Ultrathin Cobalt Films Research Articles

Short-range local order of the Co/Si(111) interface studied by the extended Auger fine-structure technique.

Extended Auger fine-structure (EXFAS) spectra have been successfully recorded on ultrathin films of cobalt deposited on silicon (111) surface. Thanks to a detailed comparison of the static disorder of the interface, the short-range order characteristics of EXFAS and its surface-structural sensitivity have been clearly demonstrated.

Measurements of fractal dimension for Co-Si interfacial layers

We report on measurements of fractal dimension for ultrathin cobalt films deposited onto silicon substrates. A new method has been used for the fractal dimension measurements, which involves an image processing of transmission electron microscopy (TEM) bright field image of the ultrathin film structure. The TEM image is digitized by 512×512 pixels with intensity levels from 0 to 255, and topographic contour lines which connect the same intensity levels are obtained from the digitized image. The fractal dimension (D) of the ultrathin film structure is calculated from the contour lines by using a relation (L=AD/2) between the areas (A) and perimeters (L) for each of the closed lines as suggested by Mandelbrot [Fractal Geometry of Nature (Freeman, New York, 1982), Chap. 12]. Results of the measurements indicate that the Co-Si interfacial dimension is increased from 2.0 to near 2.5 as the reaction is progressed. The results are compared with the fluctuating fractal dimension calculated from the noise exponent data.

A crystal cleavage device for use in LEED-Auger studies: A P Janssen and A Chambers, J Phys E-Scient Instrum, 7 (6), 1974, 425–426

To test the possibility of obtaining good Co-Pt multilayers, we studied the initial stages of growth of Co on Pt(100) by surface physics techniques in order to determine the structural order of ultra-thin Co layers. The LEED-Auger data for room temperature deposition can be explained by a quasi layer-by-layer growth showing a large surface disorder. Photoemission experiments using the synchrotron radiation in the 40–130 eV range confirmed that the interface is not really abrupt and evidenced a limited interdiffusion process below the cobalt overlayers.Annealing these cobalt ultra-thin films (2–10 ML) in the 200–400 °C range gave rise to a progressive epitaxy of a cubic phase on platinum, clearly identified by LEED and RHEED. This showed the possibility of building in this temperature range an interface structurally better defined than at room temperature.