Surface Shaping by Ion Beams at Grazing Incidence: Simulations vs. Experiment

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Miniaturization of electronic technologies highlights special approaches such as selforganization of nanostructures. Particularly, surface etching by ion beams at grazing incidence is of interest for applications, because it provides pronounced submicron size, self-organized ripples. Formation of the ripples is commonly attributed to sputter instability.1,2 However, the theory of sputter instability is generally qualitative, so that a comprehensive comparison with experiment is a challenge. In this work, we report the first quantitative simulation of self-organized nanostructures that develop on surfaces under grazing incident ion bombardment, and compare our numerical results with experiment. Relying on our original theory of sputtering,3 we have upgraded the model of sputter instability1,2 and performed simulations for Cu and Ag surfaces bombarded by 1 keV Ar+ ions incident at 80° relative to the surface normal. The surfaces considered developed wire-like nanostructures directed along the ion beam plane, with the wavelength increasing from 3 nm to 50 nm after ~100 nm are removed (Fig. 1). To compare our simulation results with experiment, we have processed a polycrystalline Cu sample and a monocrystalline (110) Ag sample by 0.6 keV and 1 keV Ar+ bombardment and investigated their surfaces by SEM. In all cases, ripple-like structures aligned parallel to the ion beam plane have been observed (Fig. 2). For Cu, we have detected ripples with the wavelength close to the predicted one (Fig.2a). However, some of the observed ripples on Cu surface and most of the ripples on Ag surface are 2-3 times wider and 5-10 times higher than predicted, and shaped differently. We have revised various shaping mechanisms proposed in the literature, and found the Wehner model of whisker growth4 to be the most relevant for our case. We have suggested a new modification of the Wehner model, proposing that the largest ripples grow through activated recrystallization. The ripples’ size and shape result from the interplay of crystal growth, etching, and sputter self-organization. In this model, specific seed crystallites must be available to activate recrystallization, which explains the difference between polycrystalline and monocrystalline surfaces. The reported analysis elucidates ways to control the ioninduced surface nanostructures.

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Journal: TechConnect Briefs
Volume: 3, Technical Proceedings of the 2003 Nanotechnology Conference and Trade Show, Volume 3
Published: February 23, 2003
Pages: 211 - 214
Industry sector: Advanced Materials & Manufacturing
Topicss: Advanced Materials for Engineering Applications, Coatings, Surfaces & Membranes
ISBN: 0-9728422-2-5