Femtosecond x-ray diffraction reveals a liquid-liquid phase transition in phase-change materials.

In phase-change memory devices, a material is cycled between glassy and crystalline states. The highly temperature-dependent kinetics of its crystallization process enables application in memory technology, but the transition has not been resolved on an atomic scale. Using femtosecond x-ray diffraction and ab initio computer simulations, we determined the time-dependent pair-correlation function of phase-change materials throughout the melt-quenching and crystallization process.

Ultrafast photovoltaic response in ferroelectric nanolayers.

We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on femtosecond time scales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction.

Ultrafast reversible ligand isomerisation in Na2[Fe(CN)5NO] x 2 H2O single crystals.

We present a time-resolved absorption study on the light-induced generation of reversible linkage NO isomers in single crystals of Na(2)[Fe(CN)(5)NO] x 2 H(2)O using laser pulses of 160 fs width. Using the pump wavelength lambda = 500 nm the singlet-singlet (1)A(1)-->(1)E excitation induces the NO rotation by about 90 degrees from the linear Fe-N-O configuration to a side-on configuration [structure: see text]. The formation of the isomer is monoexponential with a characteristic time of tau = 300(20) fs and proceeds along a diabatic potential surface without occupation of further intermediate states.

On the photophysical properties of new luminol derivatives and their synthetic phthalimide precursors.

The photophysical properties of a series of structurally related 4-aminophthalimides and the corresponding 5-aminophthalic hydrazides (luminols) are reported. Absorption, steady-state, and time-resolved fluorescence spectra of luminols exhibited substitution, solvent, and pH dependence. Singlet lifetimes have been determined by time-resolved laser flash spectroscopy.