| AVS 55th International Symposium & Exhibition | |
| Nanometer-scale Science and Technology | Thursday Sessions |
| Session NS+NC-ThM |
| Session: | Nanoscale Assembly |
| Presenter: | Y. Yokota, RIKEN (The Institute of Physical and Chemical Research), Japan |
| Authors: | Y. Yokota, RIKEN (The Institute of Physical and Chemical Research), Japan T. Yamada, RIKEN (The Institute of Physical and Chemical Research), Japan M. Kawai, RIKEN and The University of Tokyo, Japan |
| Correspondent: | Click to Email |
It has been known that atomic force microscopy (AFM), in addition to providing topographic information, can be used to discriminate surface functional groups.1 One of the most established methods is based on the surface sensitivity of the adhesion force between the tip and sample. Several groups have tried to electrochemically modify the interfacial properties by applying the appropriate potential.2 We present the force curve measurements between electroactive ferrocene (Fc)-terminated Self-assembled monolayers (SAMs) under independent control of the tip and sample potentials. From the cyclic voltammetry of Fc SAM, the electronic states of Fc moieties in each force curve measurement were characterized.3 The adhesion force of Fc SAM was drastically changed with the oxidation state of the Fc moieties (Fc or Fc+). According to the previous wettability measurements, hydrophobicity of the Fc-terminated SAMs is decreased with the oxidation of Fc moieties.4 Because the adhesion force in aqueous solutions is largely determined by hydrophobicity, the oxidation-state dependence of the hydrophobicity is responsible for the adhesion force change. We performed two control experiments using methyl (CH3) and amino (NH3+)-terminated SAMs. Unlike in the case of Fc SAM, the force curves, both the approach and retraction curves, did not change with the applied potential. This indicates that the force curve measurements in this study are largely regulated by the effects of surface functional group rather than charging of double layer. Although Fc+ and NH3+ SAMs contain almost the same amount of functional groups, their repulsive forces between the tip and sample considerably differed depending on the surrounding environment of counter anions. These results demonstrate that this AFM-based technique can be a powerful tool for investigating the ion pair formations.
1 A. Noy et al., Annu. Rev. Mater. Sci. 27, 381 (1997).
2 H.-C. Kwon et al., J. Phys. Chem. B 109, 10213 (2005).
3 Y. Yokota et al., J. Phys. Chem. C 111, 7561 (2007).
4 N. L. Abbott et al., Langmuir 10, 1493 (1994).