NER: Nanoscale Molecular Spintronic Materials and Devices

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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.