【作者】 孙毅；

【导师】 倪军；

【作者基本信息】 清华大学 ， 物理学， 2010， 博士

【摘要】 过渡金属元素被广泛应用于特种合金,半导体,电光源等诸多行业中,一般主要以掺杂的方式应用于生产实践中,以实现不同的功用。以钇掺杂的氧化锆和Fe掺杂的碳纳米管为例子,本文应用第一性原理计算研究了过渡金属元素掺杂材料的结构及其稳定性。论文研究掺杂钇原子以及氧空位,对钇稳定的立方氧化锆的结构稳定性的影响规律。发现在掺杂钇原子浓度较高的结构中,钇原子聚集成钇原子链是形成稳定结构所必需的。在沿着钇原子聚集成链的方向,氧空位的迁移势垒远远低于其他方向的迁移势垒,导致氧空位在掺杂结构中的迁移速率呈现各向异性。我们认为利用这种具有各向异性离子迁移速率的稳定结构。可以设计沿某一特定方向有很高离子迁移率的新型器件。论文研究了磁性过渡金属Fe掺杂碳纳米管的结构以及稳定性。我们发现当Fe原子吸附在小管径的碳纳米管内壁时,会使得碳纳米管变形,从而破坏碳纳米管的π键,导致吸附原子与碳纳米管之间的相互作用类型改变,以及相关性质的改变。我们发现孤立的Fe的原子能稳定的吸附在碳管内壁。而Fe原子链不能稳定的吸附在碳管内壁。我们认为,在与碳纳米管内壁相互作用时,磁性过渡金属原子d壳层中自旋向上的d电子向自旋向下的d轨道转移,导致了孤立Fe原子和Fe原子链在碳纳米管内壁不同的吸附性质。我们的计算结果很好的解释了Fe原子链在碳纳米管内壁移动时,只受到很小的剪切应力这一实验现象。根据过渡金属元素Fe在碳纳米管管内壁吸附的物理机制,我们解释了磁性过渡金属元素催化碳纳米管生长的物理机理。此外我们认为,利用过渡金属元素Fe在碳纳米管内壁吸附的物理机制,可以设计具有很高电子自旋极化率的新型电子器件。更多还原

【Abstract】 Transition metal elements have been used in many important fields for different applications, such as alloy steel, high temperature ceramic, semiconductor industry and so on. In this thesis, we have studied the structures and structure stabilities of transition metal atom doped materials, such as yttrium stabilized cubic zirconia and iron doped carbon nanotubes for examples.In this thesis, we have studied how the yttrium atoms and oxygen vacancies affect the structure stabilities of yttrium stabilized cubic zirconia. We find that the yttrium atoms assembling and forming yttrium chains are beneficial to stabilize the doped structures of cubic zirconia with high yttrium concentration. When the oxygen atoms diffuse along the directions of yttrium atoms assembling, the diffusion barrier is much lower than that of other directions. Thus, the diffusion barrier of oxygen atoms in this structure is anisotropy. We suggest that new devices with high oxygen iron conductivity on a certain direction could be produced by using this structure.We have also studied the structure stabilities of iron doped carbon nanotubes. For the adsorption of Fe atoms in the nanotubes, when the diameter of the nanotube is small, the nanotube could bedeformed by the adsorbing of atoms. This deformation changes theπbonding of the nanotubes and has significant effect on the interaction between the adsorbed atoms and the nanotube.We find that a single Fe atom bonds stably with carbon nanotubes, while Fe chains do not bond stably with carbon nanotubes. We have proposed a physical mechanism and show that the transfer energy of spin-up electrons in a half-filled d orbital to the spin-down electrons in another half-filled d orbital in Fe atoms determines the ability of the bonding of single Fe atoms and Fe chains with carbon nanotubes. The results can explain the experiment that Fe nanowires are easy to move inside the nanotubes. Our results also have important implication to the catalysis mechanism of Fe clusters in the growth of carbon nanotubes. Moreover, the electron transfer enhances the spin polarization of the Fe chains near the Fermi level, which has potential application to the high spin polarization nano-devices.更多还原