Bismuth-induced structures on Si(001) surfaces

We have examined Bi-induced surface structures of Si(001), formed in the vi cinity of its desorption temperature, by means of scanning tunnelling micro scopy and reflection high-energy electron diffraction.. Below the desorptio n temperature, adsorption of bismuth results in a (2 x n) Bi-Si(001) recons truction with second-layer Bi dimers either parallel or perpendicular to th e underlying dimers. Even after the desorption of the bismuth epitaxial lay er, some bismuth remains on the surface with characteristic structures whic h depend upon the formation pathway. Perfectly straight Bi lines 1 nm wide and hundreds of nanometres long can be formed either by annealing of the sa turated Bi epitaxial layer, or by exposure to a large flux of bismuth aroun d the desorption temperature. Exposure to a smaller flux of Bi at the desor ption temperature generates a c(4 x 4) reconstruction. The stability of the c(4 x 4) reconstruction is thought to be due to a strain effect resulting from incorporated Bi. Both the Bi line and the c(4 x 4) structures disappea r after further annealing and the remaining Bi concentration was below the detection limit of secondary ion mass spectroscopy. (C) 1999 Elsevier Scien ce B.V. All rights reserved.