Surface morphology, thermal and electrical conductivity of α-Al2O3 single crystals implanted with Au and Ag ions

With the aim to study the effects of heavy ion implantation on the morphology of α-Al2O3 single crystals with c, m and r orientations, ion implantation at room temperature, with Au or Ag ions, energy of 160 keV and fluences ranging from 5 × 1015 to 1 × 1017 ions cm−2 was performed. The microstructure and morphology of irradiated surfaces were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The presence of metal precipitates was explored by AFM and monitored by the variation of the intensity of the extinction bands associated with Mie scattering from Au and Ag colloids located at about 2.2 eV (563 nm) and 2.8 eV (443 nm), respectively. The results show a dependence on the surface roughness with the ion fluence and the implantation orientation. The dependence of thermal conductivity with the implanted conditions was studied by scanning thermal microscopy. Thermal images indicate that thermal conductivity of Al2O3 is higher in samples implanted with Ag ions at a fluence of 6 × 1016 ions cm−2 than in samples implanted with Au at a higher fluence. Successive etchings of an Ag implanted sample reveal a dependence of the thermal conductivity with the distance to the surface due to the layered damage structure produced by the implantation. The DC electrical measurements, between 273 and 445 K, using the four and two-point probe methods were used to characterize the electrical conductivity of the implanted area. The I–V characteristic of the electrical contacts reveals an ohmic behavior, independent of the ions implanted and the crystallographic orientation. Measurements of the electrical conductivity at different temperatures in the investigated range predominantly suggest a band conduction mechanism thermally activated, with energies of about 0.09 and 0.07 eV, in samples implanted with Au or Ag ions, respectively. We conclude that the enhancement in conductivity observed in the implanted regions is related to the intrinsic defects created by the implantation, rather than to the implanted Au and Ag ions.