Research On The Preparation And Properties Of FeS₂ Films And Nanorods

Precursor Fe2O3 films were deposited by sol-gel method. Pyrite films were prepared by sulfurizing the precursor at different temperatures. The surface growth and roughening of pyrite films were studied by atomic force microscopy (AFM). The effect of various crystal defects including plane defects (grain boundary and film surface) and point defects on the optical and electrical properties of pyrite films were also studied. The impedance spectroscopy was used to demonstrate the roles played by grains and grain boundaries for the pyrite films with different thicknesses. Moreover, the FeS2 nanorod arrays and films were prepared by sulfurizing precursor Fe2O3 nanorod arrays, which were deposited by hydrothermal method. The effect of sulfurization parameters on the microstructure, optical and photocurrent response properties of pyrite were investigated.The pyrite films can be prepared by sulfurizing Fe2O3 films at 400℃. The RMS roughness of pyrite films decreases from 300 to 400℃and then increases with sulfurization temperature increasing. It is considered that kinetic roughening occurs at low temperature region due to slow migration of atoms while thermal roughening appears at high temperature region. The band gap and optical absorption coefficient decrease while the electrical resistivity increases with the sulfurization temperature increasing. The interaction of point defects and plane defects maybe the main reason leading to the small changes of mobility with temperature increasing. This demonstrates that microstructure and defects should have great influence on the photoelectrical properties of pyrite films.The impedance analysis has been adopted to study the contributions of grains and grain boundaries to the electrical properties of pyrite films using brick layer model. The electrical properties are controlled by the grains for the film with the thickness of 109 nm. Both the grains and grain boundaries contribute to the electrical properties with film thickness increasing from 230 to 400 nm. In addition, the grain contribution to the electrical transport mechanism is prone to be further enhanced. According to the simulated results by ZSimpWin, with film thickness increasing, the changes of grain resistance exhibit a much more important influence on the changes of electrical resistivity. The simulated results support the discussion above well.Pyrite nanorod arrays could be obtained by sulfurizing the precursor Fe2O3 nanorod arrays at 400-500℃. Fe2O3 nanorods could transform to pyrite nanorods with great crystallinity after sulfurizing at 400℃for 2 h. Each pyrite nanorod is composed of nanoparticles arrayed according to the direction perpendicular to the substrate. Sulfurizing Fe2O3 nanorods at 600℃for different time could completely synthesize pyrite films. The crystallite size distribution is nonuniform. There appears a phenomenon of grain abnormal growth.The optical absorptions of FeS2 nanorods and films prepared by hydrothermal method can reach 105cm-1, which demonstrates the good optical absorption of FeS2. In addition, FeS2 nanorods exhibit a much better optical property than that of films prepared by hydrothermal method at different temperatures.The photocurrent density of FeS2 nanorods and films prepared by hydrothermal method could reach mA/cm2. FeS2 nanorod sulfurized at 400℃for 2 h can obtain the best photocurrent density of 9 mA/cm2. Moreover, the photoresponse of FeS2 nanorods is stronger than that of films prepared by hydrothermal method.