Without Contact Resistance, Proteins in Thin-Film Solid-State Junctions Can Be Efficient Electronic Conducting...

Area of Science:

• Molecular electronics and biophysics
• Charge transport in biological molecules
• Nanoscale electronic devices

Background:

• Solid-state protein junctions facilitate electron transport over nanometer scales.
• Understanding charge transport requires distinguishing between intrinsic protein conductivity and contact resistance.
• Previous studies often lacked methods to isolate these two factors.

Purpose of the Study:

• To quantitatively determine the contact resistance (R_C) in solid-state protein junctions.
• To investigate the influence of different contact configurations on electron transport efficiency.
• To measure the intrinsic charge transport properties of human serum albumin (HSA) and bacteriorhodopsin (bR) films.

Main Methods:

• Utilized alternating current (impedance spectroscopy) and direct current measurements.
• Employed three contact configurations: Si-Au, Au-eutectic gallium indium (EGaIn), and micropore device (MpD) with Au-Pd.
• Extracted contact resistance from measured junction resistance using extrapolated zero-length and series resistance.

Main Results:

• Si-Au and Au-EGaIn junctions showed significant contact resistance due to interfacial effects.
• The micropore device (MpD) configuration effectively eliminated contact resistance.
• Minimized contact resistance revealed exceptionally low transport decay constants (β ≈ 0.7-1.1 nm⁻¹) for HSA and bR films.

Conclusions:

• Contact resistance significantly impacts the measured electron transport in protein junctions.
• The MpD approach enables accurate measurement of intrinsic protein charge transport.
• Proteins exhibit outstanding charge transport efficiencies when contact resistance is minimized.