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Mechanically Controlled Break Junctions
Mechanically Controlled Break Junctions
Our home-built MCBJ set-up uses a piezoelectric-controlled push rod to carefully pull apart a thin gold wire, creating a nanoscopic gap in which individual molecules can bind. We then use a custom high-bandwidth amplifier to measure molecular circuits with currents as low as 8 picoamps.
Our home-built MCBJ set-up uses a piezoelectric-controlled push rod to carefully pull apart a thin gold wire, creating a nanoscopic gap in which individual molecules can bind. We then use a custom high-bandwidth amplifier to measure molecular circuits with currents as low as 8 picoamps.
The MCBJ set-up is built on a vibrationally-isolated table and placed inside a copper Faraday cage to minimize small sources of environmental noise.
A side view of a clamped-in sample with the push rod positioned underneath, ready to start bending.
Junction Fabrication
Junction Fabrication
Students working on MCBJ projects have the opportunity to learn a variety of clean room nano-fabrication techniques in order to design, create, and evaluate the samples used in experiments.
Students working on MCBJ projects have the opportunity to learn a variety of clean room nano-fabrication techniques in order to design, create, and evaluate the samples used in experiments.
Fabrication work is done in ultra-clean environments wearing "bunny suits" because even a few dust particles can cause defects.
Spin coating is used to deposit resist layers in which we will write our designs.
We use a tightly-focused beam of high energy electrons to write patterns with features as small as 100 nanometers.
We use a thermal deposition chamber under high vacuum to apply an 80 nanometer layer of gold to our samples.
A set of 16 samples immediately after being coated with ultrahigh purity gold; shiny enough for a self-portrait!
After deposition, acetone removes the excess gold and our carefully designed pattern is revealed!
Finally, we use a reactive ion etcher to create a free-standing gold bridge less than one micron long and 100 nanometers wide. It is this bridge that will be broken by bending the sample with a push rod.
To help with quality control, we use a scanning electron microscope (SEM) to image the nano-structures on finished samples.
In this SEM image of an etched sample, we can see a successfully fabricated free-standing gold bridge. When the entire sample is clamped into the MCBJ set-up shown above and bent, the very center of this bridge will be pulled apart, creating a nano-gap in which a molecule can bind.
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