Resonant two-photon photoemission study of electronically excited states at the lead phthalocyanine/graphite interface

Vibrationally resolved two-photon photoemission spectroscopy for lead phthalocyanine film on graphite

“…The HOMO peak and the LUMO+ 2 peak overlapped at the photon energy of 4.28 eV, where the pump photon was closely resonant with the energy separation between the HOMO-and LUMO+ 2-derived levels. 8 Disregarding ͑c͒ and ͑d͒, the HOMO peaks for ͑a͒, ͑b͒, ͑e͒, FIG. 2.…”

“…Note that focusing of the light to a sub-m spot as in Ref. 8 was not employed here. The spot size of the light in this experiment was estimated to be about 80 m. The large spot size was advantageous to increase the photoemission intensity while suppressing the broadening of spectrum due to the space-charge effect.…”

“…Resonant excitation from the HOMO level to the LUMO+ 2 level was observed. 8 In this Brief Report, we examined the detailed spectral profiles of the HOMO-and LUMO+ 2-derived peaks at photon energies below and above the resonance. The vibrational satellite of the HOMO peak was found to be dependent on the excitation photon energy.…”

“…The shifts of peak positions were accurately in accordance with the 2PPE processes: With the increase in the photon energy by ⌬h, the occupied state feature shifts with 2⌬h, and the unoccupied feature with 1⌬h. 8 The details of these unoccupied features will be discussed elsewhere and we focus our attention on the HOMO feature. The HOMO peak and the LUMO+ 2 peak overlapped at the photon energy of 4.28 eV, where the pump photon was closely resonant with the energy separation between the HOMO-and LUMO+ 2-derived levels.…”

“…These were due to the LUMO+ 2-derived unoccupied state and the IPS ͑n =1͒ formed on the PbPc films, respectively. 8 In order to see the origin of the weak vibronic structure, 2PPE spectra measured at 90 K with different photon energies were shown in Fig. 2.…”