High Speed Detection System for Surface Science Experiments

• Subject Area: Chemical Solid State and Surface Research
• Term: Funded in 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 547075996

Microkinetic models of heterogeneous catalysis are central to engineering efforts to improve chemical technology. Unfortunately, measuring accurate absolute rates of elementary sur-face reactions has proven to be a great challenge to the field of surface science. Only in 2017, did it become possible to routinely measure highly accurate reaction rates for surface reactions thanks to the development of Velocity Resolved Kinetics (VRK). Since then, VRK has been applied to determine: surface site-specific rates, adsorbate binding energies and diffusion barrier heights, reaction barrier heights, and adsorbate-adsorbate interaction energies, and reaction mechanisms including identification of adsorbate intermediates, demonstrating its value to provide accurate kinetic data for catalysis. In conventional VRK, the reaction at the surface is initiated by a pulsed molecular beam and the products are detected by a quasi-universal method of non-resonant multiphoton ionization with a high peak-power near-infrared pulsed laser. Ions are detected with imaging methods to determine the reaction products’ velocities, which provides the product flux. The reaction time is found by scanning the delay between the pulsed molecular beam and the pulsed ionization laser. This often requires hours of data acquisition to record ion images at all possible delays between the two pulses, restricting the experiment to samples that do not change with time. Recently, we demonstrated High-Speed Velocity Resolved Kinetics (HSVRK), an enhanced version of VRK that significantly expands its capabilities by several orders of magnitude. In proof-of-concept experiments, we could successfully monitor the single pulse desorption of NO from Pt(111) and the NH3 oxidation on platinum surfaces. HSVRK uses a single molecular beam pulse to initiate the reaction and products are detected with a 100 kHz train of laser pulses from an Ytterbium laser. This serves as a quasi-continuous detection scheme for reaction kinetics dramatically improving the duty factor of the experiment. In this way, the kinetic trace can be obtained even from a single molecular beam pulse. Additionally, a high-speed time-resolution event camera is required to handle image acquisition at this rapid rate. Our recent preliminary experiments show that HSVRK is dramatically more sensitive than conventional VRK and drastically reduces measurement times. The event camera used in this experiment also allows multi-mass imaging. Furthermore, the high-speed detection rate significantly simplifies and enhances experiments on surface reactivity of chiral molecules. This makes many new studies in surface chemistry possible. With funds provided by this grant, we will purchase an Ytterbium Laser, a pulse-compressor and a high time-resolution event camera for ion imaging. This equipment will be used to up-grade an existing VRK apparatus to be able to perform HSVRK at 100 kHz.

• DFG Programme: Major Research Instrumentation
• Major Instrumentation: Hochgeschwindigkeits-Detektionssystem für Oberflächenwissenschaftsexperimente
• Instrumentation Group: 5700 Festkörper-Laser
• Applicant Institution: Georg-August-Universität Göttingen
• Leader: Professor Dr. Alec Michael Wodtke