NER: Nanoscale Molecular Spintronic Materials and Devices

本提案是对纳米科学和工程计划NSF 01-157的响应，属于NER类别。该提案的重点是(A)。利用铁磁性电极和PI共轭材料制作平面自旋阀和发光器件；(B)有机/无机界面的研究以及界面对自旋输运的影响。虽然自旋相关效应在各种金属和传统半导体中得到了广泛的研究，但在有机半导体中应用于纳米器件的研究还很少。使用有机半导体有两个主要优点，特别是用于自旋电子的pi共轭半导体。首先，这些材料的自旋弛豫时间相对较长，在室温下通常为微秒量级。这是由构成这些半导体的轻原子和pi电子波函数的微小超精细相互作用造成的。第二个优点是，载流子注入有机半导体的主要机制是隧穿，它保留了自旋态，因此铁磁自旋准直器和半导体之间电导失配的严重问题不那么麻烦。此外，有机材料提供了广泛的功函数值，因此隧道势垒可以相对容易地设计成与自旋相关的低隧道电阻，这对于高密度信息存储和存储应用是必不可少的。我们的可行性研究包括两种类型的纳米设备。第一种类型是平面自旋阀器件，它使用圆周率共轭材料作为隔离物。其目的是探索具有高磁阻的低隧道势垒自旋阀。第二类是有机自旋发光器件，它的电致发光将受到外加磁场的调制。预计发射光效率和磁场灵敏度的提高是可以预期的。这两类器件涉及新材料制造、精细光刻和新材料加工，这些都是高度不平凡和高风险的。PI和co-PI(Shii和Vardney)在磁性隧道结材料和纳米器件制造、聚合物合成、有机晶体生长、磁传输、光学和磁光方面拥有专业知识。因此，参与这个项目的两名研究生和两名本科生将在一个相当跨学科的领域受到良好的培训。

This proposal was submitted in response to the Nanoscale Science and Engineering Initiative, Program Solicitation NSF 01-157, in the NER category. The proposal focuses on (a). the fabrication of planar spin-valve and light-emitting devices using ferromagnetic eletrodes and pi-conjugated materials; (b) the study of organic/inorganic interfaces and the effect of the interfaces on spin-transport. Although spin-dependent effects have been widely studied in a variety of metals and conventional semiconductors, very little has been done in organic semiconductors for nanoscale device applications. There are two main advantages for using organic semiconductors, in particular pi-conjugated semiconductors for spin-electronics. Firstly, the spin relaxation time in these materials is relatively long, typically of the order of a microsecond at room temperature. This is caused by the light atoms from which these semiconductors are made and the small hyperfine interaction of the pi-electron wave function. The second advantage is that the main mechanism for carrier injection into organic semiconductors is by tunneling, which preserves spin states, so that the acute problem of conductance mismatch between the ferromagnetic spin aligner and the semiconductor is less troublesome. In addition, organic materials offer a wide range of work function values so that the tunnel barrier can be relatively easily engineered for spin-dependent low tunneling resistance, which is essential for high-density information storage and memory applications. Our feasibility study consists of two types of nanoscale devices. The first type is the planar spin-valve devices using pi-conjugated materials as a spacer. The objective is to explore low tunnel barrier spin-valves with high magnetoresistance. The second type is the organic spin light-emitting devices, where the electroluminescence emission will be modulated by an external magnetic field. The improved emitted light efficiency and magnetic field sensitivity are anticipated. These two types of devices involve with new material fabrication, fine lithography, and new material processing, which are highly non-trivial and of high risk. The PI and co-PI (Shi and Vardney) have expertise in magnetic tunnel junction materials and nanoscale device fabrication, polymer synthesis, organic crystal growth, magneto-transport, optics, and magneto-optics. Thus the two graduate students and two undergraduate students participating in this project will be well-trained in a rather interdisciplinary field.