When bromine is exposed to a Cu surface, the bromine initially chemisorbs. Continued exposure however leads to the formation of bulk CuBr. The CuBr grows on top of the Cu surface in a (111) orientation. In this movie, we have all ready formed some CuBr which is visible as the white or raised islands in the center of the image. As the movie starts, you'll see Cu being eaten away from narrow patches of the steps leading to channels in the terraces. The CuBr species formed at these active sites on the step do not stay they but rather diffuse and add to the existing CuBr island causing it to grow. Remarkably, this process continues unabated even after the channel passes the edge of the CuBr layer.