Controlled Growth of Transition Metal Dichalcogenide Monolayers using Knudsen-Type Effusion Cells for the Precursors
Result of the Month
XP spectra of the grown TMD monolayers on SiO2/Si wafers. (a) Mo 3d, S 2s and S 2p spectra of the MoS2 samples. (b) W 4f and S 2p spectra of the WS2 samples. As can be derived from the W 4f spectra, the total intensity composes of ∼ 60 % of the WS2 and ∼ 40 % of the WO3 − x species. For both (a) and (b) the intensity of S 2p spectra is multiplied by a factor of two. A detailed description of the spectra and their quantitative analysis are presented in the manuscript text and in the SI. Taken from [1] (CC BY 3.0) [2]
[1] A. George et al., J. Phys. Mater. 2 (2019) 016001
[2] http://creativecommons.org/licenses/by/3.0/
The OM images were taken with a Zeiss Axio Imager Z1.m microscope equipped with a 5 megapixel CCD camera (AxioCam ICc5) in bright field operation. (a) Schematic diagram of a typical sample grown by our modified CVD method. The grown crystals have a size distribution depending on the distance to the MoO3 source. Bigger crystals grow in the area closer to the MoO3 source. As the distance increases the crystal size decreases. (b)–(d) Optical microscopy images recorded from different areas of a typical sample. A stitched image of the complete sample is presented in figure S3. Taken from [1] (CC BY 3.0) [2]
[1] A. George et al., J. Phys. Mater. 2 (2019) 016001
[2] http://creativecommons.org/licenses/by/3.0/
Scienta Omicron Multiprobe MXPS system equipped with a monochromatized X-ray source (Al Kα), fine focus Ar+ ion source and an Argus CU electron analyser with a spectral energy resolution better than 0.6 eV.
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 MoS2 and WS2 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.
Author(s): Antony George1,2, Christof Neumann1, David Kaiser1, Rajeshkumar Mupparapu2,3, Tibor Lehnert4, Uwe Hübner5, Zian Tang1, Andreas Winter1, Ute Kaiser4, Isabelle Staude2,3 and Andrey Turchanin1,2,6
Institute(s):
1) Friedrich Schiller University Jena, Institute of Physical Chemistry, D-07743 Jena, Germany.
2) Abbe Centre of Photonics, D-07745 Jena, Germany.
3) Friedrich Schiller University Jena, Institute of Applied Physics, D-07743 Jena, Germany.
4) Ulm University, Central Facility of Materials Science Electron Microscopy, D-89081 Ulm, Germany.
5) Leibniz Institute of Photonic Technology, D-07745 Jena, Germany.
6) Jena Center for Soft Matter (JCSM), D-07743 Jena, Germany.
URL of the Institute(s): http://www.apc.uni-jena.de/
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