Composition changes in Ar+ and e--bombarded SiC - an attempt to distinguish ballistic and chemically guided effects

We study with Auger electron spectroscopy (AES) the composition changes in amorphous SiC films with excess (i.e. free) C induced by bombardments either with 30 keV Ar+ or with 3 KeV e-. In Ar+-bombarded films the C accumulates at the surface without apparent depletion in the bombarded region, while the Si accumulates at the surface accompanied by major depletion near the Ar+ range. Significantly, movement of C to the surface occurs also due to e- bombardment. The C profile modifications are explained by assuming that a long range force (especially that provided by unbalanced surface charges) operates on the free C present in the SiC films, whereas the Si transport towards the surface is promoted by the bombardment-induced defects. Whether the direction of the Si motion is determined by the C enrichment at the surface (which traps the Si chemically), or by an interstitial flux (as has been established with such systems as Ni-Si) cannot be determined, but it is still possible to assert that the composition changes are more nearly due to defects (whence showing chemical guidance) than ballistic (whence random). We finally note that the C at the surface will tend to be sputtered away.