Schematic of the setup used to measure in situ in real time using spectroscopic ellipsometry. A sample stage was covered with a quartz window with semicylindrical shape, whose thickness was 2.5 mm and the variations in and were measured by flowing 4% in Ar or dry air adjusted by a mass-flow controller, into the space between the window and the sample stage.
Ellipsometric (a), (b), and transmittance (c) spectra for the Pd and , which are the initial and final states of the hydrogenation process of a Pd thin film, together with the corresponding fitted spectra. Ellipsometric spectra were measured using an incident angle of 70° for the energy range 0.75 to 3.25 eV. Inset of (a): structural model for a Pd or film to analyze ellipsometric and transmittance spectra.
Dispersion in refractive index and extinction coefficient for the Pd and , which are the initial and final states of the hydrogenation process of a Pd thin film; solid lines: Pd metal state, dotted lines: hydride state. These spectra were determined from the fits in Fig. 2.
Variation in film thickness of uniform Pd and layer during hydrogenation vs time. Each thickness was obtained by fitting and as depicted in the inset of (a) and (b). Insets: structural models to analyze the hydrogenation process of Pd thin film. Inset of (a): model (a) composed of uniform Pd and layers hypothesized that hydrogenation from the film surface Fit parameters are the thickness of Pd layer and layer . Inset of (b): model (b) composed of uniform Pd and layers hypothesized that hydrogenation from the interface between film. Fit parameters are the thickness of layer and Pd layer .
The experimental variations in ellipsometric (a) and (b) at the photon energy of 2.49, 2.01, 1.50, and 1.01 eV as a function of elapsed time of flowing 4% in Ar with a flow rate of 30 SCCM together with their fitted curves. These experimental curves were acquired using ellipsometric and spectra in the energy range of 0.7–3.3 eV measured every 3.8 s in the flowing diluted gas. Insets of (a) and (b): experimental and spectra after elapsed times of 0, 5.5, 6.5, 8, and 10 min together with the corresponding calculated curves obtained by fitting , , and as depicted in the inset of (c) using the dielectric parameters of Pd and summarized in Table I. The variation in film thickness and concentration of in the mixture layer during hydrogenation vs time (c). Since the thickness of the mixture layer was too thin in the range of elapsed time of 0 to 5 min, the values of the concentration of had large errors. Therefore, we used open circles to distinguish from the concentrations with small errors. Inset of (c): structural model (c) to analyze the hydrogenation process, which is modified model (a) composed of uniform Pd layer and mixture layer of Pd and . The mixture layer was modeled using the effective medium approximation proposed by Niklasson and Granqvist (Ref. 16). Fit parameters are the thickness of uniform Pd layer and mixture layer of Pd and , and the concentration of in the mixture layer .
Lorentz–Drude parameters obtained from ellipsometric and transmittance data (see Fig. 2) for Pd and , which are the initial and final states of the hydrogenation process of a Pd thin film. . All parameters are in eV.
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