Andrea Cavalleri

Abstract:

The coherent lattice dynamics in semiconductor heterostructures were studied using an optical-pump X-ray probe. The data provided quantitative information on the propagation of optically generated picosecond acoustic pulses inside Germanium layers, across buried interfaces and into underlying Silicon substrates. The analysis of the time resolved data from Silicon, detect transmission of the acoustic pulse across the buried Ge/Si interface into the Silicon substrate. The peak magnitude of the compressive strain is of the order of 0.006% corresponding to an absolute change in interlayer spacing of approximately 20 femtometer. The magnitude of the measured compression feature is one order of magnitude smaller than in any previous reported data.

Abstract:

A detailed characterization and optimization of the experimental conditions for efficient production of short pulse X-rays to be used in time-resolved experiments are presented. Experimental evidence indicating that the production of K-shell holes generating line radiation arises from collisions with non-thermal electrons and that the size of this source is on the order of the laser spot size is discussed. The combination of extremely small source size, high flux, and short time duration are ideal for time-resolved pump-probed X-ray diffraction and spectroscopic studies of crystalline and molecular dynamics.