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STM; AFM; silica; glass; 2D random network
Abstract:
Glasses are ubiquitous in nature and technology. They are generally classified by a lack of periodicity and order. Therefore, it is a great challenge to investigate the atomic arrangement in a glass. Silica is the prototype glass network former. The corner-sharing interconnection of the tetrahedral building units provides high flexibility in its atomic configuration. Silica glass, also known as vitreous silica, has been studied by various techniques for more than 80 years. However, most methods fail to give a direct view on the atomic arrangement in glass. Scanning probe methods possess the potential to resolve atomic surface structures in real space. To study glasses by these methods, a new class of two-dimensional glassy structures had to be designed.
In this work, we address a metal-supported silica bilayer at the atomic level. A combination of low energy electron diffraction, Auger electron spectroscopy, low temperature scanning tunneling microscopy and noncontact atomic force microscopy was applied in ultrahigh vacuum. The growth mode of the thin silica films was characterized. Local measurements revealed crystalline and vitreous regions in the silica bilayer film. We analyzed high resolution images of the vitreous bilayer at different ranges of order yielding a better understanding of vitreous structures in general. In addition, the atomic arrangement in crystalline and vitreous bilayer areas was resolved and thoroughly compared to each other. Ultimately, we unraveled the crystalline--vitreous interface in the two-dimensional silica film. The presented results show that the vitreous silica bilayer qualifies for a versatile glass model system.
