University of Twente Student Theses


Devices for spin injection & detection in graphite

Zijlstra, B. (2011) Devices for spin injection & detection in graphite.

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Abstract:Graphene is an interesting material for applications in organic spintronics, because of its high mobility and its predicted long spin relaxation times. In practice however, only spin relaxation lengths up to 1-2 μm have been observed [1]. Materials in close proximity to graphene have been suspected to significantly influence its spintronic properties. In thick stacks of graphene monolayers, aka graphite, the transport of spins would be less affected by such interface effects. The ultimate goal of this master thesis was to measure the spin relaxation length and/or time in bulk graphite. Therefore, a fabrication procedure had to be developed to make devices on graphite substrates that would allow for this type of probing. Using shadow mask deposition, devices with a vertical spin valve geometry were fabricated. However, this device geometry is not suitable for non-local probing, and electrical measurements indicated bad performance. Simultaneously, a fabrication procedure was developed, in which a combination of e-beam lithography and photolithography was used to fabricate devices with a lateral geometry. Despite of the initial problems in fabricating these devices, most difficulties in the fabrication procedure were resolved and lateral devices could, eventually, be made readily. Electrical measurements showed that these devices still often showed undesired and unpredictable behavior. The problems were presumed to be caused by defective tunnel barriers. In the final stages of this project, some electrodes were made that showed good tunneling behavior, but the fabrication modifications that had led to this improvement, had also caused the electrodes to become mechanically unstable at the low temperatures that were required for spin dependent transport measurements. Subsequent Hanle measurements with these defective tunnel barriers did not show any Hanle peaks, but instead a (spurious) LMR effect was observed
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:31 mathematics, 35 chemistry, 42 biology
Programme:Nanotechnology MSc (60028)
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