Monte Carlo study of ion-induced backward and forward secondary electron emission from thin Al foil Shakir Ullah a , A.H. Dogar a , A. Qayyum b, * a Pakistan Institute of Engineering and Applied Sciences, Nilore, Islamabad, Pakistan b Physics Division, Pakistan Institute of Nuclear Science and Technology, P.O. Nilore, Islamabad, Pakistan Received 18 September 2007; received in revised form 10 December 2007 Available online 23 December 2007 Abstract A direct Monte Carlo program has been developed to calculate the backward (c b ) and forward (c f ) electron emission yields from 20 nm thick Al foil for impact of C + , Al + , Ar + , Cu + and Kr + ions having energies in the range of 0.1–10 keV/amu. The program incor- porates the excitation of target electrons by projectile ions, recoiling target atoms and fast primary electrons. The program can be used to calculate the electron yields, distribution of electron excitation points in the target and other physical parameters of the emitted electrons. The calculated backward electron emission yield and the Meckbach factor R = c f /c b are compared with the available experimental data, and a good agreement is found. In addition, the effect of projectile energy and mass on the longitudinal and lateral distribution of the excitation points of the electrons emitted from front and back of Al target has been investigated. Ó 2008 Elsevier B.V. All rights reserved. PACS: 79.20.Rf; 79.20.Ap Keywords: Ion-induced electron emission; Monte Carlo simulation 1. Introduction It is well reported that the mechanism of kinetic electron emission (KEE) from material surface induced by the impact of energetic ions consists of the following three suc- cessive steps [1]: the generation of excited electrons in solid by kinetic energy deposited by the incoming ions, the trans- port of these electrons towards the solid surface and finally the escape of electrons through the surface into vacuum. A penetrating ion may generate cascades of recoiling target atoms and electrons in the solid. As a result the mechanism of KEE can be split into three parts: one due to collision between primary ions and target electrons, one due to col- lision between recoiling target atoms and target electrons and one due to collision between primary excited electrons and target electrons. The first part depends essentially on the electronic stopping power of the penetrating ion, while the second is related to the nuclear stopping power [2,3]. The third part depends only on the target properties, e.g. the electron mean free path inside the target bulk and their escape probability through the surface barrier. KEE is usu- ally characterized by a coefficient c defined as the average number of electrons ejected per incident ion. If the target is sufficiently thin, the ions cross the target and electrons are emitted from both surfaces of the target. The electron emission from the entrance and exit surface of the target is called backward and forward emission respectively. The ratio R between the forward electron yield (c f ) and backward electron yield (c b ) is commonly known as Mech- bach factor [4,5]. Several authors have measured c b and c f form thin foils and deduced the ratio R for projectile ions having quite high energies (10–2000 keV/amu.) [5–8]. How- ever, measurements of electron yields and the ratio R below 10 keV/amu energy region, typical for fusion edge plasma and solar wind, are quite few [9,10]. The electron emission 0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.12.059 * Corresponding author. Tel.: +92 51 9290231; fax: +92 51 9290275. E-mail address: qayyum@pinstech.org.pk (A. Qayyum). www.elsevier.com/locate/nimb Available online at www.sciencedirect.com Nuclear Instruments and Methods in Physics Research B 266 (2008) 577–582 NIM B Beam Interactions with Materials & Atoms