ZnO thin films growth by pulsed vacuum arc discharge

A study of structural and morphologic features of ZnO coatings grown by pulsed vacuum arc discharge is presented in this work. The characteristics of the plasma generated during the production process are determined by using the Optical Emission Spectroscopy technique. The system employed for growing the films consists of a vacuum chamber with two opposite electrodes (the cathode is the target of zinc and the anode is the substrate of glass). The gas used for filling the reactor was high purity oxygen. The discharge was generated at a pressure of 200 Pa and a voltage of 200 V. Coatings were characterized by using X-ray diffraction and scanning probe microscopy (SPM) techniques. XRD patterns showed a hexagonal crystalline structure with peaks produced by planes (002) and (103). The roughness observed was of 98.6 nm. No great quantity of nanodroppers was observed on the coatings surface. Plasma spectroscopic studies revealed many lines belonging to different species like Zn (328.2, 330.3, 334.5 nm), Zn+ (491.3 and 492.5 nm), O (372 nm) and O+ (336.1, 337.25 and 518 nm) and weak bands of ZnO (526.47, 531.2, 536.94 nm). The presence of ZnO is an important finding because, for coatings produced by arc techniques, authors have reported ZnO as being exclusively produced on the substrate surface and not generated into the plasma. The electron temperature (Te) and density (ne) were determined by means of spectroscopic methods such as the relation between lines of the same ionization state for Te and the calculation of Stark Broadening for ne.