Growth Control of WS2: From 2D Layer by Layer to 3D Vertical Standing Nanowalls


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Kocak Y., Gür E.

ACS APPLIED MATERIALS & INTERFACES, vol.12, no.13, pp.15785-15792, 2020 (Journal Indexed in SCI) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 12 Issue: 13
  • Publication Date: 2020
  • Doi Number: 10.1021/acsami.9b18759
  • Title of Journal : ACS APPLIED MATERIALS & INTERFACES
  • Page Numbers: pp.15785-15792
  • Keywords: WS2, WS2 nanowalls, 2D materials, RF sputtering, transition metal dichakogenides, thickness dependence of 2D materials, MONOLAYER, PHOTODETECTORS

Abstract

Large area 2D WS2 has been grown successfully by radio frequency magnetron sputtering (RFMS) method. First, in order to investigate the pressure dependence on the grown WS2 samples, WS2 were grown at 5 different growth pressures, 5, 10, 15, 20, and 25 mTorr. It has been observed that the surface morphology changes for the samples grown at higher growth pressures, 15, 20, and 25 mTorr. Vertically standing nanowall (NW)-like structures have been formed at these relatively high growth pressures. It has also been observed that the (002) plane is highly dominant, which means layer by layer growth parallel to the substrate, for the sample grown at 20 mTorr. X-ray photoelectron spectroscopy (XPS) measurements revealed an increasing atomic percentage of the S element to W element, S/W, ratio in thin films, as the growth pressure increases. Growth dynamics of WS2 has been investigated by time-dependent-growth WS2 samples, 5, 10, 20, 40, and 80 s under 20 mTorr pressure. It has been shown by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy that a highly smooth surface has been achieved in the samples grown for the duration of 5 and 10 s. Raman mapping measurements on the sample grown at 5 s have revealed large area homogeneous growth. As the growth time gets longer, the NWs emerge on the surface at some nudeation points. Only the peak that belongs to the (002) plane has been observed for samples grown at 5 and 10 s by the X-ray diffraction (XRD) measurements. XRD measurements have revealed the appearance of turbostratic peaks of (11l) and (10l) as the thickness increases. Photoluminescence measurements have indicated near-band-edge emission centered at 630 nm for only 5 and 10 s samples.