PHYSICAL REVIEW LETTERS, vol. 69, no. 15, page. 2228 - 2231, 1992-10-12
SURFACE SCIENCE, vol. 276, no. 1-3, page. 353 - 359, 1992-10-01
PHYSICAL REVIEW B, vol. 45, no. 4, page. 1705 - 1711, 1992-01-15