Two-dimensional transition metal dichalcogenides (TMDs) have attracted lots of interest because of their potential for electronic and optoelectronic applications. Atomically thin TMD flakes were believed capable to scroll into nanoscrolls (NSs) with distinct properties. However, limited by mechanical strength and chemical stability, production of high-quality TMD NSs remains challenging. Here, we scroll chemical vapor deposition-grown monolayer TMD flakes into high-quality NSs in situ in 5 s with a nearly 100% yield by only one droplet of ethanol solution. An obvious photoluminescence is demonstrated in NSs and the self-encapsulated structure makes NSs more insensitive to external factors in optical and electrical properties. Furthermore, based on the internal open topology, NSs hybridized with a variety of functional materials have been fabricated, which is expected to confer TMD NSs with additional properties and functions attractive for potential application.
It has been generally accepted that iron-group metals (iron, cobalt, nickel) consistently show the highest catalytic activity for the growth of carbon nanomaterials, including carbon nanotubes (CNTs) and graphene. However, it still remains a challenge for them to obtain uniform graphene, because of their high carbon solubility, which can be attributed to an uncontrollable precipitation in cooling process. The quality and uniformity of the graphene grown on low-cost iron-group metals determine whether graphene can be put into the mass productions or not. Here, we develop a novel strategy to form an antiperovskite layer using ambient-pressure chemical vapor deposition (APCVD), which, so far, is the only known way for iron-group metals to prepare uniform monolayer graphene with 100% surface coverage. Our strategy utilizes liquid metal (e.g., gallium) to assist iron-group metals to form an antiperovskite layer that is chemically stable throughout the high-temperature growth process and then to seal the passageway of carbon segregation from the metal bulk during cooling. With the advantage of forming antiperovskite structure, the uniform monolayer graphene can always be obtained under the variations of experimental conditions. Our strategy solves the problem about how to get uniform graphene film on high-solubility carbon substrate, to utilize the high catalytic activity of low-cost iron-group metals and to realize low-temperature growth by chemical vapor deposition.
The high‐contrast optical imaging of nearly transparent 2D materials such as clays and some oxide sheets has been an outstanding challenge; yet there is a critical research capability needed in the synthesis and processing of these materials, which show promise in a number of applications including barrier coatings, membranes, and composites. Using delaminated silicate clay and titania sheets as model systems, here it is shown that these weakly quenching, nearly transparent 2D sheets can be readily imaged by fluorescence quenching microscopy (FQM) based on a new mechanism. When these sheets are deposited on strongly quenching substrates, including doped silicon wafers and metals or indium tin oxide‐coated glass slides, they can act as a “spacer” to reduce the degree of quenching of the dye layer by the substrate, appearing as highly visible bright sheets against a dark background. This new FQM strategy can visualize dielectric 2D materials with high contrast and layer resolutions comparable to scanning electron microscopy and atomic force microscopy. When different 2D materials are co‐deposited, FQM not only differentiates them readily based on their quenching capabilities, but also can resolve their vertical stacking sequence based on the contrast of their overlapped areas.
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