We conducted photo-desorption experiments on PMMA (polymethyl methacrylate, acrylic) to verify the principle of the apparatus. The objective here is to confirm that the sample absorbs light and that different components are desorbed at different wavelengths.

Figure 1 shows the photodesorption data for a PMMA film at room temperature.
The desorption of methyl and ethyl groups can be observed at 170 nm and 210 nm.


　Figure 1: Photolysis data for a PMMA film at room temperature

Figure 2 shows photodissociation data for the same PMMA film at room temperature, comparing the mass number 29 for three samples measured on different days.
Since the signal amplification rate of the mass spectrometer was changed between each measurement and the samples were prepared separately, slight shifts in the signals were observed.


Figure 2: Changes in the PMMA film over time

Figure 3 also shows photodissociation data for the PMMA film at room temperature. This data was obtained by repeatedly performing photodissociation on a single sample while it was left stationary in an ultra-high vacuum. Only the data from the first measurement exhibits a different signal shape. Furthermore, when the thickness of the PMMA film was measured after each photodissociation measurement, a 4 nm decrease in film thickness was observed after a single photodissociation measurement. From this, it can be inferred that the data from the first measurement represents the PMMA film affected by atmospheric conditions, while the data from the second measurement and beyond represents the pure PMMA film.