Lithium nanocluster formation in Li + - ion implanted MgO
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Lithium nanocluster formation in Li+ - ion implanted MgO A. van Veen1, M.A. van Huis1, A.V. Fedorov1, H. Schut1, C.V. Falub1, S.W.H. Eijt1, F. Labohm1, B.J. Kooi2, J.Th.M. De Hosson2 1 Interfaculty Reactor Institute, Delft University of Technology, Mekelweg 15, NL-2629JB, Delft, The Netherlands. 2 Materials Science Center, University of Groningen, Nijenborgh 4, 4797 AG Groningen, The Netherlands.
ABSTRACT Photon 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 1.0x1016 6 Li 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.
INTRODUCTION Metallic nano-size precipitates embedded in optically transparent materials give rise to a number of linear and non-linear optical properties which strongly depend on the size and shape of the metallic inclusions. Optical studies on MgO containing lithium and lithium oxide colloids have been investigated by Abraham et al [1], and by Marichy et al [2]. The optical effects of lithium clusters produced by ion implantation in MgO and subsequent annealing have been investigated in detail by Treilleux et al. [3]. In this study, photon absorption and a variety of defect analysis techniques are applied to settle the relation between photon absorption behavior and the precipitates formed.
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EXPERIMENT Epi-polished monocrystals of MgO(100) were implanted with 1.0×1016 cm-2 6Li ions at an energy of 30 keV. The range of the 30 keV lithium ions was 170 nm according to SRIM calculations [4]. After the implantation the crystals were annealed in air for periods of 30 min. from room temperature to 1200K. The annealing temperatures were 550K, 750K, 950K, 1100K, and 1200K. The evolution of the Li-clusters was monitored by several techniques: 1. Photon absorption to detect absorption bands, e.g. due to Mie plasmon resonance at the metallic inclusions [5]. 2. P
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