Residence sites of 19F implants in carbon allotropes

The (p,p') reaction with a pulsed proton beam has been used in in-beam Time Differential Perturbed Angular Distribution(TDPAD) measurements to excite and recoil implant 19F ions into various carbon allotropes (single and polycrystalline graphite and vitreous and colloidal carbon). Spin rotation R(t) spectra generated from delayed time spectra of the 19F 197 keV gamma ray show that the implants take up two characteristic residence sites in the host samples. One site is sharply defined (low spread δ), and has a quadrupole coupling frequency of νq ∼ 57 MHz; the other, of lower νq, is more diffuse (large δ).The parameters of the electric field gradients at the two implant sites in the carbon allotropes are compared with similar measurements on 19F in diamond, Si and Ge hosts, and in several F-C compounds. (author)