A probe of light-harvesting efficiency at the nanoscale

SCIENTIFIC ACHIEVEMENT

Using time-resolved experiments at the Advanced Light Source (ALS), researchers found a way to count electrons moving back and forth across a model interface for photoelectrochemical cells.

SIGNIFICANCE AND IMPACT

The findings provide real-time, nanoscale insight into the efficiency of nanomaterial catalysts that help turn sunlight and water into fuel through artificial photosynthesis.

Solar-fuel tech goes for gold

In the search for clean-energy alternatives to fossil fuels, one promising solution relies on photoelectrochemical (PEC) cells: water-splitting, artificial-photosynthesis devices that turn sunlight and water into solar fuels such as hydrogen. In just a decade, researchers have achieved great progress in the development of PEC systems made of light-absorbing gold nanoparticles (NPs) attached to a semiconductor film of titanium dioxide (TiO2).

Read more on the Advanced Light Source website

Image: Laser pulses were used to excite electrons in gold nanoparticles (AuNPs) on a titanium dioxide (TiO2) substrate. X-ray pulses were used to count the electrons moving between the nanoparticles and the substrate. (Credit: Oliver Gessner/Berkeley Lab)

Laser, camera, action: Ultrafast ring opening of thiophenone tracked by time-resolved XUV photoelectron spectroscopy

Light-induced ring opening reactions form the basis of important biological processes such as vitamin D synthesis, and are also touted as promising candidates for the development of molecular switches. In recent years, new time-resolved techniques have emerged to investigate these processes with unprecedented temporal and spatial resolution.

An international research team from the USA, UK, Germany, Sweden, Australia, and the local team at the FERMI free-electron laser, combined time-resolved photoelectron spectroscopy with high-level electronic structure and molecular dynamics calculations to unravel the dynamics of a prototypical reaction along the full photochemical cycle of a ring molecule (thiophenone) – from photoexcitation, ring opening, all the way through to the subsequent ground state dynamics, and spanning a range of tens of femtoseconds  to hundreds of picoseconds. “These processes have intrigued the photochemistry community for decades” says Prof. Daniel Rolles from Kansas State University “and it is now routinely possible to visualize electronic changes and the movement of atoms in the molecule at each step of a chemical reaction”.

Read more on the ELETTRA website

Image: Artistic rendering of the photo-induced ring opening of thiophenone (left) into several open-ring products (right). The thin white lines show smoothed paths of actual trajectories. Illustration: KSU, Daniel Roles.

PHELIX beamline – delivery of analyzer and spin detector

On July 22, 2020, the last components of the PHELIX end station were delivered to SOLARIS. The delivery included a high-resolution hemispherical photoelectron energy analyzer and a VLEED spin detector.

The PHELIX end station will be exceptional: it will allow scientists to perform circular dichroism measurements (CD-ARPES) and provide direct insights into the spin texture of electron states (SP-ARPES) in the same UHV system and for the same sample. Both of these methods give information about the electron spin, but the interpretation of the CD-ARPES results alone can be challenging. However, the combination of these two methods has a number of advantages allowing for the better understanding of the systems, as it excludes differences in quality between samples and the risk of surface contamination when transferring the sample between experimental systems. Both of these factors significantly affect the obtained results, and the limited control over them reduces the reliability of the research. To our knowledge, the PHELIX beamline will be one of the very few facilities in the world where such combined measurements can be performed.

Read more on the SOLARIS website