​Earlier this month, the HiZPAD network, organised in collaboration between staff member​​s from STFC, ESRF, and PSI, held its first in-person workshop since 2019.​

A History of European Collaboration 

Its goal was to promote collaboration between European synchrotrons, research institutes, and companies to evaluate high-Z pixel sensor technologies for application to high-energy X-ray detection at synchrotron and free electron laser X-ray sources.

While the original HiZPAD activity was completed in 2011, members from across STFC, the European Synchrotron Radiation Facility (ESRF) and the Paul Scherrer Institute (PSI) recognised how valuable the collaboration had been for all involved.

The team decided to continue hosting meetings, using the network of early career researchers that the original HiZPAD had already established. 

In 2013 the team met up for their first workshop, hosted by STFC at the Rutherford Appleton Laboratory, with a focus on the simulation of high-Z materials. This was followed by subsequent events in Tomsk, Russia in 2017 and a return to RAL in 2019.

A workshop had also been planned for April 2020 at ESRF but, due to COVID-19, it was cancelled. 

In its place, the network established a series of popular online webinars which proved to be effective in maintaining a sense of community during the many challenges of 2020 – 2022.

Helping Next Generation Facilities to See

High-Z pixel detectors are and have been since HiZPAD’s conception in the late 2000s, a technology of strategic importance for the photon science community. 

Now in the 2020’s, many light sources are beginning upgrades that are further increasing the need for these technologies.

Taking the recently announced Diamond-II as an example, the average energies of the X-rays used across the facility will increase to more than 20keV. 

At these energies, existing silicon-based detector technologies become unusable due to the low density of silicon, which means many of the X-rays pass through the detector without ever being stopped. 

High-Z materials like Cadmium Zinc Telluride (CdZnTe) and Gallium Arsenide (GaAs) have densities more than double that of silicon making them much more suited to these sorts of energies.

HiZPAD Goes International

This time the event was hosted by the DESY Photon Science Detector Group at the Centre for Free-Electron Laser Science in Hamburg, Germany.

Organised by HiZPAD veterans Matt Veale (STFC), Marie Ruat (ESRF) and Dominic Grieffenberg (PSI) the workshop brought together a mix of established members of the community and early-career researchers new to the field.

The participants, 40 of whom presented their research in person with another 25 joining via Zoom, attended the workshop from across the world – as far afield as North America and Japan.

They presented the latest research in high-density semiconductor material growth, characterisation, and application to large-scale science facilities and beyond.

Some of the biggest developments discussed during the workshop were announced by industry professionals, including:

• Glen Wu of Redlen Technologies, the world’s only supplier of high-flux-capable CdZnTe, and Redlen’s new Fine Pixel Pitch (FPP) Custom Sensor.
• Juha Kalliopuska of ADVAFAB (Finland) and Pietro Zambon of DECTRIS (Switzerland) and the impressive results from their respective GaAs sensor materials.

Many of the workshop’s attendees were in their early careers, attending HiZPAD for the first time and sharing their challenges and successes in the field.

The network was also supported by the Strategic Partnership in X-Ray Instrumentation for Next Generation Synchrotrons (SPRINGS) project, part of UKRI’s International Science Partnership Fund (ISPF).

Matt Veale, Technology Department staff member and HiZPAD organiser, provided insight into the value of the workshop:

“The academics I met through the HiZPAD project helped me establish a network of contacts across Europe early in my career. Contacts like Dominic and Marie have been invaluable through the years helping me make sense of my own research and, together, coming up with new ideas that have helped drive the field forward. My hope was always that this week’s HiZPAD Workshop would help nourish these existing links but also help those newer members of the community establish networks of their own. Having seen the fantastic level of engagement between participants old and new I'm confident we achieved this!”

Ben Cline, Technology Department staff member and HiZPAD attendee, explained how virtual access supported his attendance:

“The provision of a virtual option for the workshop’s attendance was highly appreciated as it removed the barriers associated with a two-day international trip and allowed me to attend and present at an event that I otherwise would not have been able to make.  Whilst virtual attendance obviously does not easily facilitate the development of long-term connections and relationships, it did allow me to remain up-to-date with the current state of high-Z detector research within the community. The streaming of the event was flawless with few/no issues and great video/audio quality across the entire two days.”

Kavya Reddy Dudipala, Materials Scientist at the University of Oxford and HiZPAD attendee, summarised her experience of the workshop:

“The workshop was very useful for helping everyone to understand the challenges posed at different stages of detector development, from the investigation of novel materials like perovskites and understanding the influence of contact materials and contact deposition methods, to developing electronic chips for detectors, experimental equipment, and novel applications like X-ray fluorescence spectroscopy. 

“Bringing together academics with scientific acumen, engineers with innovative technological ideas, and industries with strong business strategies, all under one roof, was very thought-provoking. I strongly believe more such events, which bring together people with different skills to work towards the same common goal, must be held more often - not only to understand the challenges in the field ahead of time for faster detector development but also for advancement towards out of the box solutions to current challenges.”

As this recent workshop proved, HiZPAD continues to be a highly valued network of researchers in high-Z materials both in Europe and beyond. 

Going forward, the network plans to continue to host approximately 3 webinars a year as well as an in-person meeting. 

The organisers hope that the network will continue to foster collaboration between the community for years to come.

Written by Cat Lewin-Williams and Matt Veale.