Tungsten disulfide (WS 2 ) thin films are grown on several types of substrates by plasma-enhanced atomic layer deposition (PEALD) technique using tungsten hexacarbonyl [W(CO) 6 ] and H 2 S plasma at a relatively low temperature of 350 °C. The method delivers polycrystalline WS 2 film with (0 0 2) preferential growth and the high quality films could be successfully grown with as low as 30 ALD cycles (corresponding to ∼3 nm of thickness). Density functional theory (DFT) calculation results reveal that both adsorption of W(CO) 6 and removal of CO ligand would be facilitated by usage of H 2 S plasma by generating the different defect sites on the basal plane. The typical self-limiting film growth (growth rate of ∼0.1 nm/cycle), characteristic of ideal ALD, is clearly observed with both the precursor and reactant pulsing time. X-ray diffractometry (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Rutherford backscattering spectrometry (RBS) are performed in details to study the as-grown WS 2 film on Si/SiO 2 substrate. The analysis results confirm the formation of polycrystalline film, with high purity and well-defined stoichiometry. The as-deposited WS 2 films are then explored as an electrode in the field of energy generation as well as energy storage. The films are uniformly and conformally grown on high surface-area 3 dimensional Ni-foam that show excellent activity towards hydrogen evolution reaction (HER). Significantly low overpotential of ∼280 mV is observed at a high operational current density of 100 mA cm −2 during HER in acid electrolyte. In addition, the as-grown films on stainless steel substrate also reveal the stable electrochemical performances in Na-ion battery as an anode with reasonably high areal capacity of ∼44.5 μAh cm −2 at the end of 50 charge-discharge cycles.
Bibliographical noteFunding Information:
This work was supported by Mid-career Researcher Program through NRF grant funded by the MEST (2015R1A2A2A04004945), Korea Basic Science Institute under the R&D program (Project No. D38700) supervised by the Ministry of Science and ICT, Republic of Korea, a grant from the Advanced Technology Center (ATC) Program (10077265, Commercialization technology development of solid transition metal chloride precursor for semiconductor thin film) funded by the Ministry of Trade, Industry & Energy of the Republic of Korea, and the MOTIE (Ministry of Trade, Industry & Energy (#10080651) and KSRC (Korea Semiconductor Research Consortium) support program for the development of the future semiconductor device. The precursor used in this study was provided by UP Chemical Co. Ltd., Korea.
© 2018 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physics and Astronomy(all)
- Surfaces and Interfaces
- Surfaces, Coatings and Films