Generation of nanosized grooves and holes on metal surfaces by low-temperature electron irradiation

This paper reports a novel phenomenon in surface physics, namely the formation of aligned nanogrooves and deep nanoholes on the exit surface of thin (001) gold foils irradiated with high doses of 360, 800 and 1250 keV electrons at temperatures of about 100 K. The grooves and holes, with widths between about 1 and 2 nm, appear to be the smallest so far produced in metals. The formation of the nanogrooves depends on the irradiation direction: irradiation along [001] produces grooves extending along [100] and [010], irradiation along [011] gives grooves along [100], whereas no marked grooves have been observed for [111] irradiations. By contrast, nanoholes, which may reach depths exceeding 20 nm, develop mainly along the beam direction. At room temperature the nanoholes transform into voids of larger diameters. There is strong evidence that the formation of the groove pattern is a self-organized process. A tentative mechanism involving symmetry breaking by strongly anisotropic surface collision sequences is proposed.