Dynamic scaling behavior of mica ripples produced by low energy Ar+ ion erosion

Abstract

The scaling behavior of ion beam induced ripple patterns on mica surface is investigated by means of atomic force microscopy (AFM). The ripples were produced by 12 keV Ar+ ion beam erosion at an angle 60° with respect to the surface normal. Ripple wave-vectors are found to align parallel to the ion beam projection direction. The root-mean-square (rms) roughness and lateral correlation length of the rippled surface are observed to increase with ion fluence with a growth exponent β = 0.51 ± 0.04 and dynamic exponent 1/zx = 0.42 ± 0.07 along the ripple direction as well as 1/zy = 0.34 ± 0.09 normal to the ripple direction respectively. Ripple wavelength is also found to increase slowly with ion fluence upto ϕ ∼ 6 × 1017 ions.cm−2 and then shows a rapid coarsening behavior with an exponent n = 0.43 ± 0.04. The two different roughness exponents, αx and αy, along and normal to the ripple direction, are also calculated from their corresponding power spectral density function and found the values 1.25 ± 0.09 and 1.20 ± 0.08 respectively. The scaling properties of ripple growth for long time ion bombardment and the overall morphological changes are explored according to calculated erosive and redistribution coefficients in the framework of recently advanced continuum models of pattern formation by ion beam sputtering. The production of ripples is found to be driven by mass-redistribution effects rather than curvature dependent sputter erosion. This is an worth addition to the understanding of ion beam nanopatterning process as it ascertains mass redistribution as indispensable phenomena for pattern formation not only for ion energies less than 1 keV but also for ion irradiation of energy range 10 keV and above.