Orientation dependence of the threshold displacement energy in copper and vanadium

The threshold displacement energy E d, has been determined by high-voltage electron microscopy for copper and vanadium as a function of orientation with the following results: for copper, E d⟨100⟩=27 eV, E d⟨110⟩=18 eV, E d⟨111⟩=29 eV and for vanadium, E d⟨100⟩=30eV, E d⟨110⟩=39eV, E d⟨111⟩=34eV. The minimum threshold directions are consistent with the observation of other experimenters, ⟨110⟩ in f.c.c. and ⟨100⟩ in b.c.c. Significant sub-threshold displacements were observed in copper. This is interpreted in terms of a series collision involving interstitial hydrogen as an intermediate particle. A good correlation is found to exist between the threshold energy and the sublimation energy (E s) for a wide variety of metals, following the original suggestion of Seitz (1949). It is shown that the minimum E d is approximately 4E s and the average E d is approximately 5E s.