Self Assembled Iron Nanowires: Morphology, Electrical and Magnetic Properties
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Self assembled Iron Nanowires: Morphology, Electrical and Magnetic Properties T.P. Huelser1, H. Wiggers2, J. Knipping2, P. Roth2, and A. Lorke1 1 Institute of physics, University Duisburg-Essen, 47048 Duisburg 2 Dept. of mechanical engineering, Institute of combustion and gas dynamics, University Duisburg-Essen, 47048 Duisburg ABSTRACT We report on the self-assembled formation of iron nanowires from iron nanoparticles. Nanosized iron particles with a diameter of about 35 nm are synthesized by thermal decomposition of iron pentacarbonyl Fe(CO)5 in a hot wall reactor. This particle size is chosen to produce single domain ferromagnetic particles. As a result, the particles are attracted by magnetic forces, leading to iron nanowires of up to 300 m in length. HRTEM and EELS investigations give detailed morphological, structural and chemical information. They reveal a big metallic iron core surrounded by an iron oxide shell with a thickness of 3-4 nm, originating from self limiting surface oxidation under ambient conditions. For electrical characterization, single iron wires are thermophoretically sampled on interdigital contacts. Impedance spectroscopy on single nanowires indicates both, capacitive and ohmic contributions to the overall conductivity. Magnetic properties are investigated with SQUID magnetometry. Magnetization measurements reveal a saturation magnetization of 160 emu/g at 5 K, which is more than 70% of the iron bulk value. INTRODUCTION Iron is a very common material with a great number of technical applications, and has been intensively investigated. For the last few years, the interest in iron has increased due to possibilities of production and characterization of nanosized iron particles [1,2]. The properties of iron nanoparticles can differ from those of the bulk material because of the dominating surface and size effects associated with nanosized materials [3,4]. Pure metallic and semi-conducting particles like iron and iron oxide can be synthesized with a variety of processes such as sol-gel methods, hot wall reactor processes, laser ablation and plasma reactor processes [5–10]. Gas phase synthesis of nanoparticles by heat-induced dissociation of precursor has the added advantage of yielding particles with small particle diameter, and low levels of contamination. Size-selected iron oxide nanoparticles play an increasing role in medical applications due to their superparamagnetic properties [11]. Pure Iron nanoparticles exhibit a larger saturation magnetization and therefore they might be candidate for medical applications in the future. EXPERIMENTAL DETAILS The synthesis of pure metallic iron nanoparticles was achieved by thermal dissociation of iron pentacarbonyl (IPC) in a hot wall reactor [6]. The agglomeration in chains occurs after the condensation of pure iron nanoparticles and is assigned to magnetic interactions in flight. Investigations on the morphological and structural properties of iron nanoparticles were performed using HRTEM, SEM, XRD, EELS- and EDX-analysis. Furthermore, the e
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