The N1s spectrum of an as-deposited BMP-TFSI (sub)monolayer displays two contributions, where one is related to the nitrogen atom in the pyrrolidinium ring of the cation (NBMP, red) at 402.5 eV and the other one to that in the anion (NTFSI, cyan) at 399.3 eV, respectively (Figure ). The NBMP/NTFSI intensity ratio of 1 : 1, together with the peaks in the C1s spectral range, verifies that BMP-TFSI is molecularly adsorbed on graphite (0001) at room temperature with a balanced cation : anion ratio. In addition, there are distinct peaks in the F1s, S2p, O1s core level regions (FTFSI, STFSI, OTFSI, filled cyan), which are characteristic for the CF3 groups of the anion (F1s peak at 688.9 eV) and the SO2 groups of the anion (S2p3/2 peak at 168.8 eV, O1s peak at 532.5 eV).