Measurements of the electric field gradient at F impurity sites in crystalline Si and highly-oriented pyrolytic graphite were compared with cluster model calculations which were based upon Hartree-Fock and density functional methods. The time-differential perturbed angular distribution of -rays technique was used to derive the electric field gradient parameters following the implantation of 19F via the 19F(p,p’)19F• reaction. In the case of highly-oriented pyrolytic graphite, density functional theory gave a closer agreement with experimental values for 19F at a site between layers with point group symmetry of C2h and an inter-layer spacing of 0.37nm. In the case of 19F implantation into Si, three sites were found which corresponded to quadrupole frequencies of 23.2, 35.2 and 37.1MHz. Both the Hartree-Fock and the density functional calculations were consistent with the attribution of interstitial anti-bonding and bond center sites to 23.2 and 35.2MHz, respectively. In the former case, the F atom was located 0.181nm along a <111> direction from a Si atom. In the latter case, the Si-Si bond length expanded by 0.102nm above its normal lattice value. It was suggested that the third interaction, which occurred only at the 10% level, perhaps arose from sites which were associated with a defect or other impurity. In order to obtain a reduction in cluster size, the completion of dangling bonds with atoms other than H was investigated.

D.Surono, F.J.Hambsch, P.W.Martin: Hyperfine Interactions, 1995, 96[1-2], 23-35