Lithium nanocluster formation in Li+ - ion implanted MgO

Abstract

AbstractPhoton absorption (PA), Positron Beam Analysis (PBA) and Neutron Depth Profiling (NDP) is applied to study the relation between photon absorption behavior and the precipitates formed by ion implantation and thermal annealing. Monocrystals of MgO(100) were implanted with 1.0×10166Li ions cm−2 at an energy of 30 keV. The samples were thermally annealed in air in steps up to 1200 K. After each step Doppler broadening Positron Beam Analysis (PBA) was applied to monitor the depth profile of the implantation defects. The evolution of the depth profile of lithium was followed with the aid of NDP. During the annealing there is hardly any change in the location of the lithium implantation peak at 150 nm (peak concentration 2 at. %). Only after annealing to 1200 K the majority of the lithium has left the crystal and optical absorption effects have disappeared. During annealing at 750 K an absorption band develops between 400 and 600 nm; at 950 K the maximum absorption is centered at 450 nm corresponding to Mie absorption and scattering by lithium nanoclusters. Positron beam analysis shows a considerable increase of annihilations with low momentum electrons in the implanted zone. A positron method for measuring electron momentum distributions (2D-ACAR) coupled to an intense positron beam gave evidence for the presence of semi-coherent metallic lithium inclusions.