The zero field self-organization of cobalt/surfactant nanocomposite thin films
The zero field self-organization of cobalt/surfactant nanocomposite thin films
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DOI：
10.1088/0957-4484/20/22/225605
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发表时间：
2009-06-03
期刊：
影响因子：
3.5
通讯作者：
Liveri, Vincenzo Turco
中科院分区：
文献类型：
--
作者：
Cataldo, Sebastiano;Pignataro, Bruno;Liveri, Vincenzo Turco
本文采用双（2-乙基己基）磺基琥珀酸钴（Co（DEHSS）（2））反胶束分散于正庚烷中，通过有限空间内的Co（II）还原反应制备了钴纳米结构。该过程涉及表面活性剂软涂层的Co纳米结构的快速形成，随后由磁场响应的Co/表面活性剂纳米复合物从液相的缓慢分离过程。用扫描力显微镜（SFM）研究了Co/表面活性剂纳米复合物薄膜的详细结构。薄膜的特征在于不同的各向异性功能。已经观察到自对准的椭圆形NP（尺寸为数十纳米）的微米长域，以及可弯曲的微米长均匀纳米纤维（NF）。薄膜结构强烈地依赖于Co/表面活性剂的比例，并且通过增加Co百分比，迫使系统形成由自对准NF的各向异性带和各向异性2D紧密堆积的Co-NP超晶格组成的相互连接的超结构。透射电子显微镜（TEM）显示，通过SFM观察到的NP实际上由几乎球形和无氧的钴纳米颗粒组成，1-3纳米的尺寸，其通常组装在尺寸为数十纳米的较大椭圆体系统中。磁力显微镜（MFM）证明了这些薄膜的磁响应，突出了不同的行为（吸引/排斥）的Co-NPs聚集体对振荡磁化尖端。上述结构发现已被解释的纳米结构/基质相互作用沿着与短程各向同性排斥，货车德瓦尔斯吸引力和长程各向异性磁相互作用之间的良好平衡。
Cobalt nanostructures have been prepared by a chemical route based on the Co(II) reduction in the confined space of cobalt bis(2-ethylhexyl) sulfosuccinate (Co(DEHSS)(2)) reverse micelles dispersed in n-heptane. This procedure involves the rapid formation of surfactant softly coated Co nanostructures followed by a slow separation process of the magnetic-field responsive Co/surfactant nanocomposites from the liquid phase. The detailed structure of thin films of the Co/surfactant nanocomposites has been investigated by scanning force microscopy (SFM). The thin films were characterized by different anisotropic features. Micrometric long domains of self-aligned ellipsoidal NPs (tens of nanometers in size) have been observed, together with bendable micrometric long homogeneous nanofibers (NFs). The film structures were strongly dependent on the Co/surfactant ratio and, by increasing the Co percentage, the system was forced towards the formation of mutually connected superstructures consisting of anisotropic bands of self-aligned NFs and anisotropic 2D close packed Co-NP super-lattices.Transmission electron microscopy (TEM) showed that the NPs observed by SFM are in effect composed of almost spherical and oxygen-free cobalt nanoparticles, 1-3 nm in size, which typically assemble in larger ellipsoidal systems tens of nanometers in size. Magnetic force microscopy (MFM) demonstrates the magnetic response of these thin films, highlighting the different behavior (attractive/repulsive) of the Co-NPs aggregates towards the oscillating magnetized tip. The above structural findings have been interpreted in terms of nanostructures/matrix interaction along with a fine balance between short-range isotropic repulsions, van der Waals attractions and long-range anisotropic magnetic interactions.