Nanoscale physics
Influence of size effect on the optical characteristics of CdS thin films
Petrus R.Yu.1, Semkiv I.V.1, Ilchuk H.A.1, Zmiiovska E.O.1, Kashuba A.I.1,2, Lopatynskyi I.Y.1
1 Lviv Polytechnic National University, 12, S. Bandera Str., Lviv-79013, Ukraine. 
E-mail: Semkiv.Igor.5@gmail.com
2 Ivan Franko National University of Lviv, 107, Tarnavsky Str., Lviv-79005, Ukraine.

CdS thin films were obtained by RF magnetron sputtering (13.6 МHz) using the VUP-5M (Selmi) by methodology [1]. 16×8 mm quartz substrates were used for deposition. Before the film deposition, the substrate surface was cleaned by boiling in a high purity CCl4 solution during 0.25 h.
The target for RF magnetron sputtering was monocrystalline CdS disk with 99.999 % purity, 1 mm thickness and 40 mm diameter [1]. The distance between the target and the substrate during the deposition process was 75 mm. Sputtering was carried out in the argon atmosphere with its pressure of 1.0-1.3 Pa. The substrates temperature was maintaining ~ 400 K.
The X-ray analysis shows that CdS thin films are a single phase and belongs P63mc space group. The thickness of the films was depended by the time of deposition. The thickness of the obtained films was measured by the Dektak 8 profilometer. The optical transmission was measured using a spectrophotometer Shimadzu UV-3600.
From optical absorption spectra was obtained the value of band gaps of different CdS thin films. As well was identification that all samples belong to semiconductors with a direct band gap, which coincides with literature data [2, 3]. Also, we presented the changes in the optical absorption edge (band gap value) from the thickness of CdS films.

1.	Petrus R.Yu., Ilchuk H.A., Kashuba A.I., Semkiv I.V., Zmiiovska E.O. Optical-energy properties of CdS thin films obtained by the method of high-frequency magnetron sputtering // Optics and Spectroscopy-2019.-126, N 3.-P. 220-225.
2.	Kumar V., Sharma S.Kr., Sharma T.P., Singh V. Band gap determination in thick films from refectance measurements // Optical Materials.-1999.-12.-P. 115-119.
3.	Deligoz E., Colakoglu K., Ciftci Y. Elastic, electronic, and lattice dynamical properties of CdS, CdSe, and CdTe // Physica B.-2006.-373.-P. 124-130.