Laser-excited mechanical oscillation of semiconductor nanocrystals

In this proposal we plan to investigate tailored time-dependent strain fields as a new route to control the electronic states of nanoscale quantum objects in semiconductors. We aim to employ picosecond strain pulses to control the recombination dynamics of excitons trapped in low-dimensional nanostructures. Strain pulses are excited using a photoacoustic method and monitored via time-resolved Brillouin scattering. We focus on the structural dynamics after optical generation of coherent acoustic phonons. Time-resolved x-ray diffraction will be applied to first determine the nanomechanical eigenmodes of the nanocrystal assembly and second to control the acoustic modes of the nanostructure by multiple consecutive optical excitations. Sufficient temporal resolution is achieved by slicing the x-ray probe beam with an ultrafast photoacoustic Bragg switch. Based on this information we want to quantify the transient deformation due to photoacoustic strain in InP nanocrystals.