The role of incidence angle in the morphology evolution of Ge surfaces irradiated by medium-energy Au ions

Abstract

Germanium (Ge) surfaces have been irradiated with 26 keV gold (Au) ions at a constant fluence and at incidence angles varying from 0° to 85°. The evolution of the emerging nanostructures is studied by atomic force microscopy (AFM), scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and cross-sectional transmission electron microscopy. The obtained results are compared with findings reported in the literature. Periodic rippled patterns with the wave vector parallel to the projection of the ion beam direction onto the Ge surface develop between 30° and 45°. From 75° the morphology changes from parallel-mode ripples to parallel-mode terraces, and by further increasing the incidence angle the terraces coarsen and show a progressive break-up of the front facing the ion beam. No perpendicular-mode ripples or terraces have been observed. The analysis of the AFM height profiles and slope distributions shows in the 45°-85° range an angular dependence of the temporal scale for the onset of nonlinear processes. For incidence angles below 45°, the surface develops a sponge-like structure, which persists at higher incidence angles on the top and partially on the face of the facets facing the ion beam. The XPS and the energy-dispersive x-ray spectroscopy evidence the presence of Au nano-aggregates of different sizes for the different incidence angles. This study points out the peculiar behavior of Ge surfaces irradiated with medium-energy Au ions and warns about the differences to be faced when trying to build a universal framework for the description of semiconductor pattern evolution under ion-beam irradiation.

AFM and Raman study of graphene deposited on silicon surfaces nanostructured by ion beam irradiation

“…S1 and S2 samples were irradiated with different values of fluence and incidence angle. They were appropriately chosen to induce well‐known (Iacob et al ., 2016, Dell'Anna et al ., 2018) extreme topographical differences on the surfaces, which were in turn used to study the different out‐of‐plane graphene deformations that they induced.…”

“…In Figure 1(A), a periodic rippled pattern has formed on sample S1 with wavevector in the x direction, namely the one parallel to the projection of the ion beam direction onto the surface. These types of nanopatterns are, therefore, called parallel‐mode ripples (Dell'Anna et al ., 2018). The short, medium and long‐range regularity is confirmed by the inspection of the corresponding height‐height ACF, calculated along the x direction ( x ‐ACF, see Fig.…”

“…In Figure 1(B), the morphology of the silicon substrate S2 has transformed from parallel‐mode ripples of S1 into parallel‐mode terraces. This is a well‐known evolution, which can be observed by increasing the ion irradiation time –– and therefore the fluence (Harrison et al ., 2017), and/or by increasing the ion incidence angle (Castro et al ., 2012; Dell'Anna et al ., 2018). From an analytical point of view, the terraced topographies develop on the irradiated surfaces when nonlinear contributions cannot be ignored anymore in the equation for the surface height evolution in time (Harrison et al ., 2017).…”

“…S1 and S2 samples were irradiated with different values of fluence and incidence angle. They were appropriately chosen to induce well-known (Iacob et al, 2016, Dell'Anna et al, 2018 extreme topographical differences on the surfaces, which were in turn used to study the different out-of -plane graphene deformations that they induced. Figures 1(A) and (B) illustrate the topography evolution of a silicon surface upon 1 keV O ion irradiation when both ion fluence and incidence angle are increased (Table 1).…”

“…By suitably choosing the ion beam parameters/target combination, regular nanopatterns of well‐defined periodicity can be obtained, including ripples (see, e.g. Dell'Anna et al ., 2018) and semiconductor quantum dots (Facsko et al ., 1999). There are different physical mechanisms triggered by ion irradiation that regulate the spontaneous appearance of surface nanopatterns (Norris & Aziz, 2019), and a complete theory able to predict the specific interplay of these different mechanisms based on the different possible choices of the experimental parameters (ion species, energy and fluence, ion incidence angle, substrate material and temperature} is still missing (Iacob et al ., 2016).…”