Abstract
Reproducibility, stability and the coupling between electrical and molecular properties are central challenges in the field of molecular electronics. The field not only needs devices that fulfill these criteria but they also need to be up-scalable to application size. In this work, few-molecule based electronics devices with reproducible electrical characteristics are demonstrated. Our previously reported 5 nm gold nanoparticles (AuNP) coated with ω-triphenylmethyl (trityl) protected 1,8-octanedithiol molecules are trapped in between sub-20 nm gap spacing gold nanoelectrodes forming AuNP-molecule network. When the trityl groups are removed, reproducible devices and stable Au-thiol junctions are established on both ends of the alkane segment. The resistance of more than 50 devices is reduced by orders of magnitude as well as a reduction of the spread in the resistance histogram is observed. By density functional theory calculations the orders of magnitude decrease in resistance can be explained and supported by TEM observations thus indicating that the resistance changes and strongly improved resistance spread are related to the establishment of reproducible and stable metal-molecule bonds. The same experimental sequence is carried out using 1,6-hexanedithiol functionalized AuNPs. The average resistances as a function of molecular length, demonstrated herein, are comparable to the one found in single molecule devices.
Highlights
Sensors[16,17] and diodes[18]
We have demonstrated that the use of protection groups in the nanoparticle-molecule-nanoelectrode bridge platform followed by a deprotection step leads to a strong improvement of the reproducibility of such molecular electronics devices
Replacing the physisorbed metal-molecule junction with a chemisorbed metal-molecule junction leads to a decreased spread in the measured resistance histogram
Summary
The AuNPs can be expected to rearrange during deprotection and accommodate to a slightly smaller average inter-AuNP distance To go further in the investigation it is necessary to take into account the backbiting molecules since they might affect the distance between the electrodes when the protected molecules are clustering together The results from this calculation (setup III in Fig. 4b) shows a zero-bias conductance of 1.3 × 10−7 Go , i.e. a decrease with three orders of magnitude compared to the octanedithiol chain. The devices before removal of protective groups demonstrate much higher currents than devices with ω -trityl protected 1,8-octanedithiol, which may be attributed to the smaller size of the 1,6-hexanedithiol molecules reducing the distance between two adjacent gold surfaces. It is shown here that these devices are highly reproducible and demonstrate stable current-voltage characteristics
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