Stability of ion-implanted layers on MgO under ultrasonic cavitation

Abstract

The effects of ion implantation and ultrasonic cavitation on the near-surface region of MgO single crystals were investigated. For 150 keV, room-temperature implantations of Ar+ or K+ at 5×1016–1017 ions cm−2 into a (100)-oriented surface of MgO, a dilatometric swelling of the implanted layer is observed perpendicular to the implanted surface. When these strained surface layers are then subjected to an ultrasonic (∼20 kHz) cavitation treatment, uniform layers (∼100–200 nm) can be removed from the MgO surface in a controlled manner. The thickness of the removed layer is directly related to the duration of the ultrasonic irradiation, but does not exceed the depth of the implanted species. When MgO implanted with Ar+ or Kr+ at fluences of 5×1016–1017 ions cm−2 is subsequently irradiated with 2 MeV He+ ions at 1016–1017 ions cm−2, the region exposed to the He+ beam is effectively ‘‘stabilized’’ and is not removed by the ultrasonic treatment. K+ or Ar+ implantations at <5×1016 ions cm−2 produced no swelling of the layer, and subsequent ultrasonic irradiation with an energy flux of ∼120 W cm−2 did not remove the crystal surface as determined by profilometry. For MgO implanted with ≳2×1017 ions cm−2, the implanted layer is highly strained and detaches from the underlying crystal without exposure to ultrasonic-cavitation effects. These findings are discussed in terms of the stressed states of the implanted layers, and their potential applications to the mechanical ‘‘etching’’ of ceramics are considered.