PHYSICAL REVIEW B, vol. 33, no. 9, page. 6537 - 6540, 1986-05-01
JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS, vol. 5, no. 4, page. 1045 - 1048, 1987-07
PHYSICAL REVIEW LETTERS, vol. 56, no. 7, page. 749 - 752, 1986-02-17