An Efficient Molecular Dynamics Scheme for the Calculation of Dopant Profiles due to Ion Implantation

We present a highly efficient molecular dynamics scheme for calculating the concentration depth profile of dopants in ion irradiated materials. The scheme incorporates several methods for reducing the computational overhead, plus a rare event algorithm that allows statistically reliable results to be obtained over a range of several orders of magnitude in the dopant concentration. We give examples of using this scheme for calculating concentration profiles of dopants in crystalline silicon. Here we can predict the experimental profile over five orders of magnitude for both channeling and non-channeling implants at energies up to 100s of keV. The scheme has advantages over binary collision approximation (BCA) simulations, in that it does not rely on a large set of empirically fitted parameters. Although our scheme has a greater computational overhead than the BCA, it is far superior in the low ion energy regime, where the BCA scheme becomes invalid.Comment: 17 pages, 21 figures, 2 tables. See: http://bifrost.lanl.gov/~reed

Restrictions on Access to Social Protection by New Southern European Migrants in Belgium

peer reviewedDespite the fact that the global financial crisis has affected Belgium’s economic performance, the country has continued to be an attractive destination for migrants. Recently, however, there has been a dramatic change in migrant flows to Belgium, as a result of two phenomena. First and foremost, the country has experienced large inflows of post-accession migration from Central and Eastern European citizens. Second, 40 years after the end of the guest worker programmes, the economic crisis reactivated migration from Southern Europe. One important consequence of the economic crisis and the arrival of Central and Eastern European migrants has been the growing scepticism that has developed in Belgium towards the freedom of circulation. This has led the authorities to implement specific policies aimed at discouraging further migration of low-skilled EU migrants, who are deemed undesirable. In this chapter, we analyse a specific policy consisting of the removal of residence permits from EU jobseekers who claim social security benefits in Belgium. This policy has affected both Central and Eastern European as well as new Southern European EU migrants.Examining the mobilization of different organizations, we then show that—while they are numerically fewer—new Southern European immigrants are in a better position than other new immigrants in Belgium to challenge receiving country policies that target them