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This shows a slab through the 3-D reconstruction of particle 1 along the vertical plane with tentative atomic positions indicated. ABC repeats of {111} planes are visible. (Image Credit Monash University)

Researchers have developed a new method to capture the 3D structures of nanocrystals. Scientists believe these tiny particles could be used to fight cancer, collect renewable energy and mitigate pollution.

Metallic nanoparticles are some of the smallest particles. Their dimensions are measured in nanometres, with each nanometre being one millionth of a milimetre. Until now, it has been difficult to know how they work, because they are so small their structure is impossible to see.

The novel imaging method, developed by an international team from the US, Korea and Australia will allow researchers to investigate the 3D structure of these miniscule particles for the first time.

The research, published today in Science, was co-led by Associate Professor Hans Elmlund from the ARC Centre of Excellence in Advanced Molecular Imaging based at Monash University. The work, performed in collaboration with researchers from Princeton University, Boston University, and Harvard, reveals the details of the method and shows how it can be used to characterise the 3D structures of these miniscule particles for the first time.

The method is called “3D Structure Identification of Nanoparticles by Graphene Liquid Cell EM (SINGLE)” and it exceeds previous techniques by combining three recently developed components.

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Co-crystal structure of protein-DNA nanowires. The protein-DNA nanowire design is experimentally verified by X-ray crystallography.Credit: Yun (Kurt) Mou, Jiun-Yann Yu, Timothy M. Wannier, Chin-Lin Guo and Stephen L. Mayo/Caltech

The ability to custom design biological materials such as protein and DNA opens up technological possibilities that were unimaginable just a few decades ago. For example, synthetic structures made of DNA could one day be used to deliver cancer drugs directly to tumor cells, and customized proteins could be designed to specifically attack a certain kind of virus. Although researchers have already made such structures out of DNA or protein alone, a Caltech team recently created—for the first time—a synthetic structure made of both protein and DNA. Combining the two molecule types into one biomaterial opens the door to numerous applications.

Mou and his colleagues in the laboratory of Stephen Mayo, Bren Professor of Biology and Chemistry and the William K. Bowes Jr. Leadership Chair of Caltech's Division of Biology and Biological Engineering, began with a computer program to design the type of protein and DNA that would work best as part of their hybrid material. "Materials can be formed using just a trial-and-error method of combining things to see what results, but it's better and more efficient if you can first predict what the structure is like and then design a protein to form that kind of material," he says.

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Graphene, like the paper models, is strong but flexible, and can be stretched or pulled with forces comparable to those exerted by motor proteins. Image Credit: Joe Wilensky/Cornell Chronicle

The art of kirigami involves cutting paper into intricate designs, like snowflakes. Cornell physicists are kirigami artists, too, but their paper is only an atom thick, and could become some of the smallest machines the world has ever known.

A research collaboration led by Paul McEuen, the John A. Newman Professor of Physical Science and director of the Kavli Institute at Cornell for Nanoscale Science (KIC), is taking kirigami down to the nanoscale. Their template is graphene, single atom-thick sheets of hexagonally bonded carbon, famous for being ultra thin, ultra strong and a perfect electron conductor. The team demonstrated the application of kirigami on 10-micron sheets of graphene (a human hair is about 70 microns thick), which they can cut, fold, twist and bend, just like paper.

Graphene and other thin materials are extremely sticky at that scale, so the researchers used an old trick to make it easier to manipulate: They suspended it in water and added surfactants to make it slippery, like soapy water. They also made gold tab “handles” so they could grab the ends of the graphene shapes. Co-author Arthur Barnard, also a Cornell physics graduate student, figured out how to manipulate the graphene this way.

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Image Credit: Bilkent University UNAM

Memristors, resistors of which conductance is a function of the history of voltage applied to them, have attracted great attention in the present decade as potential components of memory and computing platforms. These long-forgotten device components were predicted over fifty years ago by Leon Chua, who described them as the fourth fundamental circuit element alongside resistors, capacitors and inductors – although the true origins of the memristor are even older than its name, as the term applies to such a broad range of electronic phenomena that the original observations of memristive behavior date over a century ago.

In the modern world, however, memristors are making a comeback: They are expected to play a major role in the development of novel computing platforms, particularly neuromorphic systems, where brain-like (cortical) computational schemes can be efficiently implemented using semiconductor technology. Recent reports on memristive switches demonstrate improvements in the uniformity and controllability of nanoionics-based memristors, though there is still a long way to go before memristors can compete with other circuit elements in forming neuromorphic systems with billions of synapses and millions of solid state neurons. On the other hand, Flash memory -another non-volatile memory technology- has reached very high densities and is readily compatible with CMOS technology, which makes it a particularly suitable model for the implementation of memristor-based applications.

In recent work at the National Nanotechnology Research Center at Bilkent University (Turkey), the Dâna group has demonstrated that junctionless flash memory cells can be operated like a memristor: The write and erase operations commonly performed through voltage pulses applied to the gate can be effected through the application of voltages through the source and drain terminals of the transistor. In fact, the equations that relate the transistor operation and charge/discharge of the floating gate show that the flash memory, when operated in this way, behaves nearly like an ideal memristor. The significance of the demonstration is that it connects the two non-volatile memory device families, the memristor and flash, and may facilitate future applications of flash memory devices in neuromorphic computing. Considering that the density of flash drives has improved to such an extent that multigigabit chips can be mass produced and have entered into virtually every cell-phone, flash technology already has the infrastructure that can enable the implemention of billions of synthetic synapses. Moreover, the flashristor mode -the new operation mode is referred to in the article- can be implemented with high uniformity and repeatability.

The group’s findings are also highlighted in the IEEE Spectrum website, which can be found at:

http://spectrum.ieee.org/tech-talk/computing/hardware/flashristors-getting-the-best-of-memristors-and-flash-memory

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The image above illustrates how proteins (copper-colored coils) modified with polyhistidine-tags (green diamonds) can be attached to nanoparticles (red circle). Credit: Jonathan Lovell/University at Buffalo.

Fastening protein-based medical treatments to nanoparticles isn’t easy. With arduous chemistry, scientists can do it. But like a doomed marriage, the fragile binding that holds them together often separates. This problem, which has limited how doctors can use proteins to treat serious disease, may soon change. University at Buffalo researchers have discovered a way to easily and effectively fasten proteins to nanoparticles – essentially an arranged marriage – by simply mixing them together. While in its infancy, the model already has shown promise for developing an HIV vaccine and as a way to target cancer cells. “Scientists have been able to attach proteins to nanoparticles for a while now. But it’s a fairly difficult process that’s only effective in a controlled environment. Nobody has been able to devise a simple method that can work inside the body,” said Jonathan F. Lovell, PhD, UB assistant professor of biomedical engineering, who led the research. He added: “We have proven that you can easily attach proteins to nanoparticles and, like Velcro that doesn’t unstick, it stays together.” Additional authors include researchers from UB’s Department of Chemical and Biological Engineering and Department of Microbiology and Immunology. The teams’ results were exciting, with the new binding model acting like a homing missile to tumors. The targeted nanoparticles have the potential to improve cancer treatment by targeting specific cancer cells in lieu of releasing anti-cancer drugs everywhere in the body. Lovell plans to follow up the research with more rigorous testing of the vaccine and tumor-targeted technologies. Moving to human clinical trials is the ultimate goal.

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Zinc oxide nanowires return to shape slowly after being bent. That property, called anelasticity, suggests that nanowires might be good in applications that require absorption of shocks or vibrations. Image Credit: Brown University Zhu lab / NC State
Researchers from Brown University and North Carolina State University have found that nanowires made of zinc oxide are highly anelastic, meaning they return to shape slowly after being bent, rather that snapping right back. The findings add one more to the growing list of interesting properties found in nanoscale wires, tiny strands thousands of times thinner than a human hair. “What’s surprising here is the magnitude of the effect,” said Huajian Gao, the Walter H. Annenberg Professor of Engineering and a coauthor of a new paper describing the research. “Anelasticity is present but negligible in many macroscale materials, but becomes prominent at the nanoscale. We show an anelastic effect in nanowires that is four orders of magnitude larger than what is observed in even the most anelastic bulk materials.”
The findings are significant in part because anelastic materials are good absorbers of kinetic energy. These results suggest that nanowires could be useful in damping shocks and vibrations in a wide variety of applications.
“During the last decade, zinc oxide nanowire has been recognized as one of the most important nanomaterials with a broad range of applications such as mechanical energy harvesting, solar cells, sensors and actuators,” Gao said. “Our discovery of giant anelasticity and high energy dissipation in zinc oxide nanowires adds a new dimension to their functionality.” The experiments for the study were done in the lab of Yong Zhu, an associate professor of mechanical and aerospace engineering at NC State. Zhu and his colleagues used a delicate apparatus to bend nanowires under a scanning electron microscope. The work showed that, after the bending strain was released, the wires returned to about 80 percent of their original shape quickly. But they recovered the rest of their original shape much more slowly, over the course of up to 20 or 30 minutes. That is a far more prominent anelastic effect than is common at the macroscale.

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Graphene, like the paper models, is strong but flexible, and can be stretched or pulled with forces comparable to those exerted by motor proteins. Image Credit: Joe Wilensky/Cornell Chronicle, Cornell University

The art of kirigami involves cutting paper into intricate designs, like snowflakes. Cornell physicists are kirigami artists, too, but their paper is only an atom thick, and could become some of the smallest machines the world has ever known. A research collaboration led by Paul McEuen, the John A. Newman Professor of Physical Science and director of the Kavli Institute at Cornell for Nanoscale Science (KIC), is taking kirigami down to the nanoscale. Their template is graphene, single atom-thick sheets of hexagonally bonded carbon, famous for being ultra thin, ultra strong and a perfect electron conductor. They have demonstrated the application of kirigami on 10-micron sheets of graphene (a human hair is about 70 microns thick), which they can cut, fold, twist and bend, just like paper. Graphene and other thin materials are extremely sticky at that scale, so the researchers used an old trick to make it easier to manipulate: They suspended it in water and added surfactants to make it slippery, like soapy water. They also made gold tab “handles” so they could grab the ends of the graphene shapes. Arthur Barnard, also a Cornell physics graduate student, figured out how to manipulate the graphene this way.

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A new 'designer carbon' invented by Stanford scientists significantly improved the power delivery rate of this supercapacitor. (Image Credit: Stanford University)

Stanford University scientists have created a new carbon material that significantly boosts the performance of energy-storage technologies. "We have developed a 'designer carbon' that is both versatile and controllable," said Zhenan Bao, a professor of chemical engineering at Stanford. "Our study shows that this material has exceptional energy-storage capacity, enabling unprecedented performance in lithium-sulfur batteries and supercapacitors." According to Bao, the new designer carbon represents a dramatic improvement over conventional activated carbon, an inexpensive material widely used in products ranging from water filters and air deodorizers to energy-storage devices.

"A lot of cheap activated carbon is made from coconut shells," Bao said. "To activate the carbon, manufacturers burn the coconut at high temperatures and then chemically treat it." The activation process creates nanosized holes, or pores, that increase the surface area of the carbon, allowing it to catalyze more chemical reactions and store more electrical charges. But activated carbon has serious drawbacks, Bao said. For example, there is little interconnectivity between the pores, which limits their ability to transport electricity. Instead of using coconut shells, Bao and her colleagues developed a new way to synthesize high-quality carbon using inexpensive – and uncontaminated – chemicals and polymers. The process begins with conducting hydrogel, a water-based polymer with a spongy texture similar to soft contact lenses. For the study, the Stanford team used a mild carbonization and activation process to convert the polymer organic frameworks into nanometer-thick sheets of carbon. "The carbon sheets form a 3-D network that has good pore connectivity and high electronic conductivity," said graduate student John To, a co-lead author of the study. "We also added potassium hydroxide to chemically activate the carbon sheets and increase their surface area." The result: designer carbon that can be fine-tuned for a variety of applications.

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Image Credit: University of Missouri

Carbon nanotubes (CNTs) are microscopic tubular structures that engineers “grow” through a process conducted in a high-temperature furnace. The forces that create the CNT structures known as “forests” often are unpredictable and are mostly left to chance. Now, a University of Missouri researcher has developed a way to predict how these complicated structures are formed. By understanding how CNT arrays are created, designers and engineers can better incorporate the highly adaptable material into devices and products such as baseball bats, aerospace wiring, combat body armor, computer logic components and micro sensors used in biomedical applications. CNTs are much smaller than the width of a human hair and naturally form “forests” when they are created in large numbers (see photo). These forests, held together by a nanoscale adhesive force known as the van der Waals force, are categorized based on their rigidity or how they are aligned. For example, if CNTs are dense and well aligned, the material tends to be more rigid and can be useful for electrical and mechanical applications. If CNTs are disorganized, they tend to be softer and have entirely different sets of properties.

Currently, most models that examine CNT forests analyze what happens when you compress them or test their thermal or conductivity properties after they’ve formed. However, these models do not take into account the process by which that particular forest was created and struggle to capture realistic CNT forest structure. Experiments conducted in University of Missouri’s lab will help scientists understand the process and ultimately help control it, allowing engineers to create nanotube forests with desired mechanical, thermal and electrical properties.

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Researchers at Rice University are working to determine the electronic properties of double-walled carbon nanotubes. In this example, the team analyzed a nanotube with two zigzag components. The individual nanotubes have band gaps and are semiconductors, but when combined, the band gaps overlap and make the double-walled a semimetal. (Illustration by Matías Soto/Rice University)

Rice University researchers have determined that two walls are better than one when turning carbon nanotubes into materials like strong, conductive fibers or transistors. Rice materials scientist Enrique Barrera and his colleagues used atomic-level models of double-walled nanotubes to see how they might be tuned for applications that require particular properties. They knew from others’ work that double-walled nanotubes are stronger and stiffer than their single-walled cousins. But they found it may someday be possible to tune double-walled tubes for specific electronic properties by controlling their configuration, chiral angles and the distance between the walls.

Carbon nanotubes, grown by various methods, come in two basic varieties: single-walled and multiwalled (those with two or more walls). But double-walled tubes hold a special place in the hierarchy because, the researchers wrote, they behave somewhat like single-walled tubes but are stronger and better able to survive extreme conditions. The Rice team found there’s even more to them when they started looking at how the inner and outer walls match up using tubes with zigzag chirality. Because the electrical properties of single-walled tubes depend on their chirality – the angles of their hexagonal arrangement of atoms – the researchers thought it would be interesting to learn more about those properties in double-walled tubes. It turned out that both the distance between the walls — as small as a fraction of a nanometer — and the individual chirality of the tubes impact the double-walls’ electrical properties. In addition, the researchers found the diameter of the tube — especially the inner one, with its more pronounced curvature — has a small but significant impact on the structure’s semiconducting properties.

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