UNIVERSITY PARK, PA – Penn State Applied Research Laboratory (ARL) recently received funding from the Defense Advanced Research Projects Agency (DARPA) to develop diamond-based photocathodes, a technology with the potential to transform next-generation electron emission systems. This award further supports ARL’s development of diamond materials through July 2026.
Photocathodes are commonly found in everyday devices such as photomultiplier tubes, image intensifiers, high power electronics, and free electron lasers as bright electron sources. Photocathodes typically use low-workfunction metals or semiconductors that are applied in sub-micron thicknesses on flat surfaces that are millimeters to centimeters in size.
While most high quantum efficiency photocathode devices are made from alkali antimonides and tellurides, they suffer a key drawback: these materials readily poison, or react to their environment. As a result, they are required to be packaged, transported, fabricated, and operated in an ultrahigh vacuum environment and still can suffer degradation due to repeated use. Effectively, current photocathode technologies are limited in size and expensive to field due to the logistics associated with these maintaining these environments during all phases of photocathode production.
ARL researchers plan to leverage the exceptional optical and electronic properties of diamond to engineer robust, high quantum efficiency photocathodes capable of operating with long lifetimes under extreme conditions, overcoming the limitations of traditional photocathodes. This effort will combine state-of-the-art materials synthesis, doping control, and surface engineering to create diamond films with high quantum efficiency that can be scaled to large areas.
Diamond’s unique chemical and physical inertness, ultrawide bandgap of 5.5 eV, and highest thermal conductivity of any material makes it uniquely suited to the challenges of photocathode manufacturing. Other attractive attributes include a negative electron affinity surface that can readily be obtained on diamond by terminating it with hydrogen atoms, controlled impurity doping with nitrogen, and its substantial resistance to poisoning.
“The key reason diamond is of interest for photocathode applications is its substantial resistance to poisoning.” said Principal Investigator Luke Lyle, Ph.D., an associate research professor in ARL’s Electronic Materials and Devices Department.
“Conventional photocathode materials have substantial drawbacks when it comes to their useable lifetime, as well as the logistics required to manufacture, transport, and operate under ultrahigh vacuum.”
This research also seeks to scale development of diamond photocathode materials to large areas. Because materials for traditional photocathodes need to be grown in highly controlled atmospheric environments, they are limited to centimeters in size. However, due to the recent developments of microwave plasma chemical vapor deposition technologies, wafer-scale growth of diamond has scaled to large diameters.
The program is led by Principal Investigator Luke Lyle, Ph.D. and co-Principal Investigator Matthew Krohn, Ph.D. The ARL project team includes research faculty Benjamin Dutton, Ph.D., and David Snyder, Ph.D., engineering staff Gregory Pastir, Mason Cleff, Daniel Erdely, Joshua Fox, and Robert Lavelle.
About the Applied Research Laboratory at Penn State
The Applied Research Laboratory at Penn State, a University Affiliated Research Center, was established in 1945 at the request of the U.S. Navy. ARL supports national security, economic competitiveness, and quality of life through education, scientific discovery, technological demonstration and successful transition to application.
For more information, visit www.arl.psu.edu