Kiani Abolfazl, Alpuche-Aviles Mario A, Eggers Paul K, Jones Michael, Gooding J Justin, Paddon-Row Michael N, Bard Allen J
Center for Electrochemistry, Chemistry and Biochemistry Department, The University of Texas at Austin, Austin, Texas 78712, USA.
Langmuir. 2008 Mar 18;24(6):2841-9. doi: 10.1021/la702811t. Epub 2008 Feb 1.
Electron transfer (ET) rate kinetics through n-alkanethiol self-assembled monolayers (SAMs) of alkanethiols of different chain lengths [Me(CH2)nSH; n=8, 10, 11, 15] on Au and Hg surfaces and ferrocene (Fc)-terminated SAMs (poly-norbornylogous and HS(CH2)12CONHCH2Fc) on Au were studied using cyclic voltammetry and scanning electrochemical microscopy (SECM). The SECM results allow determination of the ET kinetics of solution-phase Ru(NH3)63+/2+ through the alkanethiol SAMs on Au and Hg. A model using the potential dependence of the measured rate constants is proposed to compensate for the pinhole contribution. Extrapolated values of koML for Ru(NH3)63+/2+ using the model follow the expected exponential decay (beta is 0.9) for different chain lengths. For a Fc-terminated poly-norbornyl SAM, the standard rate constant of direct tunneling (ko is 189+/-31 s(-1)) is in the same order as the ko value of HS(CH2)12CONHCH2Fc. In blocking and Fc SAMs, the rates of ET are demonstrated to follow Butler-Volmer kinetics with transfer coefficients alpha of 0.5. Lower values of alpha are treated as a result of the pinhole contribution. The normalized rates of ET are 3 orders of magnitude higher for Fc-terminated than for blocking monolayers. Scanning electron microscopy imaging of Pd nanoparticles electrochemically deposited in pinholes of blocking SAMs was used to confirm the presence of pinholes.
利用循环伏安法和扫描电化学显微镜（SECM）研究了不同链长的链烷硫醇[Me(CH2)nSH；n = 8、10、11、15]在金和汞表面上的n - 链烷硫醇自组装单分子层（SAMs）以及二茂铁（Fc）封端的SAMs（聚降冰片烯同系物和HS(CH2)12CONHCH2Fc）在金表面上的电子转移（ET）速率动力学。SECM结果使得能够测定溶液相Ru(NH3)63+/2+通过金和汞表面上的链烷硫醇SAMs的ET动力学。提出了一个使用测量速率常数的电位依赖性的模型来补偿针孔贡献。使用该模型得到的Ru(NH3)63+/2+的koML外推值对于不同链长遵循预期的指数衰减（β为0.9）。对于Fc封端的聚降冰片烯SAM，直接隧穿的标准速率常数（ko为$189\pm31 s^{-1}$）与HS(CH2)12CONHCH2Fc的ko值处于同一数量级。在阻挡层和Fc SAMs中，ET速率被证明遵循巴特勒 - 沃尔默动力学，转移系数α为0.5。较低的α值被视为针孔贡献的结果。Fc封端的ET归一化速率比阻挡单分子层高3个数量级。对电化学沉积在阻挡SAMs针孔中的钯纳米颗粒进行扫描电子显微镜成像，以确认针孔的存在。
