Effect of surface impurities on low-energy implanted-ion depth distributions

The depth distributions of 80-eV ${\mathrm{D}}^{+}$ implants in W (110) have recently been measured by field-desorption microscopy. Prominent structure, consisting of seven major and several minor peaks, is observed in the measured distributions. This contrasts with conventional implantation theory which predicts two peaks, one for the channeled ${\mathrm{D}}^{+}$ and one for the nonchanneled ${\mathrm{D}}^{+}$. The observed structure is explained in the present work by a model which ascribes the various peaks to ${\mathrm{D}}^{+}$ groups which have been scattered into planar channels by the surface impurities. The model allows a determination of ${\mathrm{D}}^{+}$ stopping powers in the various planar channels and the stopping power of C and O impurities which recoil down the $〈110〉$ axis. These are the first stopping-power values obtained in this energy region. The model suggests that surface location of the impurities as well as their elastic scattering cross section for ${\mathrm{D}}^{+}$ projectiles could be extracted from more elaborate calculations and experiments.