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Researchers Cross the 'Valley of Death' in Nanocomposite Design

In the early days of nanotech commercialization, it was popular to add nanomaterials to composites-- like carbon nanotubes (CNTs) in bicycles— in order for them to be “stronger than steel”. But that was mostly just marketing copy. The CNTs merely replaced the resins that had previously filled out the material matrix. It was pretty unclear whether they actually imparted any of the capabilities that nanomaterials possessed, like strength and flexibility.

The issue has come to be known as the “Valley of Death” in composite material design. Essentially, materials scientists were finding that the extraordinary properties of nanowires were disappearing—the properties of an entire composite were limited by the properties of other materials found in the material’s matrix.

A couple of years back some joint research between industry and academia attempted to address this shortcoming and take advantage of nanomaterials' superior strength. It looks like it's finally happened.

Researchers at the University of Western Australia have found a way for composite materials to actually match the strength and flexibility of the nanowires that have been placed inside them.

"In a normal metal matrix-nanowire composite, when we pull the composite to a very high stress, the nanowires will experience a large elastic deformation of several percent,” explains Yinong Liu, a professor at the University of Western Australia, in a press release. “That is okay for the nanowires, but the normal metals that form the matrix cannot.  They can stretch elastically to no more than 1 per cent.  Beyond that, the matrix deforms plastically.”

In research published in the journal Science (“A Transforming Metal Nanocomposite with Large Elastic Strain, Low Modulus, and High Strength”), Liu and his colleagues discovered that the shape-memory alloy nickel-titanium (NiTi) had enough elasticity to be used with nanowires in a material matrix without losing the superior functionality of the nanowires.

"NiTi is a shape memory alloy, a fancy name but not totally new,” says Liu in the press release. “It is no stronger than other common metals but it has one special property that is its martensitic transformation. The transformation can produce a deformation compatible to the elastic deformation of the nanowires without plastic damage to the structure of the composite. This effectively gives the nanowires a chance to do their job, that is, to bear the high load and to be super strong. With this we have crossed the ‘Valley of Death'!”

The resulting composite has proved to be twice as strong as high-strength steels and it enjoys elastic strain limits that are 5 to 10 times greater than the best spring steels currently available.

One obvious application is in medical implants. More intriguingly, the material's high elastic strain levels could enable breakthroughs in electronics, optoelectronics, piezoelectrics, piezomagnetics, photocatalytics, and chemical sensing properties. Even better (from my perspective), it might lead to bike frames that actually benefit from the nanomaterial used in them.

Image: Shijie Hao/China University of Petroleum

Electrically Powered Nanolasers Capable of Being Operated at Room Temperature

Much of the research conducted to date with nanolasers has involved units powered by larger light sources rather than directly from electrical current.  While these light-powered nanolasers have been successfully operated at room temperature, the fact that they don't run on electricity makes them impractical for many electronic applications. For instance, in many embedded system designs adding an additional laser light source is just not feasible.

Nanolasers could serve as another key step in keeping Moore’s Law chugging along if they could run continuously at room temperature and be powered by an electric current instead of a beam of light. But heretofore, such lasers were prone to overheating and failure. Now researchers at Arizona State University (ASU) believe they have hit upon a design for an electrically powered nanolaser that has overcome that hurdle.

The laser, which was described in the journal Optics Express (“Record performance of electrical injection sub-wavelength metallic-cavity semiconductor lasers at room temperature”), is the culmination of nearly seven years of work by ASU professor Cun-Zheng Ning and his colleagues. 

“In terms of fundamental science, it shows for the first time that metal heating loss is not an insurmountable barrier for room-temperature operation of a metallic cavity nanolaser under electrical injection,” said Ning in a press release. “For a long time, many doubted if such operation is even possible at all.”

In this latest research, Ning and his team employed the same indium phosphide/indium gallium arsenide/indium phosphide (InP/InGaAs/InP) rectangular core and the same silicon nitride (SiN) insulating layer—encapsulated in a silver shell—that they used in an earlier iteration of the device that suffered from the heating problem. But this time, they adjusted the thickness of the SiN layer and refined the fabrication process.

“It is extremely challenging to get everything correct at the nanometer scale. At such a small scale, any fabrication error becomes relatively large, and there are many fabrication steps, each of which is rather complex,” Ning explains in the press release.

Other recent nanolaser designs had already shown that it's possible to operate them at room temperature if you carefully choose the driving laser that powers them. But the ASU team's breakthrough shows the way towards a nanolaser that could be operated with a simple battery rather than another complex laser light source. The impact of this capability could be felt across the entire field of electronics, with nanolasers that speed up computers, broaden Internet bandwidth and serve as light sources for computer-chip-based sensing technologies that are integral to embedded computing.

Image: K. Ding and C.Z. Ning/Arizona State University

Nanoparticle Carrying Bee Venom Could Prevent HIV Infection and Cure It

Nanoparticles are proving themselves effective carriers, delivering therapies within the human body.

Last year, nanoparticles carrying biological components proved effective as anti-viral treatments for Hepatitis C. And some years back, research also demonstrated that attaching short-interfering RNA (siRNA) molecules to a biodegradable polymer nanoparticle was effective in the treatment of sexually transmitted diseases, like the human immunodeficiency virus (HIV).

Now researchers at the Washington University in St. Louis have attacked HIV more directly. They have shown that a nanoparticle carrying bee venom effectively destroys HIV while leaving surrounding cells unharmed.

The research, which was published in the journal Antiviral Therapy ("Cytolytic nanoparticles attenuate HIV-1 infectivity"), employed a nanoparticle that had previously been abandoned when it proved ineffective for delivering oxygen to blood cells. But in its new role, carrying the toxin melittin, a poison found in bee venom, it is extremely effective at breaking down the essential structure of HIV.

“We are attacking an inherent physical property of HIV,” says Joshua L. Hood, MD, PhD, a research instructor in medicine at Washington University in a press release. “Theoretically, there isn’t any way for the virus to adapt to that. The virus has to have a protective coat, a double-layered membrane that covers the virus.”

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'Theranostic' Nanoparticle Promises Improved Cancer Treatment

The precise delivery of drugs to diseased cells is one of the key functions of nanoparticles in the treatment of cancer and other diseases. Another role for nanoparticles in medical treatment is to provide early diagnosis of diseases like cancer through the detection of biomarkers that are linked to the disease.

The ability to combine both these therapeutic and diagnostic functions into one nanoparticle has developed into a field known as a “theranostics.”

Now a research team in Sweden, including Eva Malmström-Jonsson of the KTH Royal Institute of Technology and Andreas Nyström of the Karolinska Institute, has not only developed just such a theranostic nanoparticle, but also demonstrated that it is non-toxic and biodegradable.

The research, which was published in the journal Particle & Particle Systems Characterization (“In Vitro Evaluation of Non-Protein Adsorbing Breast Cancer Theranostics Based on 19F-Polymer Containing Nanoparticles”), developed a carefully balanced self-assembly process for dendritic linear hybrid materials.

The self-assembly process required a balance between the particles’ hydrophilic (capable of dissolving in water) and hydrophobic (not dissolvable in water) parts. While the hydrophobic part of the particle was needed to carry the drug to the target site, the hydrophilic portion was needed to make sure the drug was actually released.

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Gold Nanoparticles Enable Simple and Sensitive Sensor for Early Disease Detection

When it comes to nanosensors for medical diagnostics, gold nanoparticles are often the first choice for enabling early disease detection. This is due to gold nanoparticles’ ability to detect biomarkers at very low concentrations. They undergo intense color changes when in the presence of certain targets.

Just last year, researchers from London Centre for Nanotechnology at Imperial College London used gold nanoparticles and plasmonics to create a biosensor capable of detecting minute amounts of a biomarker.

Now, in research led by Professor Warren Chan of the University of Toronto’s Institute of Biomaterials and Biomedical Engineering (IBBME), gold nanoparticles’ capabilities have been exploited again to create a simple but highly sensitive diagnostic tool for detecting diseases.

The typical design for other gold nanoparticle-based biosensors involves DNA strands being attached to the particles. In these methods, the gold nanoparticles clump together when in the presence of a target gene turning the sample blue.

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Nanotube Membrane Could Revolutionize Osmotic Power

Two years ago, Stanford University researcher Yi Cui took a break from his work on solving the silicon-versus-graphite conundrum of anodes in Lithium-ion batteries to look into an alternative method for generating electricity that has become known as pressure-retarded osmosis.

Pressure-retarded osmosis exploits the difference in salinity between fresh water and salt water to generate electricity. Norway-based Statkraft has been a leading commercial proponent of the technology, building its first pilot plant in 2009.

Despite new plants being planned and this alternative energy source theoretically capable of generating 1 terawatt—the equivalent of 1000 nuclear reactors—a group of European researchers believed the technology was still not a truly viable energy source.

Now researchers at the Institut Lumière Matière in Lyon (CNRS/Université Claude Bernard Lyon 1), in collaboration with the Institut Néel (CNRS) claim to have developed a new membrane technology that will make new pressure-retarded systems 1000 times more efficient than today's systems.

The researchers didn’t set out to create a new membrane. The original aim of the research was just to measure dynamics of fluids confined in nanometric spaces. The research, which was published in the journal Nature ("Giant osmotic energy conversion measured in a single transmembrane boron-nitride nanotube"), did succeed in achieving the world’s first measurement of osmotic flow through a single nanotube. However, in achieving their initial aim they also managed to create a membrane design that could revolutionize the nascent industry.

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Nano Beads of Silicon Could String Together Li-ion Batteries of the Future

Traditional graphite-based anodes for Lithium-ion (Li-ion) batteries just don’t measure up in terms of charge life for the demands that are being put on them in today’s personal gadget applications. Silicon-based anodes as an alternative have demonstrated drastically improved charge life, but they begin to crack after a relatively few charge-discharge cycles.

As a result, much research has been devoted to finding nanomaterials that have the improved charge life of silicon but also the ability to withstand numerous charge-discharge cycles of graphite. Nanostructured silicon has been the nanomaterial that has been looked at the longest for achieving this dual aim.

Despite all the efforts, it wasn’t until last year that Yi Cui of Stanford and SLAC found a solution that consisted of a double-walled silicon nanotube coated with a thin layer of silicon oxide. This design was capable of storing 10 times more charge than graphite anodes and could survive 6000 charge-discharge cycles.

While Cui has been simplifying the process for making the double-wall silicon nanotubes, researchers at the University of Maryland have taken a different material approach. YuHuang Wang, an assistant professor of chemistry and biochemistry, and his colleagues have successfully grown tiny beads of silicon on a carbon nanotube to serve as an anode in a Li-ion battery.

The research, which was published in the journal ACS Nano (“A Beaded-String Silicon Anode”), attached a molecule sometimes used in food flavoring to carbon nanotubes less than 50 nanometers wide. After flooding the molecule and carbon nanotube with silicon gas, the molecule caused beads of silicon to grow on the nanotube.

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Graphene Can Create "Hot Carrier" Cells for Photovoltaics

Graphene’s potential applications in photovoltaics (PVs) have remained fairly limited. Nanomaterials of nearly every stripe, including quantum dots, nanowires and carbon nanotubes, have offered alternatives in the solar collecting cells of PVs. But research has really only offered graphene as a replacement to indium-tin-oxide (ITO) used in the electrodes for organic solar cells.

Now researchers at the Barcelona, Spain-based Institute of Photonic Science (ICFO), in collaboration with the Massachusetts Institute of Technology, Max Planck Institute for Polymer Research in Germany and Graphenea S.L. Donostia-in San Sebastian, Spain have taken some initial steps in using graphene in the conversion and the conduction layers of a PV cell.

The research, which was published in the journal Nature Physics (“Photoexcitation cascade and multiple hot-carrier generation in graphene”), has demonstrated that graphene is capable of converting one photon into multiple electrons, leading to electric current.

Until now, researchers had been looking at quantum dots to generate electron multiplication or creating so-called “hot carrier” cells in PVs.  While this line of research has gained some skeptics, it has been pursued for nearly a decade. The international team in this latest research has demonstrated that graphene can be used to create these hot carrier cells.

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Why Did NanoInk Go Bust?

One of the United State’s first nanotechnology companies, NanoInk, has gone belly up, joining a host of high-profile nanotechnology-based companies that have shuttered their doors in the last 12 months: Konarka, A123 Systems and Ener1.

These other three companies were all tied to the energy markets (solar in the case of Konarka and batteries for both A123 and Ener1), which are typically volatile, with a fair number of shuttered businesses dotting their landscapes. But NanoInk is a venerable old company in comparison to these other three and is more in what could be characterized as the “picks-and-shovels” side of the nanotechnology business, microscopy tools. NanoInk had been around so long that they were becoming known for their charity work in bringing nanotechnology to the Third World

So, what happened? The news tells us that NanoInk’s primary financial backer, Ann Lurie, pulled the plug on her 10-year and $150-million life support of the company. After a decade of showing little return on her investment, Lurie decided that enough was enough. But that’s like explaining that a patient died because their heart stopped. What caused the heart to stop?

The technology foundation of NanoInk was an atomic force microscope-based dip-pen to execute lithography on the nanoscale. This so-called nanolithography would create nanostructures by delivering 'ink' via capillary transport from the AFM tip to a surface. One thing that always seemed problematic with this technology was that it wasn’t really scalable.

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Carbon Nanotube-Based Thin Film Creates Hybrid Organic/Silicon Solar Cells

Research into improving photovoltaics (PVs) is one of the most dynamic areas of nanotechnology. The range of nanomaterials and approaches to using them for increasing the energy conversion efficiency and lowering the cost of PVs are impressive.

Quantum dots have generated some of the more attractive approaches to creating solar cells with extremely high conversion efficiencies. Even the wonder material graphene has gotten into the act recently by offering an inexpensive alternative to indium-tin-oxide (ITO) used in the electrodes of organic solar cells.

But industry adoption of nanotechnology-based solar power solutions has been rocky, epitomized by last year's bankruptcy of Konarka. Often in emerging technologies—and perhaps in the case of nano-enabled PVs—it’s better not to reinvent the wheel but just figure out a way for it to roll a bit better.

To this end researchers at Yale University have developed a carbon nanotube-based thin film that, when applied to today’s crystalline silicon solar cells, create a hybrid carbon/silicon solar cells with far greater power-conversion efficiency than they currently possess.

“Our approach bridges the cost-effectiveness and excellent electrical and optical properties of novel nanomaterials with well-established, high efficiency silicon solar cell technologies,” said André D. Taylor, assistant professor of chemical and environmental engineering at Yale and a principal investigator of the research, in a university press release.

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
Editor
Dexter Johnson
Madrid, Spain
 
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Rachel Courtland
Associate Editor, IEEE Spectrum
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