3. Energy Loss Processes and Ion Range

Energetic ions are mainly subject to two loss mechanisms during interaction with target atoms, the nuclear energy loss and the electronic energy loss. The dominating interaction processes of the movement of low-energy particles through matter are elastic collisions with target atoms. In this chapter, the different approaches to determine the nuclear energy loss per unit length, also referred to as nuclear stopping power, are presented in detail. The electronic energy loss, which is less significant for low-energy ions, is briefly described. Based on the knowledge of nuclear and electronic energy loss, the range of incidence particles can be approximately determined as a function of acceleration energy. It can be shown that by use of the projected range and its standard deviation, three-dimensional concentration distribution of the implanted ion species below the surface can be determined. Since often the experimentally determined concentration profiles deviate considerably from a simple expected Gaussian distribution, higher order moments of the Gaussian distribution must be included in the calculation of the concentration distribution. Computer simulations can be used to calculate not only the concentration distribution, but also the trajectories of the particles, the number of reflected ions and sputtered atoms, the distribution of vacancies and interstitials, etc. In this chapter, the two most common computer simulation codes for the analysis of particle-solid interactions, molecular dynamical code and the Monte Carlo code, are briefly presented.