Compositional ratio effect on the physicochemical properties of SnSe thin films

In this study, tin selenide thin films with different atomic ratio combinations were fabricated utilizing the RF magnetron co-sputtering method. In order to analyze the innate physicochemical properties of the thin films, various characterization tools such as scanning electron microscope (SEM), atomic force microscope (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and contact angle measurements were used. SEM and AFM images revealed that incorporating higher amounts of Se increases the resulting grain size and surface roughness. Additionally, Se incorporated thin films were amorphous in nature, which was confirmed by XRD results. From the XPS spectra, the Sn 3d5/2 peak was deconvoluted into three peaks: (Sn4+, 487 ± 0.3 eV), (Sn2+, 486.3 ± 0.3 eV), (Sn0, 484.9 ± 0.3 eV) and the Sn4+ species only existed in pure Sn thin films potentially due to inevitable surface oxidation. UPS and Kelvin probe (KP) measurements were conducted to calculate work function values. Based on UPS results, the work function values increased from 4.29 eV to 6.01 eV with increasing Se content. Similarly, the work function values from KP measurements increased from 4.84 eV to 5.71 eV with increasing Se content. Using data from contact angle measurements, it was deduced that pure Sn thin films are hydrophobic but become more hydrophilic with increasing Se content.