Nanowires1) have been the focus of research for fundamental curiosity as one-dimensional nanosystems and promise exciting applications in nanotechnology, ranging from nanoelectronic devices to cell-separation and magnetic labeling in biomedicine. A variety of methods are devised to synthesize them f...
Nanowires1) have been the focus of research for fundamental curiosity as one-dimensional nanosystems and promise exciting applications in nanotechnology, ranging from nanoelectronic devices to cell-separation and magnetic labeling in biomedicine. A variety of methods are devised to synthesize them from magnetic, semiconductor, inorganic, organic, polymer and metallic to dielectric materials, providing novel optical, electrical, catalytic, and magnetic functionalities. In the investigation, multilayered or barcode arrangements incorporating different material components find a unique cache, attributed to their spatial arraying, multiple functionalities and enhanced properties in comparison to those of their single-component counterparts.2~4) For instance, Co/Cu barcode nanowires have been explored for giant magnetoresistance, compared to the well-studied thin films,5~9) while the coding of magnetic and optical properties in a single wire was targeted for the separation, detection and transport of cells.10) Interested in the transport properties and potential applications of nanowires in nanodevices and biomedicine, we have investigated magnetic nanowires by electrodeposition.11) For biomedical purposes, however, two issues are to be addressed for the implementation of such nanowires, surface modification and biocompatibility.14, 15) In this respect, the synthesis of iron-gold (Fe-Au) nanowires is appealing not only in magnetic properties but also in biological compatibility. On one hand, iron is favored since it is singular in the field of magnetic materials, owing to its high magnetization and physicochemical potentiality. It can be easily converted to oxides, which have been thoroughly studied in the form of magnetic nanoparticles in the biomedical field for its magnetic properties and exceptional biocompatibility.16) On the other hand, gold is a well-established material, showing attractive optical properties, biological compatibility, catalytic activity and excellent surface effects.17~18) Thus, it is anticipated that integrating these two materials into a one-dimensional barcode arrangement on the nanoscale should produce a new nanostructured material which retains the optical and magnetic properties of the respective components, offering synergistically enhanced performance and functionalities which go beyond those of the individual components. In this thesis, I report the synthesis and characterization of such a kind of multifunctional magnetic-optical Fe-Au barcode nanostructures, i.e., nanowires consisting of alternative Fe magnetic and Au optical segments. Additionally, I concentrate in the synthesis of various-type hybrid nanowires which cover from synthesis of core-shell nanowires, multilayered nanowires to new-type hybrid nanowires; multilayered nanowires involved core/shell layers. Multilayered or barcode arrangements of nanowires which incorporate different material components are a special case as a result of their spatial arraying, multiple functionalities, and enhanced properties in comparison to those of their single-component counterparts. Furthermore, to completely resolve the issue of biocompatiblility in nanowires though a thin layer of oxide exists on the surface, we conduct controlled oxidation of the Fe-Au barcode nanowires to convert iron atoms on and near the surface to iron oxide. The method has distinct advantages to retain the high magnetization arising from the iron core (core-shell nanostructure) and to produce safe biocompatible surface. The nanowires used in this study were acquired by DC electrodeposition in anodized aluminum oxide (AAO) templates (200 nm in pore diameter). Then, the nanowires were heat treated at 200~600? in air to accelerate the conversion of iron to oxides and the degree of oxidation was regulated by temperature and time. The characterization of the nanowires was accomplished by SEM, TEM, XRD, Mössbauer Spectroscopy, Raman Spectroscopy and VSM.
Nanowires1) have been the focus of research for fundamental curiosity as one-dimensional nanosystems and promise exciting applications in nanotechnology, ranging from nanoelectronic devices to cell-separation and magnetic labeling in biomedicine. A variety of methods are devised to synthesize them from magnetic, semiconductor, inorganic, organic, polymer and metallic to dielectric materials, providing novel optical, electrical, catalytic, and magnetic functionalities. In the investigation, multilayered or barcode arrangements incorporating different material components find a unique cache, attributed to their spatial arraying, multiple functionalities and enhanced properties in comparison to those of their single-component counterparts.2~4) For instance, Co/Cu barcode nanowires have been explored for giant magnetoresistance, compared to the well-studied thin films,5~9) while the coding of magnetic and optical properties in a single wire was targeted for the separation, detection and transport of cells.10) Interested in the transport properties and potential applications of nanowires in nanodevices and biomedicine, we have investigated magnetic nanowires by electrodeposition.11) For biomedical purposes, however, two issues are to be addressed for the implementation of such nanowires, surface modification and biocompatibility.14, 15) In this respect, the synthesis of iron-gold (Fe-Au) nanowires is appealing not only in magnetic properties but also in biological compatibility. On one hand, iron is favored since it is singular in the field of magnetic materials, owing to its high magnetization and physicochemical potentiality. It can be easily converted to oxides, which have been thoroughly studied in the form of magnetic nanoparticles in the biomedical field for its magnetic properties and exceptional biocompatibility.16) On the other hand, gold is a well-established material, showing attractive optical properties, biological compatibility, catalytic activity and excellent surface effects.17~18) Thus, it is anticipated that integrating these two materials into a one-dimensional barcode arrangement on the nanoscale should produce a new nanostructured material which retains the optical and magnetic properties of the respective components, offering synergistically enhanced performance and functionalities which go beyond those of the individual components. In this thesis, I report the synthesis and characterization of such a kind of multifunctional magnetic-optical Fe-Au barcode nanostructures, i.e., nanowires consisting of alternative Fe magnetic and Au optical segments. Additionally, I concentrate in the synthesis of various-type hybrid nanowires which cover from synthesis of core-shell nanowires, multilayered nanowires to new-type hybrid nanowires; multilayered nanowires involved core/shell layers. Multilayered or barcode arrangements of nanowires which incorporate different material components are a special case as a result of their spatial arraying, multiple functionalities, and enhanced properties in comparison to those of their single-component counterparts. Furthermore, to completely resolve the issue of biocompatiblility in nanowires though a thin layer of oxide exists on the surface, we conduct controlled oxidation of the Fe-Au barcode nanowires to convert iron atoms on and near the surface to iron oxide. The method has distinct advantages to retain the high magnetization arising from the iron core (core-shell nanostructure) and to produce safe biocompatible surface. The nanowires used in this study were acquired by DC electrodeposition in anodized aluminum oxide (AAO) templates (200 nm in pore diameter). Then, the nanowires were heat treated at 200~600? in air to accelerate the conversion of iron to oxides and the degree of oxidation was regulated by temperature and time. The characterization of the nanowires was accomplished by SEM, TEM, XRD, Mössbauer Spectroscopy, Raman Spectroscopy and VSM.
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