Study of electric quadrupole interactions of 111In and 111Cd following ion implantation of 111In into graphite

The nuclear electric quadrupole interaction of 111In ion-implanted in hightly oriented pyrolytic graphite has been observed by means of low-temperature nuclear orientation and by means of perturbed angular correlations. From the first kind of experiment, it is concluded that a relatively large number of indium nuclei experience a well-defined macroscopic orientation, which is partly lost after the radioactive decay to cadmium. Indeed, the second kind of experiment revealed a broad distribution of electric field gradients interacting with the 245 keV Cd excited state, as well as a small fraction experiencing a unique electric field gradient. The experimental results are compared with theoretical calculations of the electric field gradient at various lattice positions, in which carbon and indium electronic wavefunctions are allowed to hybridize. Lattice positions of the covalent indium atom between the graphite layers can explain the measured electric field gradient of Vzz=+1.47(11) x 1022 V/m2, directed parallel to the graphite c-axis. (orig.)