铁磁性石墨烯的制备与研究

发布时间：2018-01-22 12:50

本文关键词： 铁磁性还原氧化石墨烯三维石墨烯羟基氮等离子体　出处：《东南大学》2016年博士论文　论文类型：学位论文

【摘要】：自从2004年机械剥离制备出单层石墨烯的开创性工作以来,石墨烯由于其优异的电学、机械、光学和热学等性能吸引了人们的广泛关注。石墨烯拥有高的载流子迁移率、长的自旋弛豫时间、弱的自旋-轨道超精细作用,使得石墨烯在自旋电子学应用方面成为一个理想的候选材料。然而,在完美的石墨烯中,每个碳原子跟相邻三个碳原子sp2杂化,贡献一个未成键电子,形成大π键,这样的结构导致它的本征抗磁性,限制它在自旋电子器件中的实际应用。传统的磁性材料与3d(或4f)内壳层电子没有被填满的过渡金属元素(例如铁、钴、镍等)有关。在石墨烯相关材料中也报道了磁性,由于其只有sp电子,有别于传统的磁性来源,引起了人们的广泛关注。在石墨烯晶格中引入缺陷被认为可以产生局域磁矩。这些缺陷包括局域拓扑扰动、空位、在石墨烯晶格中的非碳原子、混合sp2-sp3杂化、zigzag类边界等。然而,有报道氟化石墨烯和氧化石墨烯量子点表现出典型的顺磁性,而不存在铁磁性。如何在石墨烯及其衍生物中引入高浓度缺陷,形成铁磁有序对自旋电子学的应用相当重要。本论文主要研究通过还原氧化石墨烯(弱氧化条件下)、三维石墨烯、氮等离子体处理氧化石墨烯等相关工艺,在石墨烯中获得了显著的铁磁性并进行了细致地研究。具体内容如下:(1)我们研究了弱氧化条件下的还原氧化石墨烯(w-rGO)的磁性。w-rGO是弱氧化条件下的氧化石墨烯在高温退火得到,我们在样品w-rGO中观测到较强的室温铁磁性,饱和磁化强度(Ms)为0.24 emu/g,是强氧化条件下制备还原氧化石墨烯的24倍。我们在样品w-rGO中观测到负的磁电阻回线。当温度低于15K,磁电阻[R(H)-R(0)]/R(0)数值保持在-2.5%,当温度高于15 K,磁电阻随着温度升高而减少,当温度高于50 K,磁电阻接近零,几乎消失,这是由于铁磁缺陷的自旋相关散射导致的,它证明了观测到的本征铁磁性,w-rGO中强铁磁性来源于弱氧化条件下保留的石墨结构。(2)对于石墨烯粉体(氧化石墨烯和还原氧化石墨烯粉末)而言,由于π-π作用力和范德华力的存在,石墨烯片层之间容易发生团聚,二维材料独有的性质在一定程度上遭到破坏,限制了其实际应用。三维石墨烯由二维石墨烯组装而成,不但可以保持原来石墨烯优异的性能,而且能够拓宽其应用范围。目前,三维石墨烯磁性方面研究还没有报道过。我们研究了三维石墨烯的磁性,它是氧化石墨烯溶液通过水热法制备得到。在三维石墨烯样品中,我们能够观测到一定的室温铁磁性,饱和磁化强度(Ms)为0.005 emu/g。水热还原过程中,氧化石墨烯片修复的共轭结构形成很强的三维交联石墨烯网络。高浓度的sp3类型缺陷(羟基)是三维石墨烯室温铁磁性的主要来源。(3)作为轻质非金属磁体,石墨烯及其衍生物的铁磁性在自旋电子学领域十分重要。然而,目前合成磁性石墨烯的方法,存在反应时间长、磁性污染物(Fe、Co和Ni等)容易被引入、制备过程很复杂,这阻碍了它的科学研究和实际应用。我们将氧化石墨烯直接放在氮等离子体(室温条件)下处理,氧化石墨烯被还原的同时,还掺杂引入氮,得到含氮的还原氧化石墨烯(NrGO),样品的室温铁磁性明显增强。氮等离子体曝光时间对控制石墨烯的铁磁性起到相当重要的作用。氧化石墨烯在氮等离子体曝光时间从0增加到30分钟,样品的铁磁磁化强度(Ms)从0.0006 emu/g增加到0.010 emu/g。当曝光时间从30分钟增加60分钟,样品的铁磁磁化强度开始减少,从0.010 emu/g减少到0.0010 emu/g。XPS结果显示,pyrrolicN在NrGO30(氧化石墨烯在氮等离子体下处理30分钟)所占比例(约45.8%)高于它在NrGO60(氧化石墨烯在氮等离子体下处理60分钟,约24.7%),而pyridinicN在NrGO30比例(约51.3%)低于它在 NrGO60(约 69.0%)。GraphiticN 在 NrGO30(约 2.9%)低于 NrGO60(约6.3%),而且它所占比例都相当小。因而pyrrolicN是样品NrGO中铁磁性主要来源。
[Abstract]:Since 2004, mechanical stripping prepared graphene pioneering work, graphene due to its excellent electrical, mechanical, optical and thermal properties has attracted widespread attention. Graphene has a high carrier mobility, long spin relaxation time, spin - orbit weak hyperfine interaction. The graphene is an ideal material in spintronics applications. However, in perfect graphene, each carbon atom with three adjacent carbon atoms with SP2 hybridization, a non bonding electrons, forming bond, this structure leads to the intrinsic magnetic resistance of it, limit it the actual application in spintronics. Magnetic materials and traditional 3D (or 4F) inner shell electron transition metal elements are not filled (such as iron, cobalt, nickel and so on). In graphene related materials have also been reported because of the electronic magnetic, only sp, Different from the traditional magnetic source, has attracted widespread attention. The introduction of defects are thought to produce localized magnetic moments in the graphene lattice. These defects include local topological disturbance, vacancy, non carbon atoms in the graphene lattice, mixed sp2-sp3 hybrid, zigzag boundary. However, there are reports of graphite fluoride graphene oxide and graphene quantum dots exhibit typical paramagnetic, ferromagnetic and does not exist. How to introduce the high concentration of defects in the graphene and its derivatives, the formation of application of ferromagnetic ordering of spintronics is very important. This paper mainly studies the reduction of graphene oxide (weak oxidation conditions), three-dimensional graphene. Treatment of graphene oxide and other related technology of nitrogen plasma, in graphene obtained remarkable ferromagnetism and carefully studied. The specific contents are as follows: (1) we investigated the reduction of oxygen weak oxidation conditions Graphene (w-rGO) magnetic graphene oxide.W-rGO is weak oxidation conditions in high temperature annealing, we observed strong room temperature ferromagnetism in sample w-rGO, the saturation magnetization (Ms) of 0.24 emu/g, is 24 times the strong oxidizing conditions prepared by reduction of graphene oxide. We observed the negative magnetoresistance loop in sample w-rGO. When the temperature is lower than 15K, the magnetoresistance of [R (H) -R (0)]/R (0) value in -2.5%, when the temperature is higher than 15 K, while reducing the magnetic resistance with increasing temperature, when the temperature is higher than 50 K, the magnetic resistance is close to zero, it almost disappears. Is due to spin dependent scattering of ferromagnetic defects, it is proved that the observed intrinsic ferromagnetism in graphite structure w-rGO strong ferromagnetism originates from weak oxidizing conditions. (2) reserved for graphene powder (graphene oxide and graphene powder) and said, because the Pi Pi force and Fan Dehua The force exists between the graphene layers is easy to agglomerate, the destruction of the unique properties of two-dimensional materials to a certain extent, limits its practical application. The three-dimensional graphene by two-dimensional graphene assembled, can not only keep the original performance of graphene excellent, but also can broaden the scope of its application. At present, the three-dimensional graphene the magnetic study has never been reported. We studied the three-dimensional magnetic graphene, graphene oxide solution which is prepared by hydrothermal method. The three-dimensional graphene samples, we can observed room temperature ferromagnetism. The saturation magnetization (Ms) of 0.005 emu/g. water thermal reduction process, conjugate the structure of graphene oxide film forming a three-dimensional crosslinked network repair Shi Moxi strong. The SP3 type high concentration of defects (hydroxyl) is the main source of three-dimensional graphene at room temperature ferromagnetism. (3) as a light metallic magnet, The ferromagnetism of graphene and its derivatives is very important in the field of spintronics. However, the synthesis of magnetic graphene, had a long reaction time (Fe, Co, magnetic contaminants and Ni) to be introduced, the preparation process is very complex, the way of scientific research and its practical application. We will graphite oxide graphene directly on the nitrogen plasma treatment (room temperature), graphene oxide was reduced at the same time, also the introduction of nitrogen doped graphene oxide, reduction of nitrogen (NrGO), room temperature ferromagnetism of the samples increased significantly. Nitrogen plasma exposure time is very important to control the ferromagnetic graphene graphene oxide. In nitrogen plasma exposure time increased from 0 to 30 minutes, the ferromagnetic magnetization (Ms) increased from 0.0006 emu/g to 0.010 emu/g. when the exposure time increased from 60 minutes to 30 minutes, ferromagnetic magnetization Begin to decrease, reduced from 0.010 emu/g to 0.0010 emu/g.XPS results showed that pyrrolicN in NrGO30 (graphene oxide in nitrogen plasma treatment under 30 minutes) the proportion (about 45.8%) is higher than it in NrGO60 (graphene oxide in nitrogen plasma treatment under 60 minutes, about 24.7%), and pyridinicN in the ratio of NrGO30 (about 51.3%) it is lower than in NrGO60 (69%).GraphiticN in NrGO30 (about 2.9%) than NrGO60 (about 6.3%), but the proportion is quite small. Therefore pyrrolicN is ferromagnetic sample NrGO main sources.

【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O613.71;O482.5

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