Semiconductors are indispensable in the modern age; silicon-based integrated circuits underpin the operation of all things digital, from discrete devices like computers, smartphones and home appliances to control components for every possible industrial application. A broad range of scientific research has been directed to the next steps in semiconductor design, particularly the application of novel materials to engineer more compact, efficient circuitry which leverages the quantum mechanical behavior of materials at the nanometer length scale. Of special interest are materials with a fundamentally different dimensionality; the most famous example is graphene, a two-dimensional lattice of carbon atoms which is atomically thin.

Transition metal dichalcogenides (or TMDCs) are promising candidates for incorporation into new semiconductor devices. Composed of transition metals like molybdenum and tungsten and a chalcogen (or Group 16 element) like sulfur or selenium, they can form layered crystalline structures whose properties change drastically when the metallic element is changed, from normal metals to semiconductors, even to superconductors. By controllably weaving domains of different TMDCs into a single heterostructure (made of domains with different composition), it may be possible to produce atomically thin electronics with distinct, superior properties to existing devices.

A team led by Dr. Yu Kobayashi and Associate Professor Yasumitsu Miyata from Tokyo Metropolitan University has been at the cutting edge of efforts to create two-dimensional heterostructures with different TMDCs using vapor-phase deposition, the deposition of precursor material in a vapor state onto a surface to make atomically flat crystalline layers. One of the biggest challenges they faced was creating a perfectly flat interface between different domains, an essential feature for getting the most out of these devices. Now, they have succeeded in engineering a continuous process to grow well-defined crystalline strips of different TMDCs at the edge of existing domains, creating strips as thin as 20nm with a different composition. Their new process uses liquid precursors which can be sequentially fed into a growth chamber; by optimizing the growth rate, they were able to grow heterostructures with distinct domains linked perfectly over atomically straight edges. They directly imaged the linkage using scanning tunneling microscopy (STM), finding excellent agreement with first-principles numerical simulations of what an ideal interface should look like. The team used four different TMDCs, and also realized a layer-on-layer heterostructure.

By creating atomically sharp interfaces, electrons may be effectively confined to one-dimensional spaces on these 2D devices, for exquisite control of electron transport and resistivity as well as optical properties. The team hopes that this may pave the way to devices with unparalleled energy efficiency and novel optical properties.

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But building a long-lasting solid-state battery is easier said than done. Now, researchers at the Georgia Institute of Technology have used X-ray computed tomography (CT) to visualize in real time how cracks form near the edges of the interfaces between materials in the batteries. The findings could help researchers find ways to improve the energy storage devices.

“Solid-state batteries could be safer than lithium-ion batteries and potentially hold more energy, which would be ideal for electric vehicles and even electric aircraft,” said Matthew McDowell, an assistant professor in the George W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering. “Technologically, it’s a very fast moving field, and there are a lot of companies interested in this.”

In a typical lithium-ion battery, energy is released during the transfer of lithium ions between two electrodes — a cathode and an anode — through a liquid electrolyte.

For the study, which was published June 4 in the journal ACS Energy Letters and was sponsored by the National Science Foundation, the research team built a solid-state battery in which a solid ceramic disc was sandwiched between two pieces of solid lithium. The ceramic disc replaced the typical liquid electrolyte.

“Figuring out how to make these solid pieces fit together and behave well over long periods of time is the challenge,” McDowell said. “We’re working on how to engineer these interfaces between these solid pieces to make them last as long as possible.”

In collaboration with Christopher Saldana, an assistant professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech and an expert in X-ray imaging, the researchers placed the battery under an X-ray microscope and charged and discharged it, looking for physical changes indicative of degradation. Slowly over the course of several days, a web-like pattern of cracks formed throughout the disc.

Those cracks are the problem and occur alongside the growth of an interphase layer between the lithium metal and solid electrolyte. The researchers found that this fracture during cycling causes resistance to the flow of ions.

“These are unwanted chemical reactions that occur at the interfaces,” McDowell said. “People have generally assumed that these chemical reactions are the cause the degradation of the cell. But what we learned by doing this imaging is that in this particular material, it’s not the chemical reactions themselves that are bad — they don’t affect the performance of the battery. What’s bad is that the cell fractures, and that destroys the performance of the cell.”

Solving the fracturing problem could be one of the first steps to unlocking the potential of solid state batteries, including their high energy density. The deterioration observed is likely to affect other types of solid-state batteries, the researchers noted, so the findings could lead to the design of more durable interfaces.

“In normal lithium-ion batteries, the materials we use define how much energy we can store,” McDowell said. “Pure lithium can hold the most, but it doesn’t work well with liquid electrolyte. But if you could use solid lithium with a solid electrolyte, that would be the holy grail of energy density.”

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University of Cincinnati biologist Theresa Culley warns that for some parts of Ohio, it might be too late to stop the spread of the Callery pear. But she is urging other states to be vigilant before the invasive trees begin taking over their forests, too.

Culley presented her findings to botanists from around the world during the Society of Economic Botany conference this year hosted at UC’s McMicken College of Arts and Sciences.

Like a lot of invasive species, the Callery pear, also known as the Bradford pear, was a problem of our own making, she said. Named for China historian Joseph-Marie Callery, who sent samples back to Europe in the 1800s, the tree captured the interest of American botanists a century later.

“At one point it was named urban street tree of the year,” she said. “In the mid-1990s they started to show up in the wild. Now people have recognized they’re starting to spread and it’s a problem.”

The original strain of pear tree was “self-incompatible,” incapable of reproducing with other trees of its kind. They became a best-seller because they grew quickly, regardless of climate or soil conditions. The trees bloom pretty white flowers in the spring and have leaves that turn a vibrant purple in the autumn.

For years, the pears were a welcome addition to tree-lined streets.

“I call them the lollipop tree because they have this perfect shape,” Culley said.

But homeowners soon learned the mature trees had weak trunks that split easily and toppled in heavy snow or strong winds.

“The Bradford pear was a beautiful tree with a service life of about 15 years,” said David Listerman, an Ohio landscaping broker and consultant. “But the canopy would get so heavy that in a windstorm, it would break in half.”

The solution for growers was to introduce sturdier varieties. But besides their sturdy trunks, the replacement trees had something else: genetic diversity. Suddenly, the old pear trees could now cross-pollinate with the new varieties. Their fertilized flowers began producing fruit that birds carried off into the forest. A monster was born.

Today, Listerman says the wild newcomers represent an existential threat to native trees. Their fallen leaves leach chemicals into the ground that can kill native rivals.

“Most invasives tend to have advantages over native plants. The Callery pear holds its leaves late into the fall — right up to Christmas. It grows another month to two months longer, outcompeting native species that go dormant in October,” he said. “They encroach along interstates where they need to have visual clearance. So highway departments wind up having to do more mowing or treating.”

And while some birds will eat their fruit, pear trees don’t provide as much benefit to wildlife as many native species, he said.

Listerman serves with UC’s Culley on the Ohio Invasive Plants Council, which helps the Ohio Department of Agriculture identify potentially harmful invasive species.

Listerman said pear trees aren’t just popping up along roadsides. Forest surveys are finding them in unexpected places far from the nearest subdivision. The wild pears grow in thick stands with unpleasant spur-like thorns.

On a recent field trip, Culley picked her way through the woods at the Harris Benedict Nature Preserve to show how resilient pear trees have become. UC owns the forested preserve about 15 miles north of the Uptown campus and uses it for some of its biological sciences programs and research. It’s adjacent to the Johnson Preserve in Montgomery, Ohio.

The trail is lined with several memorials to victims of a 1999 F4 tornado that killed four people and destroyed nearly 130 nearby homes and businesses. The storm cut a 10-mile long swath of destruction that toppled hundreds of trees across two counties.

Where many of the stately older trees fell during the storm, Callery pears now thrive. Culley stopped under the canopy of their leafy, green foliage. The understory was covered in Amur honeysuckle, another invasive plant from Asia that has exploded in Eastern forests.

UC conducts plant surveys in the preserve every three years. The ongoing study suggests the pear trees may be replacing many of the ash trees that were killed by emerald ash borers, another invasive species.

“In the past, pears would be found along forest edges like along highways. We’re now seeing pears invading the center of forests,” Culley said. “Once they’re established, it’s really difficult to remove them. Their roots are deep so you have to cut them and spray them with glyphosate. A lot of land managers simply can’t afford to get rid of them.”

Invasive species are a huge problem around the world. The United States spends more than $260 million fighting aquatic invaders alone, according to the Government Accountability Office. Nearly 1 in 3 species protected under the federal Endangered Species Act are at risk to invasive species, according to the U.S. Fish and Wildlife Service. Competition and predation from invasives is a leading cause of species extinction.

“A lot of states are concerned about losing the economic benefit of the Callery pear,” Culley said. “So how do we reconcile the economic value of the Callery pear and its expense as an invasive?”

Ohio’s Department of Agriculture is working with nursery growers to phase out the Callery pear in the Buckeye State. Ohio lawmakers in 2018 passed a bill banning the sale or distribution of Callery pears by 2023 to give growers a chance to plant alternatives.

Ohio grower Kyle Natorp of Natorp’s Nursery in Mason said homeowners have many alternatives to the pear. Fewer customers are asking for pear trees these days, he said.

“There are dogwoods, crabapples and cherry trees. As a business, we try to grow what the customer wants rather than try to build a market from scratch,” Natorp said.

His nursery encourages planting a diversity of trees instead of the same kind, which some builders prefer for consistency.

“They’re all the same shape and color and flower. It looks nice but it’s not a good horticultural practice,” he said. “One disease can take them all out.”

Culley said foresters should be vigilant about the proliferation of pear trees before they become established.

“We’re warning people in the northern part of the state that they’re spreading,” she said. “These trees were introduced with the best of intentions. They’ve sort of gone crazy now and we need to deal with it and learn from our mistakes.”

In an article published in the August issue of Alzheimer’s & Dementia , an interdisciplinary workgroup convened by the National Institutes of Health’s (NIH) National Institute on Aging and led by Michigan Medicine’s George A. Mashour, M.D., Ph.D., outlines what is known and unknown about paradoxical lucidity, considers its potential mechanisms, and details how a thorough scientific analysis could help shed light on the pathophysiology of dementia.

“We’ve assumed that advanced dementia is an irreversible neurodegenerative process with irreversible functional limitations,” says Mashour, professor in the department of anesthesiology, faculty in the neuroscience graduate program, and director of the Center for Consciousness Science. “But if the brain is able to access some sort of functional network configuration during paradoxical lucidity, even in severe dementia, this suggests a reversible component of the disease.”

The paper describes earlier work documenting case studies of individuals with advanced dementia, including Alzheimer’s disease, appearing to be able to communicate and recall in a seemingly normal fashion at the end of life, to the astonishment of their caregivers.

“The accumulation of anecdotal reports about paradoxical lucidity in the scientific literature prompts several important research questions,” says NIA medical officer Basil Eldadah, M.D., Ph.D. “We look forward to additional research in this area, such as better characterization of lucidity in its varying presentations, new instruments or methods to assess episodes of lucidity retrospectively or in real-time, tools to analyze speech patterns or other behavioral manifestations of lucidity, and evidence to inform decision-making challenges and opportunities prompted by unexpected lucidity.”

One precedent for investigating such events exists in the study of so-called near-death experiences. In 2013, Mashour and his collaborators at Michigan Medicine published a basic science study showing evidence of electrical brain features indicative of a conscious state following cardiac arrest. “We don’t know that the same thing is occurring with paradoxical lucidity, but the fact that this is usually happening around the time of death suggests there could be some common neural network mechanism,” he says.

Mashour admits that studying paradoxical lucidity will be a challenge, given the fleeting nature of the event. Case studies report episodes lasting from mere seconds to at most several days for a small minority of cases. The workgroup also outlines important ethical implications of this work, including the ability of vulnerable patients to participate in research and how the observation of paradoxical lucidity might change the way caregivers interact with people with dementia.

“Would research that might identify a systematically observable paradoxical lucidity provide comfort, for example, by offering loved ones a potential channel for closure, or might it induce worry if loved ones are left to wonder if a reversible cause of the dementia could have been found? We do not know the answers but these could be important research questions in their own right,” says co-first author Lori Frank, Ph.D., of the RAND Corporation and former Health and Aging Congressional fellow with the National Institute on Aging.

The workgroup hopes their paper will help raise awareness within the scientific community to advance paradoxical lucidity research, and help validate the experiences of a multitude of caregivers.

Says Mashour, “Science is now trying to be thoughtful and attentive to something that has long been reported.”

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Thanks to a redesigned, 3D-printed spectrometer, the scanner is 15 times lighter and smaller than current commercial systems and is made from parts costing less than a tenth the retail price of commercial systems — all without sacrificing imaging quality.

In its first clinical trial, the new OCT scanner produced images of 120 retinas that were 95 percent as sharp as those taken by current commercial systems, which was sufficient for accurate clinical diagnosis.

The results appear online on June 28 in Translational Vision Science & Technology, an ARVO journal.

In use since the 1990s, OCT imaging has become the standard of care for the diagnosis of many retinal diseases including macular degeneration and diabetic retinopathy, as well as for glaucoma. However, OCT is rarely included as part of a standard screening exam since machines can cost more than $100,000 — meaning that usually only larger eye centers have them.

“Once you have lost vision, it’s very difficult to get it back, so the key to preventing blindness is early detection,” said Adam Wax, professor of biomedical engineering at Duke. “Our goal is to make OCT drastically less expensive so more clinics can afford the devices, especially in global health settings.”

OCT is the optical analogue of ultrasound, which works by sending sound waves into tissues and measuring how long they take to come back. But because light is so much faster than sound, measuring time is more difficult. To time the light waves bouncing back from the tissue being scanned, OCT devices use a spectrometer to determine how much their phase has shifted compared to identical light waves that have travelled the same distance but have not interacted with tissue.

The primary technology enabling the smaller, less expensive OCT device is a new type of spectrometer designed by Wax and his former graduate student Sanghoon Kim. Traditional spectrometers are made mostly of precisely cut metal components and direct light through a series of lenses, mirrors and diffraction slits shaped like a W. While this setup provides a high degree of accuracy, slight mechanical shifts caused by bumps or even temperature changes can create misalignments.

Wax’s design, however, takes the light on a circular path within a housing made mostly from 3D-printed plastic. Because the spectrometer light path is circular, any expansions or contractions due to temperature changes occur symmetrically, balancing themselves out to keep the optical elements aligned. The device also uses a larger detector at the end of the light’s journey to make misalignments less likely.

Traditional OCT machines weigh more than 60 pounds, take up an entire desk and cost anywhere between $50,000 and $120,000. The new OCT device weighs four pounds, is about the size of a lunch box and, Wax expects, will be sold for less than $15,000.

“Right now OCT devices sit in their own room and require a PhD scientist to tweak them to get everything working just right,” said Wax. “Ours can just sit on a shelf in the office and be taken down, used and put back without problems. We’ve scanned people in a Starbucks with it.”

In the new study, J. Niklas Ulrich, retina surgeon and associate professor of ophthalmology at the University of North Carolina School of Medicine, put the new OCT scanner to the test against a commercial instrument produced by Heidelberg Engineering. He performed clinical imaging on both eyes of 60 patients, half from healthy volunteers and half with some sort of retinal disease.

To compare the images produced by both machines, the researchers used contrast-to-noise ratio — a measure often used to determine image quality in medical imaging. The results showed that, by this metric, the low-cost, portable OCT scanner provided useful contrast that was only 5.6 percent less than that of the commercial machine, which is still good enough to allow for clinical diagnostics.

“I have been very impressed by the quality of images from the low-cost device — it is absolutely comparable to our standard commercial machines,” said Ulrich. “It obviously lacks some bells and whistles of our $100k+ OCT scanners, but allows for accurate diagnosis of structural retinal disease as well as monitoring of treatment success. The setup is quick and easy with a small footprint, allowing the device to perform well in smaller satellite offices. I hope that the development of this low-cost OCT will improve patients’ access to OCT technology and contribute to saving sight in North Carolina as well as nationally and worldwide.”

Wax is commercializing the device through a startup company called Lumedica, which is already producing and selling first-generation instruments for research applications. The company hopes to secure venture backing in the near future and is also negotiating potential licensing deals with outside companies.

“There’s a lot of interest from people who want to take OCT to new parts of the globe as well as to underserved populations right here in the U.S.,” said Wax. “With the growing number of cases of diabetic retinopathy in places like the United States, India and China, we hope we can save a lot of people’s sight by drastically increasing access to this technology.”