Conducting polymers are semiconductors whose applications cover a wide range of devices. Their versatility is due, in addition to other factors, to properties that can be easily modulated according to the intended application. It is therefore important to study and map the electronic structure of these materials for a better correlation between structure and properties. Electrochemical scanning tunneling spectroscopy (EC-STS) can be a powerful tool to characterize the electronic structure of the semiconductor interface. In this work, we have used image-based EC-STS (IB-EC-STS) to describe quantitatively the band structure of an electrochemically deposited polypyrrole film. IB-EC-STS located the band edge of the polymer's valence band (VB) at 0.95 V vs. RHE (-5.33 eV in the absolute potential scale) and the intragap polaron states formed when the polymer is doped, at 0.46 V vs. RHE (-4.84 eV). The IB-EC-STS data were cross-checked with electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis of the interfacial capacitance. The DOS spectrum obtained from EIS data is consistent with the STS-deduced location of the VB and the polarons.
The support of this research by FAPESP (grants: 2013/07296-2, 2014/50249-8, 2015/12851-0, 2017/11986-5), Shell, CsF-PVE (99999.007708/2015-07), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001 and CNPq is gratefully acknowledged.
Data Availability StatementThe data that support the findings of this study are available from the corresponding author upon reasonable request.
- electrochemical scanning tunneling microscopy
- electronic structure
- impedance spectroscopy