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The Flip-chip concept: A new way to electrically characterize molecular monolayers

Wilbers, Janine (2011) The Flip-chip concept: A new way to electrically characterize molecular monolayers.

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Abstract:The biggest challenge in the fabrication of molecular monolayer junctions is the application of the top contacts without damaging the molecules. To allow statistical analysis of the molecular junctions they have to yield reliable and reproducible results. There are already several techniques for the fabrication of molecular monolayer junctions, but all of them have their own disadvantages like low yields or uncertainties in the junction system when an additional layer is introduced between the molecules and the top electrode. Until now no successful fabrication technique has been reported without a non-metallic layer between the molecules and the top contact. In this Master thesis a new concept of molecular junction fabrication called flip-chip is presented. Hereby the top and bottom electrodes are fabricated at the same time and consist of the same metal. Self-assembled molecular monolayers are formed on smooth template-stripped Au electrodes. The top contacts are gently applied on top of the molecules by wedging transfer. The top electrodes are therefore coated with a hydrophobic polymer. When the device is dipped into water the electrodes embedded in the polymer are gently released from the wafer and float on the water. Removing of the water achieves a soft, non-destructive landing on the molecules. The electrode design allows the statistical electrical analysis of self-assembled monolayers in a short period of time for different junction area sizes. No additional layer was introduced between the self-assembled monolayers and the top electrodes, eliminating the ambiguities which occur for currently reported large-area molecular junctions. Five different alkane-monothiols (from decanethiols (C10) to octadecanethiols (C18)) have been characterized and compared to literature. The tunneling decay coefficient β was found to be 0.60 ± 0.11 per carbon atom (nC-1), which is slightly lower than the most recent β coefficients reported in literature (between 0.7 and 1 nC-1). As wedging transfer is a water-based technique this lower value might be caused by water trapped in the junction. The current densities J measured for the different alkanethiols have a spread up to three orders of magnitude. This spread in J might indicate a limitation of the flip-chip concept. However, the origin is not yet known and has to be further investigated. In literature the reported J values have a mutual spread of up to eight orders of magnitude and our values lie approximately halfway in between.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:35 chemistry
Programme:Nanotechnology MSc (60028)
Link to this item:http://purl.utwente.nl/essays/61240
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