Charge-transfer effect at the interface of phthalocyanine-electrode contact studied by scanning tunneling spectroscopy

Scanning tunneling microscopy (STM) and spectroscopy (STS) are used in this work to investigate the charge-transfer effect at the molecule-substrate interface of substituted metal phthalocyanines. STS results revealed that the apparent energy gaps for both fluorinated phthalocyanines and unsubstituted phthalocyanines are essentially the same, which agree with the hybrid density functional calculations. More interestingly, there is a systematic shift of the energy level of valence bands, possibly as the result of charge-transfer effect at the molecule-substrate interface.