title: Direct observation of optically induced transient structures in graphite using ultrafast electron crystallography.
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.
authors.affiliation: Physics and Astronomy Department, Michigan State University, East Lansing, Michigan 48824-2320, USA.
authors.forename: Ramani K
authors.initials: RK
authors.lastname: Raman
authors.forename: Yoshie
authors.initials: Y
authors.lastname: Murooka
authors.forename: Chong-Yu
authors.initials: CY
authors.lastname: Ruan
authors.forename: Teng
authors.initials: T
authors.lastname: Yang
authors.forename: Savas
authors.initials: S
authors.lastname: Berber
authors.forename: David
authors.initials: D
authors.lastname: Tománek