Dechanneling from 2-MeVHe+Damage in Gold

Abstract

The dechanneling of 2-MeV ${\mathrm{He}}^{+}$ incident in the [001] direction of monocrystalline gold films has been investigated by means of the backscattering technique. The aligned spectra of the undamaged crystal indicate good agreement with channeling theories regarding the surface dechanneling and the dechanneling as a function of depth. Damage was introduced by 2-MeV ${\mathrm{He}}^{+}$ incident in a random direction and the resultant increase of the dechanneling rate was studied as a function of damage dose. It is found that the dechanneling is mainly due to defect clusters produced in energetic displacement cascades. A dechanneling cross section of ${\sigma }_d=2.3\mathrm{}\times {10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$ is derived under the assumption that all of the dechanneling is due to the clusters visible by transmission electron microscopy (TEM). The dechanneling cross section is about a factor of 5 smaller than the geometrical cross section of the clusters as determined by TEM. Deviations from linearity in the dechanneling-rate-versus-dose curve are noticeable at 5 × ${10}^{15}$ ${\mathrm{He}}^{+}$/${\mathrm{cm}}^2$. An analysis of the saturation behavior gave a value of $r_0=89\mathrm{}$ Å for the average radius of a displacement cascade.