Molecularly tunable "organic capacitors" at silicon/aqueous electrolyte interfaces

Robust and uniform n-alkyl monolayers were formed on silicon from the react ion of Grignard regents (n-CnH2n+1MgBr, n = 2, 6, 10, and 15) with hydrogen -terminated Si(111). The capacitive properties of these organic thin films on silicon in contact with aqueous electrolytes were evaluated by electroch emical impedance measurements. In particular, the reciprocal capacitance of the organic thin film modified silicon/aqueous electrolyte interfaces is p roportional to the film thickness, which is tunable by simply varying the a lkyl chain length. The derived dielectric constant of these organic thin fi lms From the best fit of the reciprocal capacitance vs ellipsometric film t hickness plot is epsilon = 3.3 +/- 0.6.