Mixing in Au/Si system by nuclear energy loss Sarvesh Kumar a, * , P.K. Sahoo b , R.S. Chauhan a , D. Kabiraj c , Umesh Tiwari d , D. Varma d , D.K. Avasthi c a Department of Physics, R.B.S. College, Agra 282 002, India b Department of Physics, Indian Institute of Technology, Kanpur 208 016, India c Nuclear Science Centre, Aruna Asaf Ali Marg, New Delhi 110 067, India d Solid State Physics Laboratory, Timarpur, Delhi 110 054, India Abstract In the present work, we report the formation of silicide phases in the Au/Si system by ion beam mixing at room temperature. The samples (58 nm Au on Si) were irradiated by 1 MeV Xe ions. The ion energy was chosen in such a way that it deposits maximum energy at the interface. The Rutherford backscattering spectrometry measurements were done on the pristine and irradiated samples to determine the composition of mixed region. Grazing incidence X-ray dif- fraction measurements were performed which showed the formation of silicide phase (Au 2 Si, Au 3 Si, Au 5 Si and Au 5 Si 2 ). Scanning electron microscopy measurements indicated the micron size crystallites in the irradiated samples. Ó 2003 Elsevier B.V. All rights reserved. PACS: 68.55.Ln; 68.55.Nq; 68.37.Hk Keywords: Ion beam mixing; Phase formation; Surface morphology 1. Introduction Ion beam mixing is a technique for the forma- tion of stable, metastable, amorphous and crys- talline phases in the bilayer and multilayer [1]. In case of low energy (keV/nucleon) region, elastic collisions between the ion and the target atoms dominate the slowing down of the ion and this nuclear energy loss induces recoil cascades. It causes interface mixing by direct displacements (ballistic mixing), diffusion in overlapping subcas- cades (thermal spike mixing) and by the thermally activated migration of the remaining radiation defects (radiation enhanced diffusion) [2–5]. Therefore nuclear energy loss is considered to be responsible for ion beam mixing. Growth of epit- axial gold silicide islands has been observed when an Au film deposited on a bromine-passivated Si(1 1 1) substrate was annealed at eutectic tem- perature. The islands grow in the shape of equi- lateral triangles, reflecting the symmetry of the (1 1 1) substrate, up to a critical size beyond which the symmetry of the structures is broken, resulting in a shape transition from triangle to trapezoid [6]. The formation of fractal and the isolateral trian- gles is also observed when the sample is irradiated at the eutectic temperature of Au–Si system. The fractal growth and triangle growth could be the effect of thermal annealing. Complete growth of shape and size of the triangles may depend on the * Corresponding author. Tel./fax: +91-562-2520075. E-mail address: guptask10@yahoo.com (S. Kumar). 0168-583X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)01738-5 Nuclear Instruments and Methods in Physics Research B 212 (2003) 238–241 www.elsevier.com/locate/nimb