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Grain boundaries are rows of defects that disrupt the electronic properties of two-dimensional materials like graphene, but new theory by scientists at Rice University shows no such effects in atomically flat phosphorus. That may make the material ideal for nano-electronic applications. (Image Credit: Evgeni Penev/Rice University)

Defects damage the ideal properties of many two-dimensional materials, like carbon-based graphene. Phosphorus just shrugs. That makes it a promising candidate for nano-electronic applications that require stable properties, according to new research by Rice University theoretical physicist Boris Yakobson and his colleagues. The Rice team analyzed the properties of elemental bonds between semiconducting phosphorus atoms in 2-D sheets. Two-dimensional phosphorus is not theoretical; it was recently created through exfoliation from black phosphorus. The researchers compared their findings to 2-D metal dichalcogenides like molybdenum disulfide; these metal compounds have also been considered for electronics because of their inherent semiconducting properties. In pristine dichalcogenides, atoms of the two elements alternate in lockstep. But wherever two atoms of the same element bond, they create a point defect. Think of it as a temporary disturbance in the force that could slow electrons down, Yakobson said.

Semiconductors are the basic element of modern electronics that direct and control how electrons move through a circuit. But when a disturbance deepens a band gap, the semiconductor is less stable. When chaos reigns in the form of multiple point defects or grain boundaries — where sheets of a 2-D material merge at angles, forcing like atoms to bond – the materials become far less useful. The Yakobson lab’s calculations show phosphorus has no such problem. Even when point defects or grain boundaries exist, the material’s semiconducting properties are stable. Like perfect graphene – but unlike imperfect graphene — it performs as expected.

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An international team led by researchers at SLAC National Accelerator Laboratory and Stanford University joined two offbeat carbon molecules – diamondoids, the square cages at left, and buckyballs, the soccer-ball shapes at right – to create “buckydiamondoids,” center. These hybrid molecules function as rectifiers, conducting electrons in only one direction, and could help pave the way to molecular electronic devices. (Image Credit: Manoharan Lab/Stanford University)

Scientists have married two unconventional forms of carbon – one shaped like a soccer ball, the other a tiny diamond – to make a molecule that conducts electricity in only one direction. This tiny electronic component, known as a rectifier, could play a key role in shrinking chip components down to the size of molecules to enable faster, more powerful devices. “We wanted to see what new, emergent properties might come out when you put these two ingredients together to create a ‘buckydiamondoid,’” said Hari Manoharan of the Stanford Institute for Materials and Energy Sciences (SIMES) at the Department of Energy’s SLAC National Accelerator Laboratory. “What we got was a basically a one-way valve for conducting electricity – clearly more than the sum of its parts.”  The research team included scientists from Stanford University, Belgium, Germany and Ukraine.

Many electronic circuits have three basic components: a material that conducts electrons; rectifiers, which commonly take the form of diodes, to steer that flow in a single direction; and transistors to switch the flow on and off. Scientists combined two offbeat ingredients – buckyballs and diamondoids – to create the new diode-like component. Buckyballs – short for buckminsterfullerenes – are hollow carbon spheres whose 1985 discovery earned three scientists a Nobel Prize in chemistry. Diamondoids are tiny carbon cages bonded together as they are in diamonds, but weighing less than a billionth of a billionth of a carat. Both are subjects of a lot of research aimed at understanding their properties and finding ways to use them. In 2007, a team led by researchers from SLAC and Stanford discovered that a single layer of diamondoids on a metal surface can efficiently emit a beam of electrons. Manoharan and his colleagues wondered: What would happen if they paired an electron-emitting diamondoid with another molecule that likes to grab electrons? Buckyballs are just that sort of electron-grabbing molecule. For this study, diamondoids were produced in the SLAC laboratory of SIMES researchers Jeremy Dahl and Robert Carlson, who are world experts in extracting the tiny diamonds from petroleum. They were then shipped to Germany, where chemists at Justus-Liebig University figured out how to attach them to buckyballs.

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This sequence shows how the Greer Lab's three-dimensional, ceramic nanolattices can recover after being compressed by more than 50 percent. Clockwise, from left to right, an alumina nanolattice before compression, during compression, fully compressed, and recovered following compression.(Image Credit: Lucas Meza/Caltech)

Imagine a balloon that could float without using any lighter-than-air gas. Instead, it could simply have all of its air sucked out while maintaining its filled shape. Such a vacuum balloon, which could help ease the world's current shortage of helium, can only be made if a new material existed that was strong enough to sustain the pressure generated by forcing out all that air while still being lightweight and flexible. Caltech materials scientist Julia Greer and her colleagues are on the path to developing such a material and many others that possess unheard-of combinations of properties. For example, they might create a material that is thermally insulating but also extremely lightweight, or one that is simultaneously strong, lightweight, and nonbreakable—properties that are generally thought to be mutually exclusive. Greer's team has developed a method for constructing new structural materials by taking advantage of the unusual properties that solids can have at the nanometer scale, where features are measured in billionths of meters. The Caltech researchers explain that they used the method to produce a ceramic (e.g., a piece of chalk or a brick) that contains about 99.9 percent air yet is incredibly strong, and that can recover its original shape after being smashed by more than 50 percent. "Ceramics have always been thought to be heavy and brittle," says Greer, a professor of materials science and mechanics in the Division of Engineering and Applied Science at Caltech. "We're showing that in fact, they don't have to be either. This very clearly demonstrates that if you use the concept of the nanoscale to create structures and then use those nanostructures like LEGO to construct larger materials, you can obtain nearly any set of properties you want. You can create materials by design."

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Nisarg J. Shah (left) and Stephen W. Morton collaborate on research to improve bone implants and cancer treatments. Shah holds a 3-D-printed implantable polymer scaffold, while Morton holds a jar of nanoparticles for targeting triple-negative breast cancer cells.(Image Credit: MIT/Denis Paiste/Materials Processing Center)

Personalized cancer treatments and better bone implants could grow from techniques demonstrated by graduate students Stephen W. Morton and Nisarg J. Shah, who are both working in chemical engineering professor Paula Hammond's lab at MIT. Morton's work focuses on developing drug-carrying nanoparticles to target hard-to-treat cancers — such as triple-negative breast cancer (TNBC) — while Shah develops coatings that promote better adhesion for bone implants. Their work shares a materials-based approach that uses layer-by-layer assembly of nanoparticles and coatings. This approach provides controlled release of desirable components from chemotherapy drugs to bone growth factors. Use of natural materials promises to reduce harmful side effects. "We have all of these different areas in which we are seeking to address different problems related to human health, certainly in the context of cancer research which is a very big part of the lab now," Shah says. "In addition to that we are also looking at how we can improve ways in which various patient diseases and injuries are managed in a way that will improve current clinical standards."

However it could take from five to seven years to move from preclinical success in lab animals through human clinical trials to public availability. "Layer-by-layer allows us to introduce very specific materials on the surface of various substrates, be it a nanoparticle, be it an implant, right from the nanoscale to the macroscale," Shah explains. "We were able to introduce all kinds of different properties by depositing very specific materials on substrates, modifying their surface properties and eventually having them do very specific things in the context of applications."

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Dr Nair with a graphene membrane. (Image Credit: The University of Manchester)

A thin layer of graphene paint can make impermeable and chemically resistant coatings which could be used for packaging to keep food fresh for longer and protect metal structures against corrosion, new findings from The University of Manchester in the UK show. The surface of graphene, a one atom thick sheet of carbon, can be randomly decorated with oxygen to create graphene oxide; a form of graphene that could have a significant impact on the chemical, pharmaceutical and electronic industries. Applied as paint, it could provide an ultra-strong, non-corrosive coating for a wide range of industrial applications. Graphene oxide solutions can be used to paint various surfaces ranging from glass to metals to even conventional bricks. After a simple chemical treatment, the resulting coatings behave like graphite in terms of chemical and thermal stability but become mechanically nearly as tough as graphene, the strongest material known to man.

The team led by Dr Rahul Nair and Nobel laureate Sir Andre Geim demonstrated previously that multilayer films made from graphene oxide are vacuum tight under dry conditions but, if expose to water or its vapour, act as molecular sieves allowing passage of small molecules below a certain size. Those findings could have huge implications for water purification. This contrasting property is due to the structure of graphene oxide films that consist of millions of small flakes stacked randomly on top of each other but leave nano-sized capillaries between them. Water molecules like to be inside these nanocapillaries and can drag small atoms and molecules along. The University of Manchester team now shows that it is possible to tightly close those nanocapillaries using simple chemical treatments, which makes graphene films even stronger mechanically as well as completely impermeable to everything: gases, liquids or strong chemicals. For example, the researchers demonstrate that glassware or copper plates covered with graphene paint can be used as containers for strongly corrosive acids. The exceptional barrier properties of graphene paint have already attracted interest from many companies who now collaborate with The University of Manchester on development of new protective and anticorrosion coatings

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A comparison between the energy corrugation of graphene (above) and fluorinated graphene (below). (Image Credit: University of Pennsylvania)

An interdisciplinary team of engineers from the University of Pennsylvania has made a discovery regarding the surface properties of graphene, the Nobel-prize winning material that consists of an atomically thin sheet of carbon atoms. On the macroscale, adding fluorine atoms to carbon-based materials makes for water-repellant, non-stick surfaces, such as Teflon. However, on the nanoscale, adding fluorine to graphene had been reported to vastly increase the friction experienced when sliding against the material. Through a combination of physical experiments and atomistic simulations, the Penn team has discovered the mechanism behind this surprising finding, which could help researchers better design and control the surface properties of new materials. Besides its applications in circuitry and sensors, graphene is of interest as a super-strong coating. As components of mechanical and electrical systems get smaller, they are increasingly susceptible to wear and tear. Made up of fewer atoms than their macroscale counterparts, each atom is that much more important to the component’s overall structure and function.

To test the friction properties of this material, the Penn researchers collaborated with Paul Sheehan and Jeremy Robinson of the Naval Research Laboratory. Sheehan and Robinson were the first to discover fluorinated graphene and are experts in producing samples of the material to specification. The researchers were surprised to find that adding fluorine to graphene increased the material’s friction but could not immediately explain the mechanism responsible.  The study determined that by adding fluorine, the energy corrugation landscape of the graphene changed. This essentially introduces electronic roughness, which at the nanoscale, can act like physical roughness in increasing friction.

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Moh El-Naggar served as corresponding author of the study. (Photo Credit: USC/Matt Meindl)

For the past 10 years, scientists have been fascinated by a type of “electric bacteria” that shoots out long tendrils like electric wires, using them to power themselves and transfer electricity to a variety of solid surfaces. A team led by scientists at USC has now turned the study of these bacterial nanowires on its head, discovering that the key features in question are not pili, as previously believed, but rather extensions of the bacteria’s outer membrane equipped with proteins that transfer electrons called “cytochromes.” Scientists had long suspected that bacterial nanowires were pili — Latin for “hair” — which are hair-like features common on other bacteria, allowing them to adhere to surfaces and even connect to one another. Understanding the way these electric bacteria work has applications well beyond the lab. Such creatures have the potential to address some of the big questions about the nature of life itself, including what types of lifeforms we might find in extreme environments, such as space. In addition, this research has the potential to inform the creation of living, microbial circuits — forming the foundation of hybrid biological-synthetic electronic devices.

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(Image Credit: University of Oregon)

Tiny diamonds invisible to human eyes but confirmed by a powerful microscope at the University of Oregon are shining new light on the idea proposed in 2007 that a cosmic event — an exploding comet above North America — sparked catastrophic climate change 12,800 years ago. Scientists from 21 universities in six countries have reported the definitive presence of nanodiamonds at some 32 sites in 11 countries on three continents in layers of darkened soil at the Earth's Younger Dryas boundary. The boundary layer is widespread, the researchers found. The miniscule diamonds, which often form during large impact events, are abundant along with cosmic impact spherules, high-temperature melt-glass, fullerenes, grape-like clusters of soot, charcoal, carbon spherules, glasslike carbon, heium-3, iridium, osmium, platinum, nickel and cobalt. In 2007, a 26-member team from 16 institutions proposed that a cosmic impact event set off a 1,300-year-long cold spell known as the Younger Dryas. Prehistoric Clovis culture was fragmented, and widespread extinctions occurred across North America.

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A small, prototype solar cell that uses CZTS, a photovoltaic semiconductor that University of Utah metallurgists produced in an old microwave oven that once heated student lunches. (Image credit: Lee J. Siegel, University of Utah)

University of Utah metallurgists have used an old microwave oven to produce a nanocrystal semiconductor rapidly using cheap, abundant and less toxic metals than other semiconductors. They hope it will be used for more efficient photovoltaic solar cells and LED lights, biological sensors and systems to convert waste heat to electricity. Using microwaves “is a fast way to make these particles that have a broad range of applications,” says Michael Free, a professor of metallurgical engineering. “We hope in the next five years there will be some commercial products from this, and we are continuing to pursue applications and improvements. It’s a good market, but we don’t know exactly where the market will go.” Free and Prashant Sarswat, a research associate in metallurgical engineering, determined the optimum time required to produce the most uniform crystals of the CZTS semiconductor – 18 minutes in the microwave oven – and confirmed the material indeed was CZTS by using a variety of tests, such as X-ray crystallography, electron microscopy, atomic force microscopy and ultraviolet spectroscopy. They also built a small photovoltaic solar cell to confirm that the material works and demonstrate that smaller nanocrystals display “quantum confinement,” a property that makes them versatile for different uses.

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This artistic rendering depicts fluid-filled nanotubes changing with time. Caltech researchers used four-dimensional electron microscopy to visualize and monitor the flow of molten lead within single zinc oxide nanotubes in real time and space. (Image credit: Caltech)

At the nanoscale, where objects are measured in billionths of meters and events transpire in trillionths of seconds, things do not always behave as our experiences with the macro-world might lead us to expect. Water, for example, seems to flow much faster within carbon nanotubes than classical physics says should be possible. Now imagine trying to capture movies of these almost imperceptibly small nanoscale movements. Researchers at Caltech now have done just that by applying a new imaging technique called four-dimensional (4D) electron microscopy to the nanofluid dynamics problem. The researchers describe how they visualized and monitored the flow of molten lead within a single zinc oxide nanotube in real time and space. The 4D microscopy technique was developed in the Physical Biology Center for Ultrafast Science and Technology at Caltech, created and directed to advance understanding of the fundamental physics of chemical and biological behavior.

In 4D microscopy, a stream of ultra-fast-moving electrons bombards a sample in a carefully timed manner. Each electron scatters off the sample, producing a still image that represents a single moment, just a femtosecond—or a millionth of a billionth of a second—in duration. Millions of the still images can then be stitched together to produce a digital movie of nanoscale motion. In the new work, single laser pulses were used to melt the lead cores of individual zinc oxide nanotubes and then, using 4D microscopy, captured how the hot pressurized liquid moved within the tubes—sometimes splitting into multiple segments, producing tiny droplets on the outside of the tube, or causing the tubes to break.

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