Waste Styrofoam can now be converted into polymers for electronics

University of Delaware and Argonne National Laboratory have come up with a chemical reaction that can convert Styrofoam into a high-value conducting polymer known as PEDOT:PSS. In a new paper published in JACS Au, the study demonstrates how upgraded plastic waste can be successfully incorporated into functional electronic devices, including silicon-based hybrid solar cells and organic electrochemical transistors.

The research group of corresponding author Laure Kayser, assistant professor in the Department of Materials Science and Engineering in UD's College of Engineering with a joint appointment in the Department of Chemistry and Biochemistry in the College of Arts and Sciences, regularly works with PEDOT:PSS, a polymer that has both electronic and ionic conductivity, and was interested in finding ways to synthesize this material from plastic waste.

After connecting with Argonne chemist David Kaphan during an event hosted by UD's research office, the research teams at UD and Argonne began evaluating the hypothesis that PEDOT:PSS could be made by sulfonating polystyrene, a synthetic plastic found in many types of disposable containers and packing materials.

Sulfonation is a common chemical reaction where a hydrogen atom is replaced by sulfonic acid; the process is used to create a variety of products such as dyes, drugs and ion exchange resins. These reactions can either be "hard" (with higher conversion efficiency but that require caustic reagents) or "soft" (a less efficient method but one that uses milder materials).

In this paper, the researchers wanted to find something in the middle: "A reagent that is efficient enough to get really high degrees of functionalization but that doesn't mess up your polymer chain," Kayser explained.

The researchers first turned to a method described in a previous study for sulfonating small molecules, one that showed promising results in terms of efficiency and yield, using 1,3-Disulfonic acid imidazolium chloride ([Dsim]Cl). But adding functional groups onto a polymer is more challenging than for a small molecule, the researchers explained, because not only are unwanted byproducts harder to separate, any small errors in the polymer chain can change its overall properties.

To address this challenge, the researchers embarked on many months of trial and error to find the optimal conditions that minimized side reactions, said Kelsey Koutsoukos, a materials science doctoral candidate and second author of this paper.

"We screened different organic solvents, different molar ratios of the sulfonating agent, and evaluated different temperatures and times to see which conditions were the best for achieving high degrees of sulfonation," he said.

The researchers were able to find reaction conditions that resulted in high polymer sulfonation, minimal defects and high efficiency, all while using a mild sulfonating agent. And because the researchers were able to use polystyrene, specifically waste Styrofoam, as a starting material, their method also represents an efficient way to convert plastic waste into PEDOT:PSS.

Once the researchers had PEDOT:PSS in hand, they were able to compare how their waste-derived polymer performed compared to commercially available PEDOT:PSS.

"In this paper, we looked at two devices -- an organic electronic transistor and a solar cell," said Chun-Yuan Lo, a chemistry doctoral candidate and the paper's first author. "The performance of both types of conductive polymers was comparable, and shows that our method is a very eco-friendly approach for converting polystyrene waste into high-value electronic materials."

Specific analyses conducted at UD included X-ray photoelectron spectroscopy (XPS) at the surface analysis facility, film thickness analysis at the UD Nanofabrication Facility, and solar cell evaluation at the Institute of Energy Conversion. Argonne's advanced spectroscopy equipment, such as carbon NMR, was used for detailed polymer characterization. Additional support was provided by materials science and engineering professor Robert Opila for solar cell analysis and by David C. Martin, the Karl W. and Renate Böer Chaired Professor of Materials Science and Engineering, for the electronic device performance analyses.

One unexpected finding related to the chemistry, the researchers added, is the ability to use stoichiometric ratios during the reaction.

"Typically, for sulfonation of polystyrene, you have to use an excess of really harsh reagents. Here, being able to use a stoichiometric ratio means that we can minimize the amount of waste being generated," Koutsoukos said.

This finding is something the Kayser group will be looking into further as a way to "fine-tune" the degree of sulfonation. So far, they've found that by varying the ratio of starting materials, they can change the degree of sulfonation on the polymer. Along with studying how this degree of sulfonation impacts the electrical properties of PEDOT:PSS, the team is interested in seeing how this fine-tuning capability can be used for other applications, such as fuel cells or water filtration devices, where the degree of sulfonation greatly impacts a material's properties.

"For the electronic devices community, the key takeaway is that you can make electronic materials from trash, and they perform just as well as what you would purchase commercially," Kayser said. "For the more traditional polymer scientists, the fact that you can very efficiently and precisely control the degree of sulfonation is going to be of interest to a lot of different communities and applications."

The researchers also see great potential for how this research can contribute to ongoing global sustainability efforts by providing a new way to convert waste products into value-added materials.

"Many scientists and researchers are working hard on upcycling and recycling efforts, either by chemical or mechanical means, and our study provides another example of how we can address this challenge," Lo said.

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This next generation blue light could potentially promote or hinder sleep on command

Blue light from LED lamps and consumer electronics can mess with your sleep because it disrupts production of the natural sleep hormone melatonin. Tinted glasses or displays in night mode can mask, but don't remove, a portion of the disruptive wavelengths. But now, researchers report in ACS Omega that they have designed more "human-centric" LEDs that could potentially enhance drowsiness or alertness on command.

Humans have evolved over millennia to be active during the day and to rest at night; we've depended on the sun to regulate our sleep/wake cycle.

But many people today spend a majority of their time indoors, shielded from the sun, so it's harder for them to maintain that optimal 24-hour circadian rhythm.

Exposure to artificial light can worsen this problem because it can decrease secretion of melatonin.

And nighttime exposure to blue light, specifically, is notorious for interfering with melatonin production and therefore sleep.

However, blue light is emitted by LEDs in lamps, computers, TVs, phones and other handheld electronics that people often use at night.

So, Changwook Kim, Young Rag Do and colleagues set out to make a light source that could support natural circadian rhythms, no matter what time of day it is used.

Blue light ranges in wavelength from 380 to 500 nanometers (nm), but not all blue light is created equal.

The wavelengths that suppress melatonin production -- and cause wakefulness -- are in the range of 460 to 500 nm. So, the researchers designed two LEDs that emitted different wavelengths of blue light.

One LED, intended for daytime use, restricted its blue emissions to wavelengths close to 475 nm. The other LED, for evening use, emitted blue wavelengths near 450 nm, outside the range that disturbs sleep.

Then the researchers built these two new LEDs into bulbs. Like conventional bulbs, they produced white light by converting some of the blue light into red and green with the help of phosphors encased in the bulbs.

The new LED bulbs were placed along with conventional LED bulbs in fixtures installed in the ceiling of a windowless room furnished with a desk, treadmill and bed.

Individual male volunteers stayed in the room for a stretch of three days.

A computer controlled which type of LED was turned on or off during their stay; that way, the researchers could compare the impact on melatonin levels of conventional bulbs versus the new daytime and evening bulbs.

Saliva samples from 22 volunteers showed that using the new LEDs increased the participants' nighttime melatonin levels by 12.2% and reduced daytime melatonin by 21.9% compared to consistent conventional LED exposure.

The researchers hope manufacturers of LED lamps and electronic displays can apply these findings to help people increase daytime vitality and work efficiency while also improving nighttime relaxation and sleep quality.

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Quantum physics sets a speed limit to electronics

Semiconductor electronics is getting faster and faster -- but at some point, physics no longer permits any increase. The speed can definitely not be increased beyond one petahertz (one million gigahertz), even if the material is excited in an optimal way with laser pulses.

How fast can electronics be? When computer chips work with ever shorter signals and time intervals, at some point they come up against physical limits. The quantum-mechanical processes that enable the generation of electric current in a semiconductor material take a certain amount of time. This puts a limit to the speed of signal generation and signal transmission.

TU Wien (Vienna), TU Graz and the Max Planck Institute of Quantum Optics in Garching have now been able to explore these limits: The speed can definitely not be increased beyond one petahertz (one million gigahertz), even if the material is excited in an optimal way with laser pulses. This result has now been published in the scientific journal Nature Communications.

Fields and currents

Electric current and light (i.e. electromagnetic fields) are always interlinked. This is also the case in microelectronics: In microchips, electricity is controlled with the help of electromagnetic fields. For example, an electric field can be applied to a transistor, and depending on whether the field is switched on or off, the transistor either allows electrical current to flow or blocks it. In this way, an electromagnetic field is converted into an electrical signal.

In order to test the limits of this conversion of electromagnetic fields to current, laser pulses -- the fastest, most precise electromagnetic fields available -- are used, rather than transistors.

"Materials are studied that initially do not conduct electricity at all," explains Prof. Joachim Burgdörfer from the Institute for Theoretical Physics at TU Wien. "These are hit by an ultra-short laser pulse with a wavelength in the extreme UV range. This laser pulse shifts the electrons into a higher energy level, so that they can suddenly move freely. That way, the laser pulse turns the material into an electrical conductor for a short period of time." As soon as there are freely moving charge carriers in the material, they can be moved in a certain direction by a second, slightly longer laser pulse. This creates an electric current that can then be detected with electrodes on both sides of the material.

These processes happen extremely fast, on a time scale of atto- or femtoseconds. "For a long time, such processes were considered instantaneous," says Prof. Christoph Lemell (TU Wien). "Today, however, we have the necessary technology to study the time evolution of these ultrafast processes in detail." The crucial question is: How fast does the material react to the laser? How long does the signal generation take and how long does one have to wait until the material can be exposed to the next signal? The experiments were carried out in Garching and Graz, the theoretical work and complex computer simulations were done at TU Wien.

Time or energy -- but not both

The experiment leads to a classic uncertainty dilemma, as it often occurs in quantum physics: in order to increase the speed, extremely short UV laser pulses are needed, so that free charge carriers are created very quickly. However, using extremely short pulses implies that the amount of energy which is transferred to the electrons is not precisely defined. The electrons can absorb very different energies. "We can tell exactly at which point in time the free charge carriers are created, but not in which energy state they are," says Christoph Lemell. "Solids have different energy bands, and with short laser pulses many of them are inevitably populated by free charge carriers at the same time."

Depending on how much energy they carry, the electrons react quite differently to the electric field. If their exact energy is unknown, it is no longer possible to control them precisely, and the current signal that is produced is distorted -- especially at high laser intensities.

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Engineers harvest WiFi signals to power small electronics

With the rise of the digital age, the amount of WiFi sources to transmit information wirelessly between devices has grown exponentially. This results in the widespread use of the 2.4GHz radio frequency that WiFi uses, with excess signals available to be tapped for alternative uses.

To harness this under-utilised source of energy, a research team from the National University of Singapore (NUS) and Japan's Tohoku University (TU) has developed a technology that uses tiny smart devices known as spin-torque oscillators (STOs) to harvest and convert wireless radio frequencies into energy to power small electronics. In their study, the researchers had successfully harvested energy using WiFi-band signals to power a light-emitting diode (LED) wirelessly, and without using any battery.

"We are surrounded by WiFi signals, but when we are not using them to access the Internet, they are inactive, and this is a huge waste. Our latest result is a step towards turning readily-available 2.4GHz radio waves into a green source of energy, hence reducing the need for batteries to power electronics that we use regularly. In this way, small electric gadgets and sensors can be powered wirelessly by using radio frequency waves as part of the Internet of Things. With the advent of smart homes and cities, our work could give rise to energy-efficient applications in communication, computing, and neuromorphic systems," said Professor Yang Hyunsoo from the NUS Department of Electrical and Computer Engineering, who spearheaded the project.

The research was carried out in collaboration with the research team of Professor Guo Yong Xin, who is also from the NUS Department of Electrical and Computer Engineering, as well as Professor Shunsuke Fukami and his team from TU. The results were published in Nature Communications on 18 May 2021.

Converting WiFi signals into usable energy

Spin-torque oscillators are a class of emerging devices that generate microwaves, and have applications in wireless communication systems. However, the application of STOs is hindered due to a low output power and broad linewidth.

While mutual synchronisation of multiple STOs is a way to overcome this problem, current schemes, such as short-range magnetic coupling between multiple STOs, have spatial restrictions. On the other hand, long-range electrical synchronisation using vortex oscillators is limited in frequency responses of only a few hundred MHz. It also requires dedicated current sources for the individual STOs, which can complicate the overall on-chip implementation.

To overcome the spatial and low frequency limitations, the research team came up with an array in which eight STOs are connected in series. Using this array, the 2.4 GHz electromagnetic radio waves that WiFi uses was converted into a direct voltage signal, which was then transmitted to a capacitor to light up a 1.6-volt LED. When the capacitor was charged for five seconds, it was able to light up the same LED for one minute after the wireless power was switched off.

In their study, the researchers also highlighted the importance of electrical topology for designing on-chip STO systems, and compared the series design with the parallel one. They found that the parallel configuration is more useful for wireless transmission due to better time-domain stability, spectral noise behaviour, and control over impedance mismatch. On the other hand, series connections have an advantage for energy harvesting due to the additive effect of the diode-voltage from STOs.

Commenting on the significance of their results, Dr Raghav Sharma, the first author of the paper, shared, "Aside from coming up with an STO array for wireless transmission and energy harvesting, our work also demonstrated control over the synchronising state of coupled STOs using injection locking from an external radio-frequency source. These results are important for prospective applications of synchronised STOs, such as fast-speed neuromorphic computing."

Next steps

To enhance the energy harvesting ability of their technology, the researchers are looking to increase the number of STOs in the array they had designed. In addition, they are planning to test their energy harvesters for wirelessly charging other useful electronic devices and sensors.

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Discovery could help lengthen lifespan of electronic devices

Ferroelectric materials are used in many devices, including memories, capacitors, actuators and sensors. These devices are commonly used in both consumer and industrial instruments, such as computers, medical ultrasound equipment and underwater sonars.

Over time, ferroelectric materials are subjected to repeated mechanical and electrical loading, leading to a progressive decrease in their functionality, ultimately resulting in failure. This process is referred to as 'ferroelectric fatigue'.

It is a main cause of the failure of a range of electronic devices, with discarded electronics a leading contributor to e-waste. Globally, tens of millions of tonnes of failed electronic devices go to landfill every year.

Using advanced in-situ electron microscopy, the School of Aerospace, Mechanical and Mechatronic Engineering researchers were able to observe ferroelectric fatigue as it occurred. This technique uses an advanced microscope to 'see', in real-time, down to the nanoscale and atomic levels.

The researchers hope this new observation, described in a paper published in Nature Communications, will help better inform the future design of ferroelectric nanodevices.

"Our discovery is a significant scientific breakthrough as it shows a clear picture of how the ferroelectric degradation process is present at the nanoscale," said co-author Professor Xiaozhou Liao, also from the University of Sydney Nano Institute.

Dr Qianwei Huang, the study's lead researcher, said: "Although it has long been known that ferroelectric fatigue can shorten the lifespan of electronic devices, how it occurs has previously not been well understood, due to a lack of suitable technology to observe it."

Co-author Dr Zibin Chen said: "With this, we hope to better inform the engineering of devices with longer lifespans."

Observational findings spark new debate

Nobel laureate Herbert Kroemer once famously asserted "The interface is the device." The observations by the Sydney researchers could therefore spark a new debate on whether interfaces -- which are physical boundaries separating different regions in materials -- are a viable solution to the unreliability of next-generation devices.

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Surveying solar storms by ancient Assyrian astronomers

A research team led by the University of Tsukuba combined observations from ancient cuneiform tablets that mention unusual red skies with radioisotope data to identify solar storms that likely occurred around 679 to 655 BCE, prior to any previously datable events. This work may help modern astronomers predict future solar flares or coronal mass ejections that can damage satellite and terrestrial electronic devices.

Humans have been looking to the skies for as long as we have been around. Some of the observations made by ancient Assyrian and Babylonian astrologers more than two millennia ago survive in the form of cuneiform records. These rectangular clay tablets were messages from professional scholars to kings who had commissioned astronomical observations for the purpose of discerning omens -- including comets, meteors, and planetary motions.

Now, a team led by the University of Tsukuba has matched three of these ancient tablets that mention an unusual red glow in the sky with the carbon-14 concentrations in tree rings and demonstrate how they are evidence of solar magnetic storms. These observations were made approximately 2,700 years ago in Babylon and the Assyrian city of Nineveh, both of which are mentioned contemporaneously in the Bible. For example, one tablet says, "red covers the sky," while another mentions a "red cloud." These were probably manifestations of what we call today stable auroral red arcs, consisting of light emitted by electrons in atmospheric oxygen atoms after being excited by intense magnetic fields. While we usually think of aurorae as confined to northern latitudes, during periods of strong magnetic activity, as with a solar mass ejection, they may be observed much further south. Moreover, because of changes in the Earth's magnetic field over time, the Middle East was closer to the geomagnetic pole during this period in history.

"Although the exact dates of the observations are not known, we were able to narrow the range considerably by knowing when each astrologer was active," co-first author Yasuyuki Mitsuma says. Based on tree-ring samples, there was a rapid rise in radioactive carbon-14 in the environment during this time, which is associated with increased solar activity.

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Breakthrough material could lead to cheaper, more widespread solar panels and electronics

Imagine printing electronic devices using a simple inkjet printer -- or even painting a solar panel onto the wall of a building.

Such technology would slash the cost of manufacturing electronic devices and enable new ways to integrate them into our everyday lives. Over the last two decades, a type of material called organic semiconductors, made out of molecules or polymers, has been developed for such purposes. But some properties of these materials pose a major hurdle that limits their widespread use.

"In these materials, an electron is usually bound to its counterpart, a missing electron known as 'hole,' and can't move freely," said Wai-Lun Chan, associate professor of physics & astronomy at the University of Kansas. "So-called 'free electrons,' which wander freely in the material and conduct electricity, are rare and can't be generated readily by light absorption. This impedes the use of these organic materials in applications like solar panels because panels built with these materials often have poor performance."

Because of this problem, Chan said "freeing the electrons" has been a focus in developing organic semiconductors for solar cells, light sensors and many other optoelectronic applications.

Now, two physics research groups at KU, led by Chan and Hui Zhao, professor of physics & astronomy, have effectively generated free electrons from organic semiconductors when combined with a single atomic layer of molybdenum disulfide (MoS2), a recently discovered two-dimensional (2D) semiconductor.

The introduced 2D layer allows the electrons to escape from "holes" and move freely. The findings have just been published in the Journal of American Chemical Society, a leading journal in chemistry and interfacing areas of science.

Over the last few years, many researchers have been investigating how free charges can be generated effectively from hybrid organic-2D interfaces.

"One of the prevailing assumptions is free electrons can be generated from the interface as long as electrons can be transferred from one material to another in a relatively short period of time -- less than one-trillionth of a second," Chan said. "However, my graduate students Tika Kafle and Bhupal Kattel and I have found the presence of the ultrafast electron transfer in itself is not sufficient to guarantee the generation of free electrons from the light absorption. That's because the 'holes' can prevent the electrons from moving away from the interface. Whether the electron can be free from this binding force depends on the local energy landscape near the interface."

Chan said the energy landscape of the electrons could be seen as a topographic map of a mountain.

"A hiker chooses his path based on the height contour map," he said. "Similarly, the motion of the electron at the interface between the two materials is controlled by the electron energy landscape near the interface."

Chan and Zhao's findings will help develop general principles of how to design the "landscape" to free the electrons in such hybrid materials.

The discovery was made by combining two highly complementary experimental tools based on ultrafast lasers, time-resolved photoemission spectroscopy in Chan's lab and transient optical absorption in Zhao's lab. Both experimental setups are located in the basement of the Integrated Science Building.

In the time-resolved photoemission spectroscopy experiment, Kafle used an ultrashort laser pulse that only exists for 10-quadrillionths (10-14) of a second to trigger the motion of electrons. The advantage of using such a short pulse is the researcher knows precisely the starting time of the electron's journey. Kafle then used another ultrashort laser pulse to hit the sample again at an accurately controlled time relative to the first pulse. This second pulse is energetic enough to kick out these electrons from the sample. By measuring the energy of these electrons (now in a vacuum) and using the principle of energy conservation, the researchers were able to figure out the energy of electrons before they were kicked out and thus reveal the journey of these electrons since they were hit by the first pulse. This technique resolved the energy of the excited electrons as it moves across the interface after the light absorption. Because only electrons near the front surface of the sample can be released by the second pulse, the position of the electron relative to the interface is also revealed with atomic precision.

In the transient optical absorption measurements, Peng Yao (a visiting student) and KU graduate Peymon Zereshki, both supervised by Zhao, also used a two-pulse technique, with the first pulse initiating the electron motion in the same way. However, in their measurements, the second pulse does the trick of monitoring electrons by detecting the fraction of the second pulse that is reflected from the sample, instead of kicking out the electrons.

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The first laser radio transmitter

This device uses a frequency comb laser to emit and modulate microwaves wirelessly. The laser uses different frequencies of light beating together to generate microwave radiation. The researchers used this phenomenon to send a song wirelessly to a receiver.

You've never heard Dean Martin like this.

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences transmitted a recording of Martin's classic "Volare" wirelessly via a semiconductor laser -- the first time a laser has been used as a radio frequency transmitter.

In a paper published in the Proceedings of the National Academy of Sciences, the researchers demonstrated a laser that can emit microwaves wirelessly, modulate them, and receive external radio frequency signals.

"The research opens the door to new types of hybrid electronic-photonic devices and is the first step toward ultra-high-speed Wi-Fi," said Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, at SEAS and senior author of the study.

This research builds on previous work from the Capasso Lab. In 2017, the researchers discovered that an infrared frequency comb in a quantum cascade laser could be used to generate terahertz frequencies, the submillimeter wavelengths of the electromagnetic spectrum that could move data hundreds of times faster than today's wireless platforms. In 2018, the team found that quantum cascade laser frequency combs could also act as integrated transmitters or receivers to efficiently encode information.

Now, the researchers have figured out a way to extract and transmit wireless signals from laser frequency combs.

Unlike conventional lasers, which emit a single frequency of light, laser frequency combs emit multiple frequencies simultaneously, evenly spaced to resemble the teeth of a comb. In 2018, the researchers discovered that inside the laser, the different frequencies of light beat together to generate microwave radiation. The light inside the cavity of the laser caused electrons to oscillate at microwave frequencies -- which are within the communications spectrum.

"If you want to use this device for Wi-Fi, you need to be able to put useful information in the microwave signals and extract that information from the device," said Marco Piccardo, a postdoctoral fellow at SEAS and first author of the paper.

The first thing the new device needed to transmit microwave signals was an antenna. So, the researchers etched a gap into the top electrode of the device, creating a dipole antenna (like the rabbit ears on the top of an old TV). Next, they modulated the frequency comb to encode information on the microwave radiation created by the beating light of the comb. Then, using the antenna, the microwaves are radiated out from the device, containing the encoded information. The radio signal is received by a horn antenna, filtered and sent to a computer.

The researchers also demonstrated that the laser radio could receive signals. The team was able to remotely control the behavior of the laser using microwave signals from another device.

"This all-in-one, integrated device holds great promise for wireless communication," said Piccardo. "While the dream of terahertz wireless communication is still a ways away, this research provides a clear roadmap showing how to get there."

The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization opportunities.

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Static electricity could charge our electronics

These images show how the surfaces of magnesia (top block) and barium titanate (bottom block) respond when they come into contact. The resulting lattice deformations in each object contributes to the driving force behind the electric charge transfer during friction.

Unhappy with the life of your smartphone battery?

Thought so.

Help could be on the way from one of the most common, yet poorly understand, forms of power generation: static electricity.

"Nearly everyone has zapped their finger on a doorknob or seen child's hair stick to a balloon. To incorporate this energy into our electronics, we must better understand the driving forces behind it," says James Chen, PhD, assistant professor in the Department of Mechanical and Aerospace Engineering in the School of Engineering and Applied Sciences at the University at Buffalo.

Chen is a co-author of a study in the December issue of the Journal of Electrostatics that suggests the cause of this hair-raising phenomenon is tiny structural changes that occur at the surface of materials when they come into contact with each other.

The finding could ultimately help technology companies create more sustainable and longer-lasting power sources for small electronic devices.

Supported by a $400,000 National Science Foundation grant, Chen and Zayd Leseman, PhD, associate professor of mechanical and nuclear engineering at Kansas State University, are conducting research on the triboelectric effect, a phenomenon wherein one material becomes electrically charged after it contacts a different material through friction.

The triboelectric effect has been known since ancient times, but the tools for understanding and applying it have only become available recently due to the advent of nanotechnology.

"The idea our study presents directly answers this ancient mystery, and it has the potential to unify the existing theory. The numerical results are consistent with the published experimental observations," says Chen.

The research Chen and Leseman conduct is a mix of disciplines, including contact mechanics, solid mechanics, materials science, electrical engineering and manufacturing. With computer models and physical experiments, they are engineering triboelectric nanogenerators (TENGs), which are capable of controlling and harvesting static electricity.

"The friction between your fingers and your smartphone screen. The friction between your wrist and smartwatch. Even the friction between your shoe and the ground. These are great potential sources of energy that we can to tap into," Chen says. "Ultimately, this research can increase our economic security and help society by reducing our need for conventional sources of power."

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