band gaps as well as the exciton binding energy of monolayer ReSe2. In particular, we detect a perfect lattice coherence and an invariable band gap across the mirror-symmetric grain boundaries in monolayer and bilayer ReSe2, which considerably differ from the traditional isotropic TMDCs featured with defect structures and additional states inside the band gap. Such essential findings should deepen our understanding of the intrinsic properties of two-dimensional anisotropic materials and provide fundamental references for their applications in related fields.