Researchers have developed a method that could make reproducible manufacturing at the nanoscale possible. The team adapted a light-based technology employed widely in biology — known as optical traps or optical tweezers — to operate in a water-free liquid environment of carbon-rich organic solvents, thereby enabling new potential applications.
The optical tweezers act as a light-based “tractor beam” that can assemble nanoscale semiconductor materials precisely into larger structures. There are no chamber surfaces involved in the manufacturing process, which minimizes the formation of strain or other defects. All of the components are suspended in solution and the size and shape of the nanostructure can be controlled as it is assembled piece by piece.
Using the technique in an organic solvent allows work with components that would otherwise degrade or corrode on contact with water or air. Organic solvents also help to superheat the material, allowing control of material transformations.
To demonstrate the approach, the researchers used the optical tweezers to build a novel nanowire heterostructure — a nanowire consisting of distinct sections comprised of different materials. The starting materials for the nanowire heterostructure were shorter nanorods of crystalline germanium, each just a few hundred nanometers long and tens of nanometers in diameter. Each is capped with a metallic bismuth nanocrystal.
The researchers then used the light-based tractor beam to grab one of the germanium nanorods. Energy from the beam also superheats the nanorod, melting the bismuth cap. They then guide a second nanorod into the tractor beam and — thanks to the molten bismuth cap at the end — solder them end-to-end. They could then repeat the process until they had assembled a patterned nanowire heterostructure with repeating semiconductor-metal junctions that was five to ten times longer than the individual building blocks.
Nanowires that contain junctions between materials — such as the germanium-bismuth junctions — may eventually be a route to creating topological qubits for applications in quantum computing. The nanosoldering approach could enable additive manufacturing of nanoscale structures with different sets of materials for other applications.
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