Stability of ω-Functionalized Self-Assembled Monolayers as a Function of Applied Potential

  • Boubour E
  • Lennox R
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Ion penetration into a series of ω-functionalized X(CH2)nS/Au (X = CH3, OH, or CO2H, and n = 15) self-assembled monolayers (SAMs) and a partially fluorinated (CF3(CF2)7(CH2)2S/Au) SAM has been investigated by electrochemical ac impedance spectroscopy in the absence of a redox probe. SAM permeability is revealed by the behavior of the phase angle at frequencies of less than ∼50 Hz, the frequency domain characteristic of diffusion processes. The permeability of these ω-functionalized SAMs, as a function of an applied potential, falls into two regimes. One regime corresponds to a state where the SAM is an ionic insulator and is well described by the Helmholtz capacitor model. The second regime begins when a critical applied potential, Vc, is exceeded. Vc corresponds to the applied potential at which ion penetration into the SAM is activated. For a chain length of 15 carbon atoms, the chemical nature of the terminal group X greatly influences the value of Vc, where Vc is +0.25 V (vs Ag/AgCl) for X = OH, +0.15...

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  • Emmanuelle Boubour

  • R Bruce Lennox

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