Conducting
polymers are versatile 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 to allow for a
better correlation between structure and properties. Electrochemical scanning
tunnelling spectroscopy (EC-STS) can be a powerful tool to characterize the electronic
structure of the semiconductor electrolyte 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 (PPy) 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 oxidised (doped) at 0.46 V vs. RHE (-4.84 eV in the absolute
potential scale). 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.
Electrochemical Characterization of Single Layer Graphene/Electrolyte Interface: Effect of Solvent on the Interfacial Capacitance
