Tsvetanova Martina, Oldenkotte Valent J S, Bertolino M Candelaria, Gao Yuqiang, Siekman Martin H, Huskens Jurriaan, Zandvliet Harold J W, Sotthewes Kai
Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands.
Molecular Nanofabrication, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands.
Langmuir. 2020 Oct 27;36(42):12745-12754. doi: 10.1021/acs.langmuir.0c02535. Epub 2020 Oct 19.
In this paper, we obtain maps of the spatial tunnel barrier variations in self-assembled monolayers of organosulfurs on Au(111). Maps down to the sub-nanometer scale are obtained by combining topographic scanning tunneling microscopy images with d/d spectroscopy. The square root of the tunnel barrier height is directly proportional to the local work function and the d/d signal. We use ratios of the tunnel barriers to study the work function contrast in various decanethiol phases: the lying-down striped β phase, the dense standing-up φ phase, and the oxidized decanesulfonate λ phase. We compare the induced work function variations too: the work function contrast induced by a lying-down striped phase in comparison to the modulation induced by the standing-up φ phase, as well as the oxidized λ phase. By performing these comparisons, we can account for the similarities and differences in the effects of the mechanisms acting on the surface and extract valuable insights into molecular binding to the substrate. The pillow effect, governing the lowering of the work function due to lying-down molecular tails in the striped low density phases, seems to have quite a similar contribution as the surface dipole effect emerging in the dense standing-up decanethiol phases. The d/d spectroscopy map of the nonoxidized β phase compared to the map of the oxidized λ phase indicates that the strong binding of molecules to the substrate is no longer present in the latter.
在本文中，我们获得了金（111）表面有机硫自组装单分子层中空间隧道势垒变化的图谱。通过将形貌扫描隧道显微镜图像与d/d光谱相结合，获得了亚纳米尺度的图谱。隧道势垒高度的平方根与局部功函数和d/d信号成正比。我们使用隧道势垒的比率来研究各种癸硫醇相中的功函数对比度：平躺条纹状的β相、密集直立的φ相和氧化的癸烷磺酸盐λ相。我们还比较了诱导的功函数变化：平躺条纹相诱导的功函数对比度与直立φ相以及氧化λ相诱导的调制之间的比较。通过进行这些比较，我们可以解释作用于表面的机制效应中的异同，并提取有关分子与底物结合的有价值见解。在条纹状低密度相中，由于平躺的分子尾部导致功函数降低的“枕形效应”，似乎与密集直立的癸硫醇相中出现的表面偶极子效应有相当相似的贡献。未氧化的β相的d/d光谱图与氧化的λ相的图谱相比表明，分子与底物的强结合在后者中不再存在。
