Researchers develop faster, precise silica coating process for quantum dot nanorods

July 11, 2016 by Matt Shipman
Morphological control of the silica shell on CdSe/CdS core/shell quantum dot nanorods is reported, giving single or double lobes of silica or a uniform silica shell. Credit: Joe Tracy

Materials researchers at North Carolina State University have fine-tuned a technique that enables them to apply precisely controlled silica coatings to quantum dot nanorods in a day - up to 21 times faster than previous methods. In addition to saving time, the advance means the quantum dots are less likely to degrade, preserving their advantageous optical properties.

Quantum dots are nanoscale semiconductor materials whose small size cause them to have electron energy levels that differ from larger-scale versions of the same material. By controlling the size of the , researchers can control the relevant energy levels - and those give quantum dots novel optical properties. These characteristics make quantum dots promising for applications such as opto-electronics and display technologies.

But quantum dots are surrounded by ligands, which are organic molecules that are sensitive to heat. If the ligands are damaged, the optical properties of the quantum dots suffer.

"We wanted to coat the rod-shaped quantum dots with silica to preserve their chemical and optical properties," says Bryan Anderson, a former Ph.D. student at NC State who is lead author of a paper on the work. "However, coating quantum dot nanorods in a precise way poses challenges of its own."

Previous work by other research teams has used water and ammonia in solution to facilitate coating quantum dot nanorods with silica. However, those techniques did not independently control the amounts of water and ammonia used in the process.

By independently controlling the amounts of water and ammonia used, the NC State researchers were able to match or exceed the precision of silica coatings achieved by previous methods. In addition, using their approach, the NC State team was able to complete the entire silica-coating process in a single day - rather than up to one to three weeks needed for other processes.

"The process time is important, because the longer the process takes, the more likely it is that the quantum dot nanorods being coated will degrade," says Joe Tracy, an associate professor of materials science and engineering at NC State and senior author on the paper. "The time factor may also be important when we think about scaling this process up for manufacturing processes."

That said, researchers still have a problem.

The process of applying the silica coating etches the cadmium sulfide surface of the quantum dot nanorods, which shortens the length of the nanorods by as much as four or five nanometers. That shortening is indicative of etching, which reduces the brightness of the light emitted by the quantum dot nanorods.

"We think ammonia may be the culprit," Tracy says. "We have some ideas that we're pursuing, focused on how to substitute another catalyst for ammonia in order to minimize the etching and better preserve the quantum dot nanorod's ."

The paper, "Silica Overcoating of CdSe/CdS Core/Shell Quantum Dot Nanorods with Controlled Morphologies," is published online in the journal Chemistry of Materials. The paper was co-authored by Wei-Chen Wu, a former Ph.D. student in Tracy's lab. The work was done with support from the National Science Foundation under grant number DMR-1056653.

Tracy has previously published related research in Chemistry of Materials on coating gold nanorods with shells.

Explore further: Catching more of the sun

More information: Bryan D. Anderson et al, Silica Overcoating of CdSe/CdS Core/Shell Quantum Dot Nanorods with Controlled Morphologies, Chemistry of Materials (2016). DOI: 10.1021/acs.chemmater.6b01225

Related Stories

Catching more of the sun

April 4, 2016

Combining quantum dots and organic molecules can enable solar cells to capture more of the sun's light.

An improved method for coating gold nanorods

March 18, 2015

Researchers have fine-tuned a technique for coating gold nanorods with silica shells, allowing engineers to create large quantities of the nanorods and giving them more control over the thickness of the shell. Gold nanorods ...

Shining a light on quantum dots measurement

January 15, 2015

Due to their nanoscale dimensions and sensitivity to light, quantum dots are being used for a number of bioimaging applications including in vivo imaging of tumor cells, detection of biomolecules, and measurement of pH changes.

Quantum dots light up under strain

September 23, 2015

Semiconductor nanocrystals, or quantum dots, are tiny, nanometer-sized particles with the ability to absorb light and re-emit it with well-defined colors. With low-cost fabrication, long-term stability and a wide palette ...

Perfectly doped quantum dots yield colors to dye for

May 10, 2013

(Phys.org) —Quantum dots are tiny nanocrystals with extraordinary optical and electrical properties with possible uses in dye production, bioimaging, and solar energy production. Researchers at the University of Illinois ...

Recommended for you

Clothing fabric keeps you cool in the heat

November 16, 2017

(Phys.org)—Researchers have designed a thermal regulation textile that has a 55% greater cooling effect than cotton, which translates to cooler skin temperatures when wearing clothes made of the new fabric. The material ...

Graphene water filter turns whisky clear

November 14, 2017

Previously graphene-oxide membranes were shown to be completely impermeable to all solvents except for water. However, a study published in Nature Materials, now shows that we can tailor the molecules that pass through these ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.