From sponge to dot arrays on (100) Ge by increasing the energy of ion impacts

Ge surfaces were subjected to normal incidence Bi+ irradiation with ion energies from 10 to 30 keV. The Ge substrate was irradiated with fluences up to 1 x10^17 / cm² and substrate temperatures up to 780 K. Surface modification was investigated using scanning electron microscopy. While at room temperature porous networks are obtained, increase of temperature during irradiation leads to formation of hexagonal dot arrays at the surface, which vanish at very high temperatures. Extensive experimental studies of energy and temperature ranges and limits for dot formation are presented. Formation of dot arrays is governed by the vacancy diffusion mechanism via different energy densities deposited in the cascade volume, as well as by substrate heating. An energy-temperature phase diagram of the obtained surface morphology is composed with respect to varying order of dot-like patterns.