Nanoclast iconNanoclast

Graphene and Molybdenite Join Forces for a New Flash Memory

As noted here earlier this week, yet another attempt has been mounted to overthrow the non-volatile memory king: flash. It's easy to be skeptical; the landscape of non-volatile memory is littered with pretenders to the throne. One of the biggest reasons for this carnage has been flash memory's ability to consistently evolve into a more powerful memory storage medium than it had been originally.

Now researchers at École polytechnique fédérale de Lausanne (EPFL) in Switzerland have combined graphene, which has already been shown to be effective as a basis for flash memory, with molybdenum disulfide (MoSor molybdenite), which is developing into graphene’s biggest two-dimensional material rival, into a flash memory prototype with improved performance.

The research, which was published in the journal ACS Nano (“Nonvolatile Memory Cells Based on MoS2/Graphene Heterostructures”), builds on the work EPFL had done in using molybdenite to create a working transistor. Since the development of a working transistor, the EPFL team has continued to focus its attention on the two-dimensional material to explore its potential applications.

To demonstrate the versatility of molybdenite, the Swiss researchers have combined it with graphene to create a flash memory prototype that is at least theoretically capable of being faster and with greater power efficiency than conventional silicon designs.

"Combining these two materials enabled us to make great progress in miniaturization, and also using these transistors we can make flexible nanoelectronic devices," says Andras Kis, author of the study, in a press release.

The flash memory prototype was built around field-effect geometry that forms the basis of field-effect transistors (FETs) used in complementary metal-oxide semiconductor (CMOS) electronics. In this case, the Swiss researchers replaced the silicon that would make up the middle layer of the sandwich-like device with the molybdenite. Graphene electrodes reside beneath this layer of molybdenite to transmit electricity into the molybdenite. The top layer of the device is several layers of graphene, which capture electrical charge and thereby stores memory.

The researchers believe this architecture should make for a more efficient flash memory design. The graphene is a much better at conducting electricity than silicon and the molybdenite is more sensitive to charge because it is far thinner than silicon.

This is all pretty early-stage at this point, so it's understandable that reports on this research seem to lack any discussion of its potential for commercialization. It’s not clear that marrying graphene and molybdenum will keep flash memory the king of the hill, but at a minimum, the king may have enlisted some new allies.

Novel Nanostructures Give Boost to Phase Change Memory

Flash memory is that non-volatile (NV) memory that everyone believes is ripe to be displaced in mobile electronics. But instead it has remained remarkably resilient undergoing just enough incremental improvements over the years to maintain its dominant position in the field.

Among the alternatives attempting to mount a commercial challenge to flash is phase-change random access memory (PCRAM or PRAM).  PRAM operates by heating a material in the memory cell that switches between a conductive crystalline phase and a resistive amorphous phase, imparting the binary characteristic necessary for memory.

While Samsung has commercialized PRAM with a 512Mb device, its writing current has to be reduced by at least one-third if it is to find wide adoption in mobile electronics, according to Korean Advanced Institute of Science and Technology (KAIST). Now those researchers claim to have taken a significant step towards achieving this lower power consumption by employing a new type of nanostructure for the PRAM.

The material, which is described in the journal ACS Nano ("Self-Assembled Incorporation of Modulated Block Copolymer Nanostructures in Phase-Change Memory for Switching Power Reduction"), employs self-assembled block copolymer silica nanostructures.  Block copolymers are particularly attractive in this application because they can produce self-ordered arrays with sub-20 nm features through relatively simple spin-coating and plasma treatments.

The real payoff with the new material is that it has resulted in a five-fold decrease in the required writing current, which corresponds to a power reduction of five percent.

One strategy for reducing switching power consumption in PRAM has been by decreasing the size of the contact area between the heating layer of the PRAM and the actual phase-change materials. The KAIST researchers achieved this by incorporating the silica nanostructures on top of the phase-change material.

"This is a very good example that self-assembled, bottom-up nanotechnology can actually enhance the performance of electronic devices,” says Keun-Jae Lee, one of the lead KAIST researchers, in a press release. “We also achieved a significant power reduction through a simple process that is compatible with conventional device structures and existing lithography tools."

Whether this will be the feature that can help PRAM compete with flash is not clear. But one can imagine that KAIST's national neighbor--Samsung--will be intrigued by this latest development.

Illustration: KAIST

Fungi Feasting on Daguerreotypes Help Reveal Nanoparticles

It’s always a bit astonishing to discover that ancient technologies like the Lycurgus Cup achieved their seemingly miraculous effects because of nanoparticles. Strictly speaking, these examples are not “nanotechnology” because the engineers who developed them did not create them intentionally or even understand how they worked. Nevertheless, these examples underline how nanotechnologies can impact the products that are around us—in some cases for centuries.

The latest addition to this list of old technologies enabled by nanotechnology was the recent discovery that daguerreotypes are in fact made up of nanoparticles. The revelation occurred after curators at George Eastman House International Museum of Photography and Film in Rochester, NY, started to notice that several of the daguerreotypes in their museum were fading or had a white haze that obscured the images.

The preservation of these images is critical because daguerreotypes represent the first form of photography when Louis-Jacques-Mandé Daguerre invented it in 1839. In addition to their historical significance, the incredible resolution that can be achieved with these images could instruct future optical technologies.

When the conservators at the Eastman House were unable to explain why the degradation was happening, they called upon Nicholas Bigelow, a physicist at the University of Rochester to determine the cause.  Bigelow confirmed earlier speculation that the damage to the images was being caused by fungi interacting with the surface of the daguerreotypes.

After discovering the cause, the Eastman House conservators started to store the images in argon gas to keep them in an a sort-of suspended animation to prevent the fungi from spreading until a more permanent solution can be developed. A video of this project can be seen below:

What may be even more significant about the work that Bigelow and his fellow researchers conducted is that it has shed further insight into the self-assembly of nanoparticles. By increasing control over the self-assembly of nanoparticles, researchers are developing better cancer treatments and a new generation of electronics.

Bigelow and his research team employed an arsenal of microscopy tools, including a focused ion beam, a scanning electron microscope and a transmission electron microscope, to determine what lay beneath the nanoparticles. They discovered there were holes, pores, and cavities that were at least part of the problem with the degradation of the daguerreotypes. But what may be a bust for daguerreotypes could be a boon for other nanoparticle applications in areas such as medicine for medical capsules, according to Bigelow in the press release.

The truth is that despite the latest microscopy tools, the researchers at the University of Rochester still don’t fully understand the fundamental physics at work with the nanoparticles in the daguerreotypes. If they can solve that riddle, a more permanent solution to preserving the images and developing new applications for the nanoparticles could be reached.

“Nobody really robustly understands what’s happening, either to create the image or what’s happening as the image degrades,” says Brian McIntyre, a senior engineer on the project. “Understanding the fundamental chemistry and physics of the daguerreotype process is seminal to understanding how to preserve them.”

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.”

Read More

'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.

Read More

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.

Read More

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.

Read More

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.

Read More


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

Dexter Johnson
Madrid, Spain
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
Load More