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We investigate the morphologies of the Ge(001) surface that are produced by bombardment with a normally incident, broad argon ion beam at sample temperatures above the recrystallization temperature. Two previously observed kinds of topographies are seen, i.e., patterns consisting of upright and inverted rectangular pyramids, as well as patterns composed of shallow, isotropic basins. In addition, we observe the formation of an unexpected third type of pattern for intermediate values of the temperature, ion energy, and ion flux. In this type of intermediate morphology, isolated peaks with rectangular cross-sections stand above a landscape of shallow, rounded basins. We also extend past theoretical work to include a second-order correction term that comes from the curvature dependence of the sputter yield. For a range of parameter values, the resulting continuum model of the surface dynamics produces patterns that are remarkably similar to the intermediate morphologies we observe in our experiments. The formation of the isolated peaks is the result of a term that is not ordinarily included in the equation of motion, a second-order correction to the curvature dependence of the sputter yield.
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Second order corrections to the sputter yield of a curved surface
We study the sputter yield Y of a curved surface that is struck by a normally incident ion for radii of curvature that are large compared to the size of the collision cascade. The leading order correction to Y is proportional to the mean curvature H at the point of impact. We demonstrate analytically that there are two second order corrections to Y. One of these is proportional to H2 and the other is proportional to the Gaussian curvature at the point of impact. The predictions of the theory are compared to the results of Monte Carlo simulations of the sputtering of a variety of silicon surface morphologies for three different noble gas ion species and three ion energies. We find that including the second order correction terms considerably extends the range of radii of curvature for which the approximate formula for Y is applicable. Finally, we highlight our theory’s implications for nanoscale pattern formation on an initially flat solid surface that is bombarded with a broad ion beam.
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- Award ID(s):
- 1814941
- PAR ID:
- 10593806
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 129
- Issue:
- 19
- ISSN:
- 0021-8979
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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