EaStCHEM School of Chemistry, University of St. Andrews , Scotland, U.K.
Langmuir. 2011 Mar 15;27(6):2567-74. doi: 10.1021/la104561j. Epub 2011 Feb 21.
The electrodeposition of Pd onto self-assembled monolayers (SAMs) of 3-(4-pyridine-4-ylphenyl)propane-1-thiol on Au(111) has been investigated by scanning tunneling microscopy. Two schemes are compared: One involves an established two-step procedure where Pd(2+) ions are first coordinated to the pyridine moieties and subsequently reduced in Pd(2+)-free electrolyte. The second deposition routine involves electroreduction in an electrolyte containing low concentration of Pd(2+) which merges both steps and, thus, significantly simplifies metal deposition onto pyridine-terminated SAMs. Both strategies produce identical Pd nanoparticles (NPs) which exhibit a narrow size distribution and an apparent STM height of ∼2.4 nm. The observation of a Coulomb blockade and easy displacement of the nanoparticles in STM experiments evidence deposition on top of the SAM. The NPs are concluded to be essentially spherical. Growth of the NPs is found to be self-limiting since repeating the complexation-deposition cycle increases the density of the nanoparticles rather than their size but only close to full coverage. At high concentration of the Pd(2+) electrolyte, deposition on top of the SAM is impeded by a competitive mushroom-type growth.
通过扫描隧道显微镜研究了 Pd 在自组装单层（SAM）上的电沉积，自组装单层是由 3-(4-吡啶-4-基苯基)丙烷-1-硫醇在 Au(111)上形成的。比较了两种方案：一种涉及到已建立的两步程序，其中首先将 Pd(2+)离子配位到吡啶部分，然后在无 Pd(2+)的电解质中还原。第二种沉积方法涉及到在含有低浓度 Pd(2+)的电解质中进行电还原，这两种方法合并了两个步骤，从而显著简化了吡啶末端 SAM 上的金属沉积。这两种策略都产生了相同的 Pd 纳米粒子（NPs），它们具有狭窄的尺寸分布和约 2.4nm 的明显 STM 高度。在 STM 实验中观察到库仑阻塞和纳米粒子的易位，证明了 NPs 沉积在 SAM 顶部。可以得出结论，这些 NPs 基本上是球形的。研究发现，NP 的生长是自限制的，因为重复配位-沉积循环会增加纳米粒子的密度，而不是它们的尺寸，但只接近完全覆盖。在 Pd(2+)电解质的高浓度下，SAM 顶部的沉积受到竞争性蘑菇型生长的阻碍。
