Scanning tunneling microscope observations of MgO fracture surfaces

Abstract

Scanning tunnel microscope (STM) observations of surfaces of single crystal MgO fractured in three-point bend and coated with thin gold films are reported. Macroscopically, the fracture geometry employed yields a smooth, approximately (027) surface along the tensile side of the sample, and a heavily stepped (001) surface along the compressive side. STM observations of the tensile side show smooth regions approximately (027) in orientation with relatively little relief. These smooth regions are separated by rough regions which often could only be partially imaged with the present instrument. The compressive side showed much more varied structures, with many (001) features as well as features approximately (720) in orientation. Fractal dimension measurements were made on topographs of tensile and compressive side features. Observations of triangular features on the compressive side of one MgO sample show evidence of interaction between the growing crack and dislocation structures. The significance of these microscopic measurements to energy dissipation processes during crack growth in MgO are discussed.