(55)Mn pulsed electron nuclear double resonance (ENDOR) experiments were performed at X-band on high spin S=5/2 Mn(2+) ions incorporated at zinc lattice sites in heteroepitaxial ZnO thin films. The films have been prepared by pulsed laser deposition and the manganese ions were doped during the growth process. We examine how the c/a lattice axes ratio of the ZnO films influences the (55)Mn hyperfine (hf) and nuclear quadrupole (nq) coupling parameters of the Mn(2+) probe ions. The results are compared with those obtained for Mn(2+) ions present as impurities in ZnO single crystals and revealed that the (55)Mn nq coupling monitors sensitively the structural distortions in the bonding environment of the Mn(2+) ions. The experiments provided the full axially symmetric (55)Mn hf and nq interaction tensors. The latter is found to be very sensitive to small axial distortions of the MnO4 tetrahedrons. In particular, the (55)Mn pulsed ENDOR spectra of the ZnO:Mn thin films are strongly subjected to strain effects in the nq coupling parameter indicating a variation of the local structural parameters for the heteroepitaxial films. In the analysis of the (55)Mn pulsed ENDOR spectra the axial and cubic zero field splitting of the Mn(2+) ions was taken into account and intensity effects in the ENDOR spectra due to the zero field splitting effects were discussed.
Keywords: ENDOR; Hyperfine interaction; Manganese; Quadrupole interaction; Thin films; ZnO.
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