Abstract
Nanoimprint lithography (NIL) is a fast, simple and high throughput technique that allows fabrication of structures with nanometre precision features at low cost. We present an advanced bilayer nanoimprint lithography approach to fabricate four terminal nanojunction devices for use in single molecule electronic studies. In the first part of this work, we demonstrate a NIL lift-off process using a bilayer resist technique that negates problems associated with metal side-wall tearing during lift-off. In addition to precise nanoscale feature replication, we show that it is possible to imprint micron-sized features while still maintaining a bilayer structure enabling an undercut resist structure to be formed. This is accomplished by choosing suitable imprint parameters as well as residual layer etching depth and development time. We then use a feedback controlled electromigration procedure, to produce room-temperature stable nanogap electrodes with sizes below 2 nm. This approach facilitates the integration of molecules in stable, solid-state molecular electronic devices as demonstrated by incorporating benzenethiol as molecular bridges between the electrodes and characterizing its electronics properties through current–voltage measurements. The observation of molecular transport signatures, showing current suppression in the I–V behaviour at low voltage, which is then lifted at high voltage, signifying on- and off-resonant transport through molecular levels as a function of voltage, is confirmed in repeated I–V sweeps. The large conductance, symmetry of the I–V sweep and small value of the voltage minimum in transition voltage spectroscopy indicates the bridging of the two benzenethiol molecules is by π–stacking.
Highlights
Since the initial ideas of using molecules to process signals, heralded by the molecular rectifier work of Aviram and Ratner[1] in 1974, scientists have steadily improved the understanding of these complex electrode-molecule systems and have developed better and more robust ways to integrate molecules into devices
We present an advanced bilayer nanoimprint lithography approach to fabricate four terminal nanojunction devices for use in single molecule electronic studies
In the first part of this work, we demonstrate a Nanoimprint lithography (NIL) lift-off process using a bilayer resist technique that negates problems associated with metal side-wall tearing during liftoff
Summary
Since the initial ideas of using molecules to process signals, heralded by the molecular rectifier work of Aviram and Ratner[1] in 1974, scientists have steadily improved the understanding of these complex electrode-molecule systems and have developed better and more robust ways to integrate molecules into devices. A single-molecule light emitting diode has been developed[2], single molecule rectification has reached levels of more than 200[3] and electrical control of the nuclear spin of a single molecule in a device has been achieved via the hyperfine Stark effect[4]. These Ac. AUTHOR SUBMITTED MANUSCRIPT - NANO-123202.R1. Many challenges in the field remain, especially at the single molecule electronic level, such as device variability, stability, improved size alignment between the “leads” and the “molecule” and upscaling from single to multiple device architectures to make computer-like systems
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