Quantum dots finally take a giant leap forward

Quantum dot technology has taken another leap forward, as researchers have discovered a way to make near-perfect superstructures out of these infinitesimal crystals.

Scientists have long harbored high hopes for these tiny crystalline structures that can precisely convert and tune incoming light, but an apparently insurmountable hurdle has been the inability to fuse them together directly. Until now.

This latest research, published Monday in the journal Nature Materials, has obliterated that obstacle, arranging quantum dots together in an order almost without blemish.

“Previously, they were just thrown together, and you hoped for the best,” says lead researcher Tobias Hanrath, of Cornell University’s School of Chemical and Biomolecular Engineering, in a telephone interview with The Christian Science Monitor.

“It was like throwing a couple thousand batteries into a bathtub and hoping you get charge flowing from one end to the other.”

Each crystal – each quantum dot – consists of about 5,000 atoms. Because of the distinct properties these crystals exhibit, not least their emission or absorption of different wavelengths of light according to how they are manipulated, they offer much promise in various fields of technology.

But the challenge has always been finding a way to connect the dots with one another, and to their surroundings, directly, without introducing another substance that would impact both purity and structure.

The breakthrough achieved by Dr. Hanrath and his team represents the culmination of several years’ work, which the professor likens to “playing lego but with atomic-sized building blocks.”

“If you take several quantum dots, all perfectly the same size, and you throw them together, they’ll automatically align into a bigger crystal,” Hanrath tells the Monitor. “It’s the same idea as a bucket of tennis balls automatically assuming an ordered pattern, or stacking cannonballs on top of each other.”

The difference here is that Hanrath’s team has enabled those quantum dots not just to arrange themselves in a random, if ordered, manner, but the crystals can now actually stick to one another.

Previous work had shown that if you placed the quantum dots on a fluid surface, similar to placing oil on water, the crystals could be fused together. But this latest work sought to take that to a new level of perfection.

They have, essentially, created crystal superstructures that are defect-free.

“Take silicon,” says Hanrath. “Every silicon atom is the same size. In our case, the building blocks are almost the same size, but there is 5 percent variability in diameter, so you can’t make a perfect crystal superstructure, but as far as you can, we’ve pushed it to the point of perfection.”

There is scope for this research to have direct technological applications, or to improve existing technologies, particularly in areas such as display screens and solar cells, or even in flexible electronics.

Yet the direct applications are not what excites the professor most of all.

He uses the example of graphene, talking of the predictions surrounding its possibilities, the uses to which it could be put, but saying that, until we have better, more stable, samples, it is hard to carry out the necessary research.

“This is what we’ve done with quantum dot solids, taking them to an unprecedented level of perfection,” says Hanrath, “so what excites us most is the scientific advance in itself and where this could take us next.”