A. Turos

Damage buildup and defect transformations in ion bombarded in GaN have been studied by the complementary use of Rutherford backscattering spectroscopy/channeling, high-resolution transmission electron microscopy and high-resolution X-ray diffraction (HRXRD) techniques. Ion bombardment was performed at room temperature with Ar ions. Parameters of the damage buildup were evaluated in the frame of the multi-step damage accumulation model. Three step damage accumulation process has been revealed. HRXRD analysis has indicated that ion bombardment to low fluences produces increase of the lattice parameter leading to a strain buildup in the implanted region. Once the critical value of the stress has been attained, plastic deformation due to the dislocation slip takes place leading to the formation of dislocations tangle. At this stage, channeling yield saturates well below the amorphization level. The transition to stage III – amorphization – takes place at high-impurity concentration and is apparently due to the defect–impurity interaction.

Channeling and back-scattering techniques were used to study single crystals of α-Al₂O₃ and MgO following bombardment with Pt- (or Xe-)ions of 30 keV energy and doses between 9 × 10¹⁵ and 8 × 10¹⁶ ions/cm², as used for catalytic investigations. The MgO crystals showed saturation damage after implantation with the lower dose. Damage recovery proceeded progressively with increasing temperature and was not complete before 1300°C was reached. The Pt formed coherent precipitates. In contrast, a quasi-amorphous zone was formed on ion bombarded Al₂O₃. Outdiffusion of the impurity and recovery of the bombardment damage started at ∼650°C, the temperature of the phase change to the recrystallized state. At temperatures in excess of 900°C, the Pt precipitated into small single crystal grains of near spherical shape. The results can be used to interpret the catalytic behavior of the systems Pt/single crystalline support.