Dresden 2020 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 22: 2D Materials and their Heterostructures I (joint session DS/HL/O)
HL 22.3: Talk
Tuesday, March 17, 2020, 10:00–10:15, CHE 89
Growth of ultra-thin large sized 2D WS2 flakes in at air-liquid interface — •Talha Nisar1, Torsten Balster1, Ali Haider2, and Veit Wagner1 — 1Department of Physics and Earth Science, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany — 2Department of Life Sciences and Chemistry, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany
2D tungsten disulfide (WS2) flakes were obtained at the air-liquid interface by a technique recently developed [1]. For this purpose, aqueous solution of ammonium tetrathiotungstate (ATTW) is used as precursor. The process exhibit a clear temperature dependence. At the room temperature, no flakes are observed. When the aqueous solution of ATTW is kept at 80∘C, formation of flakes is observed. These flakes can be transferred from the air-liquid interface to a silicon substrate by a controlled dip-coating process. Large flakes with lateral size of up to 100µm were obtained. Thicknesses ranging from bilayer WS2 to 5 MLs as measured by atomic force microscopy. Various spectroscopic techniques (FTIR, Raman, UV-Vis and XPS) are applied to investigate the chemical reaction mechanism for the formation of the flakes. These results show that the initial flakes are made of WO3. The obtained flakes are converted to WS2 by a post annealing step at 500-900 ∘C with an additional sulfur source in Ar/H2 environment. The successful conversion to WS2 after annealing is confirmed by Raman and XPS. This non-expensive growth technique can be used to produce large WS2 flakes for various applications. [1] X. Zeng, et al, Nanoscale, 2017, 9, 6575-6580