Figure 1

Experimental scheme. (a) Experimental setup for time-resolved ESCA. Part of the fundamental laser beam is focused into a neon gas target to generate EUV radiation by high-harmonic generation. A zirconium foil filters out the lower harmonics and the fundamental. The 63rd harmonic order at a wavelength of 13 nm (94.5 eV) is selected through a two-multilayer-mirror monochromator. UV pump pulses at 266 nm (4.5 eV) are generated via third harmonic generation (THG) using the rest of the fundamental beam. Both beams are refocused to about $25\mu \mathrm{m}$ diameter (FWHM) spots on the sample. The energy of the emitted electrons is analyzed in a time-of-flight (TOF) spectrometer. (b) Excitation scheme for adsorbed iodo-phenylphenol on Si with excitation pathway (right). (c) Normalized photoelectron spectra of an iodo-phenylphenol monolayer on Si for EUV excitation only (purple circles) and for EUV excitation followed by UV-pump excitation at a delay of 3 ps (blue squares). The vertical error bars correspond to the statistical uncertainty.Reuse & Permissions

Figure 2

Iodine $4d$ core-level spectra for various pump-probe delays. Positive delay corresponds to UV-pump excitation (266 nm, 50 fs, $10\mathrm{mJ}{\mathrm{cm}}^{-2}$, peak intensity of about $3\times {10}^{11}\mathrm{W}{\mathrm{cm}}^{-2}$) followed by EUV-probe excitation (94.5 eV, estimated pulse duration 7–15 fs, and flux ${10}^5$ photons per pulse). EUV reference spectra are shown in (a)–(d),(h),(i) for comparison (purple line and filled circles). Vertical dashed lines in (e)–(g) indicate the positions of the $4d$ peaks observed in the reference spectra. After background subtraction the spectra are normalized to the total peak area, except for the pump-probe spectrum shown in (b) for which the $4d_{3/2}$ peak area is set equal to the $4d_{3/2}$ peak area of the normalized EUV reference. The continuous lines are best fits obtained with a single doublet of pseudo-Voigt lines (a)–(d),(h),(i) and multiple doublets (e)–(g). Two and three different local environments for the iodine atom are obvious for (e),(f), respectively. The corresponding fit components are shown as solid lines in red, green, and purple.Reuse & Permissions

Figure 3

Pump-probe effect of core-level chemical shift and branching ratio. (a),(b) Center of the iodine $4d_{3/2}$ lines after fitting the spectra as a function of the pump-probe delay for the contribution with the energetic shifts up to 0.6 eV [(b), red squares], those with about 1.5 eV [(a), green circles], and 3 eV chemical shift [(a), purple triangles]. The error bars represent the $2\sigma$ confidence interval of the fit. The inset in (a) shows possible intermediate state configurations and a schematic of the potential energy surface. (c) Iodine $4d_{5/2}$ to $4d_{3/2}$ branching ratio variation for the pump-probe delay between $-3$ and 3 ps for three different measurements on two different samples. The solid lines represent fitted Gaussians corresponding to two data sets to allow the determination of the width and position of the observed branching ratio drop.Reuse & Permissions