JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B, vol. 17, no. 6, page. 2600 - 2602, 1999-11
APPLIED PHYSICS LETTERS, vol. 61, no. 13, page. 1516 - 1518, 1992-09-28
PHYSICA C, vol. 194, no. 3-4, page. 293 - 300, 1992-05-10