*2.9. ATR-FTIR*

IR spectra were collected by means of Bruker Optics Alpha FTIR instrument equipped with a Platinum-ATR accessory (Bruker Optics, Karlsruhe, Germany). The samples were deposited on the diamond ATR (attenuated total reflection) crystal and their spectrum was recorded at room temperature over the range 5000–400 cm−<sup>1</sup> with a 2 cm−<sup>1</sup> resolution.

## *2.10. Near Edge X-ray Absorption Fine Structure (NEXAFS)*

NEXAFS spectra were acquired at the ELETTRA storage ring using the BEAR (bending magnet for emission absorption and reflectivity) beamline, installed at the left exit of the 8.1 bending magnet exit. The BEAR beamline has a bending magnet as a source, and beamline optics deliver photons from 5 eV up to 1600 eV; the degree of ellipticity of the beam is selectable. The experimental station is in UHV, and it is equipped with a movable hemispherical electron analyzer and a set of photodiodes to collect angle-resolved photoemission spectra, optical reflectivity and fluorescence yield. In the here reported experiments ammeters to measure drain current from the sample were used. We collected C K-edge and O K-edges spectra at a magic-incidence angle (54.7◦) of the linearly polarized photon beam with respect to the sample surface. Both photon energy and spectral resolution were calibrated and experimentally tested using the absorption K-edges of Ar, N2 and Ne. The acquired spectra were normalized by subtracting a straight line that fits the part of the spectrum below the edge and imposing an Absorption Intensity value of 1 at 320.00 eV for C K-edge and 560.00 eV for O K-edge.
