ElectronicsA new process for growing wafer-scale 2D crystals could enable future super-thin electronics.

Since the discovery of the remarkable properties of graphene, scientists have increasingly focused research on the many other two-dimensional materials possible, both those found in nature and those concocted in the lab.

Growing high-quality, crystalline 2D materials at scale, however, has proven a significant challenge.

Researchers led by Joan Redwing, director of the National Science Foundation-sponsored Two-Dimensional Crystal Consortium—Materials Innovation Platform, and professor of materials science and engineering and electrical engineering at Penn State, developed a multistep process to make single crystal, atomically thin films of tungsten diselenide across large-area sapphire substrates.

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Scientists who introduced laser-induced graphene (LIG) enhanced their technique to produce what may become a new class of edible electronics.

The chemists, who once turned Girl Scout cookies into graphene, are investigating ways to write graphene patterns onto food and other materials to quickly embed conductive identification tags and sensors into the products themselves.

“This is not ink,” says James Tour, chair of chemistry and professor of computer science and of materials science and nanoengineering at Rice University. “This is taking the material itself and converting it into graphene.”

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ECS Journal of Solid State Science and TechnologyIn a recently published ECS Journal of Solid State Science and Technology paper, ECS member Roger Loo and coauthors describe a new epitaxial growth technology and address the challenges of implementation. The open access article, “Epitaxial CVD Growth of Ultra-Thin Si Passivation Layers on Strained Ge Fin Structures,” was designated Editors’ Choice due to its significance and the importance of the technology described.

“The work combines carefully thought out and elegant experimental work, with appropriate simulation work that compliments the experiments,” said Jennifer Bardwell, ECS Journal of Solid State Science and Technology technical editor in the area of electronic materials and processing. “I am certain that it will be of great interest to many of our readers.”

We recently sat down with Loo to discuss the work and its impact on the field.

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ElectronsWhile tracking electrons moving through exotic materials, researchers have discovered intriguing properties not found in conventional, silicon-based semiconductors.

Unlike current silicon-based electronics, which shed most of the energy they consume as waste heat, the future is all about low-power computing. Known as spintronics, this technology relies on a quantum physical property of electrons—up or down spin—to process and store information, rather than moving them around with electricity as conventional computing does.

On the quest to making spintronic devices a reality, scientists at the University of Arizona are studying an exotic crop of materials known as transition metal dichalcogenides, or TMDs. TMDs have exciting properties lending themselves to new ways of processing and storing information and could provide the basis of future transistors and photovoltaics—and potentially even offer an avenue toward quantum computing.

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GrapheneNew graphene printing technology can produce electronic circuits that are low-cost, flexible, highly conductive and water repellent, researchers report.

The nanotechnology “would lend enormous value to self-cleaning wearable/washable electronics that are resistant to stains, or ice and biofilm formation,” according to the new paper.

“We’re taking low-cost, inkjet-printed graphene and tuning it with a laser to make functional materials,” says Jonathan Claussen, an assistant professor of mechanical engineering at Iowa State University, an associate of the US Department of Energy’s Ames Laboratory, and the corresponding author of the paper in the journal Nanoscale.

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TransistorIncorporating organic electronic materials in the field of bioelectronics has indicated promising potential in interfacing with biological systems, including neuroscience applications. Researchers from Linköping University are taking a major step forward in that work with their development of the world’s first complementary electrochemical logic circuits that can function for long periods of time in water.

While the first printable organic electrochemical sensors appeared as early as 2002, significant advancements have developed in a few years. Organic components such as light-emitting diodes and electrochemical displays are already commercially available.

This from Linköping University:

The dominating material used until now has been PEDOT:PSS, which is a p-type material, in which the charge carriers are holes. In order to construct effective electron components, a complementary material, n-type, is required, in which the charge carriers are electrons.

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Researchers have developed an inexpensive and scalable technique that can change plastic’s molecular structure to help it cast off heat.

Advanced plastics could usher in lighter, cheaper, more energy-efficient product components, including those used in vehicles, LEDs, and computers—if only they were better at dissipating heat.

The concept can likely be adapted to a variety of other plastics. In preliminary tests, it made a polymer about as thermally conductive as glass—still far less so than metals or ceramics, but six times better at dissipating heat than the same polymer without the treatment.

“Plastics are replacing metals and ceramics in many places, but they’re such poor heat conductors that nobody even considers them for applications that require heat to be dissipated efficiently,” says Jinsang Kim, a materials science and engineering professor at the University of Michigan. “We’re working to change that by applying thermal engineering to plastics in a way that hasn’t been done before.”

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Instead of batteries, a new cell phone harvests the few microwatts of power it needs from a different source: ambient radio signals or light.

Researchers were also able to make Skype calls using the battery-free phone, demonstrating that the prototype—made of commercial, off-the-shelf components—can receive and transmit speech and communicate with a base station.

“We’ve built what we believe is the first functioning cell phone that consumes almost zero power,” says Shyam Gollakota, an associate professor of computer science & engineering at the University of Washington and coauthor of the paper.

“To achieve the really, really low power consumption that you need to run a phone by harvesting energy from the environment, we had to fundamentally rethink how these devices are designed.”

Researchers eliminated a power-hungry step in most modern cellular transmissions—converting analog signals that convey sound into digital data that a phone can understand. This process consumes so much energy that it’s been impossible to design a phone that can rely on ambient power sources.

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By: Peter Byrley, University of California, Riverside

A smartphone touchscreen is an impressive piece of technology. It displays information and responds to a user’s touch. But as many people know, it’s easy to break key elements of the transparent, electrically conductive layers that make up even the sturdiest rigid touchscreen. If flexible smartphones, e-paper and a new generation of smart watches are to succeed, they can’t use existing touchscreen technology.

We’ll need to invent something new – something flexible and durable, in addition to being clear, lightweight, electrically responsive and inexpensive. Many researchers are pursuing potential options. As a graduate researcher at the University of California, Riverside, I’m part of a research group working to solve this challenge by weaving mesh layers out of microscopic strands of metal – building what we call metal nanowire networks.

These could form key components of new display systems; they could also make existing smartphones’ touchscreens even faster and easier to use.

The problem with indium tin oxide

A standard smartphone touchscreen has glass on the outside, on top of two layers of conductive material called indium tin oxide. These layers are very thin, transparent to light and conduct small amounts of electrical current. The display lies underneath.

When a person touches the screen, the pressure of their finger bends the glass very slightly, pushing the two layers of indium tin oxide closer together. In resistive touchscreens, that changes the electrical resistance of the layers; in capacitive touchscreens, the pressure creates an electrical circuit.

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Researchers have created a flexible electronic device that can easily degrade just by adding a weak acid like vinegar.

“In my group, we have been trying to mimic the function of human skin to think about how to develop future electronic devices,” says Stanford University engineer Zhenan Bao.

She described how skin is stretchable, self-healable, and also biodegradable—an attractive list of characteristics for electronics. “We have achieved the first two [flexible and self-healing], so the biodegradability was something we wanted to tackle.”

A United Nations Environment Program report found that almost 50 million tons of electronic waste were thrown out in 2017—more than 20 percent higher than waste in 2015.

“This is the first example of a semiconductive polymer that can decompose,” says lead author Ting Lei, a postdoctoral fellow working with Bao.

In addition to the polymer—essentially a flexible, conductive plastic—the team developed a degradable electronic circuit and a new biodegradable substrate material for mounting the electrical components. This substrate supports the electrical components, flexing and molding to rough and smooth surfaces alike. When the electronic device is no longer needed, the whole thing can biodegrade into nontoxic components.

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