Stress-induced solid flow drives surface nanopatterning of silicon by ion-beam irradiation

Abstract

Ion-beam sputtering (IBS) is known to produce surface nanopatterns over macroscopic areas on a wide range of materials. However, in spite of the technological potential of this route to nanostructuring, the physical process by which these surfaces self-organize remains poorly understood. We have performed detailed experiments of IBS on Si substrates that validate dynamical and morphological predictions from a hydrodynamic description of the phenomenon. We introduce a systematic approach to perform the experiments under conditions that guarantee the applicability of a linear description, helping to clarify the experimental framework in which theories should be tested. Among our results, the pattern wavelength is experimentally seen to depend almost linearly on ion energy, in agreement with existing results for other targets that are amorphous or become so under irradiation. Our work substantiates flow of a nanoscopically thin and highly viscous surface layer, driven by the stress created by the ion beam, as an accurate description of this class of systems.

Self-organized nanopatterning of silicon surfaces by ion beam sputtering

“…In particular, the existence of a nonzero critical angle, as depicted in Fig. 2, has been also confirmed by other groups working in the low energy range [55][56][57][58]. In general, as shown in the AFM images of Fig.…”

“…Very recently, Garg et al [85] have also reported that the threshold angle for 60 keV Ar þ ions is larger than 30 and lower than 45 . These trends contradict in some way those observed for low-energy ions, where Xe þ has a larger u c than Ar þ [64], being closer to 45 in the latter case [37,38,58]. This suggests that some dependence of u c might exist with the ion species and the energy range.…”

“…3 In order to properly compare the different morphologies, it is important to assess the extent of the linear regime for each experimental condition. This is because the behaviors of W and ' with u change, depending on the time regime in which the experiment is considered [58]. This issue will be discussed with more detail in Section 5.3.…”

“…These can not be reproduced by e.g. a BH framework in which relaxation is by thermal surface diffusion (implying a decaying behavior ' $ 1=E n [26]), which suggests the need to consider alternative, non-thermal relaxation mechanisms [58], see Section 5. After the work by Madi et al [37,38], the effect of E on the pattern characteristics has not been addressed specifically.…”

“…Typically, three patterning regimes can be distinguished during ripple formation by IBS [37,38,56,58]. As an example, the evolution of a Si(1 0 0) surface under 700 eV Ar þ irradiation at u ¼ 55 is shown in Fig.…”