IOP PUBLISHING JOURNAL OF PHYSICS: CONDENSED MATTER J. Phys.: Condens. Matter 21 (2009) 224023 (14pp) doi:10.1088/0953-8984/21/22/224023 Plastic properties of gold surfaces nanopatterned by ion beam sputtering V Navarro 1 , O Rodr´ ıguez de la Fuente, A Mascaraque and J M Rojo Departamento de F´ ısica de Materiales, Universidad Complutense de Madrid, E-28040 Madrid, Spain E-mail: violeta.navarro@fis.ucm.es Received 8 January 2009 Published 12 May 2009 Online at stacks.iop.org/JPhysCM/21/224023 Abstract We review the mechanical properties of defective roughened surfaces with the major emphasis on nanoindentation work. We also report novel results in which force versus penetration curves and AFM images of the nanoindented surface are compared for a flat surface of Au(001) and an Ar + bombarded one, both with a high and a low flux of ions. We have found that bombarded surfaces yield at a lower stress than untreated flat ones. Surfaces bombarded at high flux show a large roughness and their yield point, marking the onset of surface plasticity, decreases with respect to that of the flat surface or of the surface bombarded with a low flux. The present results are compared with earlier work on nanoindented vicinal surfaces in which the sole surface modifications with respect to the flat surface were the presence of a high density of steps. It is concluded that a softening effect due to the bombardment-induced nanostructure of the surface dominates over the hardening one due to defect creation and interaction in the surface neighbourhood. (Some figures in this article are in colour only in the electronic version) 1. Introduction In recent times, the role of surfaces in governing the mechani- cal properties of solids is being increasingly recognized. This role turns pre-eminent as the size of the sample falls into the nanometre range. In the now prevailing realm of nanostruc- tures, the study of surface mechanical properties becomes, then, of paramount importance. A good example is provided by the present surge in the development of microelectromechan- ical devices (MEMS), a type of device in which a thorough characterization of their mechanical properties is mandatory. Most of our present understanding of those properties stems from studies in metals, most conspicuously in gold. Apart from being the metal which has been most thoroughly studied, gold is interesting from the point of view of applications. Good ex- amples are its continuous utilization in electronic nanostruc- tures or in the shape of catalyst nanoparticles [1, 2]. In recent times, nanoindentation has been developed as the technique of choice to characterize surface mechanical properties [3, 4]. The combination of experimental indentation work [5–9]— often carried out with the same tip which generates atomic 1 Author to whom any correspondence should be addressed. force microscopy (AFM) images—with molecular dynamics simulations has been especially fruitful. Real surfaces are known to be rich in defects, either intrinsic or introduced by external manipulation. The role of pre-existing surface defects on surface mechanical properties is a particularly important—albeit little analysed—issue. Early studies [10, 11] have shown that a certain type of such defects—surface steps—soften the crystal in their vicinity and more recent research [12] has added support to that result from experiments on more realistic surfaces, having further disclosed mechanisms for the referred softening. Ion bombardment is known to create a very diversified set of surface point defects—either individual or clustered— dislocations and changes of microstructure patterns and one should be aware that all of those features can modify the surface mechanical properties. Much experimental and theoretical research has been done during the last few years to investigate the basic atomistic processes behind the morphological evolution of the surface (for recent reviews see [13–15]). There has also been much work focused on the study on the physico- chemical properties arising from the structural modification. 0953-8984/09/224023+14$30.00 © 2009 IOP Publishing Ltd Printed in the UK 1