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

Forecasting global atmospheric CO_2

A new global atmospheric carbon dioxide (CO_2) real-time forecast is now available as part of the pre-operational Monitoring of Atmospheric Composition and Climate – Interim Implementation (MACC-II) service using the infrastructure of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS). One of the strengths of the CO_2 forecasting system is that the land surface, including vegetation CO_2 fluxes, is modelled online within the IFS. Other CO_2 fluxes are prescribed from inventories and from off-line statistical and physical models. The CO_2 forecast also benefits from the transport modelling from a state-of-the-art numerical weather prediction (NWP) system initialized daily with a wealth of meteorological observations. This paper describes the capability of the forecast in modelling the variability of CO_2 on different temporal and spatial scales compared to observations. The modulation of the amplitude of the CO_2 diurnal cycle by near-surface winds and boundary layer height is generally well represented in the forecast. The CO_2 forecast also has high skill in simulating day-to-day synoptic variability. In the atmospheric boundary layer, this skill is significantly enhanced by modelling the day-to-day variability of the CO_2 fluxes from vegetation compared to using equivalent monthly mean fluxes with a diurnal cycle. However, biases in the modelled CO_2 fluxes also lead to accumulating errors in the CO_2 forecast. These biases vary with season with an underestimation of the amplitude of the seasonal cycle both for the CO_2 fluxes compared to total optimized fluxes and the atmospheric CO_2 compared to observations. The largest biases in the atmospheric CO_2 forecast are found in spring, corresponding to the onset of the growing season in the Northern Hemisphere. In the future, the forecast will be re-initialized regularly with atmospheric CO_2 analyses based on the assimilation of CO_2 products retrieved from satellite measurements and CO_2 in situ observations, as they become available in near-real time. In this way, the accumulation of errors in the atmospheric CO_2 forecast will be reduced. Improvements in the CO_2 forecast are also expected with the continuous developments in the operational IFS

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

Debate: citizenship and migration

info:eu-repo/semantics/publishe

Low temperature performance of self-aligned, etched polysilicon emitter pseudo-heterojunction bipolar transistors

In this paper we present an investigation of the static performance over the 300K-80K temperature range of pseudo-heterojunction bipolar transistors using an advanced single-polysilicon CMOS compatible self-aligned structure and epitaxial growth for the base and the low doped emitter spacer. These devices exhibit ideal collector currents and non-ideal base currents. By analysing the base leakage current, we have been able to identify the main critical fabrication steps. The bandgap narrowing in the base has been deduced from the temperature dependence of the collector current and the effect of a parasitic boron spike in the base doping profile on the low temperature performance of the transistor has been studied