Morphological characterization of Zn-Based Nanostructured Thin Films

Electrodeposition of zinc based films in constant and pulsed regimes of electrolysis was performed and the obtained electrodeposits were examined by field emission-scanning electron microscopy. The electrodeposition is one of the most effective methods for the synthesis of nanostructures of metals and semiconductors with desired morphology and characteristics for many technological applications [1]. There are several variables that may be tailored specifically the electrolysis regime, the bath composition, pH, solution stirring and temperature [2]. Most of the depositions that will be discussed here were performed at acidic or near neutral solutions. Electrodeposition by pulse current, is a very versatile method, since more experimental conditions can be changed such as current density, duty cycle and pulse frequency with huge effect on the deposits characteristics: composition, structure, morphology and porosity [3]. The electrodeposits of zinc on different metals, namely steel, have special relevance due to their anticorrosive properties by the formation of passive layers in contact with air, and in aqueous solution. The corrosive resistance of the films is strongly connected to the morphological characteristics of metallic films that could be tailored by using additives in the bath, such as surfactants or oxide nanoparticles. The adsorption of surfactants aggregates or adsorption of nanoparticles onto electrodes can have large effects on the kinetics of the electron transfer and consequently on the electrodeposition process. The effect on the electron transfer rates includes blocking of the active sites by the surfactants, and electrostatic interactions between electroactive species and adsorbed surfactants [4]. Due to those effects it is possible to modify the growth mode of the crystals and tailor the morphology and structure of the electrodeposits. In a previous work cationic, anionic and non-ionic surfactants have been used for studying the effect of the charge of headgroups on the electrodeposition process. It was conclude that the use of the surfactant leads to a decrease in the grain size and changes in the film’s morphology and the zinc texture [5]. Due to the co-deposition process of oxide nanoparticles and metallic film, metal matrix nanocomposites can be successfully prepared [6]. It is expected that by electrolysis of plating solutions in which micron or sub-micron size particles are suspended, it is possible to obtain solid materials with improved and/or combined properties, which make them interesting for applications such as environmental remediation. Composites containing occluded TiO2 particles are suitable materials, due to the semiconducting properties of TiO2, with applications as photocatalysts, particularly in the treatment of polluted water. In recent years research efforts are underway to develop more powerful methods than those currently applied in wastewater treatment. Thus, the search for new efficient methods for the degradation of pollutants is a priority. Electrochemical and photoelectrochemical degradation can be suitable and low-cost alternatives to those used presently [7]. The implementation of these methods is closely linked with the development of stable, nonpollutant, cheap and electrocatalytic/ photocatalytic electrode materials. Composite electrodes of Ti/Zn-TiO2 have been successfully prepared by us in recent years [8]. In addition, we have tried with little success the implementation of these electrodes in the pharmaceutical degradation by photoassisted electrochemical processes. To improve the photo ability of matrix we have transformed the Zn matrix into wurtzite-structured ZnO. With a wide band gap (3.35 eV) [9], ZnO has been used as an environmental photocatalyst for water purification with the aid of artificial light source. Among the techniques used for the oxidation of Zn films, heat treatment in air seems to be the simplest due to relative low melting point of Zn. The conversion process depends on the crystallinity and orientation of as-deposited Zn. We have already achieved the formation of nanocrystalline ZnO films with higher surface area [10] and, successfully used this strategy to prepare Ti/ZnO-TiO2 photoelectrodes for the degradation of the AO7 dye and ibuprofen present in Current Microscopy Contributions to Advances in Science and Technology (A. Mendez-Vilas, Ed.)