MODIFICATION OF SURFACE BAND BENDING OF DIAMOND BY LOW-ENERGY ARGON AND CARBON ION-BOMBARDMENT

Argon and carbon ion bombardment of p-diamond at 500-5000 eV in ultrahigh vacuum were studied by in situ x-ray photoelectron spectroscopy (XPS) and low energy electron diffraction analysis. Both argon and carbon ion bombardment at room temperature in the present energy range created a defective surface layer. The radiation damage was manifested by the introduction of a distinct C 1s peak (referred to as the ''defect'' peak later) with a binding energy about 1 eV less than that of the bulklike diamond peak, and by the introduction of some additional filled states (referred to as the ''filled states'') near the valence band edge of diamond. It was found that in comparison to argon bombardment, carbon bombardment was more efficient in producing the filled states but less efficient in raising the C 1s defect peak. While the filled states disappeared by annealing at about 500-degrees-C, the C 1s defect peak did not change much even with a 1000-degrees-C anneal. These results suggest that the C 1s defect peak, which has also been observed on reconstructed diamond surfaces after hydrogen desorption [see, e.g., B. B. Pate, Surf. Sci. 165, 83(1986)], is associated with vacancy formation and aggregation which give some ''internal surfaces'' with a behavior like a reconstructed atomically clean diamond surface. The filled states introduced by ion bombardment are associated with interstitials or interstitial clusters. The amount of residual defects was found to increase with both an increasing bombardment dose and energy. For an argon bombardment at 1000 eV to a dose of 5 x 10(14)/cm2, the defective layer was estimated to be about 1.5 nm. Further, it was found that the radiation damage, particularly the ''vacancy defects'', could only be annealed (at 1000-degrees-C) when the dose was below 5 x 10(14)/cm2 at a bombardment energy of 500 eV. XPS band bending analyses also showed that room temperature bombardment induced a small reduction (0.2 eV) of the surface Fermi level position (E(Fs)) on the p-diamond. However, subsequent vacuum annealing caused a rather large increase of E(Fs)). But the E(Fs)) data from about 20 bombarded and annealed samples were always less than 2.2 eV. Thus the formation of an n-type diamond was not observed.