Molecular Electronics Meets Direct-Write Carbon Nanofabrication via Focused Electron-Beam-Induced Deposition (FEBID): A Platform for Junction Architecture Design

TL;DR

Researchers developed a method to create reliable molecular electronic devices using carbon nanofabrication and electron-beam techniques.

Contribution

A novel fabrication platform for molecular junctions using FEBID and electrografting to create uniform, reproducible devices.

Findings

Carbon top electrodes were successfully deposited with nanometer precision using FEBID.

Platinum interconnects were added via Pt-FIBID, enabling integration of molecular devices.

The fabricated junctions showed excellent reproducibility and no short circuits.

Abstract

The electrical characteristics of a molecular junction
are highly
sensitive to the nature and uniformity of the molecule|electrode contacts.
This gives rise to significant interest in the development of not
only the active molecular structures that modulate charge transport
and the anchor groups that contact them to the electrodes, but also
methods for assembling uniform molecular monolayers on a substrate
electrode and subsequent fabrication of a “top electrode”
to achieve the reliable fabrication of viable molecular electronic
devices. In this contribution, 4-(4-(4-(trimethylsilylethynyl)­phenylethynyl)­phenylethynyl)­aniline
was converted to the corresponding diazonium salt and electrografted
onto highly oriented pyrolytic graphite (HOPG), resulting in an organized
monolayer covalently bonded to the HOPG “substrate”
electrode. Subsequently, focused electron-beam-induced deposition
was used to form an amorphous carbon top electrode (C-FEBID) onto
the monolayer from a naphthalene precursor. By guiding the raster
scanning of the electron beam, the position, shape, and thickness
of the carbon electrode “written” onto the monolayer
can be controlled with nanometer precision. In addition, as a proof-of-principle
demonstration of the construction of the interconnects necessary for
integration of molecular devices, platinum was deposited precisely
on top of the C-FEBID electrodes, using focused-ion-beam-induced deposition
of PtMe3CpMe (CpMe = η5-C5H4Me) (Pt-FIBID). The HOPG|molecule|C-FEBID|Pt-FIBID
“large area” junctions produced in this manner exhibited
excellent reproducibility and were free of short circuits for top-electrode
dimensions ranging from 4 × 4 to 8 × 8 μm2. The electrical characteristics of these devices were measured and
modeled by using quantum chemical approaches. These results illustrate
alternative routes toward the fabrication of planar 2D devices based
on molecular monolayers and carbon electrodes.

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