Sami, W., and A. Yassir. “Study on The Effect of Annealing On The Optical Properties of The Pure Lead Sulfide (PbS) Films and Doping by Copper”. Al-Qadisiyah Journal of Pure Science, Vol. 19, no. 4, Aug. 2017, pp. 42-49, https://journalsc.qu.edu.iq/index.php/JOPS/article/view/284.