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Iron-dotted boron nitride nanotubes, made in Yoke Khin Yaps’ lab at Michigan Tech, could make for better wearable tech because of their flexibility and electronic behaviors.

February 5, 2016—

The road to more versatile wearable technology is dotted with iron. Specifically, quantum dots of iron arranged on boron nitride nanotubes (BNNTs). The new material is the subject of a studypublished in Scientific Reports in February, led by Yoke Khin Yap, a professor of physics at Michigan Technological University.

Yap says the iron-studded BNNTs are pushing the boundaries of electronics hardware. The transistors modulating electron flow need an upgrade.

“Look beyond semiconductors,” he says, explaining that materials like silicon semiconductors tend to overheat, can only get so small and leak electric current. The key to revamping the fundamental base of transistors is creating a series of stepping-stones.

Quantum Dots

The nanotubes are the mainframe of this new material. BNNTs are great insulators and terrible at conducting electricity. While at first that seems like an odd choice for electronics, the insulating effect of BNNTs is crucial to prevent current leakage and overheating. Additionally, electron flow will only occur across the metal dots on the BNNTs.

In past research, Yap and his team used gold for quantum dots, placed along a BNNT in a tidy line. With enough energy potential, the electrons are repelled by the insulating BNNT and hopscotch from gold dot to gold dot. This electron movement is called quantum tunneling.

“Imagine this as a river, and there’s no bridge; it’s too big to hop over,” Yap says. “Now, picture having stepping stones across the river—you can cross over, but only when you have enough energy to do so.”

Nanotech for Wearable Electronics

Unlike with semiconductors, there is no classical resistance with quantum tunneling. No resistance means no heat. Plus, these materials are very small; the nanomaterials enable the transistors to shrink as well. An added bonus is that BNNTs are also quite flexible, a boon for wearable electronics.

“Here’s where the challenge comes in,” Yap says, holding up a pen to demonstrate. He gestures along the length of the pen, which mimics a straight BNNT, tapping out a line of quantum dots. “We have an array here to do quantum tunneling, but what if we want to bend the array to be flexible like a piece of wearable electronics?”

Yap sets down the pen and curls up his index finger: “And if I bend the dots, the distance between them changes—in doing so, we change the electronic behavior.”

Changing the behavior means that the quantum tunneling may not work. The solution is to get out of line: Yap and his team arranged a grid of quantum dots around the outside of the BNNT.

“This time we used iron instead of gold,” Yap adds, explaining that gold’s melting temperature was low for the process his team used. “And when we tested the material, the electrons distributed uniformly across the whole surface of the nanotubes.”

That means that instead of having a line of stepping stones, there are many different paths across the river, and an electron will jump to the nearest one. For future use in wearable electronics, the multiplicity of paths ensures electricity is moving from one riverbank to the next, one way or another. Using scanning tunneling microscopy inside a transmission electron microscope (STM-TEM), the team successfully bent the iron dot-coated BNNT while monitoring the electron flows. The electronic behaviors remain the same even when the BNNT was bent all the way up to 75 degrees.

Next Steps

Yap says that this experiment is a proof of concept. While the iron BNNT material shows promise, it’s not a full transistor yet, capable of modulating electron movement. Right now, it’s called a flexible tunneling channel.

“Next, we’ll put the BNNT and iron onto a bendable plastic substrate,” Yap says. “Then we’ll bend this substrate and watch where the electrons go.”

This experimental work is complemented by computer simulations by John Jaszczak, professor of physics, and Paul Bergstrom, professor of electrical and computer engineering.

Which route the electricity takes is hard to track, which will be the main challenge for the next experiment. But one direction is certain, Yap’s research is headed down a path to change the basic level of electronics and make wearable tech more adaptable.

Michigan Technological University (www.mtu.edu) is a leading public research university developing new technologies and preparing students to create the future for a prosperous and sustainable world. Michigan Tech offers more than 120 undergraduate and graduate degree programs in engineering; forest resources; computing; technology; business; economics; natural, physical and environmental sciences; arts; humanities; and social sciences.

Gel For SElf Healing and Flex Electronics 151125094742_1_540x360Researchers in the Cockrell School of Engineering at The University of Texas at Austin have developed a first-of-its-kind self-healing gel that repairs and connects electronic circuits, creating opportunities to advance the development of flexible electronics, biosensors and batteries as energy storage devices.

Although technology is moving toward lighter, flexible, foldable and rollable electronics, the existing circuits that power them are not built to flex freely and repeatedly self-repair cracks or breaks that can happen from normal wear and tear.

Until now, self-healing materials have relied on application of external stimuli such as light or heat to activate repair. The UT Austin “supergel” material has high conductivity (the degree to which a material conducts electricity) and strong mechanical and electrical self-healing properties.

“In the last decade, the self-healing concept has been popularized by people working on different applications, but this is the first time it has been done without external stimuli,” said mechanical engineering assistant professor Guihua Yu, who developed the gel. “There’s no need for heat or light to fix the crack or break in a circuit or battery, which is often required by previously developed self-healing materials.”

Yu and his team created the self-healing gel by combining two gels: a self-assembling metal-ligand gel that provides self-healing properties and a polymer hydrogel that is a conductor. A paper on the synthesis of their hydrogel appears in the November issue of Nano Letters.

In this latest paper, the researchers describe how they used a disc-shaped liquid crystal molecule to enhance the conductivity, biocompatibility and permeability of their polymer hydrogel. They were able to achieve about 10 times the conductivity of other polymer hydrogels used in bioelectronics and conventional rechargeable batteries. The nanostructures that make up the gel are the smallest structures capable of providing efficient charge and energy transport.

In a separate paper published in Nano Letters in September, Yu introduced the self-healing hybrid gel. The second ingredient of the self-healing hybrid gel is a metal-ligand supramolecular gel. Using terpyridine molecules to create the framework and zinc atoms as a structural glue, the molecules form structures that are able to self-assemble, giving it the ability to automatically heal after a break.

When the supramolecular gel is introduced into the polymer hydrogel, forming the hybrid gel, its mechanical strength and elasticity are enhanced.

To construct the self-healing electronic circuit, Yu believes the self-healing gel would not replace the typical metal conductors that transport electricity, but it could be used as a soft joint, joining other parts of the circuit.

“This gel can be applied at the circuit’s junction points because that’s often where you see the breakage,” he said. “One day, you could glue or paste the gel to these junctions so that the circuits could be more robust and harder to break.”

Yu’s team is also looking into other applications, including medical applications and energy storage, where it holds tremendous potential to be used within batteries to better store electrical charge.

Yu’s research has received funding from the National Science Foundation, the American Chemical Society, the Welch Foundation and 3M.


Story Source:

The above post is reprinted from materials provided by University of Texas at Austin. Note: Materials may be edited for content and length.


Journal Reference:

  1. Yaqun Wang, Ye Shi, Lijia Pan, Yu Ding, Yu Zhao, Yun Li, Yi Shi, Guihua Yu. Dopant-Enabled Supramolecular Approach for Controlled Synthesis of Nanostructured Conductive Polymer Hydrogels. Nano Letters, 2015; 15 (11): 7736 DOI: 10.1021/acs.nanolett.5b03891

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Stretchable Conductors 092015 id41372Researchers have discovered a new stretchable, transparent conductor that can be folded or stretched and released, resulting in a large curvature or a significant strain, at least 10,000 times without showing signs of fatigue. This is a crucial step in creating a new generation of foldable electronics – think a flat-screen television that can be rolled up for easy portability – and implantable medical devices. The work, published Monday in the Proceedings of the National Academy of Sciences (“Fatigue-free, superstretchable, transparent, and biocompatible metal electrodes”), pairs gold nanomesh with a stretchable substrate made with polydimethylsiloxane, or PDMS.

Stretchable Conductors 092015 id41372

Fatigue-free flexible transparent electrode for stretchable and bendable electronics. (Image: University of Houston)
The substrate is stretched before the gold nanomesh is placed on it – a process known as “prestretching” – and the material showed no sign of fatigue when cyclically stretched to a strain of more than 50 percent.
The gold nanomesh also proved conducive to cell growth, indicating it is a good material for implantable medical devices.
Fatigue is a common problem for researchers trying to develop a flexible, transparent conductor, making many materials that have good electrical conductivity, flexibility and transparency – all three are needed for foldable electronics – wear out too quickly to be practical, said Zhifeng Ren, a physicist at the University of Houston and principal investigator at the Texas Center for Superconductivity, who was the lead author for the paper.
The new material, produced by grain boundary lithography, solves that problem, he said.
In addition to Ren, other researchers on the project included Chuan Fei Guo and Ching-Wu “Paul” Chu, both from UH; Zhigang Suo, Qihan Liu and Yecheng Wang, all from Harvard University, and Guohui Wang and Zhengzheng Shi, both from the Houston Methodist Research Institute.
In materials science, “fatigue” is used to describe the structural damage to a material caused by repeated movement or pressure, known as “strain cycling.” Bend a material enough times, and it becomes damaged or breaks. That means the materials aren’t durable enough for consumer electronics or biomedical devices.
“Metallic materials often exhibit high cycle fatigue, and fatigue has been a deadly disease for metals,” the researchers wrote.
“We weaken the constraint of the substrate by making the interface between the Au (gold) nanomesh and PDMS slippery, and expect the Au nanomesh to achieve superstretchability and high fatigue resistance,” they wrote in the paper. “Free of fatigue here means that both the structure and the resistance do not change or have little change after many strain cycles.”
As a result, they reported, “the Au nanomesh does not exhibit strain fatigue when it is stretched to 50 percent for 10,000 cycles.”
Many applications require a less dramatic stretch – and many materials break with far less stretching – so the combination of a sufficiently large range for stretching and the ability to avoid fatigue over thousands of cycles indicates a material that would remain productive over a long period of time, Ren said.
The grain boundary lithography involved a bilayer lift-off metallization process, which included an indium oxide mask layer and a silicon oxide sacrificial layer and offers good control over the dimensions of the mesh structure.
The researchers used mouse embryonic fibroblast cells to determine biocompatibility; that, along with the fact that the stretchability of gold nanomesh on a slippery substrate resembles the bioenvironment of tissue or organ surfaces, suggest the nanomesh “might be implanted in the body as a pacemaker electrode, a connection to nerve endings or the central nervous system, a beating heart, and so on,” they wrote.
Ren’s lab reported the mechanics of making a new transparent and stretchable electric material, using gold nanomesh, in a paper published in Nature Communications in January 2014.
This work expands on that, producing the material in a different way to allow it to remain fatigue-free through thousands of cycles.
Source: University of Houston

Israeli 0422 flexible-screen-811x497

Imagine an electronic screen that looks and feels like paper that could connect to your smartphone. You can shift your longer readings and video viewing to this bendable screen, then roll it up and throw it in your bag when you arrive at your subway stop. This may sound like sci-fi, but Israeli researchers have actually found a way to develop such thin, flexible screens you can use on the go.

A new Tel Aviv University study suggests that a novel DNA nanotechnology could produce a structure that can be used to produce ultra-thin, flexible screens. The research team’s building blocks are three molecules they’ve synthesized, which later self-assembled into ordered structures. Essentially, the team has built the molecular backbone of a super-slim, bendable digital display. In the field of bio-nanotechnology, scientists utilize these molecular building blocks to develop cutting-edge technologies with properties not available for inorganic materials such as plastic and metal.

DNA

This could provide a solution to roughly 2 billion smartphone users who may not want the content they view to be confined to a pocket-sized screen. That’s because currently the size of smartphone screens makes it particularly hard to read more than a few hundred words at a time or watch videos without feeling like you’re on the tilt-a-whirl at Six Flags.

The number of people using mobile devices to view media is on the rise. According to Pew Research Center, 68 percent of smartphone owners use their phone occasionally to follow breaking news stories, and 33 percent do it frequently. Moreover, YouTube reports that 50 percent of its 4 billion video views per month are watched on a mobile device.

SEE ALSO: CES 2015: The Best Of Israeli Tech

[youtube https://www.youtube.com/watch?v=IXVHEox0d50&w=560&h=315]

The structures formed by the researchers were found to emit light in every color, as opposed to other fluorescent materials that shine only in one specific color. Moreover, light emission was observed in response to electric voltage — which makes this technology a perfect candidate for display screens.

The TAU researchers, who recently published their findings in the scientific journal Nature Nanotechnology, are currently building a prototype of the screen and are in talks with major consumer electronics companies regarding the technology, which they’ve patented. “Our material is light, organic and environmentally friendly,” TAU’s Prof. Ehud Gazit said in a statement. “It is flexible, and its single layer emits the same range of light that requires several layers today.” Moreover, fewer layers are better for consumers, he says: “By using only one layer, you can minimize production costs dramatically, which will lead to lower prices.”

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Back to the good old newspaper display? 

It’s important to mention that this technology is still in its early stages and a price tag for these screens remains unknown. What is clear, however, is that the desire to consume content on portable, large screens isn’t going away and consumer preferences are trending more and more toward bigger screens.

Ironically, people seem to be drawn back to the old newspaper display – thin, flexible, and capable of being rolled up; now, all of these features are turning digital.

Regardless of flexibility, the tendency to enlarge mobile screens was already evident last year. It is widely believed that sales of Apple and Samsung (500 million smartphone in 2014) were buoyed by their newest smartphone iterations which boast larger screens than past versions. Apple especially took note of this trend, releasing the iPhone 6 (4.7 inch screen) and iPhone 6 Plus (5.5 inches) simultaneously.

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