Dynamics of pattern formation during low-energy ion bombardment of Si0 0 1) Eric Chason a, * , Jonah Erlebacher b , Michael J. Aziz b , J.A. Floro c , M.B. Sinclair c a Division of Engineering, Brown University, Providence, RI, USA b Harvard University, Cambridge, MA, USA c Sandia National Laboratories, Albuquerque, NM, USA Abstract Sputtering of surfaces by collimated, low-energy ion beams results in spontaneous pattern formation in many systems. In order to explore the mechanisms that control the pattern formation, we have used in situ light scat- tering to measure the evolution of sputtered Si0 0 1) surfaces. The results are interpreted within a linear instability model originally proposed by R.M. Bradley and J.M.E. Harper [J. Vac. Sci. Technol. A 6 1988) 2390] that includes the dependence of the sputter yield on the local surface morphology. Ó 2001 Elsevier Science B.V. All rights reserved. 1. Introduction When collimated beams of low-energy ions are used to sputter surfaces, the surfaces can develop a distinct periodicity. An example is shown in Fig. 1, reproduced from [2]. In this case, a Si0 0 1) surface has been bombarded with 750 eV Ar ions at an angle of 67.5° from the surface normal at a temperature of 555°C. The initially ¯at surface has developed a distinct ripple-like morphology with a period of approx- imately 400 nm. This eect has been observed in a wide range of materials including semiconductors [2±10], oxide glasses [11±13] and metals [14±19]. Depending on the substrate and the ion beam parameters, the periodicity can range from tens to thousands of nanometers and the structure can be organized in 1-d ripples [3] or 2-d pits [19] or hillocks [10]. The structures form spontaneously, with no template required, and can uniformly cover a wide area of the surface. At the core of this pattern formation is the interaction of the energy deposited by the in- coming ion with the substrate surface. By depos- iting energy below the surface, removal of atoms by sputtering is fundamentally dierent than de- position of atoms on the surface. In this paper, we will review recent studies of the dynamics of pattern formation on sputtered surfaces of Si001), focusing on the fundamental physical mechanisms that cause pattern formation and the modi®cation of surface kinetic processes by ion bombardment. Nuclear Instruments and Methods in Physics Research B 178 2001) 55±61 www.elsevier.nl/locate/nimb * Corresponding author. 0168-583X/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0168-583X01)00505-5