Kwon Han-Cheol, Gewirth Andrew A
Department of Chemistry and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
J Phys Chem B. 2005 May 26;109(20):10213-22. doi: 10.1021/jp044655o.
The reversible desorption and adsorption of ethanethiol (ET) and hexadecane thiol (HDT) self-assembled monolayers (SAMs) on gold substrates are addressed with potential-dependent AFM force measurements where both tip and substrate potentials are controlled independently. For HDT-modified tip and substrate, the potential dependence of the force curve corresponds to the observed voltammetric features. The adhesion interaction between HDT-modified tip and substrate exhibits a large adhesion, whereas the adhesion is reduced to one-quarter of its original value after HDT on the substrate is removed. The presence of both attractive features on the approach curve and large adhesion on retraction after thiol desorption are ascribed to micelle formation from the desorbed, insoluble, thiols above the Au surface. For the ET-modified tip and substrate, the force curve evinces time-dependent recovery after the thiol adsorption peak which arises from the finite time of diffusion of the desorbed thiol back to the substrate. However, the force curves exhibit little potential dependence when the ET-desorbed tip is interacted with ET-modified substrate.
通过独立控制针尖和基底电势的电势相关原子力显微镜力测量，研究了乙硫醇（ET）和十六烷硫醇（HDT）自组装单分子层（SAMs）在金基底上的可逆解吸和吸附。对于HDT修饰的针尖和基底，力曲线的电势依赖性与观察到的伏安特征相对应。HDT修饰的针尖与基底之间的粘附相互作用表现出较大的粘附力，而基底上的HDT去除后，粘附力降至其原始值的四分之一。在接近曲线时出现的吸引特征以及硫醇解吸后回缩时的大粘附力，归因于金表面上方解吸的不溶性硫醇形成的胶束。对于ET修饰的针尖和基底，在硫醇吸附峰之后，力曲线显示出随时间的恢复，这是由于解吸的硫醇扩散回基底的时间有限所致。然而，当ET解吸的针尖与ET修饰的基底相互作用时，力曲线几乎没有电势依赖性。
