Time-Resolved Photoemission Electron Microscopy: Development and Applications

Time-resolved photoemission electron microscopy (TR-PEEM) belongs to a class of experimental techniques
combining the spatial resolution of electron-based microscopy with the time resolution of ultrafast optical
spectroscopy. This combination provides insight into fundamental processes on the nanometer spatial and
femto/picosecond time scale, such as charge carrier transport in semiconductors or collective excitations of
conduction band electrons at metal surfaces. The high spatiotemporal resolution also offers a detailed view of the
relationship between local structure and ultrafast photoexcitation dynamics in nanostructures and nanostructured
materials, which is beneficial in exploring new materials and applications in opto-electronics and nano-optics.

This thesis describes the investigation of ultrafast photoexcitation dynamics in metal- and III-V semiconductor
nanostructures using TR-PEEM. We investigate hot carrier cooling in individual InAs nanowires where we find
evidence that electron-hole scattering strongly contributes to the intra-band energy relaxation of photoexcited
electrons on a sub-picosecond time scale and we observe ultrafast hot electron transport towards the nanowire
surface due to an in-built electric field. We demonstrate the combination of TR-PEEM with optical time-domain
spectroscopy to enable time- and excitation frequency-resolved PEEM imaging. The technique is applied to GaAs
substrates and nanowires. TR-PEEM is further used to investigate localized and propagating surface plasmon
polaritons. We explore the optical properties of disordered, porous gold nano-particles (nanosponges). Using TRPEEM,
we can resolve several plasmonic hotspots with different resonance frequencies and lifetimes within single
nanosponges. We also explore excitation and temporal control of surface plasmon polaritons by means of singlelayered
crystals of the transition metal dichalcogenide WSe2.

In addition, this thesis includes developments in ultrafast optics, aiming to expand the capabilities of the TR-PEEM
setup. We present a setup for generating tunable broadband ultraviolet (UV) laser pulses via achromatic second
harmonic generation. The setup is suitable for operation at high repetition rates and low pulse energies due to its high
conversion efficiency. Further, we describe a transmission grating-based interferometer for the generation of stable,
phase-locked pulse pairs. Pulse shaping based on liquid crystal technology allows accurate control over the temporal
shape of femtosecond laser pulses. We characterize Fabry-Perot interferences affecting the accuracy of such pulse
shapers, and we demonstrate a calibration scheme to compensate for these interference effects.