VISUALIZATION OF ETCHING MECHANISMS OF A VICINAL CU SURFACE USING SCANNING-TUNNELING-MICROSCOPY

The reaction of Br-2 with a Cu surface vicinal to (100) was studied by recording scanning tunneling microscopy (STM) movies during exposure to Br-2. Initial exposure to Br-2 resulted in the formation of a chemi sorbed layer of Br atoms with a c(2 X 2) structure on the (100) terrac es. The STM movies showed that, as the chemisorbed layer saturated, th ermal fluctuations in the step positions slowed, and the steps aligned parallel to:the [001] and [010] directions. Further exposure to Br-2 resulted in the formation of CuBr; the STM movies showed that the Cu a toms were consumed from the steps with the reaction proceeding predomi nantly perpendicular to the step edges. Channels created in the step e dges indicated that the reactivity of the steps was not uniform. The C uBr formed by the reaction did not accumulate at the sites where the C u atoms were consumed; rather, large two-dimensional CuBr islands were observed at seemingly random locations. This indicated that CuBr form ed at the step edges was mobile and that the CuBr islands formed by nu cleation of diffusing CuBr species. The CuBr islands spanned many step s suggesting that the diffusing CuBr can cross step edges. Atomic-reso lution images of the CuBr islands revealed hexagonal symmetry consiste nt with CuBr(111) parallel to the surface. (C) 1998 American Vacuum So ciety.