Tuning the Effective Work Function of Gold and Silver Using ω-Functionalized Alkanethiols: Varying Surface Composition through Dilution and Choice of Terminal Groups
Tuning the Effective Work Function of Gold and Silver Using ω-Functionalized Alkanethiols: Varying Surface Composition through Dilution and Choice of Terminal Groups
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DOI：
10.1021/jp909494r
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发表时间：
2009-11-26
影响因子：
3.7
通讯作者：
Armstrong, Neal R.
中科院分区：
文献类型：
--
作者：
Alloway, Dana M.;Graham, Amy L.;Armstrong, Neal R.
硫醇基自组装单分子膜（SAMs）已被用来调整金的有效功函数在一个范围内的约。1.8 eV通过两种策略：（i）使用ω-官能化的烷硫醇，其中尾部基团具有广泛变化的电负性，或（ii）通过由甲基封端的烷硫醇（C16）和在两个末端碳原子处氟化的烷硫醇（C16 F2）的选定混合物产生双组分SAM。UV-光电子能谱（UPS）用于监测有效功函数的变化，使用这些光电子能谱的低动能边缘的偏移来量化由表面改性剂产生的界面偶极效应引起的局部真空能级的偏移。链烷硫醇链上的尾基从-CH 3到-苯基、-Cl、-Br和-CF 3或-CF 2CF 3变化，这提供了局部真空水平的位移，其随各个改性剂的计算分子偶极矩线性变化，如先前对于其更有限范围的链烷硫醇所观察到的（J. Phys. Chem. B 2003，107，11690）。这里提出的研究证实，金-硫醇盐键中的固有偶极子很小（小于100 meV），而银-硫醇盐键似乎具有强极性特征，在Ag+-S-（ca. 900 meV）。使用一个简单的点偶极模型，以合理化这些明显的真空水平的变化，进一步探讨了使用SAM来自各种混合物的C16和C16 F2。低动能边缘的UV-光电子能谱和有效功函数的观察到单调增加的能量与C161 F2的覆盖范围，确认小的表面偏析发生在这些自组装单分子膜在一个很宽的浓度范围。
Thiol-based self-assembled monolayers (SAMs) have been used to tune the effective work function of gold over a range of ca. 1.8 eV via two strategies: (i) the use of omega-functionalized alkanethiols where the tail groups have widely varying electronegativity or (ii) by the creation of two-component SAMs from selected mixtures of methyl-terminated alkanethiols (C16) and alkanethiols fluorinated at the two terminal carbon atoms (C16F2). UV-photoelectron spectroscopy (UPS) was used to monitor changes in effective work function, using shifts in the low kinetic energy edge of these photoemission spectra to quantify the shift in local vacuum level resulting from the interface dipole effect created by the surface modifier. Tail groups on alkanethiol chains varied from -CH3, to -phenyl, -Cl, -Br, and -CF3 or -CF2CF3, which provided a shift in local vacuum level that varied linearly with the calculated molecular dipole moment of the individual modifiers, as observed previously for it more limited range of alkanethiols (J. Phys. Chem. B 2003, 107, 11690). The studies presented here confirm that the intrinsic dipole in the gold-thiolate bond is small (less than 100 meV), whereas the silver-thiolate bond appears to have a strongly polar character, in the direction Ag+-S-(ca. 900 meV). The use of a simple point dipole model to rationalize these apparent shifts in vacuum level was further explored using SAMs derived from various mixtures of C16 and C16F2. The low kinetic energy edge in the UV-photoemission spectra and the effective work function are observed to increase monotonically in energy with increasing C161F2 coverage, confirming that little surface segregation occurs in these self-assembled monolayers over a wide concentration range.