Tag Archives: Stanford University

Gold nanoparticle clusters: four new models

This research is being done at the University of Nebraska-Lincoln (UNL) which seems to be on a publishing tear lately. From an April 27, 2015 news item on Nanowerk, here’s the latest,

They may deal in gold, atomic staples and electron volts rather than cement, support beams and kilowatt-hours, but chemists have drafted new nanoscale blueprints for low-energy structures capable of housing pharmaceuticals and oxygen atoms.

Led by UNL’s Xiao Cheng Zeng and former visiting professor Yi Gao, new research has revealed four atomic arrangements of a gold nanoparticle cluster. The arrangements exhibit much lower potential energy and greater stability than a standard-setting configuration reported last year by a Nobel Prize-winning team from Stanford University.

The modeling of these arrangements could inform the cluster’s use as a transporter of pharmaceutical drugs and as a catalyst for removing pollutants from vehicular emissions or other industrial byproducts, Zeng said.

An April 24, 2015 UNL news release (also on EurekAlert), which originated the news item, provides more technical details about the work,

Led by UNL’s Xiao Cheng Zeng and former visiting professor Yi Gao, new research has revealed four atomic arrangements of a gold nanoparticle cluster. The arrangements exhibit much lower potential energy and greater stability than a standard-setting configuration reported last year by a Nobel Prize-winning team from Stanford University.

The modeling of these arrangements could inform the cluster’s use as a transporter of pharmaceutical drugs and as a catalyst for removing pollutants from vehicular emissions or other industrial byproducts, Zeng said.

Zeng and his colleagues unveiled the arrangements for a molecule featuring 68 gold atoms and 32 pairs of bonded sulfur-hydrogen atoms. Sixteen of the gold atoms form the molecule’s core; the remainder bond with the sulfur and hydrogen to form a protective coating that stems from the core.

Differences in atomic arrangements can alter molecular energy and stability, with less potential energy making for a more stable molecule. The team calculates that one of the arrangements may represent the most stable possible structure in a molecule with its composition.

“Our group has helped lead the front on nano-gold research over the past 10 years,” said Zeng, an Ameritas University Professor of chemistry. “We’ve now found new coating structures of much lower energy, meaning they are closer to the reality than (previous) analyses. So the deciphering of this coating structure is major progress.”

The structure of the molecule’s gold core was previously detailed by the Stanford team. Building on this, Zeng and his colleagues used a computational framework dubbed “divide-and-protect” to configure potential arrangements of the remaining gold atoms and sulfur-hydrogen pairs surrounding the core.

The researchers already knew that the atomic coating features staple-shaped linkages of various lengths. They also knew the potential atomic composition of each short, medium and long staple — such as the fact that a short staple consists of two sulfur atoms bonded with one gold.

By combining this information with their knowledge of how many atoms reside outside the core, the team reduced the number of potential arrangements from millions to mere hundreds.

“We divided 32 into the short, middle and long (permutations),” said Zeng, who helped develop the divide-and-protect approach in 2008. “We lined up all those possible arrangements, and then we computed their energies to find the most stable ones.

“Without those rules, it’s like finding a needle in the Platte River. With them, it’s like finding a needle in the fountain outside the Nebraska Union. It’s still hard, but it’s much more manageable. You have a much narrower range.”

The researchers resorted to the computational approach because of the difficulty of capturing the structure via X-ray crystallography or single-particle transmission electron microscopy, two of the most common imaging methods at the atomic scale.

Knowing the nanoparticle’s most stable configurations, Zeng said, could allow biomedical engineers to identify appropriate binding sites for drugs used to treat cancer and other diseases. The findings could also optimize the use of gold nanoparticles in catalyzing the oxidation process that transforms dangerous carbon monoxide emissions into the less noxious carbon dioxide, he said.

Here’s an image illustrating the work,

This rendering shows the atomic arrangements of a gold nanocluster as reported in a new study led by UNL chemist Xiao Cheng Zeng. The cluster measures about 1.7 nanometers long -- roughly the same length that a human fingernail grows in two seconds. (Joel Brehm/Office of Research and Economic Development)

This rendering shows the atomic arrangements of a gold nanocluster as reported in a new study led by UNL chemist Xiao Cheng Zeng. The cluster measures about 1.7 nanometers long — roughly the same length that a human fingernail grows in two seconds. (Joel Brehm/Office of Research and Economic Development)

Here’s a link to and a citation for the paper,

Unraveling structures of protection ligands on gold nanoparticle Au68(SH)32 by Wen Wu Xu, Yi Gao, and Xiao Cheng Zeng. Science Advances 24 Apr 2015: Vol. 1 no. 3 e1400211 DOI: 10.1126/sciadv.1400211

This is an open access article.

As for the Stanford University team’s work mentioned in the news release, I believe it’s from the Roger Kornberg (Nobel laureate) Laboratory. There’s more about that team’s work in an Aug. 21, 2014 article (A new gold standard for nano; Note: A link has been removed) by David Bradley for Chemistry World,

Characterising gold nanoparticles at atomic resolution might improve our understanding of the catalytic activity of these materials, according to an international team. These researchers have now demonstrated that it is possible to use electron microscopy to obtain data on at least one gold cluster of greater than 1nm diameter and to validate the results by comparison with small-angle x-ray scattering data, infrared absorption spectra and density functional theory calculations.

Here’s a link to and a citation for the 2014 paper,

Electron microscopy of gold nanoparticles at atomic resolution by Maia Azubel, Jaakko Koivisto, Sami Malola, David Bushnell, Greg L. Hura, Ai Leen Koh, Hironori Tsunoyama, Tatsuya Tsukuda, Mika Pettersson, Hannu Häkkinen, & Roger D. Kornberg. Science 22 August 2014: Vol. 345 no. 6199 pp. 909-912 DOI: 10.1126/science.1251959

This paper is behind a paywall.

The most recent posting here about gold nanoparticles is an April 14, 2015 piece titled: Gold atoms: sometimes they’re a metal and sometimes they’re a molecule.

Stress makes quantum dots ‘breathe’

A March 19, 2015 news item on ScienceDaily describes some new research on quantum dots,

Researchers at the Department of Energy’s SLAC National Accelerator Laboratory watched nanoscale semiconductor crystals expand and shrink in response to powerful pulses of laser light. This ultrafast “breathing” provides new insight about how such tiny structures change shape as they start to melt — information that can help guide researchers in tailoring their use for a range of applications.

In the experiment using SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science User Facility, researchers first exposed the nanocrystals to a burst of laser light, followed closely by an ultrabright X-ray pulse that recorded the resulting structural changes in atomic-scale detail at the onset of melting.

“This is the first time we could measure the details of how these ultrasmall materials react when strained to their limits,” said Aaron Lindenberg, an assistant professor at SLAC and Stanford who led the experiment. The results were published March 12 [2015] in Nature Communications.

A March 18, 2015 SLAC news release, which originated the news item, provides a general description of quantum dots,

The crystals studied at SLAC are known as “quantum dots” because they display unique traits at the nanoscale that defy the classical physics governing their properties at larger scales. The crystals can be tuned by changing their size and shape to emit specific colors of light, for example.

So scientists have worked to incorporate them in solar panels to make them more efficient and in computer displays to improve resolution while consuming less battery power. These materials have also been studied for potential use in batteries and fuel cells and for targeted drug delivery.

Scientists have also discovered that these and other nanomaterials, which may contain just tens or hundreds of atoms, can be far more damage-resistant than larger bits of the same materials because they exhibit a more perfect crystal structure at the tiniest scales. This property could prove useful in battery components, for example, as smaller particles may be able to withstand more charging cycles than larger ones before degrading.

The news release then goes on to describe the latest research showing the dots ‘breathe’ (Note: A link has been removed),

In the LCLS experiment, researchers studied spheres and nanowires made of cadmium sulfide and cadmium selenide that were just 3 to 5 nanometers, or billionths of a meter, across. The nanowires were up to 25 nanometers long. By comparison, amino acids – the building blocks of proteins – are about 1 nanometer in length, and individual atoms are measured in tenths of nanometers.

By examining the nanocrystals from many different angles with X-ray pulses, researchers reconstructed how they change shape when hit with an optical laser pulse. They were surprised to see the spheres and nanowires expand in width by about 1 percent and then quickly contract within femtoseconds, or quadrillionths of a second. They also found that the nanowires don’t expand in length, and showed that the way the crystals respond to strain was coupled to how their structure melts.

In an earlier, separate study, another team of researchers had used LCLS to explore the response of larger gold particles on longer timescales.

“In the future, we want to extend these experiments to more complex and technologically relevant nanostructures, and also to enable X-ray exploration of nanoscale devices while they are operating,” Lindenberg said. “Knowing how materials change under strain can be used together with simulations to design new materials with novel properties.”

Participating researchers were from SLAC, Stanford and two of their joint institutes, the Stanford Institute for Materials and Energy Sciences (SIMES) and Stanford PULSE Institute; University of California, Berkeley; University of Duisburg-Essen in Germany; and Argonne National Laboratory. The work was supported by the DOE Office of Science and the German Research Council.

Here’s a link to and a citation for the paper,

Visualization of nanocrystal breathing modes at extreme strains by Erzsi Szilagyi, Joshua S. Wittenberg, Timothy A. Miller, Katie Lutker, Florian Quirin, Henrik Lemke, Diling Zhu, Matthieu Chollet, Joseph Robinson, Haidan Wen, Klaus Sokolowski-Tinten, & Aaron M. Lindenberg. Nature Communications 6, Article number: 6577 doi:10.1038/ncomms7577 Published 12 March 2015

This paper is behind a paywall but there is a free preview available through ReadCube Access.

Dancing droplets—a mystery solved

I love simple yet profound discoveries like the one described in a March 12, 2015 news item on Nanowerk (Note: A link has been removed),

 A puzzling observation, pursued through hundreds of experiments, has led Stanford researchers to a simple yet profound discovery: under certain circumstances, droplets of fluid will move like performers in a dance choreographed by molecular physics.

“These droplets sense one another. They move and interact, almost like living cells,” said Manu Prakash, an assistant professor of bioengineering and senior author of an article published in Nature (“Vapour-mediated sensing and motility in two-component droplets”).

A March 11, 2015 Stanford University news release by Tom Abate, which originated the news item, describes possible applications and the genesis of this research,

The unexpected findings may prove useful in semiconductor manufacturing and self-cleaning solar panels, but what truly excites Prakash is that the discovery resulted from years of persistent effort to satisfy a scientific curiosity.

The research began in 2009 when Nate Cira, then an undergraduate at the University of Wisconsin, was doing an unrelated experiment. In the course of that experiment Cira deposited several droplets of food coloring onto a sterilized glass slide and was astonished when they began to move.

Here’s a video of the researchers discussing their work and their findings (Video by Kurt Hickman),

The news release elaborates,

Together they spent three years performing increasingly refined experiments to learn how these tiny droplets of food coloring sense one another and move. In living cells these processes of sensing and motility are known as chemotaxis.

“We’ve discovered how droplets can exhibit behaviors akin to artificial chemotaxis,” Prakash said.

As the Nature article explains, the critical fact was that food coloring is a two-component fluid. In such fluids, two different chemical compounds coexist while retaining separate molecular identities

The droplets in this experiment consisted of two molecular compounds found naturally in food coloring: water and propylene glycol.

The researchers discovered how the dynamic interactions of these two molecular components enabled inanimate droplets to mimic some of the behaviors of living cells.

Surface tension and evaporation

Essentially, the droplets danced because of a delicate balance between surface tension and evaporation.

Evaporation is easily understood. On the surface of any liquid, some molecules convert to a gaseous state and float away.

Surface tension is what causes liquids to bead up. It arises from how tightly the molecules in a liquid bind together.

Water evaporates more quickly than propylene glycol. Water also has a higher surface tension.  These differences create a tornado-like flow inside the droplets, which not only allows them to move but also allows a single droplet to sense its neighbors.

To understand the molecular forces involved, imagine shrinking down to size and diving inside a droplet.

There, water and propylene glycol molecules try to remain evenly distributed but differences in evaporation and surface tension create turmoil within the droplet.

On the curved dome of each droplet, water molecules become gaseous and float away faster than their evaporation-averse propylene glycol neighbors.

This evaporation happens more readily on the thin lower edges of the domed droplet, leaving excess of propylene glycol there. Meanwhile, the peak of the dome has a higher concentration of water.

The water at the top exerts its higher surface tension to pull the droplet tight so it doesn’t flatten out. This tugging causes a tumbling molecular motion inside the droplet. Thus surface tension gets the droplet ready to roll.

Evaporation determines the direction of that motion. Each droplet sends aloft gaseous molecules of water like a radially emanating signal announcing the exact location of any given droplet. The droplets converge where the signal is strongest.

So evaporation provided the sensing mechanism and surface tension the pull to move droplets together in what seemed to the eye to be a careful dance.

Rule for two-component fluids

The researchers experimented with varied proportions of water and propylene glycol. Droplets that were 1 percent propylene glycol (PG) to 99 percent water exhibited much the same behavior as droplets that were two-thirds PG to just one-third water.

Based on these experiments the paper describes a “universal rule” to identify any two-component fluids that will demonstrate sensing and motility.

Adding colors to the mixtures made it easier to tell how the droplets of different concentrations behaved and created some visually striking results.

In one experiment, a droplet with more propylene glycol seems to chase a droplet with more water. In actuality, the droplet with more water exerts a higher surface tension tug, pulling the propylene droplet along.

In another experiment, researchers showed how physically separated droplets could align themselves using ever-so-slight signals of evaporation.

In a third experiment they used Sharpie pens to draw black lines on glass slides. The lines changed the surface of the slide and created a series of catch basins. The researchers filled each basin with fluids of different concentrations to create a self-sorting mechanism. Droplets bounced from reservoir to reservoir until they sensed the fluid that matched their concentration and merged with that pool.

What started as a curiosity-driven project may also have many practical implications.

The deep physical understanding of two component fluids allows the researchers to predict which fluids and surfaces will show these unusual effects. The effect is present on a large number of common surfaces and can be replicated with a number of chemical compounds.

Here’s a link to and a citation for the paper,

Vapour-mediated sensing and motility in two-component droplets by N. J. Cira, A. Benusiglio, & M. Prakash. Nature  (2015) doi:10.1038/nature14272 Published online 11 March 2015

This paper is behind a paywall.

Nanoparticles in 3D courtesy of x-rays

A Feb. 4, 2015 Deutsches Elektronen-Synchrotron (DESY) press release (also on EurekAlert) announces a 3D first,

For the first time, a German-American research team has determined the three-dimensional shape of free-flying silver nanoparticles, using DESY’s X-ray laser FLASH. The tiny particles, hundreds of times smaller than the width of a human hair, were found to exhibit an unexpected variety of shapes, as the physicists from the Technical University (TU) Berlin, the University of Rostock, the SLAC National Accelerator Laboratory in the United States and from DESY report in the scientific journal Nature Communications. Besides this surprise, the results open up new scientific routes, such as direct observation of rapid changes in nanoparticles.

The press release goes on to describe the work in more detail,

“The functionality of nanoparticles is linked to their geometric form, which is often very difficult to determine experimentally,” explains Dr. Ingo Barke from the University of Rostock. “This is particularly challenging when they are present as free particles, that is, in the absence of contact with a surface or a liquid.”

The nanoparticle shape can be revealed from the characteristic way how it scatters X-ray light. Therefore, X-ray sources like DESY’s FLASH enable a sort of super microscope into the nano-world. So far, the spatial structure of nanoparticles has been reconstructed from multiple two-dimensional images, which were taken from different angles. This procedure is uncritical for particles on solid substrates, as the images can be taken from many different angles to uniquely reconstruct their three-dimensional shape.

“Bringing nanoparticles into contact with a surface or a liquid can significantly alter the particles, such that you can no longer see their actual form,” says Dr. Daniela Rupp from the TU Berlin. A free particle, however, can only be measured one time in flight before it either escapes or is destroyed by the intense X-ray light. Therefore, the scientists looked for a way to record the entire structural information of a nanoparticle with a single X-ray laser pulse.

To achieve this goal, the scientists led by Prof. Thomas Möller from the TU Berlin and Prof. Karl-Heinz Meiwes-Broer and Prof. Thomas Fennel from the University of Rostock employed a trick. Instead of taking usual small-angle scattering images, the physicists recorded the scattered X-rays in a wide angular range. “This approach virtually captures the structure from many different angles simultaneously from a single laser shot,” explains Fennel.

The researchers tested this method on free silver nanoparticles with diameters of 50 to 250 nanometres (0.00005 to 0.00025 millimetres). The experiment did not only verify the feasibility of the tricky method, but also uncovered the surprising result that large nanoparticles exhibit a much greater variety of shapes than expected.

The shape of free nanoparticles is a result of different physical principles, particularly the particles’ effort to minimize their energy. Consequently, large particles composed of thousands or millions of atoms often yield predictable shapes, because the atoms can only be arranged in a particular way to obtain an energetically favourable state.

In their experiment, however, the researchers observed numerous highly symmetrical three-dimensional shapes, including several types known as Platonic and Archimedean bodies. Examples include the truncated octahedron (a body consisting of eight regular hexagons and six squares) and the icosahedron (a body made up of twenty equilateral triangles). The latter is actually only favourable for extremely small particles consisting of few atoms, and its occurrence with free particles of this size was previously unknown. “The results show that metallic nanoparticles retain a type of memory of their structure, from the early stages of growth to a yet unexplored size range,” emphasizes Barke.

Due to the large variety of shapes, it was especially important to use a fast computational method so that the researchers were capable of mapping the shape of each individual particle. The scientists used a two-step process: the rough shape was determined first and then refined using more complex simulations on a super computer. This approach turned out to be so efficient that it could not only determine various shapes reliably, but could also differentiate between varying orientations of the same shape.

This new method for determining the three-dimensional shape and orientation of nanoparticles with a single X-ray laser shot opens up a wide spectrum of new research directions. In future projects, particles could be directly “filmed” in three dimensions during growth or during phase changes. “The ability to directly film the reaction of a nanoparticle to an intense flash of X-ray light has been a dream for many physicists – this dream could now come true, even in 3D!,” emphasises Rupp.

The researchers have provided an image showing their work,

Caption: This is a wide-angle X-ray diffraction image of a truncated twinned tetrahedra nanoparticle. Credit: Hannes Hartmann/University of Rostock

Caption: This is a wide-angle X-ray diffraction image of a truncated twinned tetrahedra nanoparticle.
Credit: Hannes Hartmann/University of Rostock

Here’s a link to and a citation for the paper,

The 3D-architecture of individual free ​silver nanoparticles captured by X-ray scattering by Ingo Barke, Hannes Hartmann, Daniela Rupp, Leonie Flückiger, Mario Sauppe, Marcus Adolph, Sebastian Schorb, Christoph Bostedt, Rolf Treusch, Christian Peltz, Stephan Bartling, Thomas Fennel, Karl-Heinz Meiwes-Broer, & Thomas Möller. Nature Communications 6, Article number: 6187 doi:10.1038/ncomms7187 Published 04 February 2015

This article is open access.

A new approach to heating: warm the clothing not the room

A Jan. 7, 2015 news item on ScienceDaily describes a new type of textile which could change the way we use heat (energy),

To stay warm when temperatures drop outside, we heat our indoor spaces — even when no one is in them. But scientists have now developed a novel nanowire coating for clothes that can both generate heat and trap the heat from our bodies better than regular clothes. They report on their technology, which could help us reduce our reliance on conventional energy sources, in the ACS journal Nano Letters.

A Jan. 7, 2015 American Chemical Society (ACS) news release (also on EurekAlert), which originated the news item, provides more information about energy consumption and the researchers’ proposed solution,

Yi Cui [Stanford University] and colleagues note that nearly half of global energy consumption goes toward heating buildings and homes. But this comfort comes with a considerable environmental cost – it’s responsible for up to a third of the world’s total greenhouse gas emissions. Scientists and policymakers have tried to reduce the impact of indoor heating by improving insulation and construction materials to keep fuel-generated warmth inside. Cui’s team wanted to take a different approach and focus on people rather than spaces.

The researchers developed lightweight, breathable mesh materials that are flexible enough to coat normal clothes. When compared to regular clothing material, the special nanowire cloth trapped body heat far more effectively. Because the coatings are made out of conductive materials, they can also be actively warmed with an electricity source to further crank up the heat. The researchers calculated that their thermal textiles could save about 1,000 kilowatt hours per person every year — that’s about how much electricity an average U.S. home consumes in one month.

Here’s a link to and a citation for the paper,

Personal Thermal Management by Metallic Nanowire-Coated Textile by Po-Chun Hsu, Xiaoge Liu, Chong Liu, Xing Xie, Hye Ryoung Lee, Alex J. Welch, Tom Zhao, and Yi Cui. Nano Lett., Article ASAP DOI: 10.1021/nl5036572 Publication Date (Web): November 30, 2014
Copyright © 2014 American Chemical Society

This paper is behind a paywall.

Buckydiamondoids steer electron flow

One doesn’t usually think about buckyballs (Buckminsterfullerenes) and diamondoids as being together in one molecule but that has not stopped scientists from trying to join them and, in this case, successfully. From a Sept. 9, 2014 news item on ScienceDaily,

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.

Here’s an illustration the scientists have provided,

Illustration of a buckydiamondoid molecule under a scanning tunneling microscope (STM). In this study the STM made images of the buckydiamondoids and probed their electronic properties.

Illustration of a buckydiamondoid molecule under a scanning tunneling microscope (STM). In this study the STM made images of the buckydiamondoids and probed their electronic properties.

A Sept. 9, 2014 Stanford University news release by Glenda Chui (also on EurekAlert), which originated the news item, provides some information about this piece of international research along with background information on buckyballs and diamondoids (Note: Links have been removed),

“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 U.S. Department of Energy’s SLAC National Accelerator Laboratory. “What we got was basically a one-way valve for conducting electricity – clearly more than the sum of its parts.”

The research team, which included scientists from Stanford University, Belgium, Germany and Ukraine, reported its results Sept. 9 in Nature Communications.

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 linked cages of carbon joined, or bonded, as they are in diamonds, with hydrogen atoms linked to the surface, 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 emit and focus electrons into a tiny beam. 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.

Details are then provided about this specific piece of research (from the Stanford news release),

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. The diamondoids were then shipped to Germany, where chemists at Justus-Liebig University figured out how to attach them to buckyballs.

The resulting buckydiamondoids, which are just a few nanometers long, were tested in SIMES laboratories at Stanford. A team led by graduate student Jason Randel and postdoctoral researcher Francis Niestemski used a scanning tunneling microscope to make images of the hybrid molecules and measure their electronic behavior. They discovered that the hybrid is an excellent rectifier: The electrical current flowing through the molecule was up to 50 times stronger in one direction, from electron-spitting diamondoid to electron-catching buckyball, than in the opposite direction. This is something neither component can do on its own.

While this is not the first molecular rectifier ever invented, it’s the first one made from just carbon and hydrogen, a simplicity researchers find appealing, said Manoharan, who is an associate professor of physics at Stanford. The next step, he said, is to see if transistors can be constructed from the same basic ingredients.

“Buckyballs are easy to make – they can be isolated from soot – and the type of diamondoid we used here, which consists of two tiny cages, can be purchased commercially,” he said. “And now that our colleagues in Germany have figured out how to bind them together, others can follow the recipe. So while our research was aimed at gaining fundamental insights about a novel hybrid molecule, it could lead to advances that help make molecular electronics a reality.”

Other research collaborators came from the Catholic University of Louvain in Belgium and Kiev Polytechnic Institute in Ukraine. The primary funding for the work came from U.S. the Department of Energy Office of Science (Basic Energy Sciences, Materials Sciences and Engineering Divisions).

Here’s a link to and a citation for the paper,

Unconventional molecule-resolved current rectification in diamondoid–fullerene hybrids by Jason C. Randel, Francis C. Niestemski,    Andrés R. Botello-Mendez, Warren Mar, Georges Ndabashimiye, Sorin Melinte, Jeremy E. P. Dahl, Robert M. K. Carlson, Ekaterina D. Butova, Andrey A. Fokin, Peter R. Schreiner, Jean-Christophe Charlier & Hari C. Manoharan. Nature Communications 5, Article number: 4877 doi:10.1038/ncomms5877 Published 09 September 2014

This paper is open access. The scientists provided not only a standard illustration but a pretty picture of the buckydiamondoid,

Caption: 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. Credit: Manoharan Lab/Stanford University

Caption: 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.
Credit: Manoharan Lab/Stanford University

SWEET, sweet transporters

A Sept. 4, 2014 news item on Azonano is all about sugar,

Sugars are an essential source of energy for microrganisms, animals and humans. They are produced by plants, which convert energy from sunlight into chemical energy in the form of sugars through photosynthesis.

These sugars are taken up into cells, no matter whether these are bacteria, yeast, human cells or plant cells, by proteins that create sugar-specific pores in the membrane that surrounds a cell. These transport proteins are thus essential in all organisms. It is not surprising that the transporters of humans and plants are very similar since they evolved from their bacterial ancestors.

Sugar transporters can also be a source of vulnerability for plants and animals alike. In plants they can be susceptible to takeover by pathogens, hijacking the source of the plant’s food and energy. In animals, mutations in sugar transporters can lead to diseases, such as diabetes.

New work from a team led by the Stanford University School of Medicine’s Liang Feng and including Carnegie’s [Carnegie Institution for Science] Wolf Frommer has for the first time elucidated the atomic structures of the prototype of the sugar transporters (termed “SWEET” transporters) in plants and humans. These are bacterial sugar transporters, called SemiSWEETs (because they are just half the size of the human and plant ones). …

A Sept. 3, 2014 Carnegie Institution for Science news release, which originated the news item, describes the importance of understanding these transporters,

Until now, there was very limited information about the unique structures of these important transport proteins, which it turns out are different from all other known sugar transporters.

Discovering the structure of these proteins is important, as it is the key to unlocking the mechanism by which they work. And understanding their mechanism is crucial for figuring out what happens when these functions fail to work properly, because that knowledge can help in addressing the resulting diseases or growth problems in both plants and animals.

The research team performed a combination of structural and functional analyses of SemiSWEETs and SWEETs and was able to crystallize two examples in different states, demonstrating not only the protein’s structure, but much about its functionality as well.

They found that the SemiSWEETs do not act as a sugar channel, or tunnel, which allow sugars to pass across the membrane. Rather they act like an airlock, moving the sugars in multiple stages, two of which can be observed in the crystal structures. The SemiSWEETs, among the smallest known transport proteins, assemble in pairs, thereby creating a structure that looks like their bigger plant and human SWEET homologs. This marks the SWEET family of proteins as drastically different from other sugar transport proteins.

“One of the most-exciting parts of this discovery is the speed with which we were able to move from discovering these novel sugar transporters, to determining their actual structure, to showing how they work,” Frommer said. “Fantastic progress made possible by a collaboration with a structural biologist from Stanford University. Our findings highlight the potential practical applications of this information in improving crop yields as well as in addressing human diseases.”

Here’s a link to and a citation for the paper,

Structures of bacterial homologues of SWEET transporters in two distinct conformations by Yan Xu, Yuyong Tao, Lily S. Cheung, Chao Fan, Li-Qing Chen, Sophia Xu, Kay Perry, Wolf B. Frommer, & Liang Feng. Nature (2014) doi:10.1038/nature13670 Published online 03 September 2014

This paper is behind a paywall.

Hummingbirds and ‘nano’ spy cameras

Hummingbird-inspired spy cameras have come a long way since the research featured in this Aug. 12, 2011 posting which includes a video of a robot camera designed to look like a hummingbird and mimic some of its extraordinary flying abilities. These days (2014) the emphasis appears to be on mimicking the abilities to a finer degree if Margaret Munro’s July 29, 2014 article for Canada.com is to be believed,

Tiny, high-end military drones are catching up with one of nature’s great engineering masterpieces.

A side-by-side comparison has found a “remarkably similar” aerodynamic performance between hummingbirds and the Black Hornet, the most sophisticated nano spycam yet.

“(The) Average Joe hummingbird” is about on par with the tiny helicopter that is so small it can fit in a pocket, says engineering professor David Lentink, at Stanford University. He led a team from Canada [University of British Columbia], the U.S. and the Netherlands [Wageningen University and Eindhoven University of Technology] that compared the birds and the machine for a study released Tuesday [July 29, 2014].

For a visual comparison with the latest nano spycam (Black Hornet), here’s the ‘hummingbird’ featured in the 2011 posting,

The  Nano Hummingbird, a drone from AeroVironment designed for the US Pentagon, would fit into any or all of those categories.

And, here’s this 2013 image of a Black Hornet Nano Helicopter inspired by hummingbirds,

Black Hornet Nano Helicopter UAVView licenseview terms Richard Watt - Photo http://www.defenceimagery.mod.uk/fotoweb/fwbin/download.dll/45153802.jpgCourtesy: Wikipedia

Black Hornet Nano Helicopter UAVView licenseview terms
Richard Watt – Photo http://www.defenceimagery.mod.uk/fotoweb/fwbin/download.dll/45153802.jpg Courtesy: Wikipedia

A July 30, 2014 Stanford University news release by Bjorn Carey provides more details about this latest research into hummingbirds and their flying ways,

More than 42 million years of natural selection have turned hummingbirds into some of the world’s most energetically efficient flyers, particularly when it comes to hovering in place.

Humans, however, are gaining ground quickly. A new study led by David Lentink, an assistant professor of mechanical engineering at Stanford, reveals that the spinning blades of micro-helicopters are about as efficient at hovering as the average hummingbird.

The experiment involved spinning hummingbird wings – sourced from a pre-existing museum collection – of 12 different species on an apparatus designed to test the aerodynamics of helicopter blades. The researchers used cameras to visualize airflow around the wings, and sensitive load cells to measure the drag and the lift force they exerted, at different speeds and angles.

Lentink and his colleagues then replicated the experiment using the blades from a ProxDynamics Black Hornet autonomous microhelicopter. The Black Hornet is the most sophisticated microcopter available – the United Kingdom’s army uses it in Afghanistan – and is itself about the size of a hummingbird.

Even spinning like a helicopter, rather than flapping, the hummingbird wings excelled: If hummingbirds were able to spin their wings to hover, it would cost them roughly half as much energy as flapping. The microcopter’s wings kept pace with the middle-of-the-pack hummingbird wings, but the topflight wings – those of Anna’s hummingbird, a species common throughout the West Coast – were still about 27 percent more efficient than engineered blades.

Hummingbirds acing the test didn’t particularly surprise Lentink – previous studies had indicated hummingbirds were incredibly efficient – but he was impressed with the helicopter.

“The technology is at the level of an average Joe hummingbird,” Lentink said. “A helicopter is really the most efficient hovering device that we can build. The best hummingbirds are still better, but I think it’s amazing that we’re getting closer. It’s not easy to match their performance, but if we build better wings with better shapes, we might approximate hummingbirds.”

Based on the measurements of Anna’s hummingbirds, Lentink said there is potential to improve microcopter rotor power by up to 27 percent.

The high-fidelity experiment also provided an opportunity to refine previous rough estimates of muscle power. Lentink’s team learned that hummingbirds’ muscles produce a surprising 130 watts of energy per kilogram; the average for other birds, and across most vertebrates, is roughly 100 watts/kg.

Although the current study revealed several details of how a hummingbird hovers in one place, the birds still hold many secrets. For instance, Lentink said, we don’t know how hummingbirds maintain their flight in a strong gust, how they navigate through branches and other clutter, or how they change direction so quickly during aerial “dogfights.”

He also thinks great strides could be made by studying wing aspect ratios, the ratio of wing length to wing width. The aspect ratios of all the hummingbirds’ wings remarkably converged around 3.9. The aspect ratios of most wings used in aviation measure much higher; the Black Hornet’s aspect ratio was 4.7.

“I want to understand if aspect ratio is special, and whether the amount of variation has an effect on performance,” Lentink said. Understanding and replicating these abilities and characteristics could be a boon for robotics and will be the focus of future experiments.

“Those are the things we don’t know right now, and they could be incredibly useful. But I don’t mind it, actually,” Lentink said. “I think it’s nice that there are still a few things about hummingbirds that we don’t know.”

Agreed, it’s nice to know there are still a few mysteries left. You can watch the ‘mysterious’ hummingbird in this video courtesy of the Rivers Ingersoll Lentink Lab at Stanford University,

High speed video of Anna’s hummingbird at Stanford Arizona Cactus Garden.

Here’s a link to and a citation for the paper, H/T to Nancy Owano’s article on phys.org for alerting me to this story.

Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors by Jan W. Kruyt, Elsa M. Quicazán-Rubio, GertJan F. van Heijst, Douglas L. Altshuler, and David Lentink.  J. R. Soc. Interface 6 October 2014 vol. 11 no. 99 20140585 doi: 10.1098/​rsif.2014.0585 Published [online] 30 July 2014

This is an open access paper.

Despite Munro’s reference to the Black Hornet as a ‘nano’ spycam, the ‘microhelicopter’ description in the news release places the device at the microscale (/1,000,000,000). Still, I don’t understand what makes it microscale since it’s visible to the naked eye. In any case, it is small.

US Air Force wants to merge classical and quantum physics

The US Air Force wants to merge classical and quantum physics for practical purposes according to a May 5, 2014 news item on Azonano,

The Air Force Office of Scientific Research has selected the Harvard School of Engineering and Applied Sciences (SEAS) to lead a multidisciplinary effort that will merge research in classical and quantum physics and accelerate the development of advanced optical technologies.

Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, will lead this Multidisciplinary University Research Initiative [MURI] with a world-class team of collaborators from Harvard, Columbia University, Purdue University, Stanford University, the University of Pennsylvania, Lund University, and the University of Southampton.

The grant is expected to advance physics and materials science in directions that could lead to very sophisticated lenses, communication technologies, quantum information devices, and imaging technologies.

“This is one of the world’s strongest possible teams,” said Capasso. “I am proud to lead this group of people, who are internationally renowned experts in their fields, and I believe we can really break new ground.”

A May 1, 2014 Harvard University School of Engineering and Applied Sciences news release, which originated the news item, provides a description of project focus: nanophotonics and metamaterials along with some details of Capasso’s work in these areas (Note: Links have been removed),

The premise of nanophotonics is that light can interact with matter in unusual ways when the material incorporates tiny metallic or dielectric features that are separated by a distance shorter than the wavelength of the light. Metamaterials are engineered materials that exploit these phenomena, producing strange effects, enabling light to bend unnaturally, twist into a vortex, or disappear entirely. Yet the fabrication of thick, or bulk, metamaterials—that manipulate light as it passes through the material—has proven very challenging.

Recent research by Capasso and others in the field has demonstrated that with the right device structure, the critical manipulations can actually be confined to the very surface of the material—what they have dubbed a “metasurface.” These metasurfaces can impart an instantaneous shift in the phase, amplitude, and polarization of light, effectively controlling optical properties on demand. Importantly, they can be created in the lab using fairly common fabrication techniques.

At Harvard, the research has produced devices like an extremely thin, flat lens, and a material that absorbs 99.75% of infrared light. But, so far, such devices have been built to order—brilliantly suited to a single task, but not tunable.

This project, however,is focused on the future (Note: Links have been removed),

“Can we make a rapidly configurable metasurface so that we can change it in real time and quickly? That’s really a visionary frontier,” said Capasso. “We want to go all the way from the fundamental physics to the material building blocks and then the actual devices, to arrive at some sort of system demonstration.”

The proposed research also goes further. A key thrust of the project involves combining nanophotonics with research in quantum photonics. By exploiting the quantum effects of luminescent atomic impurities in diamond, for example, physicists and engineers have shown that light can be captured, stored, manipulated, and emitted as a controlled stream of single photons. These types of devices are essential building blocks for the realization of secure quantum communication systems and quantum computers. By coupling these quantum systems with metasurfaces—creating so-called quantum metasurfaces—the team believes it is possible to achieve an unprecedented level of control over the emission of photons.

“Just 20 years ago, the notion that photons could be manipulated at the subwavelength scale was thought to be some exotic thing, far fetched and of very limited use,” said Capasso. “But basic research opens up new avenues. In hindsight we know that new discoveries tend to lead to other technology developments in unexpected ways.”

The research team includes experts in theoretical physics, metamaterials, nanophotonic circuitry, quantum devices, plasmonics, nanofabrication, and computational modeling. Co-principal investigator Marko Lončar is the Tiantsai Lin Professor of Electrical Engineering at Harvard SEAS. Co-PI Nanfang Yu, Ph.D. ’09, developed expertise in metasurfaces as a student in Capasso’s Harvard laboratory; he is now an assistant professor of applied physics at Columbia. Additional co-PIs include Alexandra Boltasseva and Vladimir Shalaev at Purdue, Mark Brongersma at Stanford, and Nader Engheta at the University of Pennsylvania. Lars Samuelson (Lund University) and Nikolay Zheludev (University of Southampton) will also participate.

The bulk of the funding will support talented graduate students at the lead institutions.

The project, titled “Active Metasurfaces for Advanced Wavefront Engineering and Waveguiding,” is among 24 planned MURI awards selected from 361 white papers and 88 detailed proposals evaluated by a panel of experts; each award is subject to successful negotiation. The anticipated amount of the Harvard-led grant is up to $6.5 million for three to five years.

For anyone who’s not familiar (that includes me, anyway) with MURI awards, there’s this from Wikipedia (Note: links have been removed),

Multidisciplinary University Research Initiative (MURI) is a basic research program sponsored by the US Department of Defense (DoD). Currently each MURI award is about $1.5 million a year for five years.

I gather that in addition to the Air Force, the Army and the Navy also award MURI funds.