Atomic force microscopy study of nitrogen molecule self-assembly at the HOPG–water interface

• Published in: Applied surface science 2014-06, Vol.304, p.56-64
• Main Authors: Lu, Yi-Hsien, Yang, Chih-Wen, Hwang, Ing-Shouh
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Frequency modulation; Graphite; Hydrophobic–water interfaces; Nanobubbles; Nitrogen; Physics
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2014.03.084

•Investigating evolution of nitrogen molecule self-assembly at the graphite–water interface.•Imaging with highly sensitive frequency-modulation atomic force microscopy.•Nucleation and growth of an ordered row-like structure is observed.•Nitrogen clusters appear when the coverage of the ordered structure exceeds 50%.•A model of how nitrogen molecules adsorb and self-assemble is proposed. In this work, we investigated the evolution of the graphite–water interface in a nitrogen atmosphere by using frequency-modulation atomic force microscopy (FM-AFM). A highly ordered pyrolytic graphite (HOPG) sample was immersed in pre-degassed water and subsequently placed in the nitrogen environment. The dissolved nitrogen molecules diffused in water and self-assembled into ordered row-like structural domains at the interface. Nucleation and growth processes of the domains were observed. When the coverage of the ordered structure surpassed 50%, small clusters began to appear on the ordered structure. The number density of the clusters increases as the coverage of the ordered structures increases and these clusters may hop on the ordered structures. A model is proposed to explain the evolution of the nitrogen molecule self-assembly process at the interface. The observation of nitrogen clusters may shed light on the nature and nucleation of the so-called nanobubbles at hydrophobic–water interfaces.