Controlled growth of transition metal dichalcogenide monolayers using Knudsen-type effusion cells for the precursors

Abstract

Controlling the flow rate of precursors is essential for the growth of high quality monolayer single crystals of transition metal dichalcogenides (TMDs) by chemical vapor deposition. Thus, introduction of an excess amount of the precursors affects reproducibility of the growth process and results in the formation of TMD multilayers and other unwanted deposits. Here we present a simple method for controlling the precursor flow rates using the Knudsen-type effusion cells. This method results in a highly reproducible growth of large area and high density TMD monolayers. The size of the grown crystals can be adjusted between 10 and 200 μm. We characterized the grown MoS 2 and WS 2 monolayers by optical, atomic force and transmission electron microscopies as well as by x-ray photoelectron, Raman and photoluminescence spectroscopies, and by electrical transport measurements showing their high optical and electronic quality based on the single crystalline nature.

Scalable Functionalization of Optical Fibers Using Atomically Thin Semiconductors

“…These values do not significantly differ from the ones reported on planar substrates grown by the same technique. [16] We thus conclude the material properties are comparable to those grown on planar substrates and no additional strain has been induced, e.g. due to different thermo-mechanical properties of the substrate.…”

“…Details of the method are given in ref. [16], from which no modifications were made, except for the usage of ECFs as the substrate. The grown TMDs on the ECFs were initially characterized using optical microscopy (Zeiss Axio Imager Z1.m) and Raman www.advmat.de www.advancedsciencenews.com spectroscopy (Bruker Senterra spectrometer operated in backscattering mode using 532 nm wavelength obtained with a frequency doubled Nd:YAG Laser, a 100× objective and a thermoelectrically cooled CCD detector).…”

“…The growth is facilitated by a modified chemical vapour deposition (CVD) process. [16] ECFs are compatible with this process, because they consist entirely of silica, which is a well-studied substrate material for hightemperature CVD processes and in particular for the growth of TMDs. The process yields interspersed monolayer TMD crystals of high quality with a typical length of 20 µm on ECFs with a length of a few centimeters.…”

“…This spacing is consistent with that expected for CVD-grown monolayer TMDs. [16,17] Examples of alternative growth modes together with their Raman spectra are displayed in Figure S2c-e. For more information on the growth process, please see the Experimental Section.…”

Integration of two-dimensional transition metal dichalcogenides with Mie-resonant dielectric nanostructures

“…Similar to graphene, the layered structure allows us to obtain even individual layers by direct mechanical exfoliation from a bulk crystal as shown in Figure 1(b). Recently, significant efforts went into the optimization of synthesis methods, including chemical vapor deposition (CVD) [14] and molecular beam epitaxy (MBE) [15] to achieve isolated single-crystal monolayers with high yield, high quality, and large size distribution [16]. For instance, singlecrystal MoS 2 monolayers grown by CVD are shown in Figure 1(c), typically forming a triangular shape dictated by the crystal symmetry.…”