研究目的
To analyze the surface response of amorphous silicon and crystalline aluminium under irradiation with linearly focused Ar ions to understand the mechanisms (redistribution and erosion) responsible for ripple formation.
研究成果
The redistribution mechanism is the primary driver of ripple formation in amorphous materials like a-Si, due to small atomic displacements, while the erosion mechanism dominates in crystalline materials like c-Al, where sputtering is more significant. The material structure plays a crucial role in the pattern formation process, with higher ion energies increasing the importance of erosion in both materials.
研究不足
The simulations are limited to specific ion energies and angles, and the use of a linearly focused beam may not fully represent broad beam irradiation. The finite size of the simulation cells could introduce artifacts, particularly in displacement measurements. The study focuses on two materials (a-Si and c-Al) and may not generalize to other materials. The assumption of a flat surface in some analyses may not hold for highly curved surfaces.
1：Experimental Design and Method Selection:
Molecular dynamics simulations using the PARCAS MD code to simulate sequential ion impacts on amorphous silicon (a-Si) and crystalline aluminium (c-Al) targets. The simulations were designed to study surface modification under high-fluence irradiation with Ar ions at energies of 250 eV and 1000 eV, incident at angles of 70°, 80°, 85°, and 88° off-normal. The methodology allows for the analysis of both erosive (sputtering) and redistributive (atomic displacement) mechanisms.
2：Sample Selection and Data Sources:
Simulation cells were prepared for a-Si and c-Al. The a-Si cell was reused from a previous study, and the c-Al cell was created as a periodic FCC structure, relaxed at 300 K, with an open surface. Data were generated from the simulations, including atomic displacements and sputtering yields.
3：List of Experimental Equipment and Materials:
Computational setup using the PARCAS MD code. Materials included amorphous silicon and crystalline aluminium. Ions used were Ar+ with energies of 250 eV and 1000 eV. Interaction potentials: For Al, an embedded-atom method (EAM) potential combined with ZBL repulsive potential; for Ar-Al, ZBL potential; for Ar-Ar, a potential from DFT DMol calculations joined to Lennard-Jones equilibrium part.
4：Experimental Procedures and Operational Workflow:
Sequential irradiation simulations were performed with ions focused in a stripe on the surface. After each impact, the cell was shifted randomly in the y-direction, and sputtered atoms or those reaching a fixed layer were removed. The system was relaxed between impacts with temperature rescaling to 300 K. Simulations were run for up to 10,000 impacts for 250 eV and 4,000 impacts for 1000 eV ions.
5：Data Analysis Methods:
Data on sputtered atoms and atomic displacements (using equation (1) for total displacement) were analyzed. Defect analysis was performed by identifying atoms deviating from the initial structure. Volume loss and pattern formation were quantified using surface mesh construction in OVITO software.
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