Letters to the Editor
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• Materials with wide-ranging applications: The aim is to promote research on the most promising avenues for improving the functionality and performance of existing materials, and the development of new materials with distinctly new or radically improved characteristics. • Materials production and transformation processes: As the production and transformation processes of materials have a major influence on cost and materials properties, research will focus on technologies which can ensure quality, reliability, and cost effectiveness. • Sustainable use of materials: A growing
need exists for the development of sustainable technologies. Research will focus on the environmental and safety impact of new materials and on recycling materials.
Conclusion
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New and advanced materials are a fundamental and key technology in any advanced society. The development of advanced materials is a horizontal, crosscutting technology affecting many areas of the economy. The Fifth Framework Programme of the EU recognizes the importance and cross-cutting nature of
materials research and will include a specific activity on generic materials research and technological development. Further information on EU Research Policies can be found on the EU website http: / / europa.eu.int / pol / rd / en / info.ht m and on the CORDIS RTD information service at http://www.cordis.lu/fifth/ home.html. Edith Cresson, former prime minister of France (1991-1992), is the Commissioner for Research, Innovation, Education, Training, f and Youth of the European Commission.
Letters to the Editor
Effective Mass Approximation Revisited To the Editor: In an article in the February 1998 MRS Bulletin, p. 35, Alex Zunger gives an overview of the direct diagonalization method (DDM) for calculating the electronic structure of quantum dots, presents some results of that approach, compares them with 6-band effective mass approximation (EMA) calculations and implies the EMA is a general failure. We do not share the author's conclusion. Rather, we remind him that the 6-band EMA has been spectacularly successful in describing absorption,1 hole burning,2 and photoluminescence excitation spectra34 in CdSe quantum nanocrystals, has given a quantitative description of the Stokes shift of the resonant photoluminescence and the magnetic field dependence of the fluorescence decay time,5 and magnetic circular dichroism experiments.6 The assignment of electronic states based on the EMA provides the foundation for almost every description of electronic structure in quantum dots.7 The 6-band model, however, is not appropriate for narrow and moderate bandgap semiconductors; rather, one must use its extension to the 8-band EMA8 which takes the coupling between valence and conduction bands into account. Indeed, we have found that even in narrow gap InAs nanocrystals, this model is very successful in describing transition oscillator strengths and the structure of the absorption spectra.9 In order to claim accepted standing as a legitimate model for describing the properties of qua
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