Photoemission study of Cr on a-Si:H

We report a synchrotron-radiation photoemission study of Cr evaporated on rf-sputtered a-Si:H at room temperature. The evolution of the interface qualitatively follows that on c-Si, despite differences in the valence-band emission. The interface begins with an inactive layer (≤1 Å) of Cr, followed by an intermixed Cr/a-Si:H layer (≤12 Å). With further Cr deposition, bulklike Cr metal begins to develop on top of these. Some features exhibited by the Cr/a-Si:H interface are specific to a-Si:H surfaces. For instance, Cr adatoms are found around the dangling-bond neighborhood at coverages below 1 Å, avoiding Si–H bonds. The oxygen residual is responsible for the presence of a 6-eV peak in the valence band as well as a chemical shift in the Si 2p core levels. However, it is the intermixed Cr/a-Si species occurring above 2 Å of Cr deposition that provoke the presence of the structures, even though at low coverages, the oxygen residue does not show any effect on the surface-electronic structure of the a-Si:H film. At high coverage, a slight trace of silicon atoms is still detectable.