MOBILE POINT-DEFECTS AND ATOMIC BASIS FOR STRUCTURAL TRANSFORMATIONS OF A CRYSTAL-SURFACE

Structural transformations on elemental semiconductor surfaces typical ly occur above several hundred degrees Celsius, and the atomic motions involved are extremely rapid and difficult to observe. However, on th e (111) surface of germanium, a few lead atoms catalyze atomic motions so that they can be observed with a tunneling microscope at temperatu res below 80 degrees C. Mass transport and structural changes are caus ed by the creation and propagation of both vacancy-like and interstiti al-like point defects within the crystal surface. The availability of dangling bonds on the surface is critical. A detailed atomic model for the observed motions has been developed and is used to explain the st ructural phase transition Ge(111)-c(2x8) <----> 1 x 1, which occurs ne ar 300 degrees C.