Formation of Highly Stable Interfacial Nitrogen Gas Hydrate Overlayers on Graphitic Surfaces under Ambient Conditions

Ing-Shouh Hwang^1*, Chung-Kai Fang¹, Cheng-Hao Chuang², Chih-Wen Yang¹, Zheng-Rong Guo¹, Wei-Hao Hsu¹, Chia-Hsin Wang³

¹Institute of Physics, Academia Sinica, Taipei, Taiwan
²Department of Physics, Tamkang University, New Taipei City, Taiwan
³National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Ing-Shouh Hwang, email:ishwang@phys.sinica.edu.tw

Surfaces (interfaces) dictate many physical and chemical properties of solid materials and adsorbates considerably affect these properties. Nitrogen molecules, which are the most abundant constituent in ambient air, are considered to be inert. Our study combining atomic force microscopy (AFM), X-ray photoemission spectroscopy (XPS), and thermal desorption spectroscopy (TDS) revealed that nitrogen and water molecules can self-assemble into two-dimensional domains, forming ordered stripe structures on graphitic surfaces in both water and ambient air. The stripe structures of this study were composed of approximately 90% and 10% water and nitrogen molecules, respectively, and survived in ultra-high vacuum (UHV) conditions at temperatures up to approximately 350 K. Because pure water molecules completely desorb from graphitic surfaces in a UHV at temperatures lower than 200 K, our results indicate that the incorporation of nitrogen molecules substantially enhanced the stability of the crystalline water hydrogen bonding network on graphitic surfaces. Additional studies on interfacial gas hydrates can provide deeper insight into the mechanisms underlying formation of gas hydrates.

Keywords: surfaces and interfaces, water, nitrogen, gas hydrate