UTA versus line emission for EUVL: Studies on xenon emission at the NIST   EBIT
  Spectra from xenon ions have been recorded at the NIST EBIT and the emission into a 2% bandwidth at 13.5 nm arising from 4d-5p transitions compared with that from 4d-4f and 4p-4d transitions in Xe XI and also with that obtained from the unresolved transition array (UTA) observed to peak just below 11 nm. It was found that an improvement of a factor of five could be gained in photon yield using the UTA rather than the 4d-5p emission. The results are compared with atomic structure calculations and imply that a significant gain in efficiency should be obtained using tin, in which the emission at 13.5 nm comes from a similar UTA, rather than xenon as an EUVL source material. 
K. Fahy, P. Dunne, L. Mckinney, G. O'sullivan, E. Sokell, J. White, A.   Aguilar, J. M. Pomeroy, J. N. Tan, B. Blagojevic, E...