Scale-dependent nanomechanical behavior and anisotropic friction of nanotextured silicon surfaces
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Nanoscale surface texturing of silicon was accomplished by oblique Ar+ ion beam irradiation. Atomic force microscope (AFM) imaging showed that nanotexturing produced an anisotropic morphology consisting of ordered nanometer-sized ripples. Surface force microscope (SFM) measurements showed that the nanotextured surface exhibited scale-dependent nanomechanical behavior during indentation loading/ unloading and anisotropic sliding friction, significantly different from those of the original (untextured) surface. AFM and SFM results revealed a strong dependence of the nanoindentation response and friction coefficient on the tip radius and sliding direction relative to the ripple orientation. The observed experimental trends are interpreted in terms of the applied normal load, real contact area, interfacial adhesion force, tip-ripple interaction scale, and ripple orientation. I. INTRODUCTION
Basic understanding of nanoscale surface interactions is crucial to the reliability and efficiency of many microscopic devices possessing contact interfaces. Continuing trends for device scale-down have increased the importance of surface forces at submicrometer scales. Attractive (adhesion) and repulsive (deformation) forces at contact interfaces control permanent surface adhesion (stiction) and damage caused by different microscale wear processes. Because topography and surface mechanical properties play dominant roles in nanoscale contact interactions, insight into the scale dependence of surface mechanical properties and the effect of topography features on the friction behavior is of great significance. Nanofabrication techniques and microprobe-based instruments possessing high displacement and force sensitivities have provided effective means of nanoengineering surfaces to obtain topographies with desirable mechanical and tribological properties. In particular, surface texturing has been found to be advantageous in a wide range of tribological applications. For example, surface texturing of hard disks and magnetic recording heads has been used to minimize in-plane and out-of-plane vibrations of magnetic heads, prevent lubricant depletion, and reduce the static coefficient of friction in hard-disk drives.1,2 Moreover, microdimple formation on surfaces using a laser has been shown to improve the tribological performance of magnetic tape/guide systems,3 reduce friction at piston ring and mechanical seal contact interfaces,4,5 and prevent stiction in microelectromechanical devices.6 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0384
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http://journals.cambridge.org
J. Mater. Res., Vol. 24, No. 10, Oct 2009 Downloaded: 13 Mar 2015
Surface nanotexturing attracted significant attention in recent years because of the emergence of technologies where friction control is critical to the component performance and longevity. Oblique ion beam irradiation is one of the most effective methods of nanoscale surface modification. For instance, ripples with an average wavelength of 10
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