Characterization of transparent conducting oxide surfaces using self-assembled electroactive monolayers

The electronic properties of various transparent conducting oxide (TCO) surfaces are probed electrochemically via self-assembled monolayers (SAMs). A novel graftable probe molecule having a tethered trichlorosilyl group and a redox-active ferrocenyl functionality (Fc(CH2)(4)SiCl3) is synthesized for this purpose. This molecule can be self-assembled via covalent bonds to form monolayers on various TCO surfaces. On as-received ITO, saturation coverage of 6.6 x 10(-10) mol/cm(2) by a close-packed monolayer and an electron-transfer rate of 6.65 s(-1) is achieved after 9 h of chemisorption, as determined by cyclic voltammetry (CV) and synchrotron X-ray reflectivity. With this molecular probe, it is found that O-2 plasma-treated ITO has a significantly greater electroactive coverage of 7.9 x 10(-10) mol/cm(2) than as-received ITO. CV studies of this redox SAM on five different TCO surfaces reveal that MOCVD-derived CdO exhibits the greatest electroactive coverage (8.1 x 10(-10) mol/cm(2)) and MOCVD-derived ZITO (ZnIn2.0Sn1.5O) exhibits the highest electron transfer rate (7.12 s(-1)).