IDES have been realized in modulation doped AIGaAs/GaAs heterostructures by fabricating split-gate configurations and ultrafine etched structures with optimized lithography and etching techniques. With deep-mesa etching technique it is possible to prepare single and multi-layered quantum wire systems. From dc magnetotransport typical confinement energies of 2me V are determined. The FIR response is strongly governed by collective effects which give the resonances the character of local plasmon modes. In multi-layered quantum wire structures a splitting of the plasmon dispersion in longitudinal and acoustical type of layer-coupled local plasmon modes is observed. ACKNOWLEDGEMENT We would like to thank K Ploog for providing us with excellent samples and acknowledge financial support from the Bundesministerium fur Forschung und Tech- nologie, Bonn. REFERENCES 1K-F. Berggren, T. J. Thornton, D. J. Newson, and M. Pepper, Phys. Rev. Lett. 57, 1769 (1986) 2H. van Houten, B. J. van Wees, M. G. J. Heijman, J. P. Andre, D. Andrews, and G. J. Davies, Appl. Phys. Lett. 49, 1781 (1986) 3J. Cibert, P. M. Petroff, G. J. Dolan, S. J. Pearton, A. C. Gossard, and J. H. English, Appl. Phys. Lett.
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