Structural and Optical Properties of Nanocrystalline Cuxs Solid Thin Films

Review Article

Austin J Chem Eng. 2014;1(1): 1002.

Structural and Optical Properties of Nanocrystalline Cuxs Solid Thin Films

Singh Ajaya Kumar1*, Mehra Swati2 and Thool Gautam Sheel1

1Department of Chemistry, Govt. VYT PG Autonomous College, Durg, 491001 (C.G.), India.

2Department of Chemistry, Rungta College of Engineering and Technology, Bhilai, 490024, (C.G.), India.

*Corresponding author: Singh Ajaya Kumar, Department of Chemistry, Govt. VYT PG Autonomous College, Durg, 491001 (C.G.), India

Received: April 28, 2014; Accepted: May 26, 2014; Published: May 27, 2014


Copper sulphide thin films were deposited by chemical bath deposition method at 65oC. These were then annealed at 100°C and 200°C. All films exhibit nanocrystalline nature, having Chalcosite low phase, with grain size ranging from a minimum of 5.71nm to maximum of 30.67nm. Effect of annealing shows increased grain size nano-thin film formation. Optical properties show that films can find application in optoelectronic devices as band gap ranging between minimum of Eg = 2.64 eV to highest of 2.92 eV. AFM studies shows that nanothin film formed has spiky and bumpy surfaces.

Keywords: Copper sulphide; Chemical bath deposition; Thermal annealing; XRD; Optical properties


It is found that CuxS thin films act as p-type semiconductor material mainly due to that of copper vacancies occurring within the lattice [1,2] and its variable property exhibition depending upon the stoichiometry, 1 ≥ x ≥ 2. Due to variable optical and electrical properties this found to have many potential applications in various fields as in solar cells, fluorescent devices [3-10], photo thermal conversion of solar energy, microwave shielding coatings, electro conductive electrodes, catalyst [11-14], selective radiation filters, photodetectors, as polarizers of infrared radiation [15], active absorbent of radio waves [16], semiconductors, electroconductive coatings, low temperature gas sensor applications [17], field emission [18], switching [19], sensing devices [20], themoreflecting coatings [21], eyeglass coatings, anti reflecting coatings [22], thermoelectric cooling materials [23], optical filters, optical recording materials, nanoscale switches, and superionic materials [24] etc. Copper sulphide at room temperature occurs in five stable phases namely: covellite (Cu1.00S), anilite (Cu1.75S), digenite (Cu1.80S), djurleite (Cu1.97S), and chalcocite (Cu2.00S). Other phases that exist include yarowite (Cu1.12S) and spionkopite (Cu1.14S).

It has been found that Cu2-xS exists in four crystallographic modifications. The monoclinic phase, low-chalcocite (αCh) is stable up to temperatures between 90 - 104°C, depending on the chemical composition x's. Above 90°C, the hexagonal phase, high-chalcocite (βCh) is stable. At a composition close to x = 0, this phase is stable up to 435°C. The third, cubic phase called digenite (Dg-Cu2-xS), stable between temperatures of 72 - 1130°C. The fourth crystallographic modification being orthorhombic phase denoted as djurleite (Dj), which is stable up to a temperature of 93°C. The compound Cu7S4 denoted as anilite (An) is stable up to 75°C. The copper sulfide, CuS (covellite, Cv), is stable up to a temperature of 507°C. Several phases of copper sulfides are metastable, but these may convert to the thermodynamically more stable ones. For example, after a few hours, the high digenite (Cu1.80S) began to convert into the low digenite (Cu1.765S), which in turn, converts to anilite (Cu1.75S) [25,26]. At 41°C, anilite decomposes into CuS and low digenite, whereas low digenite transforms into high digenite around 82°C [25,27].

For reproducing copper sulphide thin films, chemical bath deposition method is being opted, because it is a low cost simple method, a large area of deposition is available which can occur at a low temperatures. Principle of CBD method follows a controlled chemical reaction which eventually leads to deposition of thin film by precipitation. CBD method involves specified reaction conditions, which generally involves substrates immersed in a beaker having an alkaline solution containing chalcogenide source ions, metal ions and added base, where complexing agent is being added to control release of metal ion. This process itself depends on various parameters like ionic product, solubility product, super saturation, type of precipitation etc.

In the present paper, an attempt is made to deposit nano crystalline thin film of copper sulphide on glass substrates by chemical bath deposition method. Effect of variation in chemical bath composition on the structural and optical properties has been studied specifically for as-deposited and post deposited thermal annealed thin films.

Experimental Details

Preparation of Glass Substrate

For deposition of thin film, glass substrate (micro slides - 75mm L x 25 mm wide) were taken. Pretreatment of glass substrate follows:-

Preparation of CuS thin film

To prepare Copper sulphide thin films, 10 ml of 0.1 M CuSO4.5H2O (Cu2+ ion source) and 10 ml of 0.1 M C4H6O6 (being used as complexing agent) were taken in 50 ml beaker. After constantly stirring for 5 min, add 1 ml NH3 and 3ml or 4ml of TEA concentration, to obtain reaction pH maintained1.02 .9� . Other than for maintaining optimum pH for reaction bath, the concentration of TEA was varied over a wide range and optimized condition was found to be 3 ml and 4 ml for adherent and uniform thin film deposition. This followed by addition of 10 ml of 0.1 M (NH2)2CS ( S2- ion source). Stir the solution for 20 to 25 min. Keep the reaction mixture in a water bath at 65°C with vertically placed slides in it. After 180 mins, slides were taken out from reaction bath (the temperature and deposition time being controlled over for good deposition of thin film on glass substrate and optimum condition found for stable adherent film deposition). The slides which were taken out washed with deionised water and air dried. Out of two sets of slides (three slides each), one slides restored as-deposited slides, other two annealed at 100°C, 200°C for an hour in the oven. The slides, S1 and S4 being as-deposited / 180 min for 1:3 and 1:4 ratio of NH3: TEA, S2 and S5 are being their annealed samples at 100°C and S3 and S6 annealed sample at 200°C.

Mechanism of thin film formation