The Effect of Thickness and Deposition Angle on Optical Transmittance of ZnS/Ag Nanostructures

Abstract

This paper presents the optical transmittance properties of thermally evaporated coatings of ZnS/Ag nanostructures as a function of film thickness and deposition angle designed to mitigate the challenges of indoor heating and their effects on low temperature storage facilities. The nanostructures were deposited on glass by varying the film thickness and deposition angle of both silver and zinc sulphide nanofilms at a pressure of 2.5×10^-5 mBars in the diffusion pump microprocessor vacuum coater (Edwards AUTO 306). The optical transmittance of the coatings was measured at normal incidence in the wavelength range of 250-2500 nm of the incident electromagnetic radiation. Spectral studies showed that the transmittance decreased with increase in the film thickness of the ZnS/Ag nanostructures and the optical transmittance increased with increase in deposition angle of zinc sulphide in the infrared region. The transmittance of (4 nm)ZnS/Ag, (7 nm)ZnS/Ag,  (10 nm)ZnS/Ag and  (15 nm)ZnS/Ag samples deposited at normal angle in the visible region had peaks at 61.7%, 66.3%, 54.9%, and 18.0% respectively. The transmittance of the nanostructures increased with the increase in deposition angle of silver nanoparticles.  Thus optical transmittance measured at 1800 nm wavelengths for ZnS(0^o)/Ag(0^o), ZnS(0^o)/Ag(30^o) and ZnS(0^o)/Ag(60^o) were 2.8%, 21.7% and 22.1% respectively.  The coating of ZnS at high deposition angle decreased transmittance in the visible wavelength. The transmittance peak values in the visible region measured up to 51.1%, 53.5%, and 45.1% for (4 nm)ZnS(0^o)/Ag(0^o) and (4 nm)ZnS(0^o)/Ag(30^o) and (4 nm)ZnS(0^o)/Ag(60^o) samples respectively. However, increase in deposition angle of (10nm)ZnS/Ag nanostructures measured at 1000 nm; ZnS(0^o)/Ag(30^o), ZnS(30^o)/Ag(30^o) and ZnS(60^o)/Ag(30^o) increased transmittance in the infrared wavelengths from 9% to 12% and 34% respectively. Therefore, to increase transmittance in the visible region, the Zinc sulphide nanoparticles should be coated on silver at low deposition angles.