Cathodic electrodeposition of thin ceramic oxide films

• Main Author: Wang, Hao
• Published: Imperial College London 2008
• Subjects: 666
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485418

Cathodic electrodeposition (CELD) is achieved via hydrolysis of metal ions by electrogenerated base to form metal oxideihydroxide films on a cathodic substrate. Hydroxides and peroxides can then be converted to oxides by thermal treatment. In this study, Ti02 thin films (both rutile and anatase phases) and cobalt-doped anatase films were successfully produced through this method. These materials have presented applications in electronic and magnetic devices, such as piezo-ceramics as well as in catalysis. The CELD technology and the characterization of these thin films are described in detail in this thesis. The various parameters (deposition time, current density and annealing temperature etc.) that affect the characteristics ofTi02 films deposited on Pt and Ti substrates have been explored. Focus ion beam imaging (FIB) and scanning electron microscopy (SEM) analysis show that the thickness of the film increases as the deposition time increases. Applying current density greater than 30 mA'cm-2 results in the film having a porous structure, however, little difference between films was observed when the current density was 20 mA'cm-2 or less. XRD data gave an indication that the as-deposited films were amorphous; after annealing at elevated temperatures (400°C ~ 1000°C) anatase and rutile phases were formed successfully. Samples were thermally treated under three different atmospheres: air, argon and argon/hydrogen (10% hydrogen). Different characteristics were observed after annealing. SEM and atomic force microscopy (AFM) show that the particle size increased after annealing in argon and argon/hydrogen. Preferred orientation ofthe films annealed in different atmospheres was observed and further investigated using high temperature in-situ XRD. Ti1-xCOx02-o films were successfully prepared on Ti and Si substrates. When the annealing temperature was above 600°C a CoTi03 phase was detected in the film, whilst maintaining the anneal temperature below 600°C resulted in only anatase peaks ((101) and (200)) being observed. The films annealed at 400°C show room-temperature ferromagnetism as determined by vibrating sample magnetometry, and the magnetization per unit volume was of the right order of magnitude (0.2-0.6JlB/CO) for dilute ferromagnetic oxide thin films. X-ray absorption spectroscopy studies showed that the cobalt was present as Co2+ and the XRD data were consistent with cobalt substituted anatase lattice as the lattice parameter increased from 9.0080(2) to 9.4780 (3)