Sputtered atom ejection patterns from (100) Ge surfaces

The sputtered atom ejection patterns from (100) Ge bombarded with 5, 10 and 15 kev Ar+ ions have been studied as a function of dose, dose rate and target temperature. An abrupt transition from a disordered to an ordered surface structure is observed at 330 +/- 5 degrees C, and this temperature is energy independent. Spot patterns showing preferential ejection along a < 111 > direction are obtained above the transition temperature. This has been interpreted as an assisted focusing sequence. The pattern further mirrors the symmetry of the (100) surface and the ejection process has been interpreted as a combination of focusing sequences and surface effects of the type suggested by Lehmann and Sigmund.