DIRECT OBSERVATION OF COMPOSITIONALLY HOMOGENEOUS A-C-H BAND-GAP-MODULATED SUPERLATTICES

It is shown that amorphous hydrogenated carbon (a-C:H) band-gap-modula ted superlattices can be observed by transmission electron microscopy. The layering proves to be well defined and it is demonstrated that ch anges in the band gap from 1.5 to 2.8 eV cannot be associated with ord ered graphitic regions, in that crystalline regions larger than 0.5 nm are not observed. Differences in the amount of pi bonding are found t o lead to changes in the average atomic scattering factor. It is sugge sted that the changes in pi bonding are associated with changes in loc al ordering that control the band gap.