High-yield parallel fabrication of quantum-dot monolayer single-electron devices displaying Coulomb staircase, contacted by graphene

Joel M Fruhman,Marcus L Böhm,Hippolyte P.A.G Astier,Ugo Sassi,Alexander J Robson,Piran R Kidambi,Andrea C Ferrari,Stephan Hofmann,Lissa F L Eyre,Christopher J B Ford,Bruno Ehrler,Domenico De Fazio,Benjamin J Robinson,Jonathan P Griffiths

doi:10.1038/s41467-021-24233-2

Abstract

It is challenging for conventional top-down lithography to fabricate reproducible devices very close to atomic dimensions, whereas identical molecules and very similar nanoparticles can be made bottom-up in large quantities, and can be self-assembled on surfaces. The challenge is to fabricate electrical contacts to many such small objects at the same time, so that nanocrystals and molecules can be incorporated into conventional integrated circuits. Here, we report a scalable method for contacting a self-assembled monolayer of nanoparticles with a single layer of graphene. This produces single-electron effects, in the form of a Coulomb staircase, with a yield of 87 ± 13% in device areas ranging from < 800 nm2 to 16 μm2, containing up to 650,000 nanoparticles. Our technique offers scalable assembly of ultra-high densities of functional particles or molecules that could be used in electronic integrated circuits, as memories, switches, sensors or thermoelectric generators.

Highlights

It is challenging for conventional top-down lithography to fabricate reproducible devices very close to atomic dimensions, whereas identical molecules and very similar nanoparticles can be made bottom-up in large quantities, and can be self-assembled on surfaces
These are created by sandwiching a single layer of semiconducting PbS quantum dots (QDs) between Au and single-layer graphene (SLG)
The QDs are capped with insulating ligands and bonded to an alkanethiol molecule that is itself part of a molecular self-assembled monolayer (SAM) assembled on the Au

Summary

Introduction

It is challenging for conventional top-down lithography to fabricate reproducible devices very close to atomic dimensions, whereas identical molecules and very similar nanoparticles can be made bottom-up in large quantities, and can be self-assembled on surfaces. Single-electron transport (SET), as realised in this way, can produce novel electronic behaviours that are desirable in commercial systems, such as negative differential resistance[2,3] Such transport was demonstrated in scanning-tunnelling-microscope experiments on granular films[4], which progressed to lithographically defined quantum dots (QDs) with adjustable tunnel barriers[5]. Tunable barrier gates were added with an extra ‘plunger’ gate to control the number of electrons without changing the tunnelling probability[6] These dots are too large to work much above 1 K, so self-assembled, nm-sized clusters[7] and singlemolecule junctions[8,9] were investigated using scanning-probe techniques. Most research studying these behaviours has addressed individual NPs, which is incompatible with mass-fabrication

Methods

Results

Conclusion