Chemically sensitive structure-imaging with a scanning transmission electron microscope

Abstract

Conventional high-resolution electron microscopy uses the phase-contrast method¹, in which the diffracted beams emerging from the sample are recombined on the viewing screen of the microscope. The resultant contrast depends on the relative phases of the diffracted beams, which is sensitive to microscope and sample parameters, so that images must be interpreted by means of simulation, and defect models are somewhat empirical. By using a high-angle detector in a scanning transmission electron microscope, these problems may be avoided and high atomic-number contrast may be obtained. Here we present results of this technique applied to single crystals of the high-transition-temperature superconductors YBa₂Cu₃O_7–x and ErBa₂Cu₃O_7–x. The heavy-atom planes are directly imaged as bright lines, and the probable structure of an observed defect is directly inferred from its image.