Tag Archives: King Abdullah University of Science and Technology (KAUST)

Turning wasted energy back into electricity

This work comes from the King Abdullah University of Science and Technology (KAUST; Saudi Arabia). From a June 27, 2019 news item on Nanowerk (Note: A link has been removed),

Some of the vast amount of wasted energy that machines and devices emit as heat could be recaptured using an inexpensive nanomaterial developed at KAUST. This thermoelectric nanomaterial could capture the heat lost by devices, ranging from mobile phones to vehicle engines, and turn it directly back into useful electricity (Advanced Energy Materials, “Low-temperature-processed colloidal quantum dots as building blocks for thermoelectrics”).

A June 27, 2019 KAUST press release, which originated the news item, provides more detail,

The nanomaterial is made using a low-temperature solution-based production process, making it suitable for coating on flexible plastics for use almost anywhere.

“Among the many renewable energy sources, waste heat has not been widely considered,” says Mohamad Nugraha, a postdoctoral researcher in Derya Baran’s lab. Waste heat emitted by machines and devices could be recaptured by thermoelectric materials. These substances have a property that means that when one side of the material is hot and the other is cold, an electric charge builds up along the temperature gradient.

Until now, thermoelectric materials have been made using expensive and energy-intensive processes. Baran, Nugraha and their colleagues have developed a new thermoelectric material made by spin coating a liquid solution of nanomaterials called quantum dots.

The team spin coated a thin layer of lead-sulphide quantum dots on a surface and then added a solution of short linker ligands that crosslink the quantum dots together to enhance the material’s electronic properties.

After repeating the spin-coating process layer by layer to form a 200-nanometer-thick film, gentle thermal annealing dried the film and completed fabrication. “Thermoelectric research has focused on materials processed at very high temperatures, above 400 degrees Celsius,” Nugraha says. The quantum-dot-based thermoelectric material is only heated up to 175 degrees Celsius. This lower processing temperature could cut production costs and means that thermoelectric devices could be formed on a broad range of surfaces, including cheap flexible plastics.

The team’s material showed promising thermoelectric properties. One important parameter of a good thermoelectric is the Seebeck coefficient, which corresponds to the voltage generated when a temperature gradient is applied. “We found some key factors leading to the enhanced Seebeck coefficient in our materials,” Nugraha says.

The team was also able to show that an effect called the quantum confinement, which alters a material’s electronic properties when it is shrunk to the nanoscale, was important for enhancing the Seebeck coefficient. The discovery is a step toward practical high-performance, low-temperature, solution-processed thermoelectric generators, Nugraha says.

Here’s a link to and a citation for the paper,

Low‐Temperature‐Processed Colloidal Quantum Dots as Building Blocks for Thermoelectrics by Mohamad I. Nugraha, Hyunho Kim, Bin Sun, Md Azimul Haque, Francisco Pelayo Garcia de Arquer, Diego Rosas Villalva, Abdulrahman El‐Labban, Edward H. Sargent, Husam N. Alshareef, Derya Baran. Advanced Energy Materials Volume 9, Issue 13 1803049 April 4, 2019 DOI: https://doi.org/10.1002/aenm.201803049 First published [online]: 14 February 2019

This paper is behind a paywall.

Structural colo(u)r from transparent 3D printed nanostructures

Caption: Light hits the 3-D printed nanostructures from below. After it is transmitted through, the viewer sees only green light — the remaining colors are redirected. Credit: Thomas Auzinger [downloaded from http://visualcomputing.ist.ac.at/publications/2018/StructCol/]

An August 17, 2018 news item on ScienceDaily announces the work illustrated by the image above,

Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and certain color effects are impossible to achieve. The natural world, however, also exhibits structural coloration, where the microstructure of an object causes various colors to appear. Peacock feathers, for instance, are pigmented brown, but — because of long hollows within the feathers — reflect the gorgeous, iridescent blues and greens we see and admire. Recent advances in technology have made it practical to fabricate the kind of nanostructures that result in structural coloration, and computer scientists from the Institute of Science and Technology Austria (IST Austria) and the King Abdullah University of Science and Technology (KAUST) have now created a computational tool that automatically creates 3D-print templates for nanostructures that correspond to user-defined colors. Their work demonstrates the great potential for structural coloring in industry, and opens up possibilities for non-experts to create their own designs. This project will be presented at this year’s top computer graphics conference, SIGGRAPH 2018, by first author and IST Austria postdoc Thomas Auzinger. This is one of five IST Austria presentations at the conference this year.

SIGGRAPH 2018, now ended, was mentioned in my Aug. 9, 2018 posting.but since this presentation is accompanied by a paper, it rates its own posting. For one more excuse, there’s my fascination with structural colour.

An August 17, 2018 Institute of Science and Technology Austria press release (also on EurekAlert), which originated the news item, delves into the work,

The changing colors of a chameleon and the iridescent blues and greens of the morpho butterfly, among many others in nature, are the result of structural coloration, where nanostructures cause interference effects in light, resulting in a variety of colors when viewed macroscopically. Structural coloration has certain advantages over coloring with pigments (where particular wavelengths are absorbed), but until recently, the limits of technology meant fabricating such nanostructures required highly specialized methods. New “direct laser writing” set-ups, however, cost about as much as a high-quality industrial 3D printer, and allow for printing at the scale of hundreds of nanometers (hundred to thousand time thinner than a human hair), opening up possibilities for scientists to experiment with structural coloration.

So far, scientists have primarily experimented with nanostructures that they had observed in nature, or with simple, regular nanostructural designs (e.g. row after row of pillars). Thomas Auzinger and Bernd Bickel of IST Austria, together with Wolfgang Heidrich of KAUST, however, took an innovative new approach that differs in several key ways. First, they solve the inverse design task: the user enters the color they want to replicate, and then the computer creates a nanostructure pattern that gives that color, rather than attempting to reproduce structures found in nature. Moreover, “our design tool is completely automatic,” says Thomas Auzinger. “No extra effort is required on the part of the user.”

Second, the nanostructures in the template do not follow a particular pattern or have a regular structure; they appear to be randomly composed—a radical break from previous methods, but one with many advantages. “When looking at the template produced by the computer I cannot tell by the structure alone, if I see a pattern for blue or red or green,” explains Auzinger. “But that means the computer is finding solutions that we, as humans, could not. This free-form structure is extremely powerful: it allows for greater flexibility and opens up possibilities for additional coloring effects.” For instance, their design tool can be used to print a square that appears red from one angle, and blue from another (known as directional coloring).

Finally, previous efforts have also stumbled when it came to actual fabrication: the designs were often impossible to print. The new design tool, however, guarantees that the user will end up with a printable template, which makes it extremely useful for the future development of structural coloration in industry. “The design tool can be used to prototype new colors and other tools, as well as to find interesting structures that could be produced industrially,” adds Auzinger. Initial tests of the design tool have already yielded successful results. “It’s amazing to see something composed entirely of clear materials appear colored, simply because of structures invisible to the human eye,” says Bernd Bickel, professor at IST Austria, “we’re eager to experiment with additional materials, to expand the range of effects we can achieve.”

“It’s particularly exciting to witness the growing role of computational tools in fabrication,” concludes Auzinger, “and even more exciting to see the expansion of ‘computer graphics’ to encompass physical as well as virtual images.”

Here’s a link to and a citation for the paper,

Computational Design of Nanostructural Color for Additive Manufacturing by Thomas Auzinger, Wolfgang Heidrich, and Bernd Bickel. ACM Trans. Graph. 37, 4, Article 159 (August 2018). 16 pages. doi.org/10.1145/3197517.3201376

This appears to be open access.

There is also a project page bearing the same title as the paper, Computational Design of Nanostructural Color for Additive Manufacturing.