Modeling of high-fluence irradiation of amorphous Si and crystalline Al by linearly focused Ar ions

Abstract

Long time ion irradiation of surfaces under tilted incidence causes formation of regular nanostructures known as surface ripples. The nature of mechanisms leading to ripples is still not clear, this is why computational methods can shed the light on such a complex phenomenon and help to understand which surface processes are mainly responsible for it. In this work, we analyse the surface response of two materials, a semiconductor (silicon) and a metal (aluminium) under irradiation with the 250 eV and 1000 eV Ar ions focused at 70 • from the normal to the surface. We simulate consecutive ion impacts by the means of molecular dynamics to investigate the effect on ripple formation. We find that the redistribution mechanism seems to be the main creator of ripples in amorphous materials, while the erosion mechanism is the leading origin for the pattern formation in crystalline metals.

Direct observation of ion-induced self-organization and ripple propagation processes in atomistic simulations

“…The empty volume below the original surface can be found by using the OVITO surface mesh tool [33] similarly to Ref. [16]. The estimated difference in solid volume between the initial and the final configurations results in approximately 4500 atoms.…”

“…A few studies have taken into account this effect as a non-linear extension term related to the erosion rate [9][10][11][12][13][14]. However, it was recently shown the erosive component alone is not able to capture the complex phenomenon [15,16]. Norris et al [17,18] proposed a mathematical model predicting patterns based on the crater function formalism, which allows also describing atom redistribution as an additional term contributing to ripple formation.…”

Observation of ripples under different angles

“…A flat-surface cell of amorphous Si containing 73584 atoms was relaxed 14,18 to 300 K in order to perform the sequential bombardment. The final size of the cell is 16.56 x 16.56 x 5.15 nm 3 .…”

“…A new method of sequential impacts in MD was recently applied 14,18 to study the reasons behind the surface modification under different energies and angles over different materials. The results show that the contribution of the erosion in counter-position to redistribution, is strongly dependent on the material and the ion energy.…”

Comparative study regarding the sputtering yield of nanocolumnar tungsten surfaces under Ar+ irradiation

“…The selection of φ = 45 • was motivated by the randomness of the orientation with respect to the ion beam. A sequential-impacts scheme 69,70 was used, considering 2000 random impacts in the same cell in order to follow the evolution of the surface up to a certain fluence. Two different nano-columnar W structures were created on the basis of a (1 0 0) surface (see Figure 4) as input to the simulations, resulting in a flat top (NC-cyl) and in a dome top (NC-dome) cylinder.…”