Ion bombardment, ultrasonic, and pulsed laser beam effects on small metallic clusters of potassium in MgO

Small metallic precipitates of potassium were produced in ion-implanted layers (5 × 10 16 K + ions cm -2, 150 keV, 300 K) on {100} faces of single crystals of MgO by thermal annealing in air at 1000 K. The resulting potassium aggregates had a mean size of 7 nm as characterized by optical absorption measurements and analytical electron microscopy. The effects of three distinct treatments on these precipitates and the implanted layer as a whole were investigated. Ion bombardment with Ar 2+ (1 × 10 16 ions cm -2, 300 keV, 300 K) results in a dissolution of the metallic clusters and the production of F + and V - centers, as evidenced by the relative changes in the corresponding absorption bands. Rutherford backscattering spectroscopy indicates that this dissolution of precipitates does not result in any long-range redistribution of the potassium. Laser irradiation at a frequency near the absorption resonance of the potassium metal (1 μm wavelength) produces an exfoliation of the implanted layer. A similar effect occurs in ultrasonically treated samples where the entire implanted layer is removed after a 12 min exposure to an energy flux of 120 W cm -2. The similarities and differences among these treatments are discussed along with suggestions for further study.