铁磁/有机系统的界面极化、注入与输运研究

【作者】 付吉永；

【导师】 解士杰；

【作者基本信息】 山东大学 ， 凝聚态物理， 2006， 博士

【摘要】 有机半导体作为一种新型的功能材料，人们已经逐渐认识到其丰富的功能特性。从小分子到高分子，其电磁光等特性越来越明显。对具有准一维特征的导电聚合物的结构和物性，特别是它的电特性，可以说已经有了一个比较准确的理解，无论从量化还是物理建模出发，都得到了与实验基本一致的理论结果。有机发光二极管(OLEDs)是有机分子材料的二个重要应用，目前以小分子合成的发光器件已经实用化，高分子有机发光二极管也达到实用标准。另一方面，聚合物是软凝聚态物质的典型代表，也是理解有机体、生物物质的基础。有机分子电子学、DNA分子电子学等都引起了人们的关注和研究。单个分子开关和分子导线已经研制成功，由此可设计分子尺度的电子逻辑计算。DNA分子处于动力学无形态，具有宽带隙的非晶半导体特征。所有这些工作都揭示出有机材料存在丰富的物理功能特性，同时也表明对有机材料的研究必须综合物理、化学甚至生物学的各种手段。 随着巨磁电阻(GMR)现象的发现，磁电子学或自旋电子学已成为凝聚态物理或微电子学中一个快速增长的领域。电子自旋注入和自旋相关输运是当前感兴趣和被广泛研究的课题。自旋注入包括从铁磁金属到超导体、铁磁金属到导体、铁磁金属到非磁性半导体以及磁性半导体到非磁性半导体，或这些构型的复合。有机半导体由于其弱的自旋—轨道耦合和超精细相互作用，相应的自旋扩散长度比较长，因而是实现自旋极化输运理想的候选材料。研究有机半导体内的自旋注入和输运对进一步理解有机材料的物理性质，探讨其在自旋电子学及生命系统中的功能和应用具有重要的科学意义。虽然有机功能材料的很多表观性质与无机半导体类似，但是有机材料也有它的特殊性，如具有结构上的“软”性，低维性等。自旋注入有机材料与通常的无机半导体材料相比，有着本质的不同，更重要的是注入电子(或空穴)不是以扩展态的形式存在，而是形成所谓的“自陷态”或“局域元激发”，如孤子，极化子或双极化子，它们具有不同的电荷—自旋关系，只有中性孤子和带单个电荷的极化子携带1／2自旋。当前关于极化子和双极化子的相对稳定性问题一直存有争议。选择极化子容易产生的材料和条件对于实现有机体内的自旋极化输运至关重要。更多还原

【Abstract】 As a new kind of functional material, conjugated polymers or small oligomers have been attracting much theoretical and experimental interest both because of the unique electric, magnetic and optical properties that occur in these materials and because of the technological potential of electronic devices fabricated from them. In particular, they are already the basis of effective organic light-emitting diodes (OLEDs) and a wider range of devices and applications such as organic spin valves and magnetic resistance. On the other hand, conjugated polymers have common characteristic of the soft condensed matters and can serve as a medium to understand other organic and even biological molecules. Up to now, there have been extensive studies on organic and DNA molecular electronics. The single molecular switch and wire have been successfully fabricated and can be used to design the devices focusing on the logical computation in the scale of a single molecule. In addition, DNA molecules exist in a form of the dynamic random state, so that they can behave as a metallic conductor, a semiconductor, or an insulator, according to different contacts, molecular lengths, and ambient surroundings. In conclusion, all the studies indicate that the organic materials have abundant physical and functional properties and we have to investigate such materials using a comprehensive method which may be related with physics, chemistry and even biology.Magneto-electronics or spintronics is a field of growing interest. Since the discovery of giant magneto-resistance (GMR), rapid progress has been made in this field. Electron spin injection and spin-dependent transport are essential aspects of spintronics and have been extensively studied in a number of different contexts including: ferromagnetic metals to superconductors, ferromagnetic metals to normal metals, ferromagnetic metals to nonmagnetic semiconductors, magnetic semiconductors to nonmagnetic semiconductors, or a combination of these configurations. Conjugated polymers have been ideal materials for spin injection since the discovery of long spin diffusion length due to the very small spin-orbit coupling更多还原