Host isotope mass effects on the hyperfine interaction of group-V donors   in silicon
  The effects of host isotope mass on the hyperfine interaction of group-V donors in silicon are revealed by pulsed electron nuclear double resonance (ENDOR) spectroscopy of isotopically engineered Si single crystals. Each of the hyperfine-split P-31, As-75, Sb-121, Sb-123, and Bi-209 ENDOR lines splits further into multiple components, whose relative intensities accurately match the statistical likelihood of the nine possible average Si masses in the four nearest-neighbor sites due to random occupation by the three stable isotopes Si-28, Si-29, and Si-30. Further investigation with P-31 donors shows that the resolved ENDOR components shift linearly with the bulk-averaged Si mass. 
T. Sekiguchi, A. M. Tyryshkin, S. Tojo, E. Abe, R. Mori, H. Riemann,   N. V. Abrosimov, P. Becker, H.-J. Pohl, J. W. Ager, E...
cond-mat.mtrl-sci cond-mat.mes-hall