Effect of a temperature gradient on ellipsometry measurements in supercritical CO<sub>2sub>
- 作者：A. Mendoza-Galvá ; n ; C. Trejo-Cruz<sup> ; sup><sup>ctrejo@udec.clsup> ; O. Solí ; s-Canto<sup>1sup> ; G. Luna-Bá ; rcenas
- 关键词：Mueller matrix ellipsometry ; Anomalous swelling ; Supercritical CO2 ; Mirage effect
- 刊名：The Journal of Supercritical Fluids
- 出版年：2012
- 期刊代码：60_08968446
- 类别：ce
- 出版时间：April, 2012
- 卷：64
- 期：Complete
- 页码：25-31
- 文件大小：829 K
摘要
Phase modulated spectroscopic ellipsometry measurements were performed in supercritical CO<sub>2sub> using a Mueller matrix approach allowing the explicit assessment of the cell windows effect on the measurements. The adsorption of CO<sub>2sub> on thermal SiO<sub>2sub> and the swelling of PMMA thin films on a silicon substrate were studied from atmospheric pressure up to 13.89 MPa at 35 and 50 掳C. A systematic analysis of the deviations between experimental and calculated spectra reveals the presence of a temperature gradient in the vicinity of CO<sub>2sub>'s critical point where large density fluctuations are present. The temperature gradient produces a graded CO<sub>2sub> refractive index resulting in a pressure-dependent angle of incidence. This mirage effect is analyzed with a simple model that considers the equation of state for CO<sub>2sub> allowing the evaluation of the temperature gradient. Our results are intended to provide a better understanding of spectroscopy ellipsometry studies in supercritical CO<sub>2sub>.