Dresden 2017 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 6: 2D Materials Beyond Graphene I (jointly with O)
DS 6.9: Vortrag
Montag, 20. März 2017, 12:30–12:45, REC/PHY C213
Van der Waals Epitaxy of Single Layer Transition Metal Dichalcogenides — •Joshua Hall1, Borna Pielić2, Tobias Wekking1, Marko Kralj2, and Thomas Michely1 — 1II. Physikalisches Institut, Universität zu Köln, Zülpicherstr. 77, D-50937 Köln — 2Center of Excellence for Advanced Materials and Sensing Devices, Institute of Physics, Bijenička 46, HR-10000 Zagreb
We employ molecular beam epitaxy on van der Waals substrates to grow epitaxial mono- to bilayer samples of transition metal dichalcogenides (TMDC). The scalability of the method allows for subsequent investigations such as angle resolved photo emission spectroscopy.
As substrates for our two step synthesis of the TMDC we use in situ fabricated graphene or a monolayer of hexagonal boron nitride. In the first synthesis step, at temperatures in the range from 100 K to 400 K, we expose the substrate to a metal vapor in the background of a sulfur pressure. As signified by low energy electron diffraction, already after this step, the TMDC forms. We find that the ratio of metal to sulfur flux is crucial for the growth mode of the TMDC. As a second step, the sample is annealed in the range of 800 K to 1100 K in a sulfur background. Annealing decreases epitaxial orientation scatter and enlarges domain sizes. It is limited in time and temperature by the onset of TMDC decomposition and intercalation of the educts under the van der Waals substrate monolayer. Our scanning tunneling microscopy studies document the versatility of the two step synthesis by providing examples for excellent quality monolayers of MoS2, WS2, TaS2 and VS2.