Investigation of the adsorption behavior of PbPc on graphene by Raman spectroscopy

Abstract

Using graphene-enhanced Raman scattering, the Raman signals of molecules attached to graphene can be obtained. For different molecules and vibrational modes, the enhancement factors are different. Here, we have investigated the variation in the adsorption behavior of lead phthalocyanine (PbPc) Langmuir-Blodgett (LB) films on graphene under annealing using Raman spectroscopy. With increasing annealing temperature, it was found that the Raman intensity of the PbPc molecules first increased and then decreased. At the sublimation temperature, the enhanced Raman signal was the strongest, indicating that the orientation of the PbPc molecules had changed from perpendicular to parallel to the graphene surface. As the annealing temperature was increased towards the sublimation temperature, some vibrational modes with low Raman scattering cross-section appeared, and they were enhanced at higher temperatures. This indicates that the PbPc molecules are deformed due to π-π interactions with graphene, and change their structure from nonplanar to planar. When the annealing temperature was increased even further, some new vibrational modes appeared, which can be attributed to the reduction of Pb(II) to Pb(0) in the PbPc molecules. © Editorial office of Acta Physico-Chimica Sinica.