Koji Yokoyama
22 Sep 2021



Beamline scientist on the muon instrument EMU

Koji next to EMU

After high school, Koji attended Shizuoka University in Japan to study physics. “In my early years at university, I hoped to become a scientist and have been on that path ever since."

His PhD was based in a laser lab, studying optical physics in semiconductors. In 2007, a collaboration with RIKEN took him to ISIS to carry out photo-excited µSR experiments. He joined RIKEN in 2009 as a postdoctoral researcher working on slow muon generation, known as 'low-energy muons'.

Low energy muon generation at the RIKEN facility at ISIS requires the use of muons and a laser. Koji explains, “Surface muons commonly used for material studies have a defined momentum, so their energy cannot be changed and they become deeply implanted into materials. However, with slow muons, we can change their energy by re-acceleration and therefore their implantation depth." Because slow muons can stop near the surface, a wide range of µSR experiments can be conducted on the surface-subsurface range of materials.

After joining the European Research Council funded muon group as a postdoctoral researcher, to build a laser system for the ISIS muon instrument HiFi and carry out photo-excited µSR experiments, Koji is now a full-time beamline scientist on the EMU instrument.

“Currently I'm focusing on studying charge carrier kinetics in semiconductors with photo-excited µSR, which has a wide range of applications from photovoltaics to power semiconductors." Understanding the charge carrier dynamics ultimately helps to optimise device performance and feeds into developing better models and designs. Koji's pioneering research has shown that muons can be used to probe the carrier density and give us an idea of how they move around in bulk, which previous research hasn't been able to do.

“It's extremely fruitful seeing the user community engaging with our research and then coming to ISIS to use the techniques we have developed."

Contact: de Laune, Rosie (STFC,RAL,ISIS)