Orientation dependence of the threshold displacement energy in copper and vanadium

The threshold displacement energy Esub(d), has been determined by high-voltage electron microscopy for copper and vanadium as a function of orientation with the following results: for copper, Esub(d)(100)=27eV, Esub(d)(110)=18eV, Esub(d)(111)=29eV and for vanadium, Esub(d)(100)=30eV, Esub(d)(110)=39eV, Esub(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 (E8) for a wide variety of metals, following the original suggestion of Seitz (1949). It is shown that the minimum Esub(d) is approximately 4Esub(s) and the average Esub(d) is approximatekly 5Esub(s). (author)