Disorder and Roughening at Surfaces of Silver/Gold Alloys

Attempts to obtain a clean and well-ordered surface in ultrahigh vacuum for several low index faces of a 50 at\% silver/gold alloy gave rise to an unexpected phenomenon. After several cycles of sputtering and annealing, the surfaces appeared clean using Auger spectroscopy but yielded low energy electron diffraction spots of poor quality (in the case of AgAu(110), no diffraction was observed at all). Many further time/temperature annealing protocols were attempted with no improvement. In addition to the diffraction results, which indicate a lack of long-range microscopic order at the surface, continued processing resulted in macroscopic roughening of the surfaces. Electron microscopy revealed the presence of features with sizes on the order of microns at the roughened surfaces. Analysis of the lineshapes of the diffuse LEED beams for the AgAu(111) surface indicates that the sizes of the ordered patches on the surface are less than a nanometer. These results will be presented in more detail and possible explanations for this extraordinary behavior will be discussed.