Electrodeposition of ZnSe-Fe and ZnSe-Co Granular Films

Abstract

ZnSe-Fe and ZnSe-Co granular films have been successfully obtained by electrodeposition under potentiostatic conditions. Cyclic voltammograms of the solutions containing all precursors of the systems are consistent with anomalous codeposition of the zinc and iron-group metals. Electron microscopy analyses reveal a network of Fe and Co particles dispersed in polycrystalline ZnSe without evidence of intermediate compound formation.Electrochemical deposition is an attractive approach for growing semiconductor compounds as ZnSe 1-6 and different kinds of nanosized heterostructures, 7 because it is an economical technique. Recently, theoretical calculations 8,9 and experimental evidences 10 have demonstrated that a tunnel barrier consisting of ZnSe spacer layer between ferromagnetic electrodes can induce spin-polarization in the tunneling current. Thus, ZnSe-Fe and ZnSe-Co granular films become interesting in view of their potential applications to explore spin-based transport processes.In this paper, we report for the first time the successful preparation of both ZnSe-Fe and ZnSe-Co granular films using electrochemical deposition. Detailed information on the electrochemical experiments and procedures as well as structural characterization are described. ExperimentalZnSe-Fe and ZnSe-Co granular thin films were electrodeposited under potentiostatic conditions on stainless steel substrates. All electrochemical experiments were performed with a galvanostat/ potentiostat ͑EG&G model 273A͒ using conventional stationary parallel-plate system. Stainless steel sheets of 2.0 cm 2 in surface area were used as cathodes, whereas the anode was a platinum disk of 2.8 cm 2 in area. An Ag/AgCl/1 M KCl reference electrode was employed. All potentials thereafter are referred to this electrode. Plating solutions were prepared with reagent grade chemicals ͓ZnSO 4 , SeO 2 , CoSO 4 , and ͑NH 4 ͒ 2 Fe͑SO 2 ͒ 2 ͔ immediately prior to each experiment by dissolving the requisite amount of the precursors in distilled water. All films were deposited at 65°C in cathodic potential of Ϫ1000 mV vs. Ag/AgCl reference electrode from the solutions containing 200 mM Zn, 1 mM Se, and different Fe or Co amounts ͑from 0.25 to 1 mM͒ per liter. The pH factor was adjusted between 1.8 and 2.0 by suitable addition of sulfuric acid. Voltammetric experiments were started at 0 mV with scanning in the cathodic direction and then in the anodic direction with a potential sweep rate of 2 mV/s. Only one cycle was run in each voltammetric experiment.The X-ray diffraction ͑XRD͒ studies were performed using Co K␣ radiation to avoid fluorescence in a conventional BraggBrentano geometry. X-ray photoelectron spectroscopy ͑XPS͒ measurements were carried out using a commercial VG ESCA3000 system with a base pressure of 10 Ϫ10 mbar; while XPS profiles were obtained by sputtering with Ar ϩ ions ͑5 keV, 5 A͒. The spectra were collected using Mg K␣ radiation and the overall energy resolution was approximately of 0.8 eV. Transmission electron microscopy ͑TEM͒ analysis were performe...

Growth and Properties of Electrodeposited ZnSe-Fe and ZnSe-Co Granular Films

“…5 However, selenium oxide and quasiamorphous selenium was also observed. 18 Progressive accumulation of Se onto practically stoichiometric ZnSe was revealed by photoemission depth profiling.…”

“…Voltammetry studies have shown that when the applied potential is scanned toward negative values in the solutions containing all chemical precursors a complex reduction wave is obtained. 18 The presence of iron and cobalt in the solution even at low concentrations significantly changes the deposition process. It seems that anomalous codeposition of zinc and iron-group metals [21][22][23] becomes predominant with a reduction potential shift to negative values compared to their standard redox potential.…”

“…The specific experimental conditions of electrodeposition optimize the crystalline structure of the deposits and minimize the accumulation of Se at the surface of thicker electrodeposits, according to X-ray diffraction ͑XRD͒ and photoemission measurements. 18 Transmission electron microscopy ͑TEM͒ analyses were performed with a JEOL 1200EX-II electron microscope. X-ray photoemission spectroscopy ͑XPS͒ experiments were carried out on a commercial ͑VG Microtech ESCA3000͒ system with a base pressure below 3 ϫ 10 Ϫ10 mbar using unmonochromated Mg K␣ ͑1253.6 eV͒ radiation and a hemispherical energy analyzer with an overall resolution of about 0.8 eV, which was positioned at 45°from the surface normal of the sample.…”

“…Recently, we have reported successful preparation of both ZnSe-Fe and ZnSe-Co granular films using electrochemical deposition. 18 Morphology and crystalline structure of these granular films and their correlation to surface-enhanced Raman scattering were reported elsewhere. 19,20 In this work we discuss important aspects of the growth process.…”