NER: Hybrid Organic-Inorganic Devices for Future Spintronics Applications

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This proposal was received in response to the Nanoscale Science and Engineering initiative, Program Solicitation NSF 01-157, in the NER category. The proposal focuses on testing the feasibility of using self-assembly of organic monolayers onto inorganic substrates to control spin phenomena, namely magnetism. The work is a collaboration between the Gwinn group at UCSB, which has expertise in semiconductor physics, and the Naaman group at the Weizmann Institute, which has expertise in the assembly of organized, organic thin films (QOTF) onto inorganic substrates. In these hybrid devices, organic molecules with large electric dipole moments chemisorb onto an inorganic substrate, forming an organized, close-packed dipole sheet. The energetics of forming the adsorbate favors transfer of electrons between the organic molecules and the substrate, somewhat similar to the effect of gates in field-effect devices, but without the need for a gate or gate insulator. This chemically-induced charge transfer modifies the electronic properties of both adsorbate and substrate.The proposed feasibility experiments will test for spin-related phenomena in hybrid devices of organized organic adsorbates on inorganics. The advantages of using organic material is the large versatility in properties that can be tailored relatively easily, its low cost, and the ease of production due to self-assembling processes that can replace expensive high resolution lithography. The enormous variety of organic molecules that self-assemble provides a chemical ~knob" that may make possible new classes of organic/inorganic spintronic devices.Two lines of investigation will be pursued during this year-long project: studies of chemical manipulation of the magnetic properties of GaAs-based semiconductor devices via the organic adsorbate; and studies of the magnetic properties of organic inonolayers of chiral molecules on non-magnetic substrates. Ferromagnetic GaAs heterostructures with near-surface Mn-doped layers will be covered with OOTF to test the feasibility of chemically controlling magnetism in ferromagnetic semiconductors. The effects of the OOTF will be investigated by magnetometry and by magnetotransport measurements. Adsorption of OOTF onto the sidewalls of non-magnetic GaAs/A1GaAs superlattices will be used to attempt to modify the sheath of edge states that appears in the quantum Hall regime. Signatures of the effects of the OOTF would appear in low-temperature magnetotransport experiments. Studies of chiral OOTF will investigate further their previously observed magnetic properties, when adsorbed onto Au; and whether the chiral QQTF retain their magnetic properties when adsorbed onto GaAs.