UHV TRANSMISSION ELECTRON-MICROSCOPY OF IR(001) .1. MICROSTRUCTURE OF THE (1X1) AND THE RECONSTRUCTED (5X1) SURFACES

Experimental results on the unreconstructed Ir(001)-(1 x 1) and the reconstructed (5 x 1) surfaces using plan view ultra-high vacuum transmission electron microscopy (UHV-TEM) are presented. The contamination-stabilized Ir(001)-(1 x 1) surface is moderately well ordered with steps preferentially aligned along [110] and [100] directions, but is fairly rough on the atomic scale as evidenced by both dark field and high resolution imaging. The step evolution and the microstructure of the surface with repeated annealing are described. The Ir(001)-(5 x 1) reconstruction is determined by electron diffraction to be a simple quasi-hexagonal surface layer with very little distortion in a (5 x 1) registry with respect to the bulk. This surface is a much flatter one than the (1 x 1). The basic morphology of the reconstructed surface layer is shown by dark field microscopy, and the transition from (1 x 1) to (5 x 1) is a nucleation and growth process. Evidence for subsurface IrO2 precipitate particles is also presented.