KTH Royal Institute of Technology, Department of Chemistry, Division of Surface and Corrosion Science, SE-100 44 Stockholm, Sweden.
KTH Royal Institute of Technology, Department of Applied Physics, Material and Nano Physics, SE-164 40 Stockholm, Sweden.
J Colloid Interface Sci. 2021 Jan 1;581(Pt B):816-825. doi: 10.1016/j.jcis.2020.07.058. Epub 2020 Jul 15.
The self-assembly of amphiphilic molecules onto solid substrates can result both in the formation of monolayers and multilayers. However, on oxidized and non-oxidized copper (Cu), only monolayer formation was reported for phosphonic acids possessing one phosphate head group. Here, the adsorption of octadecylphosphonic acid (ODPA) on Cu substrates through a self-assembly process was investigated with the initial hypothesis of monolayer formation.
The relative amount of ODPA adsorbed on a Cu substrate was determined by infrared reflection/absorption spectroscopy (IRRAS) and by atomic force microscopy (AFM) investigations before and after ODPA deposition. X-ray photoelectron spectroscopy (XPS) with sputtering was used to characterize the nature of the layers.
The results show that the thickness of the ODPA layer increased with deposition time, and after 1 h a multilayer film with a thickness of some tens of nm was formed. The film was robust and required long-time sonication for removal. The origin of the film robustness was attributed to the release of Cu ions, resulting in the formation of Cu-ODPA complexes with Cu ions in the form of Cu(I). Preadsorbing a monolayer of octadecylthiol (ODT) onto the Cu resulted in no ODPA adsorption, since the release of Cu(I) ions was abolished.
两亲分子在固体基底上的自组装既能形成单层膜，也能形成多层膜。然而，在氧化和非氧化的铜（Cu）上，仅报道了具有一个磷酸基团的膦酸形成单层膜。在这里，通过自组装过程研究了十八烷基膦酸（ODPA）在 Cu 基底上的吸附，初始假设为单层膜形成。
通过红外反射/吸收光谱（IRRAS）和原子力显微镜（AFM）研究在 ODPA 沉积前后，确定吸附在 Cu 基底上的 ODPA 的相对量。使用溅射的 X 射线光电子能谱（XPS）来表征层的性质。
结果表明，ODPA 层的厚度随沉积时间的增加而增加，1 小时后形成了厚度约几十纳米的多层膜。该膜具有较强的稳定性，需要长时间超声才能去除。膜的稳定性源于 Cu 离子的释放，导致形成了以 Cu(I)形式存在的 Cu-ODPA 配合物。在 Cu 上预先吸附一层十八烷基硫醇（ODT）会导致没有 ODPA 吸附，因为 Cu(I)离子的释放被阻止了。
