New Method for Building Complex Structures from Quantum Dots Proposed

Quantum dots with the help of DNA form nano-antennae for capturing wavelengths of light

2 min read
New Method for Building Complex Structures from Quantum Dots Proposed

Edward Sargent, Professor in The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto, has been a busy man of late.

At the end of last month, I wrote on his work in using colloidal quantum dots for multi-junction solar cells.

This month Sargent along with Shana Kelley, a Professor in the Department of Biochemistry at the University of Toronto, are reporting in the journalNature Nanotechnology that they have developed a strategy by which to build complex structures out of varying types of quantum dots. In this case, the structure that they built serves as a kind of antenna for light.

As testament to how multi-disciplinary investigations into nanotechnologies can be, expertise in both semiconductor engineering and DNA had to be combined to realize their results. 

"The credit for this remarkable result actually goes to DNA: its high degree of specificity – its willingness to bind only to a complementary sequence – enabled us to build rationally-engineered, designer structures out of nanomaterials," says Sargent in a Physorg.com article

"The amazing thing is that our antennas built themselves – we coated different classes of nanoparticles with selected sequences of DNA, combined the different families in one beaker, and nature took its course,” adds Sargent. “The result is a beautiful new set of self-assembled materials with exciting properties."

The analogy to an antenna comes from the fact that like a traditional antenna these nano-antennae capture dispersed energy and then concentrate that captured energy to a specific location. According to Sargent, this particular kind of antenna for light is seen in the leaves of trees.

While creating light absorbing antennae from quantum dots is an interesting way to manipulate the material, it would seem that developing a method for building various structures with disparate types of quantum dots would be the more impressive bit of this research.

"What this work shows is that our capacity to manipulate materials at the nanoscale is limited only by human imagination,” says Kelley in the article. “If semiconductor quantum dots are artificial atoms, then we have rationally synthesized artificial molecules from these versatile building blocks."

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How the First Transistor Worked

Even its inventors didn’t fully understand the point-contact transistor

12 min read
A phot of an outstretched hand with several transistors in the palm of it.

A 1955 AT&T publicity photo shows [in palm, from left] a phototransistor, a junction transistor, and a point-contact transistor.

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The vacuum-tube triode wasn’t quite 20 years old when physicists began trying to create its successor, and the stakes were huge. Not only had the triode made long-distance telephony and movie sound possible, it was driving the entire enterprise of commercial radio, an industry worth more than a billion dollars in 1929. But vacuum tubes were power-hungry and fragile. If a more rugged, reliable, and efficient alternative to the triode could be found, the rewards would be immense.

The goal was a three-terminal device made out of semiconductors that would accept a low-current signal into an input terminal and use it to control the flow of a larger current flowing between two other terminals, thereby amplifying the original signal. The underlying principle of such a device would be something called the field effect—the ability of electric fields to modulate the electrical conductivity of semiconductor materials. The field effect was already well known in those days, thanks to diodes and related research on semiconductors.

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