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Abstract
We report the design, fabrication, and application of robust ultrathin (~20 nm) metal-protein-metal junctions. These junctions are formed by sandwiching protein layers between a roughness-controlled bottom Au substrate/electrode and an evaporated Pd top contact within a micropore device (MpD) configuration. Our bottom-up fabrication approach incorporates extensive control and optimization strategies to ensure device reproducibility. A specialized protocol was developed to maintain the nanoscale roughness of the bottom electrode also within the micropore region, facilitating uniform protein layer integration. Multi-layered protein films composed of a globular or a membrane protein, human serum albumin, and reconstituted bacteriorhodopsin, respectively, were used to test device feasibility. For reliable top electrode deposition, a refined E-beam evaporation process was designed to mitigate void-induced short-circuiting of the junctions. Palladium (Pd) was selected for its preferred two-dimensional growth to decrease the chance of metal penetration between proteins. Impedance phase response analysis at high frequencies identified ~60% of the junctions as transport-active, highlighting the efficacy of the fabrication approach. These protein-based MpD junctions offer a firm platform for electron transport studies of a variety of soft materials esp. biomaterials such as proteins.
Supplementary materials
Title
Details of Device Fabrication Techniques with Supporting Figures
Description
This discussion provides a detailed overview of the fabrication processes, including photolithography, electron beam evaporation, lift-off, atomic layer deposition (ALD), and reactive ion etching (RIE). Supporting figures illustrate key aspects of the fabrication: tapping mode AFM topographic images showcase high-quality, uniform alumina grown via ALD on an Au/Cr substrate; a schematic represents the micropore (MpD) chip unit; and an image captures the reactive ion-etched Cr surface over the micropore window. Additionally, AFM topography reveals the micropore electrode, where the top alumina layer exhibits shrinkage around the micropore region beneath the undercut chromium layer. Another AFM image highlights the micropore electrode following soft O-plasma treatment. Furthermore, the high-frequency phase response in the Bode plot effectively differentiates active protein junctions from partially or fully shorted devices, demonstrating the integrity of the fabricated structures.
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