Regular Article

Space-filling, multifractal, localized thermal spikes in Si, Ge and ZnO

¹ CASP, Government College University (GCU), Church Road, Lahore 54000, Pakistan
² Abdus Salam National Center for Physics, QAU Campus, Islamabad 44000, Pakistan
³ Department of Physics, University of Engineering and Technology, Lahore 54000, Pakistan
⁴ PINSTECH, PO Nilore, Islamabad 44000, Pakistan

^a e-mail: sahmad.ncp@gmail.com

Received: 3 March 2017
Published online: 30 April 2018

Abstract

The mechanism responsible for the emission of clusters from heavy ion irradiated solids is proposed to be thermal spikes. Collision cascade-based theories describe atomic sputtering but cannot explain the consistently observed experimental evidence for significant cluster emission. Statistical thermodynamic arguments for thermal spikes are employed here for qualitative and quantitative estimation of the thermal spike-induced cluster emission from Si, Ge and ZnO. The evolving cascades and spikes in elemental and molecular semiconducting solids are shown to have fractal characteristics. Power law potential is used to calculate the fractal dimension. With the loss of recoiling particles’ energy the successive branching ratios get smaller. The fractal dimension is shown to be dependent upon the exponent of the power law interatomic potential D = 1/2m. Each irradiating ion has the probability of initiating a space-filling, multifractal thermal spike that may sublime a localized region near the surface by emitting clusters in relative ratios that depend upon the energies of formation of respective surface vacancies.