Spontaneous Pattern Formation from Focused and Unfocused Ion Beam Irradiation

Abstract

We study the formation and self-organization of "ripples" and "dots" spontaneously appearing during uniform irradiation of Si, Ge, and GaSb with energetic ion beams. Features have been produced both with sub-keV unfocused Ar + ions and with a 30 keV Ga + Focused Ion Beam. We follow the evolution of features from small amplitude to "nanospikes" with increasing ion dose. It appears that the edge of the sputtered region influences the patterns formed, an effect that may make it possible to guide the self-organization by the imposition of lateral boundary conditions on the sputter instability.

Nanohole pattern formation on germanium induced by focused ion beam and broad beam Ga+ irradiation

“…We used a 30 keV broad Ga þ beam at RT, normal incidence and a fluence of 1.0 Â 10 18 ions/cm 2 and obtained a sponge like structure (not shown) which is also observed using FIB. 14 In conclusion, normal incidence irradiation of Ge (100) surfaces with 5 keV Ga þ ions produces self-organized nanohole patterns. The pattern formation has been discussed and modelled on the base of the recently proposed Bradley-Shipman model reaching a qualitative agreement with the experimentally observed patterns and the increasing ordering with fluence.…”

A Review on Less-common Nanostructures

“…Nanospikes are known for several inorganic phases/compounds, such as, for instance TiO [125] 2 or Ag-Au (bimetallic nanostructures with hollow interiors and bearing nanospikes), [126] and are obtained, in particular, by lithography [127] or ion beam irradiation. [128] The formation of dense arrays of nanospikes occurs also under laser ablation of bulk targets (Ag, Au, Ta, Ti) immersed in liquids such as H 2 O or EtOH. [129,130] Similarly, exposing a germanium surface to femtosecond laser pulses in an environment of SF 6 leads to nearly regular arrays of nanospikes atop conical microstructures.…”

Non-Equilibrium Nanoscale Self-Organization

“…Not only has this observation of pattern evolution under FIB irradiation served as an excellent test of theory and motivated new theory, it has also lead to entirely unanticipated discoveries, as shown in Fig. 3 [75] .…”

“…We are studying larger lateral length scales in Si because of the availability of in-situ probes, e.g. optical diffraction techniques [5,86] and Focused Ion Beam (FIB)-Scanning Electron Microscopy (SEM) [75,76] and because Si is a monatomic system amenable to atomistic modeling. As a result we can learn much more about the fundamental aspects of the phenomenon with measurements at these length scales.…”

“…Our objective has been a fundamental understanding that permits us to answer the question, "How much morphology control can one attain without having to write each individual feature?" A significant new discovery [73,75] has been sputter patterning under uniform rastering of a focused ion beam (FIB), which is a machine typically used to micromachine surfaces in computer-controlled patterns. The rapid feedback possible with in-situ real-space imaging in a FIB instrument has accelerated the understanding of the phenomena believed to be common to both focused and unfocused ion irradiation.…”