Ion erosion induced nanogrooves: temporal evolution and azimuth dependence

Ion sputtering at grazing incidence of the Cu(001) surface leads to the formation of a regular pattern of nanogrooves with a well defined separation distance between the grooves. The grooves are only two atomic layers deep for a low ion flux and their height remains the same independent of sputter time. The average separation distance of the nanogrooves is at least 5 nm and can be increased beyond 40 nm, depending on substrate temperature, fluence, the ion's mass and energy. Anneal experiments of a nanogroove pattern also show an increase in average nanogroove separation with anneal time. The increase of the average nanogroove separation with time is larger for nanogrooves created along a 100 azimuth compared to the 110 azimuth. The 100 oriented step edges show a high density of kinks, suggesting that detachment from kinks is the rate limiting step in the process that governs the periodicity. Also both adatoms and vacancies are involved in this process, while the grazing incident ion beam continuously creates new nanogrooves. The creation of new nanogrooves and the movement observed during annealing are used as ingredients for a description of the temporal behaviour of the average nanogroove periodicity.