Copper nanocolloids in MgO crystals implanted with Cu ions

Abstract

Rutherford backscattering and optical absorption measurements were used to characterize both intrinsic and extrinsic defects produced in MgO single crystals by implantation with 250 keV Cu 2+ ions at a fluence of 1 × 10 17 ions/cm 2. Several absorption bands identical to those found in neutron irradiated crystals were observed and have been previously associated with oxygen vacancies and higher-order defects involving oxygen vacancies. In addition, a broad extinction band centered at ≈3.0 eV is observed and is attributed to copper precipitates. The maximum concentration of the implanted Cu ions occurs at a penetration depth of ≈130 nm. The copper colloids start to dissolve at temperatures above 1100 K and by 1500 K most of the copper ions have diffused into substitutional sites. Hardening induced by implantation was characterized by nanoindentation measurements.