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Schematic illustration of the sample chamber for the experiments (not to the scale). (a) Silicon frame, (b) SiN film window, (c) Kapton foil spacer, (d) BaF2 scintillator, and (e) temperature-humidity probes.
Temperature dependence of the thickness for the polyvinyl alcohol (PVA) and polycaprolactam (PA6) films. The data were obtained using a thermo-variable spectroscopic ellipsometer under a dry nitrogen flow. The glass transition temperature T g for each film was determined as the temperature at the crossing of linear interpolation between the fittings (shown by the broken lines) for the data in the lower and higher temperature regions, providing the linear thermal expansion coefficients α T [10− 5 °C− 1] of 9.0 and 34 for PVA and of 26 and 50 for PA6, respectively.
Typical positron annihilation lifetime data for the PVA film samples and a Kapton foil obtained with an incident energy of 4 keV at 30 °C. The values in the parentheses represent the respective relative humidity during the measurements. The pulsed positron beam was first generated by a chopper with an interval time of 16/f (f is the bunching frequency, set to 165 MHz) and its time width was further shortened through the subsequent bunchers in the beam line. Minor background peaks are visible around 7 ns and 13 ns in the data. These peaks were caused by the bunching, with a period of 1/f (∼6 ns), of a small fraction of positrons, which pass through the chopper even when closed.
Humidity dependence of the ortho-positronium (o-Ps) lifetimes τ or hole radii R for the PVA and PA6 films obtained at 30 °C. The broken lines are drawn for visual clarification only.
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