Simulation of redistributive and erosive effects in a-Si under Ar+ irradiation

Abstract

Ion beams are frequently used in industry for composition control of semiconducting materials as well as for surface processing and thin films deposition. Under certain conditions, low-and medium energy ions at high fluences can produce nanoripples and quantum dots on the irradiated surfaces. In the present work, we focus our attention on the study of irradiation of amorphous silicon (a-Si) target with 250 eV and 1 keV Ar + ions under different angles, taking into special consideration angles close to the grazing incidence. We use the molecular dynamics (MD) method to investigate how much the cumulative displacement of atoms due to the simulated ion bombardment contribute to the patterning effect. The MD results are subsequently analysed using a numerical module Pycraters that allows the prediction of the rippling effect. Ripple wavelengths estimated with Pycraters are then compared with the experimental observations, as well as with the results obtained by using the binary collisions approximation (BCA) method. The wavelength estimation based on the MD results demonstrates a better agreement with the experimental values. In the framework of the utilized analytical model, it can be mainly attributed to the fact that the BCA ignores low energy atomic interactions, which, however, provide an important contribution to the displacement of atoms following an ion impact.

Pattern formation on ion-irradiated Si surface at energies where sputtering is negligible

“…The Ar-Ar interaction were described using the pair potential with high energy repulsive part from DFT DMol calculations 25 joined smoothly at small distances to the LJ equilibrium part 27 . This combination has already been tested in the previous work and demonstrated a reasonable representation of Si and a-Si properties under high energy impacts 28 .…”

“…In all simulations presented in this work, we used the simulation cell, which was cut out from the larger amorphous Si cell, which was previously carefully relaxed in Ref. 28. The size of the cell was selected to be sufficient to enclose fully the collision cascades developed during the simulations of low energy ion impacts.…”

“…In this type of simulations, we cannot apply the same crater function formalism as in Ref. 11,28, and 35 to analyze the results obtained in the sequential ion impact simulations. Since the total displacement is a cumulative quantity it may depend on the curvature of the surface, which is gradually changing in these simulations during the bombardment as a function of ion fluence and energy of incoming ions.…”

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

“…More detail can be found in Refs. [15,31]. The size of the flat-surface cell used as a starting point 16.56 × 16.56 × 5.15 nm 3 ; it contained 73,584 atoms.…”

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

“…A periodic FCC Al structure was created at 0 K and then heated up to 300 K during 10 ps while maintaining the zero pressure. After this initial step, the surface in z direction was opened, and the system was simulated for another 10 As we can observe from the FIG. 2, the system reached the final temperature of 300 K, and there was sufficient time to allow for stabilization of the potential energy and the pressure.…”