Effect of process parameters on structural and optical properties of sputter deposited WS2 films

In this work, tungsten disulfide films have been deposited by sputtering at room temperature on Si and glass substrates. The dependence of plasma power and deposition pressure on film properties was examined by X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, Raman spectroscopy, photoluminescence and ultraviolet-visible spectroscopy. SEM images clearly showed WS2 nanowall formation in which the lateral size is dependent on the growth conditions. The nano-wall dimensions increased with higher deposition pressure. The optical transmission, independent of the plasma power, was approximately 65% for films deposited at 1.99 Pa pressure, while the films deposited at 0.93 Pa showed a transmission of 20% between 600 and 2500 nm wavelength range. Raman spectra of the films indicated two prominent modes E12g which appears at -354 cm -1 due to in -plane vibration, and A1g mode which appears at -416 cm - 1 due to out -of -plane vibration mode. The peak positions slightly changed with deposition conditions. In addition, longitudinal vibration modes 2LA also observed around 351 cm -1. The photoluminescence measurements confirmed that the optical band gap of films was 1.97 eV. The photoluminescence full width at half maximum values decreased with increasing deposition pressure indicating improved optical transmission.