Abstract
In this project, we have utilized synchrotron radiation photoemission to investigate how the organic semiconductor CuPc interacts with Ca at different thicknesses. According to our observations, the interaction at the Ca/CuPc interface can be divided into four stages. In stage I, where the evaporation time is less than 15 s, the Ca atoms transfer some charge to CuPc, making both the HOMO and the cutoff shift to high binding energies. In stage II, where the evaporation time is less then 100 s, a new peak appears inside the CuPc gap, while the HOMO and the cutoff remain unshifted. The new peak increases in intensity with increasing Ca thickness. As to the N 1s and C 1s core-level spectra, they become broadened. Furthermore, a new Cu 3p core appears at low binding energy, shifted away from the pristine 3p core by 1.6 eV. In stage III, where the evaporation time is less than 500 s, the strength of the new valence peak does not increase, and the whole valence band spectra change insignificantly. However, the new Cu 3p core increases in intensity at the expense of the original Cu 3p core. In the final stage, where the evaporation time is greater 500 s, the metallic Ca appears.