Non-metal Substrates Research Articles

Extremely High Intrinsic Carrier Mobility and Quantum Hall Effect Of Single Crystalline Graphene Grown on Ge(110)

AbstractThe successful synthesis of wafer‐scale single crystalline graphene on semiconducting Ge substrate has been considered a significant breakthrough toward the manufacturing of graphene‐based electronic and photonic devices; however, the assumed extremely high electrical mobility has not been found yet due to the lack of an adequate characterization method. Herein, state‐of‐the‐art transfer methods are developed to encapsulate the single crystalline graphene, which is grown on semiconducting Ge(110), in two hexagonal boron nitride (hBN) flakes, then acquire its inherent electrical mobility precisely via edge‐contact technique. It is found that single crystalline graphene grown on Ge(110) possesses a maximum carrier mobility of over 100 000 cm2 V−1 s−1 at low temperatures (2.3 K), which is superior to that obtained from graphene grown on other nonmetal substrates. Due to the extremely high mobility, well‐defined quantum Hall effect and Shubnikov‐de Haas oscillations can be observed at low temperatures as well. The study suggests that the excellent carrier mobility of graphene grown on Ge(110) may open an avenue to develop the practical graphene‐based nanodevices with high performance.

Versatile Epoxidized Soybean Oil-Based Resin with Excellent Adhesion and Film-Forming Property

Deriving environmentally friendly and renewable polymers from epoxidized plant oils (EPOs) is one of the promising strategies for realizing the sustainable development of materials industry. Direct crosslinking EPOs without pre-modifications is a straightforward, efficient, and cost-effective way for the utilization of EPOs. Herein, a facile and green strategy that crosslinks epoxidized soybean oil with highly branched and flexible polyamine via ring-opening and amidation polymerizations successfully produced a novel resin with exceptional properties and versatile potential applications. After completely cured, the resin appeared to be super strong structural adhesive as it provided a room-temperature bonding strength of 12–24 MPa for metal and non-metal substrates, as well as a steel bonding strength of 11.6 MPa at cryogenic temperature (−196 °C), which is far superior to the previously reported oil-based adhesives. Meanwhile, the resin exhibited excellent film-forming ability. Particularly, by controlling the curing temperature, the films with tunable mechanical properties were obtained with a tensile strength of 3–40 MPa and an elongation at break of 17–230%. The features of uncured resin, including liquid viscoelasticity, good wettability, and high molecular weight, make it a qualified pressure-sensitive adhesive which demonstrated satisfied peel strength for various substrates.

Semiconductor SERS on Colourful Substrates with Fabry-Pérot Cavities.

Non-metallic materials have emerged as a new family of active substrates for surface-enhanced Raman scattering (SERS), with unique advantages over their metal counterparts. However, owing to their inefficient interaction with the incident wavelength, the Raman enhancement achieved with non-metallic materials is considerably lower with respect to the metallic ones. Herein, we propose colourful semiconductor-based SERS substrates for the first time by utilizing a Fabry-Pérot cavity, which realize a large freedom in manipulating light. Owing to the delicate adjustment of the absorption in terms of both frequency and intensity, resonant absorption can be achieved with a variety of non-metal SERS substrates, with the sensitivity further enhanced by ≈100 times. As a typical example, by introducing a Fabry-Pérot-type substrate fabricated with SiO2 /Si, a rather low detection limit of 10-16 M for the SARS-CoV-2S protein is achieved on SnS2 . This study provides a realistic strategy for increasing SERS sensitivity when semiconductors are employed as SERS substrates.

The effect of enhanced heat transfer across metal-nonmetal interfaces subject to femtosecond laser irradiation.

The heat transfer across metal-nonmetal interfaces inevitably affects the femtosecond laser processing of thin metal films coated on nonmetal substrates. In the present work, a two-temperature model with a metal-nonmetal interface is employed to numerically investigate the heat transfer across a metal-nonmetal interface. A parallel-series thermal circuit is considered under the drastic electron-phonon nonequilibrium induced by femtosecond laser irradiation. The interfacial thermal resistance affects temporal evolutions of surface electron temperature and phonon temperature, as well as the optical response simulated by the Drude-Lorentz model. By inserting an interlayer and reducing the interfacial thermal resistance, the enhanced heat transfer across Au-Al2O3 and Au-Si interfaces is confirmed. More heat transfers from a metal to a nonmetal due to lower total interfacial thermal resistance, which reshapes the temperature distributions of metal-electrons, metal-phonons, and nonmetal-phonons. Consequently, the higher damage threshold of thin Au films and the lower sensitivity of damage threshold versus film thickness are determined. It implies that the heat transfer across metal-nonmetal interfaces is found to affect the transient thermal reflectivity detection and the repeatable femtosecond laser processing of thin metal films.

Formation of Titanium Oxide on Nonmetal Substrates and the Coordination Structure of Titanium Ions in Molten Lif-KF

Electrodeposition of titanium materials on substrates is an important technique to improve and functionalize the surface properties. Especially electrodeposition of titanium and titanium oxide on a material that is an insulator. However, electrodeposition of an insulator on another insulator is considered to be difficult. If such deposition can be accomplished, it would have a variety of practical applications in both mechanical and electronic industries. We are thus proposing a new method for electrodeposition of titanium oxide on alumina substrates in LiF-KF with the addition of TiO2 and metal titanium. We have carried out the electrodeposition to test hypotheses on deposition of titanium oxide on the alumina surface by employing the three electrodes method in the molten salt. The nickel-wire in contact with alumina substrate was employed as a working electrode to grow titanium oxide on the substrate by the proposed electrochemical process. Titanium oxide deposition grew from the three-phase interface of nickel wire, molten salt and alumina substrate in a radial pattern. The growth rate of the deposition was controlled by adjusting the electrochemical parameters. We have also investigated the melt structure of LiF-KF with the addition of TiO2 and the addition of bulk titanium by combining high temperature Raman spectroscopic technique and density functional theory calculations. These results provide new insight into the growth process of titanium oxide crystals and possibly a new comprehensive plating procedure for titanium oxide on insulator substrates.

Transfer- and lithography-free CVD of N-doped graphenic carbon thin films on non-metal substrates

Although CVD is a very promising approach to the synthesis of nitrogen-doped graphenic carbon thin films (N-GCTFs), the vast majority of methods require the use of a metal catalyst, and a post-deposition transfer process, which complicates the technology, as well as damages and contaminates the films. Here, we described a simple, low-cost and scalable approach for the completely direct (transfer- and lithography-free) deposition of N-GCTFs on dielectric substrates through pyrolysis of acetonitrile (CH3CN). GCTFs are defined as multi-layer graphene films with few-nm thickness. The N/C ratio is about 2–3%, and nitrogen is mainly contained in the graphitic form. Raman spectroscopy and TEM indicate a nanocrystalline structure of the films. The values of transmittance and sheet resistance are found significantly depending on the synthesis temperature and time. The films can be grown selectively on the e-beam pre-patterned areas of the substrates. We demonstrate this by lithography-free growing of N-GCTF microstructure.

Van der Waals Heteroepitaxy of Air-Stable Quasi-Free-Standing Silicene Layers on CVD Epitaxial Graphene/6H-SiC.

Graphene, consisting of an inert, thermally stable material with an atomically flat, dangling-bond-free surface, is by essence an ideal template layer for van der Waals heteroepitaxy of two-dimensional materials such as silicene. However, depending on the synthesis method and growth parameters, graphene (Gr) substrates could exhibit, on a single sample, various surface structures, thicknesses, defects, and step heights. These structures noticeably affect the growth mode of epitaxial layers, e.g., turning the layer-by-layer growth into the Volmer-Weber growth promoted by defect-assisted nucleation. In this work, the growth of silicon on chemical vapor deposited epitaxial Gr (1 ML Gr/1 ML Gr buffer) on a 6H-SiC(0001) substrate is investigated by a combination of atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Raman spectroscopy measurements. It is shown that the perfect control of full-scale almost defect-free 1 ML Gr with a single surface structure and the ultraclean conditions for molecular beam epitaxy deposition of silicon represent key prerequisites for ensuring the growth of extended silicene sheets on epitaxial graphene. At low coverages, the deposition of Si produces large silicene sheets (some hundreds of nanometers large) attested by both AFM and SEM observations and the onset of a Raman peak at 560 cm-1, very close to the theoretical value of 570 cm-1 calculated for free-standing silicene. This vibrational mode at 560 cm-1 represents the highest ever experimentally measured value and is representative of quasi-free-standing silicene with almost no interaction with inert nonmetal substrates. From a coverage rate of 1 ML, the silicene sheets disappear at the expense of 3D Si dendritic islands whose density, size, and thickness increase with the deposited thickness. From this coverage, the Raman mode assigned to quasi-free-standing silicene totally vanishes, and the 2D flakes of silicene are no longer observed by AFM. The experimental results are in very good agreement with the results of kinetic Monte Carlo simulations that rationalize the initial flake growth in solid-state dewetting conditions, followed by the growth of ridges surrounding and eventually covering the 2D flakes. A full description of the growth mechanism is given. This study, which covers a wide range of growth parameters, challenges recent results stating the impossibility to grow silicene on a carbon inert surface and is very promising for large-scale silicene growth. It shows that silicene growth can be achieved using perfectly controlled and ultraclean deposition conditions and an almost defect-free Gr substrate.

Amorphous Co(OH)2 nanocages achieving efficient photo-induced charge transfer for significant SERS activity

Boosting substrate–molecule interactions, especially the strong vibronic coupling and efficient photo-induced charge transfer (PICT) transitions, is a critical issue to improve the surface-enhanced Raman scattering (SERS) sensitivity of non-metal substrates.

Amorphous Ni(OH)2 nanocages as efficient SERS substrates for selective recognition in mixtures

Surface-enhanced Raman scattering (SERS) technology has become one of the most powerful tools for identifying trace analytes due to its outstanding merit of fingerprint spectrum. It has been found that noble metal (Ag, Au) materials can produce obvious surface plasmon resonance under visible light illumination, which can bring out a strong SERS effect. However, due to poor stability and non-selectivity, its practical applications are seriously hindered, especially for the detection of polluted water contaminating mixture organic pollutants. Herein, we designed an amorphous Ni(OH)2 nanocages (a-Ni(OH)2 NCs) substrate that exhibits an excellent SERS performance with good spectral stability and selectivity, which is attributed to the strong interfacial photo-induced charge transfer (PICT) mechanism between a-Ni(OH)2 NCs and molecules. Due to the effective vibrational coupling of a-Ni(OH)2 NCs and molecule under laser irradiation, the PICT transitions between a-Ni(OH)2 NCs and molecules evidently increase the molecular polarizability tensor and magnify molecular Raman scattering cross-section, resulting in a remarkable SERS activity. Besides, in wastewater containing several nitrogen and phosphorus pollutants, we successfully identified methylene blue and crystal violet molecules by using a-Ni(OH)2 NCs due to their selective recognition function. This research points out a new application direction for SERS technology in water pollution detection based on non-metal substrates, which widely broadens application prospects of SERS spectroscopy.

Growth of wrinkle-free and ultra-flat Bi-layer graphene on sapphire substrate using Cu sacrificial layer

The transfer process of chemical vapor deposition graphene film leads to unavoidable crack, wrinkles, doping, and contamination, which limits its function to establish stable and high-performance devices. It raises a growing interest to fabricate high-quality graphene on the target substrate directly. Here, bi-layer graphene (BLG) film can be grown on sapphire substrate by a Cu sacrificial layer using atmospheric-pressure chemical vapor deposition. The as-obtained BLG at the interface between sapphire and Cu layer is free of wrinkles, and the corresponding surface roughness Ra is as low as 0.66 nm. The square resistance of the graphene is 898.1 ohm sq−1, which is the lowest among the records of graphene film directly grown on nonmetal substrates.

Characterization of Surface Coating Techniques for Improved Performance

Surface coating has evolved with time, tracking the demands of the processing industry. This research activity, studies the significance of powder coatings in the evolution of existing conventional surface coating technology for their practical applications in the field of metal coating, particularly office and home appliances. The first objective of this work involves a systematic comparison between polymer powder coatings with liquid-based coatings. In the second objective, a comparison between the polymer coatings with additive filled powder coating was performed. Various conventional substrates (such as copper, aluminium, galvanized iron, brass, cement plank, wood block) were used for this study. The materials were first dry scuffed and then dipped in 3 in 1 chemical (zinc phosphate chemical and magnesium phosphate) for the primer coat. The prepared substrates were surface coated with liquid paint (on one side of the panel) using spray gun and powder paint (on another side of panel) using electrostatic spraying. The coated panels are then subjected to various standard (ISO) characterization techniques such as Scratch hardness test, Flexibility test, Thickness test, Adhesion test, Impact resistance test etc to analyze the effectiveness of the coatings applied. The quantitative and qualitative results thus obtained using powder coatings were promising (e.g: As the load progressively kept increasing i.e. 1000-2000 gm, mild scratches were noticeable on liquid coated substrates whereas powder coated metal panels have shown a greater resistance to scratch damage) as the test values determined high strength quality and durability (in-line with the standards) in comparison with liquid coatings. Also, the doping of additive (graphene) in small quantity has improved characteristics and qualities of the powder coated materials (e.g: graphene based powder coating has endured scratch hardness test beyond 2500 gms load force compared to simple powder coating). The findings of the current research study has confirmed the advantage of the powder coating technology and also deliberated the effect of fine powder flow ability. The important future prospects of this research work is that., powder coatings will stand on the threshold of exciting breakthroughs thus opening new frontiers by being able to coat thick steel components and even non-metal substrates. Also, the recent advances in powder coating technology with anticorrosive additives will result in bonded metallic coatings that deliver a unique, quality appearance.

Effects of active adsorption on thermodynamic equilibrium of solid-liquid interface

The effect of active adsorption on thermodynamic equilibrium of solid-liquid interface is analyzed. The results show that the Young’s equation is inapplicable in case of active adsorption at the solid-liquid interface. For the case of wetting balance with active adsorption, a new thermodynamic equilibrium equation was deduced, which has the same form of Young’s equation but implies a different physical meaning. The wetting force caused by adsorption is presented as an imaginative force, which promotes the liquid wetting at non-metal substrates. The estimation of wetting force for silicon reveals that the active element segregated at the solid-liquid interface plays an important role in thermodynamic equilibrium, and the wetting force is sufficient to drive the high-energy liquid metal to wet and spread on the surface of non-metal substrate.

Group-IV 2D materials beyond graphene on nonmetal substrates: Challenges, recent progress, and future perspectives

The family of two-dimensional materials has been expanding rapidly over the last few years. Within it, a special place is occupied by silicene, germanene, and stanene due to their inherent compatibility with the existing semiconductor technology (notably for the case of silicene and germanene). Although obtaining them is not trivial due to the lack of layered bulk counterparts from which they could be mechanically exfoliated, they have been recently synthesized on a number of metallic substrates. The remarkable interaction between metals and these puckered materials, however, strongly modifies their intrinsic electronic properties, and also jeopardizes their integration into functional devices. In this context, first experimental efforts are now being devoted to the synthesis of silicene, germanene, and stanene on nonmetal substrates. Here, we review these pioneering works, present the ongoing debate, analyze, and discuss the major technical challenges and finally suggest possible novel solutions worth exploring.

Chemical vapor deposition design of graphene powders toward energy applications

Graphene, sp2-bonded carbon atoms being regularly packed into a two-dimensional (2D) honeycomb structure, has attracted wide attentions, owing to its excellent electrical (the carrier mobility ~105 cm2 V–1 s–1), mechanical (~1.1 TPa), optical (the transparency of single layer graphene is about 97.7%) and thermal (the thermal conductivity ~5000 W m–1 K–1) properties. These unique properties make it suitable for use in transparent conductivity electrodes, field-electric transistors, photodetectors, light-emitting diodes, energy storage materials and many other areas. In particular, in comparison with the conventional 2D graphene films, three-dimensional graphene powders have presented great potentials in energy related applications because of their controllable structures, high specific surface areas and excellent electrical conductivity. There are mainly two synthetic routes for preparing graphene powder materials with specific structures and morphologies. One route deals with the preparation of graphite oxide sheets, then throughout chemical reduction process to obtain reduced graphene oxide. Although this method enables the realization of mass production of graphene powders with a relatively low cost, the materials obtained show quite poor crystal quality with high defect density, thereby greatly limiting the fast electron transport in high-energy-density and high-power-density energy storage devices. The other route is the chemical vapor deposition (CVD) growth of graphene powders with/without template-direction. Taking advantage of the CVD method, the crystal quality and electrical conductivity properties of graphene powders can be obviously improved. Meanwhile, the templates used during growth process can effectively control the morphologies of graphene powders, realizing graphene materials with high specific surface areas. Moreover, by selecting proper carbon sources or other reaction precursors, graphene powders with heteroatomic (N, B, P, S) doping can be achieved. This route facilitates mass production of high-crystal quality graphene with specific architecture, controllable layer numbers and effective heteroatomic doping, thus greatly promoting the application of graphene-based energy related devices. Herein, this review highlights the recent advances in the chemical vapor deposition design of graphene materials and their related energy applications. Firstly, a brief introduction with respect to the CVD synthesis of graphene powders, including template-directed growth and template-free growth is provided. Taking use of metal particles, oxide powders, chloride particles and biomineral materials as the growth substrates (templates), graphene powders with circular, cubic or other specific morphologies have been successfully synthesized. The growth mechanisms of graphene on metal substrates and non-metal substrates are also probed. Upon summarizing the direct growth methods of graphene powders by CVD and the related growth mechanisms, energy applications pertaining to batteries (lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, potassium-ion batteries), supercapacitors, printed energy storage devices and catalysts are further highlighted. Because of the unique characteristics of high electrical conductivity, large accessible surface area, and excellent electrochemical properties, graphene-based materials exhibit high performances in energy-related applications. Finally, further development and challenges of the CVD graphene materials in this emerging field are proposed.

Low-temperature epitaxy of transferable high-quality Pd(111) films on hybrid graphene/Cu(111) substrate

The continuous pursuit of miniaturization in the electronics and optoelectronics industry demands all device components with smaller size and higher performance, in which thin metal film is one heart material as conductive electrodes. However, conventional metal films are typically polycrystalline with random domain orientations and various grain boundaries, which greatly degrade their mechanical, thermal and electrical properties. Hence, it is highly demanded to produce single-crystal metal films with epitaxy in an appealing route. Traditional epitaxy on non-metal single-crystal substrates has difficulty in exfoliating away due to the formation of chemical bonds. Newly developed epitaxy on single-crystal graphene enables the easy exfoliation of epilayers but the annealing temperature must be high (typical 500–1,000 °C and out of the tolerant range of integrated circuit technology) due to the relative weak interfacial interactions. Here we demonstrate the facile production of 6-inch transferable high-quality Pd(111) films on single-crystal hybrid graphene/Cu(111) substrate with CMOS-compatible annealing temperature of 150 °C only. The interfacial interaction between Pd and hybrid graphene/Cu(111) substrate is strong enough to enable the low-temperature epitaxy of Pd(111) films and weak enough to facilitate the easy film release from substrate. The obtained Pd(111) films possess superior properties to polycrystalline ones with ~ 0.25 eV higher work function and almost half sheet resistance. This technique is proved to be applicable to other metals, such as Au and Ag. As the single-crystal graphene/Cu(111) substrates are obtained from industrial Cu foils and accessible in meter scale, our work will promote the massive applications of large-area high-quality metal films in the development of next-generation electronic and optoelectronic devices.

Gas adsorption induces the electronic and magnetic properties of metal modified divacancy graphene

In this study, based on density functional theory calculations, we investigated the stable configurations, electronic structures, and magnetic properties of metal and non-metal atom-modified graphene substrates. The single-atom metal embedded divacancy (555–777) graphene (555-777-graphene-M, M = Fe, Ni and Pd) exhibited high stability, and the 555-777-graphene-Fe system had a larger magnetic moment than the Ni-doped system. The adsorption of NO on 555-777-graphene-Fe (or -Ni) was more stable than that of the HCN, NH3 and SO2 molecules. Among the other substrates, the NO adsorbed on 555-777-graphene-Fe system had the largest magnetic moment (3.0 μB). The metal atoms anchored on 3Si doped 555–777 graphene (3Si-graphene-M) had larger adsorption energies than the corresponding cohesive energy values for the bulk metal. The gas molecules adsorbed on 3Si-graphene-M sheets were more stable than those on 555-777-graphene-M. NO can be detected easily as a specific gas molecule because it has the largest adsorption energy. The NH3 or NO adsorbed on different 3Si-graphene-M substrates could lose or gain less transferred electrons and they exhibited moderate stability, thereby indicating that they are more sensitive than other gases and can be detected easily. Moreover, the electronic structures and magnetic properties of 3NM-graphene-M sheets were regulated by selecting different gas molecules, thereby facilitating the design of novel graphene-based spintronic or gas sensor devices.

Influence of current density on the adhesion of seedless electrodeposited copper layers on silicon

Electrodeposition of metals directly on non-metal substrates without any seed layer reduces process steps; however, adhesion of the electrodeposited layer is a challenge. In this work, the influence of current density during seedless electroplating on the adhesion of Cu layers on Si substrates was investigated. Cu was electrodeposited on phosphorus-doped Si samples having different orientations in two stages. During the first stage, higher current densities were used for a few minutes to reach instantaneous nucleation and maximize the number of Cu islands on the substrate. The second stage had the goal of growing the nuclei previously formed. Therefore, lower current densities were used to create progressive nucleation. Adhesion values of Cu layers on Si were derived from scratch tests and tensile measurements. Higher adhesion was obtained either at higher current densities or at lower cathodic potentials at the beginning of potentiostatic or galvanostatic processes. To study the influence of hydrogen evolution on the adhesion of seedless electrodeposited Cu on Si, the transition time which indicates the moment when transferred charges are used to create hydrogen at the cathode, was determined experimentally. The transition time shows a strong dependence on current density. Therefore, control and optimization of adhesion by an appropriate choice of current densities within the two-stage process is possible.

Performance investigation of a new carbon–silver microspheres/epoxy resin superhydrophobic coating

ABSTRACTBased on the reaction of AgNO3 and dopamine-hydrochloride in the weak alkaline conditions, carbon–silver microspheres with layered structure were produced, which subsequently were surface-modified with 1H,1H,2H,2H-perfluorodecyltriethoxysilane to produce a superhydrophobic carbon–silver powder. By using the advantage of high viscosity epoxy resin, this powder can be used to various nonmetal substrates to form robust superhydrophobic coatings. The hydrophobicity, surface morphology, chemical composition, mechanical stability, chemical durability, self-cleaning, antifouling and thermal stability are studied by means of the contact angle metre, scanning electron microscope, X-ray photoelectron spectroscope measurements, three-dimensional topography metre and thermal gravimetric analyses. The results indicate that the prepared powder can be applied to most nonmetal substrates to form excellent superhydrophobic coatings with very good comprehensive performance.

Direct CVD Growth of Graphene on Traditional Glass: Methods and Mechanisms.

Chemical vapor deposition (CVD) on catalytic metal surfaces is considered to be the most effective way to obtain large-area, high-quality graphene films. For practical applications, a transfer process from metal catalysts to target substrates (e.g., poly(ethylene terephthalate) (PET), glass, and SiO2 /Si) is unavoidable and severely degrades the quality of graphene. In particular, the direct growth of graphene on glass can avoid the tedious transfer process and endow traditional glass with prominent electrical and thermal conductivities. Such a combination of graphene and glass creates a new type of glass, the so-called "super graphene glass," which has attracted great interest from the viewpoints of both fundamental research and daily-life applications. In the last few years, great progress has been achieved in pursuit of this goal. Here, these growth methods as well as the specific growth mechanisms of graphene on glass surfaces are summarized. The typical techniques developed include direct thermal CVD growth, molten-bed CVD growth, metal-catalyst-assisted growth, and plasma-enhanced growth. Emphasis is placed on the strategy of growth corresponding to the different natures of glass substrates. A comprehensive understanding of graphene growth on nonmetal glass substrates and the latest status of "super graphene glass" production are provided.

Ultrafast Growth of High-Quality Monolayer WSe2 on Au.

The ultrafast growth of high-quality uniform monolayer WSe2 is reported with a growth rate of ≈26 µm s-1 by chemical vapor deposition on reusable Au substrate, which is ≈2-3 orders of magnitude faster than those of most 2D transition metal dichalcogenides grown on nonmetal substrates. Such ultrafast growth allows for the fabrication of millimeter-size single-crystal WSe2 domains in ≈30 s and large-area continuous films in ≈60 s. Importantly, the ultrafast grown WSe2 shows excellent crystal quality and extraordinary electrical performance comparable to those of the mechanically exfoliated samples, with a high mobility up to ≈143 cm2 V-1 s-1 and ON/OFF ratio up to 9 × 106 at room temperature. Density functional theory calculations reveal that the ultrafast growth of WSe2 is due to the small energy barriers and exothermic characteristic for the diffusion and attachment of W and Se on the edges of WSe2 on Au substrate.