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Subject: Direct observations ×

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Now showing 1 - 3 of 3
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    The thermal stability of epitaxial GeSn layers
    (Melville, NY : AIP Publ., 2018) Zaumseil, P.; Hou, Y.; Schubert, M.A.; von den Driesch, N.; Stange, D.; Rainko, D.; Virgilio, M.; Buca, D.; Capellini, G.
    We report on the direct observation of lattice relaxation and Sn segregation of GeSn/Ge/Si heterostructures under annealing. We investigated strained and partially relaxed epi-layers with Sn content in the 5 at. %-12 at. % range. In relaxed samples, we observe a further strain relaxation followed by a sudden Sn segregation, resulting in the separation of a β-Sn phase. In pseudomorphic samples, a slower segregation process progressively leads to the accumulation of Sn at the surface only. The different behaviors are explained by the role of dislocations in the Sn diffusion process. The positive impact of annealing on optical emission is also discussed.
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    Direct Observation of Shock-Induced Disordering of Enstatite Below the Melting Temperature
    (Hoboken, NJ [u.a.] : Wiley, 2020) Hernandez, J.-A.; Morard, G.; Guarguaglini, M.; Alonso-Mori, R.; Benuzzi-Mounaix, A.; Bolis, R.; Fiquet, G.; Galtier, E.; Gleason, A.E.; Glenzer, S.; Guyot, F.; Ko, B.; Lee, H.J.; Mao, W.L.; Nagler, B.; Ozaki, N.; Schuster, A.K.; Shim, S.H.; Vinci, T.; Ravasio, A.
    We report in situ structural measurements of shock-compressed single crystal orthoenstatite up to 337 ± 55 GPa on the Hugoniot, obtained by coupling ultrafast X-ray diffraction to laser-driven shock compression. Shock compression induces a disordering of the crystalline structure evidenced by the appearance of a diffuse X-ray diffraction signal at nanosecond timescales at 80 ± 13 GPa on the Hugoniot, well below the equilibrium melting pressure (>170 GPa). The formation of bridgmanite and post-perovskite have been indirectly reported in microsecond-scale plate-impact experiments. Therefore, we interpret the high-pressure disordered state we observed at nanosecond scale as an intermediate structure from which bridgmanite and post-perovskite crystallize at longer timescales. This evidence of a disordered structure of MgSiO3 on the Hugoniot indicates that the degree of polymerization of silicates is a key parameter to constrain the actual thermodynamics of shocks in natural environments. © 2020. The Authors.
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    Direct observation of modal hybridization in nanofluidic fiber [Invited]
    (Washington, DC : OSA, 2021) Gomes, André D.; Zhao, Jiangbo Tim; Tuniz, Alessandro; Schmidt, Markus A.
    Hybrid-material optical fibers enhance the capabilities of fiber-optics technologies, extending current functionalities to several emerging application areas. Such platforms rely on the integration of novel materials into the fiber core or cladding, thereby supporting hybrid modes with new characteristics. Here we present experiments that reveal hybrid mode interactions within a doped-core silica fiber containing a central high-index nanofluidic channel. Compared with a standard liquid-filled capillary, calculations predict modes with unique properties emerging as a result of the doped core/cladding interface, possessing a high power fraction inside and outside the nanofluidic channel. Our experiments directly reveal the beating pattern in the fluorescent liquid resulting from the excitation of the first two linearly polarized hybrid modes in this system, being in excellent agreement with theoretical predictions. The efficient excitation and beat of such modes in such an off-resonance situation distinguishes our device from regular directional mode couplers and can benefit applications that demand strong coupling between fundamental- and higher-order- modes, e.g. intermodal third-harmonic generation, bidirectional coupling, and nanofluidic sensing.