Tag Archives: letter-dd-tech

Juelich physicists have discovered unexpected effects in doped graphene – i.e. graphene that is mixed with foreign atoms. They investigated samples of the carbon compound enriched with the foreign atom nitrogen on various substrate materials. Unwanted interactions with these substrates can influence the electric properties of graphene. The researchers at the Peter Gruenberg Institute have now shown that effective doping depends on the choice of substrate material. The scientists’ results were published in the journal Physical Review Letters.

Harder than diamond and tougher than steel, light weight, transparent, flexible, and extremely conductive: the mesh material graphene is regarded as the material of the future. It could make computers faster, mobile phones more flexible, and touchscreens thinner. But so far, the industrial production of the carbon lattice, which is only one atom thick, has proven problematic: in almost all cases, a substrate is required. The search for a suitable material for this purpose is one of the major challenges on the path towards practical applications because if undesirable interactions occur, they can cause the graphene to lose its electric properties.

For some years, scientists have been testing silicon carbide – a crystalline compound of silicon and carbon – for its suitability as a substrate material. When the material is heated to more than 1400 degrees Celsius in an argon atmosphere, graphene can be grown on the crystal. However, this ‘epitaxial monolayer graphene’ displays – very slight – interaction with the substrate, which limits its electron mobility.

In order to circumvent this problem, hydrogen is introduced into the interface between the two materials. This method is known as hydrogen intercalation. The bonds between the graphene and the substrate material are separated and saturated by the hydrogen atoms. This suppresses the electronic influence of the silicon crystal while the graphene stays mechanically joined with the substrate: quasi-free-standing monolayer graphene.

High-precision measurements with standing X-rays

For practical applications, the electrical properties of graphene must be modifiable – for example by introducing additional electrons into the material. This is effected by targeted “contamination” of the carbon lattice with foreign atoms. For this process, known as doping, the graphene is bombarded with nitrogen ions and then annealed. This results in defects in the lattice structure: some few carbon atoms – fewer than 1 % – separate from the lattice and are replaced with nitrogen atoms, which bring along additional electrons.

Scientists at Juelich’s Peter Gruenberg Institute – Functional Nanostructures at Surfaces (PGI-3) have now, for the first time, studied whether and how the structure of the substrate material influences this doping process. At the synchrotron radiation source Diamond Light Source in Didcot, Oxfordshire, UK, Francois C. Bocquet and his colleagues doped samples of epitaxial and quasi-free-standing monolayer graphene and investigated its structural and electronic properties. By means of standing X-ray wave fields, they were able to scan both graphene and substrate at a precision of a few millionths of a micrometre – less than a tenth of the radius of an atom.

Nitrogen atoms in the interface layer are also suitable for doping

Their findings were surprising. “Some of the nitrogen atoms diffused from the graphene into the silicon carbide,” explains Bocquet. “It was previously believed that the nitrogen bombardment only affected the graphene, but not the substrate material.”

Although both samples were treated in the same way, they exhibited different nitrogen concentrations, but almost identical electronic doping: not all nitrogen atoms were integrated in the graphene lattice, nevertheless the number of electrons in the graphene rose as if this were the case. The key to this unexpected result lies in the different behaviour of the interface layers between graphene and substrate. For the epitaxial graphene, nothing changed: the interface layer remained stable, the structure unchanged. In the quasi-free-standing graphene, however, some of the hydrogen atoms between graphene and substrate were replaced with nitrogen atoms. According to Bocquet: “If you examine the quasi-free-standing graphene, you will find a nitrogen atom underneath the graphene coat in some places. These nitrogen atoms, although they are not part of the graphene, can dope the lattice without destroying it. This unforeseen result is very promising for future applications in micro- and nanoelectronics.”

Two-dimensional electronic devices could inch closer to their ultimate promise of low power, high efficiency and mechanical flexibility with a processing technique developed at the Department of Energy’s Oak Ridge National Laboratory.

A team led by Olga Ovchinnikova of ORNL’s Center for Nanophase Materials Sciences Division used a helium ion microscope, an atomic-scale “sandblaster,” on a layered ferroelectric surface of a bulk copper indium thiophosphate. The result, detailed in the journal ACS Applied Materials and Interfaces, is a surprising discovery of a material with tailored properties potentially useful for phones, photovoltaics, flexible electronics and screens.

This diagram illustrates the effect of helium ions on the mechanical and electrical properties of the layered ferroelectric: a.) Disappearance domains in the exposed area; as the mound forms yellow regions (ferroelectricity) gradually disappear; b.) Mechanical properties of the material; warmer colors indicate hard areas, cool colors indicate soft areas; c.) Conductivity enhancement; warmer colors show insulating areas, cooler colors show more conductive areas. Credit: ORNL

This diagram illustrates the effect of helium ions on the mechanical and electrical properties of the layered ferroelectric: a.) Disappearance domains in the exposed area; as the mound forms yellow regions (ferroelectricity) gradually disappear; b.) Mechanical properties of the material; warmer colors indicate hard areas, cool colors indicate soft areas; c.) Conductivity enhancement; warmer colors show insulating areas, cooler colors show more conductive areas. Credit: ORNL

“Our method opens pathways to direct-write and edit circuitry on 2-D material without the complicated current state-of-the-art multi-step lithographic processes,” Ovchinnikova said.

She and colleague Alex Belianinov noted that while the helium ion microscope is typically used to cut and shape matter, they demonstrated that it can also be used to control ferroelectric domain distribution, enhance conductivity and grow nanostructures. Their work could establish a path to replace silicon as the choice for semiconductors in some applications.

“Everyone is looking for the next material – the thing that will replace silicon for transistors,” said Belianinov, the lead author. “2-D devices stand out as having low power consumption and being easier and less expensive to fabricate without requiring harsh chemicals that are potentially harmful to the environment.”

Reducing power consumption by using 2-D-based devices could be as significant as improving battery performance. “Imagine having a phone that you don’t have to recharge but once a month,” Ovchinnikova said.

EV Group (EVG), a supplier of wafer bonding and lithography equipment for the MEMS, nanotechnology and semiconductor markets, today introduced the EVG 7200 LA SmartNIL system for display manufacturing and other applications that require large-area substrates.

Leveraging EVG’s proprietary SmartNIL technology, the automated UV nanoimprint lithography (UV-NIL) system enables cost-efficient nano-patterning in high-volume manufacturing (HVM) applications. The EVG7200 LA is specifically designed for Gen 2 (370 mm x 470 mm) display panel manufacturing but can address a wide spectrum of biotechnology, photonics and optics applications. A few examples of imprinted patterns and devices supported by the EVG7200 LA include: wire grid polarizers, which enable better clarity and lower power consumption; lenticular lenses for direct-view 3D screens; and other functional surfaces that enable new features and specifications.

EVG7200 LA in cleanroom at EVG headquarters

EVG7200 LA in cleanroom at EVG headquarters

NIL is a highly cost-efficient method of enabling nano-scale patterns on large areas since it is not limited by sophisticated optics that are required with optical lithography, and since it can provide optimal pattern fidelity for extremely small (sub-100nm) structures. EVG, which has the largest installed base of NIL systems in production, has continually extended the capabilities of its NIL solutions to address new and emerging market needs and technology requirements. The latest addition to EVG’s NIL portfolio–the EVG7200 LA–brings nanoimprint lithography to a whole new level by enabling high-quality nano-patterning on panel-size substrates. As a result, novel structures based on nanotechnology that can improve device performance are now available for use in display manufacturing and other demanding large-area applications.

“EV Group’s market and technology leadership in nanoimprint lithography is built on years of field experience working with our partners and customers in multiple markets, as well as research and development work in our demo labs and NIL Photonics Competence Center,” stated Dr. Thomas Glinsner, corporate technology director at EV Group. “Driven by customer demand, we took our robust SmartNIL technology–which has already achieved outstanding imprint results on substrates up to 200 mm in diameter in high-volume manufacturing–and scaled it up to Gen 2 panel size. With the EVG7200 LA, we can now offer a full patterning solution for the display market, where companies have not previously considered NIL for their manufacturing efforts.”

The EVG7200 LA features EVG’s SmartNIL technology, which in combination with multi-use soft working stamp technology adapts to uneven and rough surfaces to provide unmatched conformal imprinting (down to 40nm) with high uniformity and pattern fidelity. This capability is especially critical to successfully manufacture wire grid polarizers, where pattern transfer into metal layers is needed and where critical dimensions of the device features fall below 100nm. In addition, SmartNIL’s soft stamp fabrication technology combined with automated low-force detachment extends the lifetime of master stamps, which results in significant cost savings for customers.

Demonstrations of the EVG7200 LA SmartNIL system are available at EVG’s headquarters in St. Florian, Austria.

Scientists have created the world’s thinnest lens, one two-thousandth the thickness of a human hair, opening the door to flexible computer displays and a revolution in miniature cameras.

Lead researcher Dr Yuerui (Larry) Lu from The Australian National University (ANU) said the discovery hinged on the remarkable potential of the molybdenum disulphide crystal.

Larry Lu (left), and Jiong Yang with the lens shown on screen. Credit: Stuart Hay, ANU

Larry Lu (left), and Jiong Yang with the lens shown on screen. Credit: Stuart Hay, ANU

“This type of material is the perfect candidate for future flexible displays,” said Dr Lu, leader of Nano-Electro-Mechanical System (NEMS) Laboratory in the ANU Research School of Engineering.

“We will also be able to use arrays of micro lenses to mimic the compound eyes of insects.”

The 6.3-nanometre lens outshines previous ultra-thin flat lenses, made from 50-nanometre thick gold nano-bar arrays, known as a metamaterial.

“Molybdenum disulphide is an amazing crystal,” said Dr Lu. “It survives at high temperatures, is a lubricant, a good semiconductor and can emit photons too.

“The capability of manipulating the flow of light in atomic scale opens an exciting avenue towards unprecedented miniaturisation of optical components and the integration of advanced optical functionalities.”

Molybdenum disulphide is in a class of materials known as chalcogenide glasses that have flexible electronic characteristics that have made them popular for high-technology components.

Dr Lu’s team created their lens from a crystal 6.3-nanometres thick – 9 atomic layers – which they had peeled off a larger piece of molybdenum disulphide with sticky tape.

They then created a 10-micron radius lens, using a focussed ion beam to shave off the layers atom by atom, until they had the dome shape of the lens.

The team discovered that single layers of molybdenum disulphide, 0.7 nanometres thick, had remarkable optical properties, appearing to a light beam to be 50 times thicker, at 38 nanometres. This property, known as optical path length, determines the phase of the light and governs interference and diffraction of light as it propagates.

“At the beginning we couldn’t imagine why molybdenum disulphide had such surprising properties,” said Dr Lu.

Collaborator Assistant Professor Zongfu Yu at the University of Wisconsin, Madison, developed a simulation and showed that light was bouncing back and forth many times inside the high refractive index crystal layers before passing through.

Molybdenum disulphide crystal’s refractive index, the property that quantifies the strength of a material’s effect on light, has a high value of 5.5. For comparison, diamond, whose high refractive index causes its sparkle, is only 2.4, and water’s refractive index is 1.3.

This study is published in the Nature serial journal Light: Science and Applications.

With just a tiny tweak, researchers at Kyushu University greatly increased the device lifetime of organic light-emitting diodes (OLEDs) that use a recently developed class of molecules to convert electricity into light with the potential for increased efficiency at a lower cost in future displays and lighting.

Using the OLED structure in this schematic, researchers were able to delay the degradation in brightness of an OLED with the TADF emitter 4CzIPN by eight to sixteen times. Credit: Daniel Ping-Kuen Tsang and William John Potscavage Jr.

Using the OLED structure in this schematic, researchers were able to delay the degradation in brightness of an OLED with the TADF emitter 4CzIPN by eight to sixteen times. Credit: Daniel Ping-Kuen Tsang and William John Potscavage Jr.

The easily implemented modifications can also potentially increase the lifetime of OLEDs currently used in smartphone displays and large-screen televisions.

Typical OLEDs consist of multiple layers of organic films with various functions. At the core of an OLED is an organic molecule that emits light when a negatively charged electron and a positively charged hole, which can be thought of as a missing electron, meet on the molecule.

Until recently, the light-emitting molecules were either fluorescent materials, which can be low cost but can only use about 25% of electrical charges, or phosphorescent materials, which can harvest 100% of charges but include an expensive metal such as platinum or iridium.

Researchers at Kyushu University’s Center for Organic Photonic and Electronics Research (OPERA) changed this in 2012 with the demonstration of efficient emitters based on a process called thermally activated delayed fluorescence (TADF).

Through clever molecular design, these TADF materials can convert nearly all of the electrical charges to light without the expensive metal used in phosphorescent materials, making both high efficiency and low cost possible.

However, OLEDs under constant operation degrade and become dimmer over time regardless of the emitting material.

Devices that degrade slowly are key for practical applications, and concerns remained that the lifetime of early TADF devices was still on the short side.

But with the leap in lifetime reported in a paper published online March 1, 2016, in Scientific Reports, many of those concerns can now be put to rest.

“While our initial TADF devices lost 5% of their brightness after only 85 hours,” said postdoctoral researcher Daniel Tsang, lead author on the study, “we have now extended that more than eight times just by making a simple modification to the device structure.”

The newly developed modification was to put two extremely thin (1-3 nm) layers of the lithium-containing molecule Liq on each side of the hole blocking layer, which brings electrons to the TADF material, the green emitter 4CzIPN in this case, while preventing holes from exiting the device before contributing to emission.

The devices will last even longer in practical applications because the tests are performed at extreme brightnesses to accelerate the degradation.

Applying additional optimizations that have been previously reported, the 5% drop was further delayed to longer than 1,300 hours, over 16 times that of the initial devices.

“What we are finding is that the TADF materials themselves can be very stable, making them really promising for future displays and lighting,” said Professor Chihaya Adachi, director of OPERA.

The benefits of the Liq layers are not limited to TADF-based OLEDs as the researchers also found an improvement using a similar device structure with a phosphorescent emitter.

Though still trying to completely unravel the degradation mechanism, the researchers found that devices with the Liq layers contain a much lower number of traps, a type of defect that can capture and hold a charge, preventing it from moving freely in the device.

These defects were observed by measuring tiny electrical currents created when charges that were frozen in the traps at extremely cold temperatures escape by receiving a jolt of thermal energy as the device is heated, a process called thermally stimulated current.

Having charges stuck in these traps may increase the chance for interactions with other charges and electrical excitations that can destroy the molecules and lead to degradation.

One of the next major challenges for TADF is stable and efficient blue emitting materials, which are necessary for full color displays and are also still difficult using phosphorescence.

“With the continued development of new materials and device structures,” said Prof. Adachi, “we think that TADF has the potential to solve the challenge of efficient and stable blue emission.”

SEMI today announced the “Call for Papers” for technical sessions and presentations for SEMICON Europa 2016 which takes place 25-27 October in Grenoble, France.

SEMICON Europa 2016 will feature more than 100 hours of technical sessions and presentations focused on critical industry topics that are shaping the design and manufacturing of semiconductors, MEMS, printed and flexible electronics, and other related technologies.  Abstracts for presentations are now being accepted for:

  • Advanced Packaging Conference: “The Balancing Act between Consumer and Harsh Environment Packaging”
  • Power Electronics Conference: “The Power Awakens”
  • 2016FLEX Europe: “Silicon Electronics + Flexible Systems Enabling New Markets”

The SEMICON Europa 2016 abstract submission deadline is 29 April.  Prospective presenters are invited to submit abstracts (1,000-2,000 characters). Material must be original, non-commercial and non-published. Abstracts must clearly detail the nature, scope, content, organization, key points, and significance of the proposed presentation.  Visit www.semiconeuropa.org or contact Christina Fritsch, SEMI Europe, at Tel: +49 30 303080770 or email [email protected].

Co-located and leveraging SEMICON Europa 2016, 2016FLEX Europe(formerly known as PE Europe)will also take place in Grenoble from 25-27 October.

SEMICON Europa and 2016FLEX Europe (now powered by SEMI’s Strategic Association Partner FlexTech) will attract over 5,500 attendees involved in the microelectronics supply chain, from equipment and material suppliers, IC manufacturers, system integrators to end users. Special programs this year focus on advanced and smart manufacturing (Industry 4.0), power electronics, imaging, electronics and materials for the medical and automotive applications, creating an opportunity to explore applications and manufacturing solutions for flexible, printed and hybrid electronics.

Veeco Instruments Inc. announced today the launch of the new TurboDisc K475i Arsenic Phosphide (As/P) Metal Organic Chemical Vapor Deposition (MOCVD) System for the production of red, orange, yellow (R/O/Y) light emitting diodes (LEDs), as well as multi-junction III-V solar cells, laser diodes and transistors.

“Veeco continues to drive innovation with MOCVD technology that enables us to lower manufacturing costs and increase production with systems that are reliable, flexible and easy to use,” said Shuangxiang Zhang, General Manager of Yangzhou Changelight Co., Ltd.

According to research firm Strategies Unlimited, R/O/Y LED demand is expected to grow at a 10 percent compound annual rate through 2023. This demand for red, orange and yellow LEDs is being driven by signage, automotive, display and general lighting applications, as well as the emergence of new applications such as wearable smart devices.

Incorporating proprietary TurboDisc and Uniform FlowFlange MOCVD technologies, the new K475i system enables Veeco customers to reduce LED cost per wafer by up to 20 percent compared to alternative systems through higher productivity, best-in-class yields and reduced operating expenses.

Veeco’s proprietary Uniform FlowFlange technology produces films with very high uniformity and improved within-wafer and wafer-to-wafer repeatability resulting in the industry’s lowest cost of ownership. This patented technology provides ease-of-tuning for fast process optimization and fast tool recovery time after maintenance enabling the highest productivity for applications such as lighting, display, solar, laser diodes, pseudomorphic high electron mobility transistors (pHEMTs) and heterojunction bipolar transistors (HBTs).

Graphene, the two-dimensional powerhouse, packs extreme durability, electrical conductivity, and transparency into a one-atom-thick sheet of carbon. Despite being heralded as a breakthrough “wonder material,” graphene has been slow to leap into commercial and industrial products and processes.

Now, scientists have developed a simple and powerful method for creating resilient, customized, and high-performing graphene: layering it on top of common glass. This scalable and inexpensive process helps pave the way for a new class of microelectronic and optoelectronic devices–everything from efficient solar cells to touch screens.

The collaboration–led by scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, Stony Brook University (SBU), and the Colleges of Nanoscale Science and Engineering at SUNY Polytechnic Institute–published their results February 12, 2016, in the journal Scientific Reports.

“We believe that this work could significantly advance the development of truly scalable graphene technologies,” said study coauthor Matthew Eisaman, a physicist at Brookhaven Lab and professor at SBU.

The scientists built the proof-of-concept graphene devices on substrates made of soda-lime glass–the most common glass found in windows, bottles, and many other products. In an unexpected twist, the sodium atoms in the glass had a powerful effect on the electronic properties of the graphene.

“The sodium inside the soda-lime glass creates high electron density in the graphene, which is essential to many processes and has been challenging to achieve,” said coauthor Nanditha Dissanayake of Voxtel, Inc., but formerly of Brookhaven Lab. “We actually discovered this efficient and robust solution during the pursuit of something a bit more complex. Such surprises are part of the beauty of science.”

Crucially, the effect remained strong even when the devices were exposed to air for several weeks–a clear improvement over competing techniques.

The experimental work was done primarily at Brookhaven’s Sustainable Energy Technologies Department and the Center for Functional Nanomaterials (CFN), which is a DOE Office of Science User Facility.

The graphene tweaks in question revolve around a process called doping, where the electronic properties are optimized for use in devices. This adjustment involves increasing either the number of electrons or the electron-free “holes” in a material to strike the perfect balance for different applications. For successful real-world devices, it is also very important that the local number of electrons transferred to the graphene does not degrade over time.

“The graphene doping process typically involves the introduction of external chemicals, which not only increases complexity, but it can also make the material more vulnerable to degradation,” Eisaman said. “Fortunately, we found a shortcut that overcame those obstacles.”

The team initially set out to optimize a solar cell containing graphene stacked on a high-performance copper indium gallium diselenide (CIGS) semiconductor, which in turn was stacked on an industrial soda-lime glass substrate.

The scientists then conducted preliminary tests of the novel system to provide a baseline for testing the effects of subsequent doping. But these tests exposed something strange: the graphene was already optimally doped without the introduction of any additional chemicals.

“To our surprise, the graphene and CIGS layers already formed a good solar cell junction!” Dissanayake said. “After much investigation, and the later isolation of graphene on the glass, we discovered that the sodium in the substrate automatically created high electron density within our multi-layered graphene.”

Pinpointing the mechanism by which sodium acts as a dopant involved a painstaking exploration of the system and its performance under different conditions, including making devices and measuring the doping strength on a wide range of substrates, both with and without sodium.

“Developing and characterizing the devices required complex nanofabrication, delicate transfer of the atomically thin graphene onto rough substrates, detailed structural and electro-optical characterization, and also the ability to grow the CIGS semiconductor,” Dissanayake said. “Fortunately, we had both the expertise and state-of-the-art instrumentation on hand to meet all those challenges, as well as generous funding.”

The bulk of the experimental work was conducted at Brookhaven Lab using techniques developed in-house, including advanced lithography. For the high-resolution electron microscopy measurements, CFN staff scientists and study coauthors Kim Kisslinger and Lihua Zhang lent their expertise. Coauthors Harry Efstathiadis and Daniel Dwyer–both at the College of Nanoscale Science and Engineering at SUNY Polytechnic Institute–led the effort to grow and characterize the high-quality CIGS films.

“Now that we have demonstrated the basic concept, we want to focus next on demonstrating fine control over the doping strength and spatial patterning,” Eisaman said.

The scientists now need to probe more deeply into the fundamentals of the doping mechanism and more carefully study material’s resilience during exposure to real-world operating conditions. The initial results, however, suggest that the glass-graphene method is much more resistant to degradation than many other doping techniques.

“The potential applications for graphene touch many parts of everyone’s daily life, from consumer electronics to energy technologies,” Eisaman said. “It’s too early to tell exactly what impact our results will have, but this is an important step toward possibly making some of these applications truly affordable and scalable.”

For example, graphene’s high conductivity and transparency make it a very promising candidate as a transparent, conductive electrode to replace the relatively brittle and expensive indium tin oxide (ITO) in applications such as solar cells, organic light emitting diodes (OLEDs), flat panel displays, and touch screens. In order to replace ITO, scalable and low-cost methods must be developed to control graphene’s resistance to the flow of electrical current by controlling the doping strength. This new glass-graphene system could rise to that challenge, the researchers say.

An engineering research team at the University of Alberta has invented a new transistor that could revolutionize thin-film electronic devices.

Their findings, published in the prestigious science journal Nature Communications, could open the door to the development of flexible electronic devices with applications as wide-ranging as display technology to medical imaging and renewable energy production.

The team was exploring new uses for thin film transistors (TFT), which are most commonly found in low-power, low-frequency devices like the display screen you’re reading from now. Efforts by researchers and the consumer electronics industry to improve the performance of the transistors have been slowed by the challenges of developing new materials or slowly improving existing ones for use in traditional thin film transistor architecture, known technically as the metal oxide semiconductor field effect transistor (MOSFET).

But the U of A electrical engineering team did a run-around on the problem. Instead of developing new materials, the researchers improved performance by designing a new transistor architecture that takes advantage of a bipolar action. In other words, instead of using one type of charge carrier, as most thin film transistors do, it uses electrons and the absence of electrons (referred to as “holes”) to contribute to electrical output. Their first breakthrough was forming an ‘inversion’ hole layer in a ‘wide-bandgap’ semiconductor, which has been a great challenge in the solid-state electronics field.

Once this was achieved, “we were able to construct a unique combination of semiconductor and insulating layers that allowed us to inject “holes” at the MOS interface,” said Gem Shoute, a PhD student in the Department of Electrical and Computer Engineering who is lead author on the article. Adding holes at the interface increased the chances of an electron “tunneling” across a dielectric barrier. Through this phenomenon, a type of quantum tunnelling, “we were finally able to achieve a transistor that behaves like a bipolar transistor.”

“It’s actually the best performing [TFT] device of its kind–ever,” said materials engineering professor Ken Cadien, a co-author on the paper. “This kind of device is normally limited by the non-crystalline nature of the material that they are made of”

The dimension of the device itself can be scaled with ease in order to improve performance and keep up with the need of miniaturization, an advantage that modern TFTs lack. The transistor has power-handling capabilities at least 10 times greater than commercially produced thin film transistors.

Electrical engineering professor Doug Barlage, who is Shoute’s PhD supervisor and one of the paper’s lead authors, says his group was determined to try new approaches and break new ground. He says the team knew it could produce a high-power thin film transistor–it was just a matter of finding out how.

“Our goal was to make a thin film transistor with the highest power handling and switching speed possible. Not many people want to look into that, but the raw properties of the film indicated dramatic performance increase was within reach,” he said. “The high quality sub 30 nanometre (a human hair is 50,000 nanometres wide) layers of materials produced by Professor Cadien’s group enabled us to successfully try these difficult concepts”

In the end, the team took advantage of the very phenomena other researchers considered roadblocks.

“Usually tunnelling current is considered a bad thing in MOSFETs and it contributes to unnecessary loss of power, which manifests as heat,” explained Shoute. “What we’ve done is build a transistor that considers tunnelling current a benefit.”

The team has filed a provisional patent on the transistor. Shoute says the next step is to put the transistor to work “in a fully flexible medium and apply these devices to areas like biomedical imaging, or renewable energy.”

Researchers at North Carolina State University have discovered a new phase of the material boron nitride (Q-BN), which has potential applications for both manufacturing tools and electronic displays. The researchers have also developed a new technique for creating cubic boron nitride (c-BN) at ambient temperatures and air pressure, which has a suite of applications, including the development of advanced power grid technologies.

“This is a sequel to our Q-carbon discovery and converting Q-carbon into diamond,” says Jay Narayan, the John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State and lead author of a paper describing the research. “We have bypassed what were thought to be the limits of boron nitride’s thermodynamics with the help of kinetics and time control to create this new phase of boron nitride.

“We have also developed a faster, less expensive way to create c-BN, making the material more viable for applications such as high-power electronics, transistors and solid state devices,” Narayan says. “C-BN nanoneedles and microneedles, which can be made using our technique, also have potential for use in biomedical devices.” C-BN is a form of boron nitride that has a cubic crystalline structure, analogous to diamond.

Early tests indicate that Q-BN is harder than diamond, and it holds an advantage over diamond when it comes to creating cutting tools. Diamond, like all carbon, reacts with iron and ferrous materials. Q-BN does not. The Q-BN has an amorphous structure, and it can easily be used to coat cutting tools, preventing them from reacting with ferrous materials.

“We have also created diamond/c-BN crystalline composites for next-generation high-speed machining and deep-sea drilling applications,” Narayan says. “Specifically, we have grown diamond on c-BN by using pulsed laser deposition of carbon at 500 degrees Celsius without the presence of hydrogen, creating c-BN and diamond epitaxial composites.”

The Q-BN also has a low work function and negative electron affinity, which effectively means that it glows in the dark when exposed to very low levels of electrical fields. These characteristics are what make it a promising material for energy-efficient display technologies.

To make Q-BN, researchers begin with a layer of thermodynamically stable hexagonal boron nitride (h-BN), which can be up to 500-1000 nanometers thick. The material is placed on a substrate and researchers then use high-power laser pulses to rapidly heat the h-BN to 2,800 degrees Kelvin, or 4,580 degrees Fahrenheit. The material is then quenched, using a substrate that quickly absorbs the heat. The whole process takes approximately one-fifth of a microsecond and is done at ambient air pressure.

By manipulating the seeding substrate beneath the material and the time it takes to cool the material, researchers can control whether the h-BN is converted to Q-BN or c-BN. These same variables can be used to determine whether the c-BN forms into microneedles, nanoneedles, nanodots, microcrystals or a film.

“Using this technique, we are able to create up to a 100- to 200-square-inch film of Q-BN or c-BN in one second,” Narayan says.

By comparison, previous techniques for creating c-BN required heating hexagonal boron nitride to 3,500 degrees Kelvin (5,840 degrees Fahrenheit) and applying 95,000 atmospheres of pressure.

C-BN has similar properties to diamond, but has several advantages over diamond: c-BN has a higher bandgap, which is attractive for use in high-power devices; c-BN can be “doped” to give it positively- and negatively-charged layers, which means it could be used to make transistors; and it forms a stable oxide layer on its surface when exposed to oxygen, making it stable at high temperatures. This last characteristic means it could be used to make solid state devices and protective coatings for high-speed machining tools used in oxygen-ambient environments.

“We’re optimistic that our discovery will be used to develop c-BN-based transistors and high-powered devices to replace bulky transformers and help create the next generation of the power grid,” Narayan says.