Similar as before, intensity losses occur mainly in the BMP-TFSI related core level peaks. Also these losses are not identical for the different core level regions, which would be expected for desorption of molecular species. The BMP-related N1s peak decreases by about 1 /3 during Li deposition, and annealing to 400 K leaves only slightly more than 20% of its initial intensity. In contrast, the TFSI related N1s peak lost about 60% during Li deposition, and disappeared almost completely upon annealing to 400 K. Obviously, reaction with Li affects adsorbed BMP in a different way than adsorbed TFSI. In addition, the new peak at lower BE (NTFSI,dec-2, yellow), which started as a shoulder during Li deposition, turned into a distinct broad asymmetric peak upon annealing. Closer inspection reveals two components in this peak at about 400.7 eV and 399.0 eV, respectively. This decomposition behavior clearly differs from what would be expected from the trends in the F1s peak, where considerable amounts of TFSI-like species seemed still to be present even after 400 K annealing. These apparently contradictory findings were resolved recently for the interaction between Li and thick BMP-TFSI multilayer films in a model, which is compatible also with the monolayer situation. According to that interpretation, interaction / reaction of Li with BMP leads to a product denoted as NBMP,dec-1, which appears at only slightly higher BE than the NTFSI+Li peak after RT deposition. This downshift in BE is significantly more than a back-shift to the position of the NBMP signal for the asdeposited IL. Therefore, it cannot simply result from the lack of interaction between adsorbed BMP and coadsorbed Li + , which could occur, e.g., as a consequence of a reaction between adsorbed TFSI and Li + . During stepwise Li deposition of 0.2 up to 1.4 ML, this species coexists with the NTFSI+Li peak (combined NBMP,dec-1 / NTFSI+Li peak, filled green-cyan), which results in the slight broadening of that peak. After heating to 400 K, part of the TFSI is decomposed by reaction with Li, leading to the lower-BE peaks NTFSI,dec-1 (blue-yellow) and NTFSI,dec-2 (yellow) at 400.7 eV and 398.8 eV, respectively. At least part of the TFSI decomposition products exhibits molecular structures that closely resemble that of TFSI for most elements such as O, S and in particular F, and thus differ only slightly from TFSI itself in these core level spectra based on their BE. For NTFSI+Li, in contrast, they clearly differ, as indicated by the new NTFSI,dec-1 peak, which emerges at 400 K. BMP seems to be somewhat more stable than TFSI, as the NBMP+Li peak (red) does not disappear completely, although it lost much of its intensity upon annealing to 400 K. While we cannot exclude that the remaining BMP-related intensity is due to a molecular interaction / reaction product of BMP with rather similar chemical environment of the N atom as in BMP, we have no evidence for that. These aspects will be discussed in more detail in section 3.2.2.