Fig. 4: Demonstrating hydrogen desorption in the EUV range using XPEEM at the SIM beamline.

a, c XPEEM images taken with a start voltage of −0.8 V and 50 μm field-of-view after a (a) 93 eV and (c) 106 eV irradiation for 157 min. A vertical, rectangular band was irradiated by narrowing the beamline exit slit to be smaller than the PEEM field-of-view, after which it was widened to reveal both the unexposed and irradiated areas (see Methods for more details). b, d A cumulative series of secondary electron (SE) curves, extracted every 1 min during the (b) 93 eV and (d) 106 eV irradiations. In (b), a shift of the SE peak of +0.3 V is observed. In (d) the vertical, black, solid lines indicate the SE peak position (at 0 min) and the Si 2p photoelectron peak position. In (c), the inset at the bottom shows a line profile extracted from the XPEEM image (denoted by the yellow, dashed line), with the measured FWHM of the edge being 4.5 μm. e Plot of the density of clean silicon atoms as a function of the photon irradiance. The purple and green curves show the results from the SIM beamline irradiation and the red curve is the best fit made to the PEARL experiments of Fig. 2b. Note that the presence of the Si 2p shoulder in (d) can obfuscate the true SE peak height, causing it to be underestimated; this is what causes the purple curve in (e) to deviate from the PEARL curve. This is absent in (b), where only a single SE peak is observed, since 93 eV is below the Si 2p excitation threshold. In (e), the vertical error-bars are ~0.02 ML.