Nanoindentation on MgO crystals implanted with lithium ions

As-grown MgO single crystals, both nominally pure and lithium-doped, were implanted with Li ions with an energy of 175 KeV and a dose of 10(17) ions/cm(2). MgO:Li crystals were also implanted after oxidation at 1550 K for 30 min. TRIM calculations yield a range of 610 nm for the implanted ions. Hardness and Young's modulus were measured in all the samples before and after implantation using a nanoindentation technique. As-grown MgO and MgO:Li crystals show the same hardness value of (9.1 +/- 0.2) GPa and Young's modulus of (290 +/- 115) GPa. After oxidation of MgO:Li crystals the hardness is (10.1 +/- 0.2) GPa. Implantation of Li ions hardens the near-surface region of all three samples: MgO, MgO:Li and oxidized MgO:Li. Implantation in MgO and MgO:Li showed the same behavior: hardness reaches a maximum value of (16.3 +/- 0.2) GPa at a penetration depth of approximate to175 nm, and slowly diminishes with depth. In oxidized MgO: Li crystals the maximum hardness is (17.7 +/- 0.2) GPa at a penetration depth of 175 nm. The considerable hardening observed in the implanted regions is attributed to the extraordinarily large concentration of interstitials in this region. (C) 2002 Published by Elsevier Science B.V.