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Author Nguyen, Duc ♦ Nienhaus, Lea ♦ Haasch, Richard T. ♦ Lyding, Joseph ♦ Gruebele, Martin
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY ♦ NANOSCIENCE AND NANOTECHNOLOGY ♦ CONTROL ♦ CRYSTALS ♦ GLASS ♦ LASERS ♦ NANOSTRUCTURES ♦ SCANNING TUNNELING MICROSCOPY ♦ SILICON CARBIDES ♦ STRESSES ♦ SURFACES ♦ THERMAL DIFFUSION
Abstract Illumination is known to induce stress and morphology changes in opaque glasses. Amorphous silicon carbide (a-SiC) has a smaller bandgap than the crystal. Thus, we were able to excite with 532 nm light a 1 μm amorphous surface layer on a SiC crystal while recording time-lapse movies of glass surface dynamics by scanning tunneling microscopy (STM). Photoexcitation of the a-SiC surface layer through the transparent crystal avoids heating the STM tip. Up to 6 × 10{sup 4} s, long movies of surface dynamics with 40 s time resolution and sub-nanometer spatial resolution were obtained. Clusters of ca. 3-5 glass forming units diameter are seen to cooperatively hop between two states at the surface. Photoexcitation with green laser light recruits immobile clusters to hop, rather than increasing the rate at which already mobile clusters hop. No significant laser heating was observed. Thus, we favor an athermal mechanism whereby electronic excitation of a-SiC directly controls glassy surface dynamics. This mechanism is supported by an exciton migration-relaxation-thermal diffusion model. Individual clusters take ∼1 h to populate states differently after the light intensity has changed. We believe the surrounding matrix rearranges slowly when it is stressed by a change in laser intensity, and clusters serve as a diagnostic. Such cluster hopping and matrix rearrangement could underlie the microscopic mechanism of photoinduced aging of opaque glasses.
ISSN 00219606
Educational Use Research
Learning Resource Type Article
Publisher Date 2015-06-21
Publisher Place United States
Journal Journal of Chemical Physics
Volume Number 142
Issue Number 23


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