Improved properties arise in transition metal dichalcogenide (TMDC) materials when they are stacked onto insulating hexagonal boron nitride (h-BN). Therefore, the scalable fabrication of TMDCs/h-BN heterostructures by direct chemical vapor deposition (CVD) growth is highly desirable. Unfortunately, to achieve this experimentally is challenging. Ideal substrates for h-BN growth, such as Ni, become sulfides during the synthesis process. This leads to the decomposition of the pregrown h-BN film, and thus no TMDCs/h-BN heterostructure forms. Here, we report a thoroughly direct CVD approach to obtain TMDCs/h-BN vertical heterostructures without any intermediate transfer steps. This is attributed to the use of a nickel-based alloy with excellent sulfide-resistant properties and a high catalytic activity for h-BN growth. The strategy enables the direct growth of single-crystal MoS2 grains of up to 200 μm(2) on h-BN, which is approximately 1 order of magnitude larger than that in previous reports. The direct band gap of our grown single-layer MoS2 on h-BN is 1.85 eV, which is quite close to that for free-standing exfoliated equivalents. This strategy is not limited to MoS2-based heterostructures and so allows the fabrication of a variety of TMDCs/h-BN heterostructures, suggesting the technique has promise for nanoelectronics and optoelectronic applications.
Owing to the development of electronic devices moving toward high power density, miniaturization, and multifunction, research on thermal interface materials (TIMs) is become increasingly significant. Graphene is regarded as the most promising thermal management material owing to its ultrahigh in-plane thermal conductivity. However, the fabrication of high-quality vertical graphene (VG) arrays and their utilization in TIMs still remains a big challenge. In this study, a rational approach is developed for growing VG arrays using an alcohol-based electric-field-assisted plasma enhanced chemical vapor deposition. Alcohol-based carbon sources are used to produce hydroxyl radicals to increase the growth rate and reduce the formation of defects. A vertical electric field is used to align the graphene sheets. Using this method, high-quality and vertically aligned graphene with a height of 18.7 µm is obtained under an electric field of 30 V cm −1 . TIMs constructed with the VG arrays exhibit a high vertical thermal conductivity of 53.5 W m −1 K −1 and a low contact thermal resistance of 11.8 K mm 2 W −1 , indicating their significant potential for applications in heat dissipation technologies.
Magnetite (Fe3O4) is an attractive electrode material due to its high theoretical capacity, eco-friendliness, and natural abundance. However, its commercial application in lithium-ion batteries is still hindered by its poor cycling stability and low rate capacity resulting from large volume expansion and low conductivity. We present a new approach which makes use of supercritical carbon dioxide to efficiently anchor Fe3O4 nanoparticles (NPs) on graphene foam (GF), which was obtained by chemical vapor deposition in a single step. Without the use of any surfactants, we obtain moderately spaced Fe3O4 NPs arrays on the surface of GF. The particle size of the Fe3O4 NPs exhibits a narrow distribution (11 ± 4 nm in diameter). As a result, the composites deliver a high capacity of about 1200 mAh g(-1) up to 500 cycles at 1 C (924 mAh g(-1)) and about 300 mAh g(-1) at 20 C, which reaches a record high using Fe3O4 as anode material for lithium-ion batteries.
Developing a simple and industrially scalable method to produce graphene with high quality and low cost will determine graphene's future. The two conventional approaches, chemical vapor deposition and liquid-phase exfoliation, require either costly substrates with limited production rate or complicated post treatment with limited quality, astricting their development. Herein, an extremely simple process is presented for synthesizing high quality graphene at low-cost in the gas phase, similar to "snowing," which is catalyst-free, substrate-free, and scalable. This is achieved by utilizing corona discharge of SiO /Si in an ordinary household microwave oven at ambient pressure. High quality graphene flakes can "snow" on any substrate, with thin-flakes even down to the monolayer. In particular, a high yield of ≈6.28% or a rate of up to ≈0.11 g h can be achieved in a conventional microwave oven. It is demonstrated that the snowing process produces foam-like, fluffy, 3D macroscopic architectures, which are further used in strain sensors for achieving high sensitivity (average gauge factor ≈ 171.06) and large workable strain range (0%-110%) simultaneously. It is foreseen that this facile and scalable strategy can be extended for "snowing" other functional 2D materials, benefiting their low-cost production and wide applications.
Zhang and co-workers developed a rational approach to growing a new family of semiconducting SWNTs: (n, n À 1) carbon nanotubes. Combined with catalyst design, both large-diameter (>2 nm) (n, n À 1) SWNTs and single-chirality (10, 9) SWNTs with abundances of 88% and >80%, respectively, were successfully realized. This strategy opens up a new route for the growth of SWNT families beyond catalyst design.
Finding the best applications of graphene, and the continuous and scalable preparation of graphene with high quality and high purity, are still two major challenges. Herein, a “pulse‐etched” microwave‐induced “snowing” (PEMIS) process is developed for continuous and scalable preparation of high‐quality and high‐purity graphene directly in the gas phase, which is found to have excellent thermotherapeutic effects. The obtained graphene exhibits small size (≈180 nm), high quality, low oxygen content, and high purity, together with a high gas–solid conversion efficiency of ≈10.46%. Considering the intrinsic characteristics of this high‐purity and small‐sized biocompatible graphene, in particular the low‐frequency microwave absorption property as well as the good thermal transformation ability, a graphene‐based combination therapeutic system is demonstrated for microwave thermal therapy (MTT) for the first time, exhibiting a high tumor ablation rate of ≈86.7%. This is different from the principle of ions vibrating in a confined space used by current MTT sensitization materials. Not limited to this application, it is foreseen that this PEMIS‐based high‐quality graphene will allow the search for further suitable applications of graphene.
Conversion reaction electrode materials (CREMs) have gained significant interest in lithium-ion batteries (LIBs) owing to their high theoretical gravimetric capacity. However, traditional CREMs-based electrodes, with large strain arising from Li(+) intercalation/deintercalation causes pulverization or electrical breakdown and cracking of the active materials which leads to structural collapse, limiting performance. Therefore, in order to construct electrodes with a strong tolerance to the strain incurred during the conversion reaction process, we design a coral-like three-dimensional (3D) hierarchical heterostructure by using cross-linked nanoflakes interspersed with nanoparticles (NPs) standing vertically on graphene foam (GF). The coral-like 3D hierarchical heterostructures can efficiently disperse the strain from both internal and external forces as well as increase the specific surface area for enhanced electrochemical reactions. These features lead to long-cycle stability and excellent flexibility in LIBs. Fe3O4 NPs and CoO NFs are utilized as a model system to demonstrate our strategy. The as-prepared coral-like hierarchical electrode is studied as an anode in LIBs for the first time and is shown to deliver a high reversible specific gravimetric capacity of ∼1200 mA h g(-1) at a rate of 0.5 A g(-1) for 400 cycles. In addition, our batteries can even power a green light-emitting diode when bent to high degrees confirming the excellent flexibility of the material.
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