‘Surprising’ hidden activity of semiconductor material spotted by researchers

New research suggests that materials commonly overlooked in computer chip design actually play an important role in information processing, a discovery which could lead to faster and more efficient electronics.

Using advanced imaging techniques, an international team led by Penn State researchers found that the material that a semiconductor chip device is built on, called the substrate, responds to changes in electricity much like the semiconductor on top of it.

The researchers worked with the semiconductor material, vanadium dioxide, which they said shows great potential as an electronic switch. They also studied how vanadium dioxide interacts with the substrate material titanium dioxide and said they were surprised to discover that there seems to be an active layer in the substrate that behaves similarly to the semiconductor material on top of it when the semiconductor switches between an insulator — not letting electricity flow — and a metal — letting electricity flow. The revelation that substrates can play an active role in semiconductor processes is significant for designing future materials and devices, said study lead Venkatraman Gopalan, professor of materials science and engineering and of physics at Penn State.

The potential of vanadium dioxide as a metal-to-insulator transistor is well-documented and the material is considered promising for semiconductor technology due to its low energy consumption, Gopalan said. However, the material’s properties are still not fully understood, and until now, it has usually been observed in isolation rather than while functioning in a real device.

Vanadium dioxide has strongly correlated electronic effects, meaning the repulsion between electrons interferes with the device, so cannot be ignored as is currently done in silicon-based electronics. This characteristic can result in materials with novel functionalities such as high-temperature superconductivity and enhanced magnetic properties.

The team investigated vanadium dioxide in a device rather than in isolation, applying a voltage to it to make it switch from an insulating to a conducting state. They used the Advanced Photon Source (APS) at Argonne National Laboratory, which uses powerful X-ray beams to study the behavior and structure of materials on the atomic level. When mapping the spatial and temporal response of the material to the switching event, the researchers observed unexpected changes to the structure of the material and substrate.

“What we found was that as the vanadium dioxide film changes to a metal, the whole film channel bulges, which is very surprising,” Gopalan said. “Normally it is supposed to shrink. So clearly something else was going on in the film geometry that was missed before.”

The APS X-ray penetrated through the vanadium dioxide film and into the titanium dioxide (TiO2) substrate — which is normally considered an electrically and mechanically passive material — that the thin film was grown on.

To understand these findings, the theory and simulation effort — led by Long-Qing Chen, Hamer Professor of Materials Science and Engineering, professor of engineering science and mechanics and of mathematics at Penn State — developed a theoretical framework to explain the entire process of the film and the substrate bulging instead of shrinking. When their model incorporated naturally occurring missing oxygen atoms in this material of two types, charged and uncharged, the experimental results could be satisfactorily explained.

Gopalan credited the multidisciplinary team’s combined expertise in material growth, synthesis, structure analysis and synchrotron beamline operation with the new understanding. Using a collaborative approach led by Greg Stone, a physical scientist with the U.S. Army and the lead experimental author, and Yin Chi, postdoctoral scholar at Penn State and the lead theory author, the researchers disentangled the material’s responses and observed them individually using phase field simulations, a simulation that helps scientists understand material changes over time by depicting various states of matter in a virtual setting.

The responses themselves require further investigation, researchers said, but they believe that understanding them will assist in identifying previously unknown capabilities of vanadium dioxide, including potential yet-to-be discovered phenomena in the TiO2 substrate that was considered passive before this study. The study itself unfolded over 10 years, Gopalan noted, including validating the results.

“This is what it takes to go from interesting science to a working device you can hold in the palm of your hand,” Gopalan said. “Experiments and theory are complex and require large-scale collaborative teams working closely together over an extended period of time to solve difficult problems that could have a large impact. We hope and expect that this will accelerate the progress towards a new generation of electronic devices.”

For more information: AdvancedMaterials

Image: Venkatraman Gopalan, professor of materials science and engineering and of physics, in his optical lab

Columbia physicists see light waves moving through a metal

When we encounter metals in our day-to-day lives, we perceive them as shiny. That’s because common metallic materials are reflective at visible light wavelengths and will bounce back any light that strikes them. While metals are well suited to conducting electricity and heat, they aren’t typically thought of as a means to conduct light.

But in the burgeoning field of quantum materials, researchers are increasingly finding examples that challenge expectations about how things should behave. In new research, Dmitri Basov, Higgins Professor of Physics at Columbia University, describes a metal capable of conducting light through it.

“These results defy our daily experiences and common conceptions,” said Basov.

Whereas graphene is a single, atom-thin layer of carbon, ZrSiSe is a three-dimensional metallic crystal made up of layers that behave differently in the in-plane and out-of-plane directions, a property known as anisotropy.

“It’s sort of like a sandwich: one layer acts like a metal while the next layer acts like an insulator,” explained Yinming Shao, a postdoc at Columbia. “When that happens, light starts to interact unusually with the metal at certain frequencies. Instead of just bouncing off, it can travel inside the material in a zig-zag pattern, which we call hyperbolic propagation.”

In their current work, Shao and his collaborators at Columbia and The University of California, San Diego observed such zig-zag movement of light, so-called hyperbolic waveguide modes, through ZrSiSe samples of varying thicknesses. Such waveguides can guide light through a material and here, result from photons of light mixing with electron oscillations to create hybrid quasiparticles called plasmons.

Although the conditions to generate plasmons that can propagate hyperbolically are met in many layered metals, it is the unique range of electron energy levels, called electronic band structure, of ZrSiSe that allowed the team to observe them in this material.

Plasmons can “magnify” features in a sample, allowing researchers to see beyond the diffraction limit of optical microscopes, which cannot otherwise resolve details smaller than the wavelength of light they use.

“Using hyperbolic plasmons, we could resolve features less than 100 nanometers using infrared light that’s hundreds of times longer,” said Shao.

ZrSiSe can be peeled to different thicknesses, making it an interesting option for nano-optics research that favors ultra-thin materials, said Shao. But, it’s likely not the only material to be valuable—from here, the group wants to explore others that share similarities with ZrSiSe but might have even more favorable waveguiding properties. That could help researchers develop more efficient optical chips, and better nano-optics approaches to explore fundamental questions about quantum materials.

For more information: ScienceAdvances

SkyWater and Lumotive announce qualification and production start for world’s first commercially available optical beamforming chip

SkyWater Technology, Bloomington, Minn., the trusted technology realization partner, and Lumotive, Redmond, Wash., a pioneer in optical semiconductor technology for 3D sensing, announced a collaboration on the production implementation of Lumotive’s groundbreaking solid-state optical beamforming technology in SkyWater’s manufacturing environment.

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Penn State, Morgan Advanced Materials partner to improve semiconductor materials

Penn State and Morgan Advanced Materials have signed an MOU to accelerate research and development of silicon carbide (SiC), a semiconductor material that excels at high voltages. This collaborative agreement spans a new five-year, multimillion-dollar initiative. The initiative brings together industry leaders, academic institutions, and government support, aiming to advance SiC crystal research and workforce development.

The agreement also includes a commitment by Morgan to become a founding member of the recently launched Penn State Silicon Carbide Innovation Alliance, as well as to supply the graphite materials and solutions needed for SiC development to Penn State for use by internal and external partners.

The initiative is a coalition of industry leaders, academic institutions and government support led by Joshua Robinson, professor of materials science and engineering and acting associate dean for research in Penn State’s College of Earth and Minerals Sciences.

The MOU outlines how the partners aim to advance carbon research and evaluate how Morgan’s carbon material product impacts SiC wafer fabrication. SiC wafers are a semiconductor material that is increasingly important in the global transition to a greener energy infrastructure and surging demand for semiconductors, as demonstrated by the bipartisan support for the CHIPS for America Act. Traditionally, semiconductor devices have been manufactured from silicon. Silicon carbide is made from tightly arranged silicon and carbon atoms that enable superior performance in a wide range of high-voltage applications, such as high-speed charging stations and power converters in electric vehicles.

Silicon carbide crystals are grown at extreme temperatures — greater than 3,600 degrees Fahrenheit — in a physical vapor transport (PVT) furnace that utilizes a significant amount of carbon to maintain the temperature during the growth process. Similar to insulation in a home, carbon materials made by Morgan act as insulating layers that reduce heat loss and the amount of electricity needed to keep the furnaces running in this weekslong process.

Morgan Advanced Materials is a global company that has been innovating and manufacturing carbon and graphite-based materials essential for growing silicon carbide crystals since the 1990s.

“The new agreement with Penn State seamlessly aligns our goal of establishing Morgan as a key player in the silicon carbide market — we are not only advancing our own graphite competencies but also contributing to the development of high-value products in the market,” said Thomas Connolly, chief technology officer at Morgan Advanced Materials.

A new SiC growth facility in Penn State’s Academic Activities Building at University Park, funded via support from Penn State’s Office for the Senior Vice President for Research and the U.S. Air Force Office of Scientific Research, is expected to be fully operational by the beginning of 2025. This will house a pilot-scale facility that will emulate the entire SiC bulk crystal growth supply chain.

“To have the opportunity to continue our partnership with Morgan Advanced Materials will further solidify the University’s reputation as a leader in silicon carbide research and position us to create bigger and more impactful innovations in the future,” said Clive Randall, director of Penn State’s Material Research Institute.

The Corporate Engagement Center played a key role in expanding Morgan’s commitment to Penn State. The center’s leadership has noted that they anticipate that the alliance will attract additional industry partners.

“Partnerships with public and private entities have allowed Penn State to be the first university in decades to house SiC equipment from boule to wafer processing,” said Andrew Read, senior vice president for research at Penn State. We greatly appreciate Morgan’s continued commitment to Penn State and are looking forward to the discoveries we will make together.”

For more information:

Image: Morgan Advanced Materials visited Penn State recently to sign a memorandum of understanding. From left are: Fernando “Nando” Vallejos-Burgos, Global Testing Labs manager at Morgan Advanced Materials; Michael Wade Smith, senior vice president and chief of staff at Penn State; Joe Abrahamson, lead at Morgan Advanced Materials’ Carbon Center of Excellence; Andy Goshe, director of strategy for Morgan Advanced Materials’ Performance Carbon Division; David Fecko, director of industry collaborations in the Materials Research Institute at Penn State; Thomas Connolly, global technology director and chief technology officer for Morgan Advanced Materials’ Performance Carbon Division; Wendy Pryce Lewis, president of Morgan Advanced Materials’ Performance Carbon Division; Neeli Bendapudi, president of Penn State; Andrew Read, senior vice president for research at Penn State; Ashley Chan, director of corporate engagement at Penn State; Josh Robinson, acting associate dean for research in earth and minerals sciences and director of the Silicon Carbide Crystal Center; Aleksandra Slavkovic, associate dean for research and innovation, Eberly College of Science at Penn State; Tonya Peeples, Harold and Inge Marcus Dean of Engineering and professor of chemical engineering at Penn State; Lee Kump, John Leone Dean of College of Earth and Minerals Science and professor of geosciences at Penn State; and David Lieb, interim vice president development and alumni relations at Penn State

“Nanostitches” enable lighter and tougher composite materials

Interest has been growing in the development of nanostructured hybrid composite materials, where nanoparticles such as carbon nanotubes (CNTs) are used alongside microscale-fiber composite laminates.

Composite materials have one main vulnerability: the space between layers, which is typically filled with polymer “glue” to bond the layers together. In the event of an impact or strike, cracks can easily spread between layers and weaken the material, even though there may be no visible damage to the layers themselves. Over time, as these hidden cracks spread between layers, the composite could suddenly crumble without warning.

Now, MIT engineers have shown they can prevent cracks from spreading between composite’s layers, using an approach they developed called “nanostitching,” in which they deposit chemically grown microscopic forests of carbon nanotubes between composite layers. The tiny, densely packed fibers grip and hold the layers together, like ultrastrong Velcro, preventing the layers from peeling or shearing apart.

In experiments with an advanced composite known as thin-ply carbon fiber laminate, the team demonstrated that layers bonded with nanostitching improved the material’s resistance to cracks by up to 60 percent, compared with composites with conventional polymers. The researchers say the results help to address the main vulnerability in advanced composites.

“Just like phyllo dough flakes apart, composite layers can peel apart because this interlaminar region is the Achilles’ heel of composites,” says Brian Wardle, professor of aeronautics and astronautics at MIT. “We’re showing that nanostitching makes this normally weak region so strong and tough that a crack will not grow there. So, we could expect the next generation of aircraft to have composites held together with this nano-Velcro, to make aircraft safer and have greater longevity.”

At MIT, Wardle is director of the necstlab (pronounced “next lab”), where he and his group first developed the concept for nanostitching. The approach involves “growing” a forest of vertically aligned carbon nanotubes — hollow fibers of carbon, each so small that tens of billions of the the nanotubes can stand in an area smaller than a fingernail. To grow the nanotubes, the team used a process of chemical vapor deposition to react various catalysts in an oven, causing carbon to settle onto a surface as tiny, hair-like supports. The supports are eventually removed, leaving behind a densely packed forest of microscopic, vertical rolls of carbon.

The lab has previously shown that the nanotube forests can be grown and adhered to layers of composite material, and that this fiber-reinforced compound improves the material’s overall strength. The researchers had also seen some signs that the fibers can improve a composite’s resistance to cracks between layers.

In their new study, the engineers took a more in-depth look at the between-layer region in composites to test and quantify how nanostitching would improve the region’s resistance to cracks. In particular, the study focused on an advanced composite material known as thin-ply carbon fiber laminates.

The study’s experiments were led by Carolina Furtado, who joined the effort as part of the MIT-Portugal program in 2016, continued the project as a postdoc, and is now a professor at the University of Porto in Portugal, where her research focuses on modeling cracks and damage in advanced composites.

In her tests, Furtado used the group’s techniques of chemical vapor deposition to grow densely packed forests of vertically aligned carbon nanotubes. She also fabricated samples of thin-ply carbon fiber laminates. The resulting advanced composite was about 3 millimeters thick and comprised 60 layers, each made from stiff, horizontal fibers embedded in a polymer sheet.

She transferred and adhered the nanotube forest in between the two middle layers of the composite, then cooked the material in an autoclave to cure. To test crack resistance, the researchers placed a crack on the edge of the composite, right at the start of the region between the two middle layers.

“In fracture testing, we always start with a crack because we want to test whether and how far the crack will spread,” Furtado explains.

The researchers then placed samples of the nanotube-reinforced composite in an experimental setup to test their resilience to “delamination,” or the potential for layers to separate.

“There’s lots of ways you can get precursors to delamination, such as from impacts, like tool drop, bird strike, runway kickup in aircraft, and there could be almost no visible damage, but internally it has a delamination,” Wardle says. “Just like a human, if you’ve got a hairline fracture in a bone, it’s not good. Just because you can’t see it doesn’t mean it’s not impacting you. And damage in composites is hard to inspect.”

To examine nanostitching’s potential to prevent delamination, the team placed their samples in a setup to test three delamination modes, in which a crack could spread through the between-layer region and peel the layers apart or cause them to slide against each other, or do a combination of both. All three of these modes are the most common ways in which conventional composites can internally flake and crumble.

The tests, in which the researchers precisely measured the force required to peel or shear the composite’s layers, revealed that the nanostitched held fast, and the initial crack that the researchers made was unable to spread further between the layers. The nanostitched samples were up to 62 percent tougher and more resistant to cracks, compared with the same advanced composite material that was held together with conventional polymers.

“This is a new composite technology, turbocharged by our nanotubes,” Wardle says.

For more information: ACS Applied Materials and Interfaces

New quantum material promises over 190% quantum efficiency in solar cells

The need for sustainable and clean energy sources has never been greater, and solar energy has emerged as a promising solution. To meet the growing demand for efficient and cost-effective solar cells, researchers are constantly exploring emerging and innovative approaches to enhance the performance of solar cells. One exciting development in this field is an emerging material from Lehigh University researchers that has the potential to revolutionize clean energy generation by enabling the efficient conversion of sunlight into electrical energy.

A prototype using the material as the active layer in a solar cell exhibits an average photovoltaic absorption of 80%, a high generation rate of photoexcited carriers, and an external quantum efficiency (EQE) up to an unprecedented 190%—a measure that far exceeds the theoretical Shockley-Queisser efficiency limit for silicon-based materials and pushes the field of quantum materials for photovoltaics to new heights.

“This work represents a significant leap forward in our understanding and development of sustainable energy solutions, highlighting innovative approaches that could redefine solar energy efficiency and accessibility in the near future,” said Chinedu Ekuma, professor of physics.

The material’s efficiency leap is attributable largely to its distinctive “intermediate band states,” specific energy levels that are positioned within the material’s electronic structure in a way that makes them ideal for solar energy conversion.

These states have energy levels within the optimal subband gaps—energy ranges where the material can efficiently absorb sunlight and produce charge carriers—of around 0.78 and 1.26 electron volts.

In addition, the material performs especially well with high levels of absorption in the infrared and visible regions of the electromagnetic spectrum.

In traditional solar cells, the maximum EQE is 100%, representing the generation and collection of one electron for each photon absorbed from sunlight. However, some advanced materials and configurations developed over the past several years have demonstrated the capability of generating and collecting more than one electron from high-energy photons, representing an EQE of over 100%.

While such Multiple Exciton Generation (MEG) materials are yet to be broadly commercialized, they hold the potential to greatly increase the efficiency of solar power systems. In the Lehigh-developed material, the intermediate band states enable the capture of photon energy that is lost by traditional solar cells, including through reflection and the production of heat.

The researchers developed the novel material by taking advantage of “van der Waals gaps,” atomically small gaps between layered two-dimensional materials. These gaps can confine molecules or ions, and materials scientists commonly use them to insert, or “intercalate,” other elements to tune material properties.

To develop their novel material, the Lehigh researchers inserted atoms of zerovalent copper between layers of a two-dimensional material made of germanium selenide (GeSe) and tin sulfide (SnS).

Ekuma, an expert in computational condensed matter physics, developed the prototype as a proof of concept after extensive computer modeling of the system demonstrated theoretical promise.

“Its rapid response and enhanced efficiency strongly indicate the potential of Cu-intercalated GeSe/SnS as a quantum material for use in advanced photovoltaic applications, offering an avenue for efficiency improvements in solar energy conversion,” he said. “It’s a promising candidate for the development of next-generation, high-efficient solar cells, which will play a crucial role in addressing global energy needs.”

Although integrating the newly designed quantum material into current solar energy systems will need further research and development, Ekuma points out that the experimental technique used to create these materials is already highly advanced. Scientists have, over time, mastered a method that precisely inserts atoms, ions, and molecules into materials.

For more information: ScienceAdvances

Image: Schematic of the thin-film solar cell with CuxGeSe/SnS as the active layer.

Two-faced solar panels can generate more power at up to 70% less cost

Researchers at the University of Surrey, England, University of Cambridge, the Chinese Academy of Sciences, Xidian University, and Zhengzhou University, China, built a new kind of two-faced (bifacial) solar panel using single-walled carbon nanotubes as both front and back electrodes that are the highest efficiency single junction solar cells to date.

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Allegheny Technologies corrosion conference to address energy challenges

Allegheny Technologies Inc., Pittsburgh, will sponsor a four-day Corrosion Solutions Conference geared toward materials selection, fabrication issues, innovations, and solutions in the chemical processing, oil and gas, and energy industries. Presented Sept. 15-18 in San Diego, it will provide the latest information on working with advanced alloys such as stainless steels, nickel-base and specialty alloys, titanium, niobium, tantalum, and zirconium.

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Innovnano invests in facility for nanostructured powders

Innovnano, Lisbon, Portugal, has invested in a high-tech, brand new facility for production of its nanostructured powders, including 3 and 4 mol % yttria stabilized zirconia (YSZ). The new site is based in a dedicated technology park in Coimbra, Portugal, and has been designed to allow high capacity expansion and industrial-scale nanotechnology, enabling the production of up to 1000 metric tons per annum.

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University of Albany Nano College to become a separate institution

State University of New York, Albany, N.Y., announces that the pioneering College of Nanoscale Science and Engineering will become a separate institution within the SUNY system by the 2014-15 academic year. The establishment of SUNY CNSE will further cement New York’s position as a global center for nanotechnology innovation, high tech industry and research, and unmatched educational opportunities.

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Helicopter test is a smash hit

Engineers at NASA’s Langley Research Center in Hampton, Va., dropped an old Marine CH-46E helicopter fuselage filled with 15 dummy occupants from a height of about 30 ft to test improved seats and seatbelts and gather data on the odds of surviving a helicopter crash.   They used cables to hoist the helicopter fuselage with its mock passengers into the air and swing it to the ground, much like a pendulum.

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