Direct observation of optically induced transient structures in graphite using ultrafast electron crystallography |
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Authors: | Raman Ramani K Murooka Yoshie Ruan Chong-Yu Yang Teng Berber Savas Tománek David |
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Institution: | Physics and Astronomy Department, Michigan State University, East Lansing, Michigan 48824-2320, USA. |
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Abstract: | We use ultrafast electron crystallography to study structural changes induced in graphite by a femtosecond laser pulse. At moderate fluences of < or =21 mJ/cm2, lattice vibrations are observed to thermalize on a time scale of approximately 8 ps. At higher fluences approaching the damage threshold, lattice vibration amplitudes saturate. Following a marked initial contraction, graphite is driven nonthermally into a transient state with sp3-like character, forming interlayer bonds. Using ab initio density functional calculations, we trace the governing mechanism back to electronic structure changes following the photoexcitation. |
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