Nanofabricated low emittance field emitter array cathodes were demonstrated for the first time, and successfully applied to observe the low-energy electron diffraction from suspended 1 monolayer graphene. The work has an impact on the future development of compact X-ray free electron lasers, THz/RF vacuum electronic sources, and ultrafast electron imaging and diffraction experiments.
Development of a high brightness and high current electron source has a significant impact on the compact X-ray free electron lasers, such as the SwissFEL under commissioning at the Paul Scherrer Institut (PSI), RF/THz vacuum electronic amplifiers, as well as for electron imaging and diffraction experiments. Field emitters are distinct from thermionic emitters requiring heating current or photocathode demanding UV laser excitation: they can efficiently produce coherent electron pulses by fast electrical switching or near infrared laser excitation. Field emitter arrays (FEAs), combining the field emission from thousands of nanotips, have been studied as high current sources but their inherently large angular electron velocity spread hiders their application for high brightness and coherent applications.
The possibility to realize a low-emittance nanofabricated FEA, producing collimated field emission beamlet from an array of metal nanotips with on-chip, integrated focusing electrode, has been intensely studied theoretically and experimentally in literature. The recent experiments by the Vacuum Nanoelectronics group in the Laboratory for Micro- and Nanotechnology in collaboration with the Max-Planck Institute demonstrated this for the first time by fabricating such a device with an optimized device structure, Figure 1, and performing the beam characterization experiments. In addition, the nanofabricated FEA was successfully applied to observe the electron diffraction from suspended graphene for the first time, Figure 2. The observations were well described by theory on the emittance and coherence of field emitters
These results were published in Nature Communications.
The work has been partially supported by the SwissFEL project, PSI, and the Swiss National Science Foundation.
Measurement of transverse emittance and coherence of double-gate field emitter array cathodes
Soichiro Tsujino, Prat Das Kanungo, Mahta Monshipouri, Chiwon Lee, & R. J. Dwayne Miller
NATURE COMMUNICATIONS, 7:13976 (2016), DOI: 10.1038/ncomms13976