A.K. Schmid

In-situ STM studies of strain-stabilized thin-film dislocation networks under applied stress

Abstract The effect of uniaxial applied stress on dislocation networks present in the atomic surface layer of Au(111) was studied. Themeasurements were made using a novel instrument combining ultrahigh vacuum scanned-probe microscopy with an in-situstress-strain testing machine. The technique provides microscopic information, up to atomic resolution, about the large scaleplasticity of surface layers under applied loads. The herringbone reconstruction of the Au(111) surface is a classic example of astrain stabilized dislocation network. We find that under 0.5% uniaxially applied compressive strain a dramatic restructuring ofthe network takes place. The three-fold orientational degeneracy of the system is removed and threading edge dislocations areannihilated.

Linking dislocation dynamics and chemical reactivity on strained metal films

The interaction of a model strained metal film with oxygen is studied by scanning tunneling microscopy. Two monolayers of copper on Ru(0001) present a well-defined dislocation network composed of threading dislocations and Shockley partial dislocations separating areas of fcc and hcp stacking. We find that oxygen first reacts with these threading dislocations. Then, for exposures up to ~0.4 L O 2 , new threading dislocation arrays appear on the surface. With the addition of more oxygen, the mesoscopic structure of the film changes from a striped array of Shockley partials to a disordered array of triangular fcc regions bounded by dislocations, as oxygen proceeds to etch away the hcp areas of the copper film.

Multiplication of threading dislocations in strained metal films under sulfur exposure

Strained thin films often contain ordered networks of misfit dislocations which can determine their chemical and mechanical properties. We consider the reaction of sulfur with two-monolayer films of Cu on Ru(0001). These films contain a network of parallel partial dislocations, separating regions of fcc and hcp stacking, with threading edge dislocations where partial dislocations meet. Sulfur reacts with the threading dislocations and dissociates them. The increase in the threading dislocation density is accommodated by modifying the dislocation network.