Optical characterization of ceramic thin films: Applications in low-temperature solid oxide fuel-cell materials research
- PDF / 560,076 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 32 Downloads / 222 Views
Characterization of thin film solid oxide fuel-cell materials can be difficult due to the range of porosities in electrodes and electrolytes as well as the nano-sized pores and particles. In this study, optical characterization techniques such as ultraviolet–visible transmission and reflection spectrophotometry are illustrated as methods for achieving information about the film density from the film refractive index as well as the film thickness. These techniques were used to investigate the sintering process of colloidal CeO2 on sapphire substrates and polymeric precursor-derived ZrO2:16%Y (YSZ) thin films on silicon over the temperature range 400–1000 °C, and the results were compared with traditional characterization techniques such as electron microscopy, profilometry, ellipsometry, and x-ray diffraction line broadening analyses. Most of the techniques were in good agreement with the CeO2 grain size changing from 5–65 nm and the film thickness changing from 0.8–0.5 m. Comparisons of transmission and reflection spectrophotometry with ellipsometry illustrated that scattering effects from the porous CeO2 films caused an overestimation of the refractive index from ellipsometry, but allowed for accurate grain size measurements from transmission and reflection data. Both techniques were in good agreement during the sintering of the YSZ thin films, with the density changing from 90–100% theoretical after heating between 400 and 800 °C.
I. INTRODUCTION
Thin film inorganic solid oxide fuel-cell (SOFC) structures have seen a large increase in research because of the possibility for decreased operating temperatures and concomitant increase in reliability and performance. To maintain microstructural integrity and retain full density, thin film electrolytes should have nanocrystalline grain sizes to prevent pinhole defects.1 These grain sizes may have effects on the electrical and optical properties as well as the morphology of the resulting surface.2,3 Thin film electrodes with nano-sized porosity are being developed to prevent microstructural defects in the electrolyte. In most thin film electrolyte SOFC structures, the porous electrode also acts as the support for the electrolyte. If the surface roughness resulting from large pores in the electrode is similar to the thickness of the electrolyte, electrical shorts or holes in the electrolyte may result, decreasing the efficiency of the device. Graded porosity electrodes are currently being developed where a thin electrode film with nano-sized porosity is
a)
Present address: Department of Physics, University of North Texas, Denton, TX 76203. J. Mater. Res., Vol. 19, No. 2, Feb 2004
http://journals.cambridge.org
Downloaded: 13 Apr 2015
deposited on macroporous substrates to process electrolytes with thickness less than 1 m.4 Decreasing the feature sizes to these small dimensions (typically less than 10 nm) also increases the difficulty of microstructural characterization. X-ray diffraction (XRD) line broadening has been used to estimate grain sizes in the nanocrystal
Data Loading...
