Application of a nondestructive single-spectrum proton activation technique to study oxygen diffusion in zinc oxide

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Abstract
18O diffusion coefficients were measured directly and without serial sectioning, using proton activation analysis of 18O via the nuclear reaction 18O (p, α)15N. In this technique, the α-particle spectrum recorded during proton irradiation is used to determine the 18O concentration profile; submicron resolution can be achieved. The suitability of this approach was demonstrated by studying oxygen self-diffusion along the c axis of ZnO single crystals. In the temperature range 940–1140°C and at Po2 of 700 mm, D=1.2(−0.6+1.1)10−10exp[−(29.6±1.6) kcal/RT] (cm2/sec). The results are interpreted as indicating extrinsic behavior; the activation energy is then that for oxygen mobility only. The surface exchange coefficient, characteristic of the reaction between gaseous and lattice oxygen, was also determined, in the temperature range 940–1040°C, as K=5.7(−4.6+23.8)105 exp[−(91.2±4.0 kcal)/RT] (cm/sec). A detailed analysis of the technique is presented. Using a convolution procedure, the oxygen self-diffusion coefficient, at a given temperature, is determined in a single irradiation run with a precision better than 10%, which is limited only by counting statistics. However, uncertainty in the values of the stopping powers for protons and alphas may cause an additional systematic uncertainty in D of up to [inverted lazy s]50%; since this error is identical for all temperatures, it causes an uncertainty in the preexponential but not in the activation energy. The technique is optimum for determining D in the range [inverted lazy s]5 × 10−12−[inverted lazy s]5 × 10−17 cm2/sec and is useful for testing models of the exchange kinetics.