At the home-based spectrometer, a monochromatized aluminum Kα source (XR 50 M, Specs) and a duoplasmatron type discharge UV light source (UVS 300, Specs) were employed for XPS and UPS measurements, respectively. Energy calibration at the home-based spectrometer was performed using Au, Ag and Cu foils (Goodfellow Cambridge Ltd.), which were also cleaned by argon ion sputtering, calibrating to the binding energies of Au4f7/2 (84.00 eV), Ag3d5/2 (368.21 eV) and Cu2p3/2 (932.63 eV). Here, the energy resolution for XPS and UPS were 400 meV and 150 meV, respectively. Molybdenum disulfide (2H-MoS2) crystals were purchased from 2D Semiconductors Inc. and fixed to sample holders with silver glue. To ensure a clean surface the MoS2 crystals were cleaved in situ using adhesive tape. Successful cleavage was evidenced by a carbon-and oxygen-free surface, as confirmed by XPS and work function measurements (home lab). Phthalocyanines (Porphyrin Systems Hombrecher e.K. and Sigma Aldrich) were deposited on the prepared surfaces under UHV conditions using molecular beam epitaxy. A Knudsen cell and resistive heating in the range of 390 -410 °C were employed for deposition. The deposition rate was monitored with a quartz crystal microbalance and the temperature adjusted to reach an approximate rate of 0.2 nm/min. The nominal layer thickness was determined by photoemission, comparing the intensities of the C1s and Mo3d core levels (Figure , Supporting Information). Photoionization cross sections were taken from Yeh and Lindau and employed for calculations, while the inelastic mean free path of photoelectrons was determined according to Seah and Dench. For each series of experiments, a crystal was freshly cleaved. Different crystals were used for the experiments, but care was taken to ensure that specific phthalocyanines were only studied with certain crystals, preventing any crosscontamination.