Research Journal of Engineering Sciences ___________________________________________ ISSN 2278 – 9472 Vol. 2(2), 23-25, February (2013) Res. J. Engineering Sci. International Science Congress Association 23 Short Communication Effect of Film Thickness on the Transmittivity of Chemical Bath Synthesized PbS Thin Film Ezenwa I.A. Department of Industrial Physics, Anambra State University, Uli, NIGERIA Available online at: www.isca.in Received 18 th October 2012, revised 3 rd November 2012, accepted 20th December 2012 Abstract Thin films of PbS were deposited at room temperature on glass substrates immersed in a bath mixture containing aqueous solutions of lead nitrate [Pb(NO 3 )] 2, and thiourea (SC(NH 2 ) 2 ), using EDTA disodium salt as a complexing agent and ammonia solution as a pH adjuster at 300K. Optical and surface morphology of the films were investigated using a Janway 6405 UV/ Visible spectrophotometer and an Olympus optical microscope. The optical microscopy image showed that this film has uniform, small crystal size and covered the entire substrate surface completely. The films also have high transmittance in the visible/ near infrared region of the electromagnetic spectrum. We also established that increase in the film thickness in the chemical bath deposition of PbS thin film reduces the transmittance of the film. Keywords: Transmittance, PbS thin films, chemical bath deposition technique, complexing agent. Introduction Thin film technology has attracted much attention because of its unique size dependent properties and applications in optoelectronic devices, solar cells, sensors, and laser materials. In the past few decades, several technique have been adopted for thin film deposition such as Sol –gel 1 ionized Cluster Beam Deposition 2,3 dc reactive magnetron, Sputtering 4 , pulsed laser deposition 5 , chemical bath deposition 6 . Chemical bath deposition technique is currently attracting a great deal of attention as the technique is relatively cost effective, has minimum material wastage, does not need sophisticated instrument and can be applied in large area deposition at low temperature. It is well studied and produces films that have comparable structural and opto-electronic properties to those produced using other sophisticated thin film deposition technique. The chemical bath deposition method uses a controlled chemical reaction to deposit a thin film. In the typical experimental approach, the substrates are immersed in solution containing the chalcogenide source, metal ion, and complexing agent. The preparation and characterization of thin films by chemical bath deposition have been reported by many researchers. For example 7 , deposited CuO thin film 8 , deposited BaSe thin film 9 , deposited PbSe thin film. The present work report the influence of thickness on the transmittivity of chemical bath synthesized PbS thin films at 300K bath temperature. The chemical bath contains lead nitrate and thiourea (SC(NH 2 ) 2 ), which provide Pb 2+ and S 2- ions, respectively, while EDTA acted as a complexing agent. Material and Methods Thin films of PbS were deposited at room temperature on glass substrates immersed in a bath containing lead nitrate [Pb(NO 3 )] 2, and thiourea (SC(NH 2 ) 2 ), using EDTA disodium salt as a complexing agent and ammonia solution as a pH adjuster at 300K. Thiourea is used as our sulphide ion source and lead nitrate as our lead ion source. Deposition time as a parameter was optimized and the growth of PbS was determined with respect to it. In this experiment, five reaction baths (50mls beaker) were used. 5mls of lead nitrate was measured into a 50ml beaker using burette; 5mls of E.D.T.A, was then added. On addition of E.D.T.A, the solution remained clear. Thiourea was now added to the solution, it turned milky and on addition of 5mls of ammonia solution turned brown. The mixture was then topped to 50mls level by addition of distilled water and stirred gently to ensure uniformity of the mixture. The experiment was performed at a pH of 10.8 and at 300K. A glass substrate was then dipped vertically into all of the five reaction baths with the aid of a synthetic form cover, which also acted as a lid for the reaction baths. Each bath was allowed to stand for various time intervals as shown in table 1, after which they were removed and dried in air. The reaction mechanism is of the form: Pb(NO 3 ) 2 + EDTA (Pb(EDTA) 2+ + 2NO 3 2- (Pb(EDTA] 2+ Pb 2+ + EDTA (SC(NH 2 ) 2 + OH - CH 2 N 2 + H 2 0 + HS - HS - + OH - H 2 O + S 2- Pb 2+ + S 2- PbS The transmittance spectra of the fabricated films were obtained with a Janway 6405 UV/ Visible spectrophotometer. Surface morphology of the films was carried out using an Olympus optical microscope. Other solid state and optical properties of the films had been investigated in my earlier publication.