Rice University – Flexible insulator offers high strength and superior thermal conduction – Applications for Flexible Electronics and Energy Storage


 

flexible insulator offers high strength and superior thermal conduction
Rice University research scientist M.M. Rahman holds a flexible dielectric made of a polymer nanofiber layer and boron nitride. The new material stands up to high temperatures and could be ideal for flexible electronics, energy storage and electric devices where heat is a factor. Credit: Jeff Fitlow/Rice University

A nanocomposite invented at Rice University’s Brown School of Engineering promises to be a superior high-temperature dielectric material for flexible electronics, energy storage and electric devices.

The nanocomposite combines one-dimensional  nanofibers and two-dimensional  nanosheets. The nanofibers reinforce the self-assembling material while the “white graphene” nanosheets provide a thermally conductive network that allows it to withstand the heat that breaks down common dielectrics, the polarized insulators in batteries and other devices that separate positive and negative electrodes.

The discovery by the lab of Rice  scientist Pulickel Ajayan is detailed in Advanced Functional Materials.

Research scientist M.M. Rahman and postdoctoral researcher Anand Puthirath of the Ajayan lab led the study to meet the challenge posed by next-generation electronics: Dielectrics must be thin, tough, flexible and able to withstand .

“Ceramic is a very good dielectric, but it is mechanically brittle,” Rahman said of the common material. “On the other hand, polymer is a good dielectric with good mechanical properties, but its thermal tolerance is very low.”

Boron  is an electrical insulator, but happily disperses heat, he said. “When we combined the polymer nanofiber with boron nitride, we got a material that’s mechanically exceptional, and thermally and chemically very stable,” Rahman said.

A lab video shows how quickly heat disperses from a composite of a polymer nanoscale fiber layer and boron nitride nanosheets. When exposed to light, both materials heat up, but the plain polymer nanofiber layer on the left retains the heat far longer than the composite at right. Credit: Ajayan Research Group/Rice University

The 12-to-15-micron-thick material acts as an effective heat sink up to 250 degrees Celsius (482 degrees Fahrenheit), according to the researchers. Tests showed the polymer nanofibers-boron nitride combination dispersed heat four times better than the polymer alone.

In its simplest form, a single layer of polyaramid nanofibers binds via van der Waals forces to a sprinkling of boron nitride flakes, 10% by weight of the final product. The flakes are just dense enough to form a heat-dissipating network that still allows the composite to retain its flexibility, and even foldability, while maintaining its robustness. Layering polyaramid and boron nitride can make the material thicker while still retaining flexibility, according to the researchers.

“The 1D polyaramid  has many interesting properties except thermal conductivity,” Rahman said. “And  nitride is a very interesting 2-D material right now. They both have different independent properties, but when they are together, they make something very unique.”

Rahman said the material is scalable and should be easy to incorporate into manufacturing.


Explore further

New material to pave the way for more efficient electronic devices


More information: Muhammad M. Rahman et al. Fiber Reinforced Layered Dielectric Nanocomposite, Advanced Functional Materials (2019). DOI: 10.1002/adfm.201900056

Journal information: Advanced Functional Materials
Provided by Rice University
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India’s first foldable phone in 2019 will be a Samsung Galaxy, A50 with Infinity-O also in pipeline … What Will this Mean to the’Flexible Electronics Markets’?


Galaxy_fold

The foldable Samsung smartphone will demand an extremely higher price for its foldable display technology. The Galaxy A50 will also bring the Infinity-O display technology to the Indian market.

  • Rumours have stated that Samsung will either use a Snapdragon 855 or an Exynos 9820 chipset.
  • Samsung said at the time that the phone will act as a conventional smartphone when folded with is a smaller display panel.
  • The Galaxy A50 will be the first smartphone in India to offer Samsung’s Infinity-O display featuring narrow bezels.

Since Samsung showed off the foldable smartphone at the Samsung Developer Conference in October 2018, the world has been eager to see Samsung’s premium lineup for 2019. The Galaxy A8s unveiled a few weeks ago showed off the Infinity-O display with narrow bezels all around. Therefore, consumers are looking forward to an exciting smartphone lineup from Samsung for this year for the Indian markets. The good news is that India will also be one of the first few markets to enjoy Samsung’s latest and greatest.

According to a report from MySmartPrice, Samsung will unveil both the Galaxy Fold and Galaxy A50 within the next few months and India will witness them soon after. The Galaxy Fold will come to Indian market a few after weeks its launch in European markets. Rumours have stated that Samsung will either use a Snapdragon 855 or an Exynos 9820 chipset for powering the foldable smartphones. Additionally, it could feature 8GB RAM and 128GB internal storage.

At the SDC 2018, Samsung mentioned that they were working with Google to optimise Android for the new foldable form factor. The optimisation with Google will make all apps, as well as the entire Android interface, adapt to the newer display. Samsung said at the time that the phone will act as a conventional smartphone when folded with is a smaller display panel. When unfolded, the device will reveal a large tablet-like display for a bigger viewing experience.

It is also known that the Galaxy Fold will feature dual batteries. Each half of the device will contain a battery, which means the Galaxy Fold could end up having a total battery capacity of up to 6000mAh. This would be necessary considering the demanding nature of the hardware as well as the software. The report also states a probable price for the Galaxy Fold. Samsung could eventually end offering the most expensive smartphones in its history by selling the Galaxy Fold for around $2,000 (approximately Rs 1,50,000). The device would be available in limited numbers as well.

Apart from the Galaxy Fold, Samsung will also bring the much-awaited Galaxy A50 to the Indian market. The A50 will be the first smartphone in India to offer Samsung’s Infinity-O display featuring narrow bezels. The panel will be Samsung’s Super AMOLED one rendering a full HD+ pixel resolution. The A50 is also rumoured to sport an in-display fingerprint sensor. Underneath, the A50 will be powered by an Exynos 9610 chipset accompanied by 4GB RAM and offered with a choice of either 64GB or 128GB storage variants. The A50 will be powered by Samsung’s OneUI based on Android 9 Pie out of the box. The A50 is also expected to kept alive by a 4000mAh battery.

The Galaxy A50 will be a midrange smartphone in India, with prices expected to start under Rs 25,000. The A50 is expected to be announced a few weeks after the Galaxy S10 is unveiled. The Infinity-O display is expected to trickle down to other budget Samsung smartphones in the future as well.

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** A ‘Flex-form high Power density and Cycle Life battery from Tenka Energy could be just what this phone will need to EXCEL! **

50 nm thick ‘Nanosheet Semiconductors’ – Ideal as biosensors, flexible electronics, displays and solar cells


Decal semiconductoA 50nm pentacene film spanned across a 2 mm hole. Credit: Simon Noever, LMU

No more error-prone evaporation deposition, drop casting or printing: Scientists at LMU Munich and FSU Jena have developed organic semiconductor nanosheets, which can easily be removed from a growth substrate and placed on other substrates.

Today’s computer processors are composed of billions of transistors. These electronic components normally consist of material, insulator, , and electrode. A dream of many scientists is to have each of these elements available as transferable sheets, which would allow them to design new electronic devices simply by stacking.

This has now become a reality for the organic semiconductor material pentacene: Dr. Bert Nickel, a physicist at LMU Munich, and Professor Andrey Turchanin (Friedrich Schiller University Jena), together with their teams, have, for the first time, managed to create mechanically stable pentacene nanosheets.

The researchers describe their method in the journal Advanced Materials. They first cover a small silicon wafer with a thin layer of a water-soluble organic film and deposit pentacene molecules upon it until a layer roughly 50 nanometers thick has formed. The next step is crucial: by irradiation with low-energy electrons, the topmost three to four levels of pentacene molecular layers are crosslinked, forming a “skin” that is only about five nanometers thick. This crosslinked layer stabilizes the entire pentacene film so well that it can be removed as a sheet from a silicon wafer in water and transferred to another surface using ordinary tweezers.

Apart from the ability to transfer them, the new semiconductor nanosheets have other advantages. The new method does not require any potentially interfering solvents, for example. In addition, after deposition, the nanosheet sticks firmly to the electrical contacts by van der Waals forces, resulting in a low contact resistance of the final electronic devices. Last but not least, organic semiconductor nanosheets can now be deposited onto significantly more technologically relevant substrates than hitherto.

Of particular interest is the extremely high mechanical stability of the newly developed pentacene nanosheets, which enables them to be applied as free-standing nanomembranes to perforated substrates with dimensions of tens of micrometers. That is equivalent to spanning a 25-meter pool with plastic wrap. “These virtually freely suspended semiconductors have great potential,” explains Nickel. “They can be accessed from two sides and could be connected through an electrolyte, which would make them ideal as biosensors, for example”. “Another promising application is their implementation in flexible electronics for manufacturing of devices for vital data acquisition or production of displays and solar cells,” Turchanin says.

Explore further: Nano-imaging probes molecular disorder

More information: Simon J. Noever et al. Transferable Organic Semiconductor Nanosheets for Application in Electronic Devices, Advanced Materials (2017). DOI: 10.1002/adma.201606283

 

Breakthrough in ‘wonder’ materials paves way for flexible tech


breakthrough-2d-structures

Credit: University of Warwick

 

Gadgets are set to become flexible, highly efficient and much smaller, following a breakthrough in measuring two-dimensional ‘wonder’ materials by the University of Warwick.

Dr Neil Wilson in the Department of Physics has developed a new technique to measure the electronic structures of stacks of two-dimensional materials – flat, atomically thin, highly conductive, and extremely strong materials – for the first time.

Multiple stacked layers of 2-D materials – known as heterostructures – create highly efficient optoelectronic devices with ultrafast electrical charge, which can be used in nano-circuits, and are stronger than materials used in traditional circuits.

Various heterostructures have been created using different 2-D materials – and stacking different combinations of 2-D materials creates new with new properties.

Dr Wilson’s technique measures the electronic properties of each layer in a stack, allowing researchers to establish the optimal structure for the fastest, most efficient transfer of electrical energy.

The technique uses the photoelectric effect to directly measure the momentum of electrons within each layer and shows how this changes when the layers are combined.

The ability to understand and quantify how 2-D material heterostructures work – and to create optimal semiconductor structures – paves the way for the development of highly efficient nano-circuitry, and smaller, flexible, more wearable gadgets.

Solar power could also be revolutionised with heterostructures, as the atomically thin layers allow for strong absorption and efficient power conversion with a minimal amount of photovoltaic material.

Dr Wilson comments on the work: “It is extremely exciting to be able to see, for the first time, how interactions between atomically thin layers change their electronic structure. This work also demonstrates the importance of an international approach to research; we would not have been able to achieve this outcome without our colleagues in the USA and Italy.”

Dr Wilson worked formulated the technique in collaboration with colleagues in the theory groups at the University of Warwick and University of Cambridge, at the University of Washington in Seattle, and the Elettra Light Source, near Trieste in Italy.

Understanding how interactions between the atomic layers change their required the help of computational models developed by Dr Nick Hine, also from Warwick’s Department of Physics.

Explore further: Model accurately predicts the electronic properties of a combination of 2-D semiconductors

More information: Neil R. Wilson et al. Determination of band offsets, hybridization, and exciton binding in 2D semiconductor heterostructures, Science Advances (2017). DOI: 10.1126/sciadv.1601832

 

Graphene-based transparent electrodes for highly efficient flexible OLEDS


OLED 060316 1-graphenebaseOLED with the composite structure of TiO2/graphene/conducting polymer electrode in operation. The OLED exhibits 40.8% of ultrahigh external quantum efficiency (EQE) and 160.3 lm/W of power efficiency. The device prepared on a plastic …more

The arrival of a thin and lightweight computer that even rolls up like a piece of paper will not be in the far distant future. Flexible organic light-emitting diodes (OLEDs), built upon a plastic substrate, have received greater attention lately for their use in next-generation displays that can be bent or rolled while still operating.

A Korean research team led by Professor Seunghyup Yoo from the School of Electrical Engineering, KAIST and Professor Tae-Woo Lee from the Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH) has developed highly flexible OLEDs with excellent efficiency by using graphene as a (TE) which is placed in between titanium dioxide (TiO2) and conducting polymer layers. The research results were published online on June 2, 2016 in Nature Communications.

OLEDs are stacked in several ultra-thin layers on glass, foil, or plastic substrates, in which multi-layers of organic compounds are sandwiched between two electrodes (cathode and anode). When voltage is applied across the electrodes, electrons from the cathode and holes (positive charges) from the anode draw toward each other and meet in the emissive layer. OLEDs emit light as an electron recombines with a positive hole, releasing energy in the form of a photon. One of the electrodes in OLEDs is usually transparent, and depending on which electrode is transparent, OLEDs can either emit from the top or bottom.

In conventional bottom-emission OLEDs, an anode is transparent in order for the emitted photons to exit the device through its substrate. Indium-tin-oxide (ITO) is commonly used as a transparent anode because of its high transparency, low sheet resistance, and well-established manufacturing process. However, ITO can potentially be expensive, and moreover, is brittle, being susceptible to bending-induced formation of cracks.

Graphene-based transparent electrodes for highly efficient flexible OLEDS
The new architecture to develop highly flexible OLEDs with excellent efficiency by using graphene as a transparent electrode (TE). Credit: KAIST

Graphene, a two-dimensional thin layer of carbon atoms tightly bonded together in a hexagonal honeycomb lattice, has recently emerged as an alternative to ITO. With outstanding electrical, physical, and chemical properties, its atomic thinness leading to a high degree of flexibility and transparency makes it an ideal candidate for TEs. Nonetheless, the efficiency of graphene-based OLEDs reported to date has been, at best, about the same level of ITO-based OLEDs.

As a solution, the Korean research team, which further includes Professors Sung-Yool Choi (Electrical Engineering) and Taek-Soo Kim (Mechanical Engineering) of KAIST and their students, proposed a new device architecture that can maximize the efficiency of graphene-based OLEDs. They fabricated a transparent anode in a composite structure in which a TiO2 layer with a high refractive index (high-n) and a hole-injection layer (HIL) of conducting polymers with a low refractive index (low-n) sandwich graphene electrodes. This is an optical design that induces a synergistic collaboration between the high-n and low-n layers to increase the effective reflectance of TEs. As a result, the enhancement of the optical cavity resonance is maximized. The optical cavity resonance is related to the improvement of efficiency and color gamut in OLEDs. At the same time, the loss from surface plasmon polariton (SPP), a major cause for weak photon emissions in OLEDs, is also reduced due to the presence of the low-n conducting polymers.

Under this approach, graphene-based OLEDs exhibit 40.8% of ultrahigh external quantum efficiency (EQE) and 160.3 lm/W of power efficiency, which is unprecedented in those using graphene as a TE. Furthermore, these devices remain intact and operate well even after 1,000 bending cycles at a radius of curvature as small as 2.3 mm. This is a remarkable result for OLEDs containing oxide layers such as TiO2 because oxides are typically brittle and prone to bending-induced fractures even at a relatively low strain. The research team discovered that TiO2 has a crack-deflection toughening mechanism that tends to prevent bending-induced cracks from being formed easily.

Professor Yoo said, “What’s unique and advanced about this technology, compared with previous graphene-based OLEDs, is the synergistic collaboration of high- and low-index layers that enables optical management of both resonance effect and SPP loss, leading to significant enhancement in efficiency, all with little compromise in flexibility.” He added, “Our work was the achievement of collaborative research, transcending the boundaries of different fields, through which we have often found meaningful breakthroughs.”

Professor Lee said, “We expect that our technology will pave the way to develop an OLED light source for highly flexible and wearable displays, or flexible sensors that can be attached to the human body for health monitoring, for instance.”

Explore further: Nanometer Graphene Makes Novel OLEDs Display

More information: Jaeho Lee et al, Synergetic electrode architecture for efficient graphene-based flexible organic light-emitting diodes, Nature Communications (2016). DOI: 10.1038/NCOMMS11791

 

U of Penn Engineers develop first transistors made entirely of nanocrystal ‘inks’


U Penn Nano Inks 2-pennengineerThe transistor is the most fundamental building block of electronics, used to build circuits capable of amplifying electrical signals or switching them between the 0s and 1s at the heart of digital computation. Transistor fabrication is a highly complex process, however, requiring high-temperature, high-vacuum equipment.

Now, University of Pennsylvania engineers have shown a new approach for making these devices: sequentially depositing their components in the form of liquid nanocrystal “inks.”

Their new study, published in Science, opens the door for electrical components to be built into flexible or wearable applications, as the lower-temperature process is compatible with a wide array of materials and can be applied to larger areas.

The researchers’ nanocrystal-based field effect transistors were patterned onto flexible plastic backings using spin coating but could eventually be constructed by additive manufacturing systems, like 3-D printers.

The study was lead by Cherie Kagan, the Stephen J. Angello Professor in the School of Engineering and Applied Science, and Ji-Hyuk Choi, then a member of her lab, now a senior researcher at the Korea Institute of Geoscience and Mineral Resources. Han Wang, Soong Ju Oh, Taejong Paik and Pil Sung Jo of the Kagan lab contributed to the work. They collaborated with Christopher Murray, a Penn Integrates Knowledge Professor with appointments in the School of Arts & Sciences and Penn Engineering; Murray lab members Xingchen Ye and Benjamin Diroll; and Jinwoo Sung of Korea’s Yonsei University.

Penn engineers develop first transistors made entirely of nanocrystal 'inks'
Because this entirely ink-based fabrication process works at lower temperatures than existing vacuum-based methods, the researchers were able to make several transistors on the same flexible plastic backing at the same time. Credit: University of Pennsylvania

The researchers began by taking nanocrystals, or roughly spherical nanoscale particles, with the electrical qualities necessary for a transistor and dispersing these particles in a liquid, making nanocrystal inks.

Kagan’s group developed a library of four of these inks: a conductor (silver), an insulator (aluminum oxide), a semiconductor (cadmium selenide) and a conductor combined with a dopant (a mixture of silver and indium). “Doping” the semiconductor layer of the transistor with impurities controls whether the device transmits a positive or negative charge.

“These materials are colloids just like the ink in your inkjet printer,” Kagan said, “but you can get all the characteristics that you want and expect from the analogous bulk materials, such as whether they’re conductors, semiconductors or insulators.

“Our question was whether you could lay them down on a surface in such a way that they work together to form functional transistors.”

The electrical properties of several of these nanocrystal inks had been independently verified, but they had never been combined into full devices.

“This is the first work,” Choi said, “showing that all the components, the metallic, insulating, and semiconducting layers of the transistors, and even the doping of the semiconductor could be made from nanocrystals.”

Such a process entails layering or mixing them in precise patterns.

First, the conductive silver nanocrystal ink was deposited from liquid on a flexible plastic surface that was treated with a photolithographic mask, then rapidly spun to draw it out in an even layer. The mask was then removed to leave the silver ink in the shape of the transistor’s gate electrode. The researchers followed that layer by spin-coating a layer of the aluminum oxide nanocrystal-based insulator, then a layer of the cadmium selenide nanocrystal-based semiconductor and finally another masked layer for the indium/silver mixture, which forms the transistor’s source and drain electrodes. Upon heating at relatively low temperatures, the indium dopant diffused from those electrodes into the semiconductor component.

“The trick with working with solution-based materials is making sure that, when you add the second layer, it doesn’t wash off the first, and so on,” Kagan said. “We had to treat the surfaces of the nanocrystals, both when they’re first in solution and after they’re deposited, to make sure they have the right electrical properties and that they stick together in the configuration we want.”

Because this entirely ink-based fabrication process works at lower temperatures than existing vacuum-based methods, the researchers were able to make several transistors on the same flexible plastic backing at the same time.

“Making transistors over larger areas and at lower temperatures have been goals for an emerging class of technologies, when people think of the Internet of things, large area flexible electronics and wearable devices,” Kagan said. “We haven’t developed all of the necessary aspects so they could be printed yet, but because these materials are all solution-based, it demonstrates the promise of this materials class and sets the stage for additive manufacturing.”

Explore further: Particle-free silver ink prints small, high-performance electronics

More information: “Exploiting the colloidal nanocrystal library to construct electronic devices” DOI: 10.1126/science.aad0371

 

Nanotubes “Line-Up” to Form Films for Flexible Electonics: Video


Rice logo_rice3 Rice University researchers discover way to make highly aligned, wafer-scale films 

A simple filtration process helped Rice University researchers create flexible, wafer-scale films of highly aligned and closely packed carbon nanotubes.

Scientists at Rice, with support from Los Alamos National Laboratory, have made inch-wide films of densely packed, chirality-enriched single-walled carbon nanotubes through a process revealed today in Nature Nanotechnology.

In the right solution of nanotubes and under the right conditions, the tubes assemble themselves by the millions into long rows that are aligned better than once thought possible, the researchers reported.

The thin films offer possibilities for making flexible electronic and photonic (light-manipulating) devices, said Rice physicist Junichiro Kono, whose lab led the study. Think of a bendable computer chip, rather than a brittle silicon one, and the potential becomes clear, he said.

“Once we have centimeter-sized crystals consisting of single-chirality nanotubes, that’s it,” Kono said. “That’s the holy grail for this field. For the last 20 years, people have been looking for this.”Rice scanning 040616 0215.WAFERS-5-rn-26x5r2v

A scanning electron microscope image shows highly aligned and closely packed carbon nanotubes gathered into a film by researchers at Rice. Courtesy of the Kono Lab

 

The Rice lab is closing in, he said, but the films reported in the current paper are “chirality-enriched” rather than single-chirality. A carbon nanotube is a cylinder of graphene, with its atoms arranged in hexagons. How the hexagons are turned sets the tube’s chirality, and that determines its electronic properties. Some are semiconducting like silicon, and others are metallic conductors.

A film of perfectly aligned, single-chirality nanotubes would have specific electronic properties. Controlling the chirality would allow for tunable films, Kono said, but nanotubes grow in batches of random types.

For now, the Rice researchers use a simple process developed at the National Institute of Standards and Technology to separate nanotubes by chirality. While not perfect, it was good enough to let the researchers make enriched films with nanotubes of different types and diameters and then make terahertz polarizers and electronic transistors.

Rice CNT Inventors 040616 0215.WAFERS-1-rn-168jkgm

Rice graduate students Xiaowei He, left, and Weilu Gao, center, and Professor Junichiro Kono show a film of highly aligned carbon nanotubes made in Kono’s lab. Photo by Jeff Fitlow

The Rice lab discovered the filtration technique in late 2013 when graduate students and lead authors Xiaowei He and Weilu Gao inadvertently added a bit too much water to a nanotube-surfactant suspension before feeding it through a filter assisted by vacuum. (Surfactants keep nanotubes in a solution from clumping.)

The film that formed on the paper filter bore further investigation. “Weilu checked the film with a scanning electron microscope and saw something strange,” He said. Rather than drop randomly onto the paper like pickup sticks, the nanotubes – millions of them – had come together in tight, aligned rows.

“That first picture gave us a clue we might have something totally different,” He said. A year and more than 100 films later, the students and their colleagues had refined their technique to make nanotube wafers up to an inch wide (limited only by the size of their equipment) and of any thickness, from a few to hundreds of nanometers.

Further experiments revealed that each element mattered: the type of filter paper, the vacuum pressure and the concentration of nanotubes and surfactant. Nanotubes of any chirality and diameter worked, but each required adjustments to the other elements to optimize the alignment.

The films can be separated from the paper and washed and dried for use, the researchers said.

They suspect multiwalled carbon nanotubes and non-carbon nanotubes like boron nitride would work as well.

Co-author Wade Adams, a senior faculty fellow at Rice who specializes in polymer science, said the discovery is a step forward in a long quest for aligned structures.

“They formed what is called a monodomain in liquid crystal technology, in which all the rigid molecules line up in the same direction,” Adams said. “It’s astonishing. (The late Rice Nobel laureate) Rick Smalley and I worked very hard for years to make a single crystal of nanotubes, but these students have actually done it in a way neither of us ever imagined.”

Why do the nanotubes line up? Kono said the team is still investigating the mechanics of nucleation — that is, how the first few nanotubes on the paper come together. “We think the nanotubes fall randomly at first, but they can still slide around on the paper,” he said. “Van der Waals force brings them together, and they naturally seek their lowest-energy state, which is in alignment.” Because the nanotubes vary in length, the researchers suspect the overhangs force other tubes to line up as they join the array.

The researchers found their completed films could be patterned with standard lithography techniques. That’s yet another plus for manufacturers, said Kono, who started hearing buzz about the discovery months before the paper’s release.

“I gave an invited talk about our work at a carbon nanotube conference, and many people are already trying to reproduce our results,” he said. “I got so much enthusiastic response right after my talk. Everybody asked for the recipe.”

Co-authors are Rice graduate students Qi Zhang, Sidong Lei and John Robinson and postdoctoral researcher Bo Li; Lijuan Xie of Zhejiang University, who has a complimentary appointment at Rice.

Rice alumnus Erik Haroz and Stephen Doorn of Los Alamos National Laboratory; Robert Vajtai, a faculty research fellow at Rice; Pulickel Ajayan, chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry; and the late Robert Hauge, distinguished faculty fellow in chemistry and in materials science and nanoengineering at Rice.

Adams is a senior faculty fellow in materials science and nanoengineering. Kono is a Rice professor of electrical and computer engineering, of physics and astronomy and of materials science and nanoengineering.

The Department of Energy and the Robert A. Welch Foundation supported the research.

 

Quantum Dots of Iron Arranged on Boron Nitride Nanotubes (BNNTs) for Better Wearable Tech Without Semiconductors: “Iron Stepping Stones” with Video


Nanotube Iron QDs image131438-horiz

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.

New ‘self-healing’ gel makes Electronics More Flexible


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