Quantum dot solids: This generation's silicon wafer?

February 25, 2016

ITHACA, N.Y. - Just as the single-crystal silicon wafer forever changed the nature of communication 60 years ago, a group of Cornell researchers is hoping its work with quantum dot solids - crystals made out of crystals - can help usher in a new era in electronics.

The team, led by Tobias Hanrath, associate professor in the Robert Frederick Smith School of Chemical and Biomolecular Engineering, and graduate student Kevin Whitham, has fashioned two-dimensional superstructures out of single-crystal building blocks. Through a pair of chemical processes, the lead-selenium nanocrystals are synthesized into larger crystals, then fused together to form atomically coherent square superlattices.

The difference between these and previous crystalline structures is the atomic coherence of each 5-nanometer crystal (a nanometer is one-billionth of a meter). They're not connected by a substance between each crystal - they're connected to each other. The electrical properties of these superstructures potentially are superior to existing semiconductor nanocrystals, with anticipated applications in energy absorption and light emission.

"As far as level of perfection, in terms of making the building blocks and connecting them into these superstructures, that is probably as far as you can push it," Hanrath said, referring to the atomic-scale precision of the process.

The Hanrath group's paper, "Charge transport and localization in atomically coherent quantum dot solids," is published in this month's issue of Nature Materials.

This latest work has grown out of previous published research by the Hanrath group, including a 2013 paper published in Nano Letters that reported a new approach to connecting quantum dots through controlled displacement of a connector molecule, called a ligand. That paper referred to "connecting the dots" - i.e. electronically coupling each quantum dot - as being one of the most persistent hurdles to be overcome.

That barrier seems to have been cleared with this new research. The strong coupling of the nanocrystals leads to formation of energy bands that can be manipulated based on the crystals' makeup, and could be the first step toward discovering and developing other artificial materials with controllable electronic structure.

Still, Whitham said, more work must be done to bring the group's work from the lab to society. The structure of the Hanrath group's superlattice, while superior to ligand-connected nanocrystal solids, still has multiple sources of disorder due to the fact that all nanocrystals are not identical. This creates defects, which limit electron wave function.

"I see this paper as sort of a challenge for other researchers to take this to another level," Whitham said. "This is as far as we know how to push it now, but if someone were to come up with some technology, some chemistry, to provide another leap forward, this is sort of challenging other people to say, 'How can we do this better?'"

Hanrath said the discovery can be viewed in one of two ways, depending on whether you see the glass as half empty or half full.

"It's the equivalent of saying, 'Now we've made a really large single-crystal wafer of silicon, and you can do good things with it,'" he said, referencing the game-changing communications discovery of the 1950s. "That's the good part, but the potentially bad part of it is, we now have a better understanding that if you wanted to improve on our results, those challenges are going to be really, really difficult."
This work made use of the Cornell Center for Materials Research, which is supported by the National Science Foundation through its Materials Research Science and Engineering Center program. X-ray scattering was conducted at the Cornell High Energy Synchrotron Source, which is supported by the NSF and the National Institutes of Health.

Video: http://www.cornell.edu/video/quantum-dot-solids

Cornell University

Related Nanocrystals Articles from Brightsurf:

A new kind of liquid scintillator via hybridizing perovskite nanocrystals with organic molecules
Highly-efficient scintillators are playing an essential role in various fundamental science and industrial applications.

CU student helps bridge teams at Clemson
Three teams of researchers at Clemson University have joined forces to unravel some of the mysteries surrounding perovskite nanocrystals, which are semiconductors with numerous applications, including LEDs, lasers, solar cells and photodetectors.

Nanocrystals from recycled wood waste make carbon-fiber composites tougher
In a new study, Texas A&M University researchers have used a natural plant product, called cellulose nanocrystals, to pin and coat carbon nanotubes uniformly onto the carbon-fiber composites.

A safe and powerful safeguard for your whole body against deadly radiation
IBS scientists have reported a highly effective and safe nanocrystal to combat dangers doses of radiation by growing manganese oxide (Mn3O4) nanocrystals on top of the Cerium oxide (CeO2) nanocrystals.

Antiferromagnetic fluoride nanocrystals
Recently, researchers from Peking University, Shenzhen University and National Institute for Materials Science (NIMS) report that the altered passivation of specified facets can direct the synthesis of fluoride nanocrystals into dimension-controlled products in a colloidal approach.

Scientists develop stable luminescent composite material based on perovskite nanocrystals
An international team of scientists that includes researchers from ITMO University has developed a new composite material based on perovskite nanocrystals for the purpose of creating miniature light sources with improved output capacity.

Ultrafast stimulated emission microscopy of single nanocrystals in Science
ICFO researchers report on a new ultrafast stimulated emission microscopy technique that allows imaging of nano-objects and investigating their dynamics.

Armored with plastic 'hair' and silica, new perovskite nanocrystals show more durability
Researchers at the Georgia Institute of Technology have demonstrated a novel approach aimed at addressing the perovskite's durability problem: encasing the perovskite inside a double-layer protection system made from plastic and silica.

Single-particle spectroscopy of CsPbBr3 perovskite reveals the origin low electrolumine
Researchers from Tokyo Institute of Technology (Tokyo Tech) used the method of single-particle spectroscopy to study electroluminescence in light-emitting devices.

University of Konstanz researchers create uniform-shape polymer nanocrystals
Researchers from the University of Konstanz's Collaborative Research Centre (CRC) 1214 'Anisotropic Particles as Building Blocks: Tailoring Shape, Interactions and Structures' successfully generate uniform-shape nanocrystals using direct polymerization

Read More: Nanocrystals News and Nanocrystals Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.