Thermal Stability of Alkanethiolate and Aromatic Thiolate Self-Assembled Monolayers on Au(111): An X‑ray Photoelectron Spectroscopy Study

• Published in: Journal of physical chemistry. C Vol. 125; no. 39; pp. 21754 - 21763
• Main Authors: Asyuda, Andika, Das, Saunak, Zharnikov, Michael
• Format: Journal Article
• Language: English
• Published: American Chemical Society 07.10.2021
• Subjects: C: Physical Properties of Materials and Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.1c06984

Applications of functional self-assembled monolayers (SAMs) rely to a large extent on their stability, with the thermal stability being of particular importance. In this context, thermal stability of archetypical, non-substituted alkanethiolate (AT) and aromatic thiolate (ArT) SAMs on gold was studied by synchrotron-based high-resolution X-ray photoelectron spectroscopy, taking several monolayers with different lengths of the molecular backbones as representative examples and heating them in UHV. Evaporated, grain-structured Au(111) was used as the support, in view of broad practical relevance of this substrate type. AT and ArT SAMs were found to be stable up to temperatures of ∼373 and ∼383–393 K, respectively, followed by extensive molecular desorption and decomposition upon further heating. The decomposition was mediated by the cleavage of C–S bonds, which represented the so-called “weak or weakest link” in the systems. This process contributed minorly to the temperature-induced degradation of AT SAMs but was the dominant degradation channel for the ArT case. The residual films exhibited ∼10% (AT) or ∼ 35% (ArT) of the initial packing density and represented a superposition of the laying-down phase and atomically adsorbed sulfur, with a possible coexistence of a restructured, standing-up phase in the ArT case.