AVS 45th International Symposium
    Surface Science Division Wednesday Sessions
       Session SS3-WeM

Paper SS3-WeM4
Direct Observation of Etching Mechanisms of Cu Surfaces with STM

Wednesday, November 4, 1998, 9:20 am, Room 314/315

Session: Surface Dynamics and Roughening
Presenter: E.I. Altman, Yale University
Authors: C.Y. Nakakura, Yale University
E.I. Altman, Yale University
Correspondent: Click to Email
Scanning tunneling microscopy movies of the halogenation and subsequent etching of Cu(100) and Cu(11 1 0) were recorded. Adsorption of both Br@sub 2@ and Cl@sub 2@ resulted in a c(2x2) structure on the Cu(100) terraces. As the adsorbate coverage approached saturation, the substrate steps faceted to align along the close-packed directions of the adlayer. The faceted steps were the Cu atom source for subsequent halide formation and etching. For Cl@sub 2@, the reaction was initiated at facet corners and proceeded by stripping away rows of atoms parallel to the steps. In contrast, Br@sub 2@ could also react perpendicular to the step edge creating channels etched into the terraces. For both Cl@sub 2@ and Br@sub 2@, the halide formed by reaction diffused across the surface, nucleating and growing halide clusters independently of the reaction step. At room temperature, three-fold symmetric CuBr(111) islands were observed that grew by addition of CuBr units to <100> island edges. Remarkably, the presence of these islands did not block further reaction of the underlying Cu surface. The CuBr islands formed at room temperature roughened either with time or annealing. At temperatures above 440 K, the halide formed by reaction sublimes resulting in etching. Under these conditions, a new CuBr morphology was observed: four-fold symmetric islands. These square islands nucleated at step edges and then sublimed at rates far in excess of those of similar sized three-dimensional clusters, suggesting that controlling the morphology of the CuBr can lead to reductions in etching temperatures.