Magnetoresistive, Mechanically Hard Superlattices of CrN, NbN, TiN Multilayers Deposited on Monocrystalline Si Wafers
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Magnetoresistive, mechanically hard superlattices of CrN, NbN, TiN multilayers deposited on monocrystalline Si wafers* Andrzej Wolkenberg1,2 e-mail: [email protected], Hanna Wrzesinska2, Andrzej Bochenek1, Adam Tokarz1, Zygmunt Nitkiewicz1, Tomasz Przeslawski2, Jacek Ratajczak2, Piotr Dluzewski3 1 Institute of Materials Engineering, Department of Metallurgy and Materials Engineering, Technical University of Częstochowa;2Institute of Electron Technology, al. Lotników 32/46, 02668 Warsaw; 3Institute of Physics, P.Ac.Sci., al. Lotników 32/46, 02-668 Warsaw ABSTRACT Hardness measurements on thin films have to face the problem of the effect of the substrate hardness on the obtained result. Also the method of hardness measurement exerts a considerable influence on the experimental data. Some models, which take such effects into account, are presented. We describe experimental results of hardness measurements made with the Vickers 5g probe. Nitride layers (CrN, TiN, NbN), superlattices composed of these nitrides and thin metal films deposited either on the monocrystalline Si or metallic substrates such as steel or copper have been investigated. We also present measurements of the magnetoresistivity (MR) effect. on superlattices, which consist of the multilayers TiN/NbN deposited on Si substrates. Layers of different thickness of TiN and NbN obtained by the reactive sputtering method with different superlattice period values (Λ) and number have been studied. The composite hardness of the structures (superlattice on Si) was found to reach 80 GPa and MR value in the best probes was ~80% (for fields from some Gs to kGs). When the supporting thin metallic layer was present, then its influence on the composite hardness was also observed. INTRODUCTION All of the basic physical and chemical properties of a material are independent of its size. This picture changes dramatically in the nanoworld, where materials are only a few tens of atoms across. Ever smaller structures are being developed that will soon approach the point where the material properties start to change. One can take the advantage of the size dependence to tune the electronic, mechanical and chemical properties to create specially designed materials. The change of any material properties could find its source in the fact that on the macroscopic level only a tiny fraction of the atoms (~10-7) reside on the surface, so their influence can generally be neglected. But for a part of superlattice which consist, e.g., of ~100 atoms, about 80% of them are on the surface or on the interface [1]. EXPERIMENTAL DETAILS CrN, NbN and TiN films were prepared on silicon wafers planes oriented (100) or (111).and polished polycrystalline metal surfaces. After substrate cleaning the nitride films were deposited on monocrystalline silicon wafers and on polished metal substrates in the chamber of a planar DC reactive sputtering apparatus of LEYBOLD L400Sp sputtering system by using very pure Ar and N2 as sputtering gases. The background pressure was kept below 1.10-6 mbar. During
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