PREPARATION OF NICKEL ULTRATHIN FILM BY THE LANGMUIR–BLODGETT TECHNIQUE AND CHEMICAL REDUCTION

The nickel ion containing Langmuir–Blodgett (LB) multilayer was prepared by transferring first dissolving nickel acetate and the solution was poured into a subphase of ultrapure water and stearic acid-chloroform. The resultant mixture was then spread onto a hydrophilic water or glass plate. Then the multilayer was converted into nickel ultrathin film after chemical reduction by sodium borohydride. The optimized parameters for monolayer formation, such as concentration of subphase, pH value, barrier speed and standing time, were determined by the measurement of the surface pressure–surface area (Π–A) isotherms. The expended areas after deposition with nickel ions inferred the interaction of stearic acid with nickel ion during the formation of monolayer at air–water interface. The optimized parameters for multilayer deposition, such as surface pressure and dipping speed were determined by the measurement of the transfer coefficient. The Fourier transform infrared spectroscopy (FTIR) was used to investigate the interactions of nickel ions with stearic acid at air–water interface and in nickel ion/stearic acid LB film, as well as the metal transformations of nickel ion in ultrathin film. The disappearance of peak at 1689 cm-1 verified the interactions between stearic acid and nickel ion. The further reduction made the organic phase dissolve and remove from the multilayer mostly. The surface morphologies of the LB multilayer and ultrathin film after reduction were detected by atomic force microscopy (AFM). A uniform and flat surface of nickel ultrathin film within nanometer ranges were obtained after reduction. The particle sizes of nickel were approximately 50 nm.