Engineering news
When light waves form into arrays of bright and dark spots, they create static holographic images - the illusion of a material object. These frozen waves are a result of images encoded into a material that controls the direction and timing of the oscillations within the electromagnetic waves.
To move these holographic images, the emitted light waves need to ‘twist’ themselves. The Michigan researchers have now found a way to create spiral semiconductors that can perform this task.
Previously, scientists struggled with creating twisting semiconductors, because they tend to naturally configure into sheets or wires while forming. The Michigan researchers found a way to do just that by guiding the attachment of semiconductor nanoparticles to each other into twists with help from amino acids in DNA molecules.
"The direction of the spiral of proteins is determined by the geometrical property of amino acids,” says Wenchun Feng, a semiconductor expert at the university and lead author of the study. “We found that a common amino acid – cysteine - working together in large numbers can twist not only proteins but also semiconductors."
The scientists coated nanoparticles made of cadmium telluride – a light-emitting semiconductor - with cysteine, chiral molecules that are asymmetrical and cannot be superimposed. Then spontaneously, “millions of nanoparticles can come together and build large spirals in a highly precise way,” Feng adds. “The twisting direction of these spirals is decided by the specific chiral molecules coating the nanoparticles.”
The researchers discovered that 98% of the semiconductor spirals uniformly twisted in the same direction. Shining light through the semiconductors showed protons swirling through them. Using a combination of computer simulations and experiments, the team engineered optical properties of the semiconductor spirals into different colours for future holography devices.
However, “correlating experimental data with simulations was challenging,” says Feng. The team had to measure more than 100 individual spiral molecules before they were able to build an accurate model for simulations. The spirals also need the right solvent for their optical properties to be measured, and after a great deal of trial and error the team finally settled on water. The simulations also had to take into account the random orientation of the spiral molecules in the solvent.
The Michigan scientists think it might take up to a decade for the technology to be commercialised. “We still need to increase the yield, incorporate them into devices, and optimise the quality of holography,” Feng says.
The University of Michigan’s relationship with holography dates back to the mid-20th century, when in 1962 researchers unveiled the world’s first 3D holographic images using laser light. Holographic technology was first developed by British scientist Dennis Gabor.
The research appears in
Science Advances.