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