Ordered Arrays of II/VI Diluted Magnetic Semiconductor Quantum Wires: Formation within Mesoporous MCM-41 Silica FelixJ.Brieler, [a] MichaelFrˆba,* [a] LimeiChen, [b] PeterJ.Klar,* [b] WolframHeimbrodt, [b] Hans-Albrecht Krug von Nidda, [c] and Alois Loidl [c] Abstract: We present a novel way of synthesising highly ordered arrays of hollow Cd 1x Mn x S quantum wires with lateral dimensions of 3 ± 4 nm separated by 1±2nm SiO 2 barriers by forming Cd 1x Mn x S (0  x  1) semiconductors inside the pore system of mesoporous MCM-41 SiO 2 host structures. X-ray diffraction and transmission electron microscopy (TEM) studies reveal the hexagonal symmetry of these arrays (space group p6m) and confirm the high degree of order. Physisorption measure- ments show the filling of the pores of the MCM-41 SiO 2 . The X-ray absorption near-edge structure (XANES), extend- ed X-ray absorption fine structure (EX- AFS), electron paramagentic resonance (EPR), and Raman studies confirm the good crystalline quality of the incorpo- rated (Cd,Mn)S guest. The effects of reducing the lateral dimensions on the magnetic and electronic properties of the diluted magnetic semiconductor were studied by photoluminescence (PL) and PL excitation spectroscopy and by SQUID and EPR measurements in the temperature range 2 ± 400 K. Due to the quantum confinement of the excitons in the wires, an increase of about 200 meV in the direct band gap was observed. In addition, the p-d hy- bridisation-related bowing of the band gap as a function of Mn concentration in the wires is much stronger than in the bulk. This effect is related to the in- crease in the band gap due to quantum confinement, which shifts the p-like valence band edge closer to the 3d- related states of Mn in the valence band. Thus, the p-d hybridisation and the strength of the band gap bowing are increased. Compared to bulk (II,Mn)VI compounds, antiferromagnetic coupling between the magnetic moments of the Mn 2 ions is weaker. For the samples with high Mn concentrations (x > 0.8) this leads to a suppression of the phase transition of the Mn system from paramagnetic to antiferromagnet- ic. This effect can be explained by the fact that the lateral dimensions of the wires are smaller than the magnetic length scale of the antiferromagnetic ordering. Keywords: host ± guest systems ¥ mesoporous materials ¥ nanostruc- tures ¥ semiconductors Introduction The group of molecular sieves was enriched in 1992 by the discovery of a new family of materials called M41S phases. [1] These materials expanded the range of pore sizes from the micro- to the mesoporous range, and this attracted great attention for size-selective applications such as catalysis, [2±4] nanostructured host ± guest compounds [5] and sorption mate- rials. [6] The original synthetic pathway used tetraalkylammo- nium halides as structure-directing agents and tetraethyl orthosilicate (TEOS) as the silica source under alkaline conditions. This route led to three types of mesostructured materials: hexagonal (MCM-41), cubic (MCM-48) and lamel- lar (MCM-50). Since then a variety of syntheses has been developed. Different kinds of amphiphilic molecules have been utilised, for example, nonionic [7] or neutral surfactant molecules, [8] which lead not only to powders but also to thin films [9] and even monolithic structures. [10] The range of different morphologies enhances the options for possible [a] Prof. Dr. M. Frˆba, [] Dipl.-Chem. F. J. Brieler Institute of Inorganic and Analytical Chemistry Justus-Liebig-University Giessen Heinrich-Buff-Ring 58, 35392 Giessen (Germany) Fax: ( 49)-641-99-34109 E-mail: michael.froeba@anorg.chemie.uni-giessen.de [b] Dr. P. J. Klar, Dr. L. Chen, Prof. Dr. W. Heimbrodt Department of Physics and Materials Science Centre Philipps-University of Marburg Renthof 5, 35032 Marburg (Germany) Fax: ( 49)-6421-28-27036 E-mail: Klarp@mailer.uni-marburg.de [c] Dr. H.-A. Krug von Nidda, Prof. Dr. A. Loidl Department of Physics University of Augsburg Augsburg (Germany) [  ] Former affiliations during the period of this research project: Institute of Inorganic and Applied Chemistry, University of Hamburg, Hamburg (Germany) Institute of Inorganic Chemistry, University of Erlangen-Nuremberg, Erlangen (Germany) FULL PAPER Chem. Eur. J. 2002, 8, No. 1 ¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0947-6539/02/0801-0185 $ 17.50+.50/0 185