Single molecules can serve as convenient templates or scaffolds for metal deposition.
Single molecules have been used as ultrathin templates or scaffolds for metal deposition. To make an ultra-thin wire, just a few nanometers in diameter, one can place a carbon nanotube over a trench. Then a few nanometer thick metallic film is deposited over the suspended carbon nanotube. Such metal decoration of the nanotube molecule results in a very thin metallic wire. Thus extremely thin nanowires (5-15 nanometers in diameter) have been fabricated.
Read more here Superconductivity in nanowires: Fabrication and Quantum transport
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Single molecules can be used as perfect templates or scaffolds for metal deposition.
For example, it is possible to decorate a single nanotube with a film of amorphous metal and produce a homogeneous nanowire of width in the range 5-10 nm.
The suspended molecular template process begins with the preparation of a substrate. This substrate is a silicon wafer covered with a 0.5 µm layer of SiO2 followed by a 50 nm layer of SiN. E-beam lithography is used to define a 50-500 nm-wide trench across the length of the substrate.
The trench is further defined using hydrofluoric acid. The HF etches the SiO2 layer much more quickly than the top layer of SiN, resulting in an under-etched trench.
Carbon nanotubes are deposited in solution onto the substrate. The nanotubes are allowed to settle and stick to the surface of the substrate.
The substrate is dried off with forced nitrogen gas, and those nanotubes that settled onto the surface of the susbstrate may remain (highlighted). Some of these nanotubes my span the trench.
The surface of the substrate, including any nanotubes crossing the trench, are sputter-coated with several nanometers of a superconducting MoGe. The MoGe covering a nanotube suspended across a trench makes up a superconducting nanowire.
An individual nanowire is located under the SEM and then isolated using photolithography. First, photoresist is spin-coated onto the entire surface of the substrate.
An optical mask is aligned over the substrate and the sample is exposed to UV light. The mask is designed to isolate a single nanotube and simultaneously create an electrode pattern for later measurements.
The substrate is then rinsed in a photoresist developer solution, in which all parts of the photoresist exposed to light are removed