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Abstract
Tunnel junctions have been suggested as high-throughput electronic single molecule sensors in liquids, with several seminal experiments conducted using break junctions with reconfigurable gaps. For practical single molecule sensing applications, arrays of on-chip integrated fixed-gap tunnel junctions that can be built into compact systems are preferable. Fabricating nanogaps by electromigration is one of the most promising approaches to realize on-chip integrated tunnel junction sensors. However, the electrical behavior of fixed-gap tunnel junctions immersed in liquid media has not been systematically studied to date, and the formation of electromigrated nanogap tunnel junctions in liquid media has not yet been demonstrated. In this work, we perform a comparative study of the formation and electrical behavior of arrays of gold nanogap tunnel junctions made by feedback-controlled electromigration immersed in various liquid and gaseous media (deionized water, mesitylene, ethanol, nitrogen, and air). We demonstrate that tunnel junctions can be obtained from microfabricated gold nano-constrictions inside liquid media. Electromigration of junctions in air produces the highest yield (61 %), electromigration in deionized water and mesitylene results in a lower yield than in air (44–48 %), whereas electromigration in ethanol fails to produce viable tunnel junctions due to interfering electrochemical processes. We map out the stability of the conductance characteristics of the resulting tunnel junctions and identify medium-specific operational conditions which have an impact on the yield of forming stable junctions. Furthermore, we highlight the unique challenges associated with working with arrays of large numbers of tunnel junctions in batches. Our findings will inform future efforts to build single-molecule sensors using on-chip integrated tunnel junctions.
Supplementary materials
Title
Supplementary Information
Description
Supplementary Information contains: Table summarizing key statistics of all measurement batches, detailed description of feedback-controlled electromigration and self-breaking, description of characterization of feedback-controlled electromigration and self-breaking of Cr/Au devices in air, SEM images of the progression of electromigration in air, description and illustration of devices used for SEM imaging after feedback-controlled electromigration and self-breaking under liquid immersion, further details of parametric classification of stability of tunnel junctions from I-V characteristics, graphical summary of the experimental procedure and results from a measurement series in mesitylene.
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