Papers by Author: Joaquim Carneiro

Abstract: Nanocrystalline vanadium oxide thin films have been deposited by reactive DC magnetron sputtering onto glass substrates under different processing conditions. Structural analysis and phase identification have been carried out by means of X-ray diffractometry (XRD). The surface morphologies of the different films have been examined by both scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD results revealed single and multiple phase oxides such as VO2(B), VO2(M), V2O5, etc. with considerable differences concerning to surface morphologies, as observed by SEM and AFM. The effects the O2/Ar flow ratio, DC current, and working pressure on the phases formed and growth rates is discussed. Moreover, VO2(M) films exhibited different morphologies concerning to grain size and shape as well as dissimilar preference in crystal orientation, as a result of the processing conditions. The optical/thermochromic response of the VO2(M) specimens deposited under different growth rate conditions was evaluated by optical spectrophotometry and related to the respective structural characteristics.

Abstract: Vanadium oxides are a class of materials with outstanding physical and chemical properties. They find a wide field of technological applications such as optical and electrical switching devices, light detectors, temperature sensors, micro batteries, etc. There are several studies regarding the production of vanadium oxide films by radio-frequency (RF) magnetron sputtering, and with increasing interest on the thermochromic VO2 phase. However, literature with focus on vanadium oxide films deposited by direct current (DC) magnetron sputtering is very limited. In this work, we have successfully deposited vanadium oxide thin films by reactive DC magnetron sputtering under several processing conditions. The effect of substrate type, temperature, and O2/Ar flow ratio on phase formation has been studied. Structural analysis and phase determination have been carried out by X-ray diffractometry (XRD). Some single phase samples were also analysed with respect to surface morphology by means of scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermochromic behaviour of single phase VO2(M) films has been evaluated by optical spectrophotometry.

Abstract: Zirconia (ZrO2) exhibits three different polymorphic phases as a function of the thermal and pressure conditions (cubic, tetragonal and monoclinic). The use of zirconia coatings at high temperatures requires it to be stabilized at room temperature in order to maintain the high temperature phases when subjected to thermal cycles. For this purpose, this work reports different ways to stabilize ZrO2 coatings produced by DC reactive magnetron sputtering. We have produced stabilized ZrO2 coatings by doping with other metallic and rare earth oxides (Y2O3 and Gd2O3), depositing nanostructured ZrO2 crystallites in an amorphous Al2O3 matrix and using a ZrO2/Al2O3 nanolaminated structure. A comparative study of the coatings produced is presented along with their structural stabilization using different approaches. For the doped coatings the tetragonal or cubic phases were obtained as a function of the dopant percentage and for the nanostructured and nanolayered structures the stabilization mechanism is related to the constraining of the zirconia nanocrystallites and the capacity to maintain its size under certain value.