High-Resolution Photoelectron and Photovoltage Spectroscopy at MHz Repetition Rates

Photoemission spectroscopy (PES) is a fundamental tool for probing the electronic structure of amorphous and quantum materials, including at buried interfaces. Enhancing its sensitivity and throughput is crucial for resolving fine spectroscopic details and enabling data-intensive measurements to drive new understanding of materials and devices, such as scanning photoemission microscopy and pump-probe experiments. However, a limitation commonly encountered in these studies has been the low repetition rate of conventional tabletop-scale light sources, which restricts data acquisition rates and introduces space-charge broadening effects that degrade energy resolution at high photon fluxes.

In this talk, we present the development of a table-top ultraviolet PES system with fast acquisition times and high spatial resolution. Its light source relies on efficient nonlinear photon upconversion to the vacuum UV range in a hollow gas-filled waveguide, driven either by high-harmonic generation or cascaded four wave mixing of a Yb-based femtosecond laser. Operating at MHz repetition rates and coupled with a highly efficient time-of-flight analyzer, this system can achieve high photoelectron count rates while keeping low photon flux per pulse. We further report on progress toward applications in photovoltage spectroscopy for characterizing band bending and defect states in metal-oxide-semiconductor structures.