Category Archives: electronics

Hyper stretchable nanogenerator

There’s a lot of talk about flexibility, stretchability and bendability in electronics and the latest is coming from Korea. An April 13, 2015 Korea Advanced Institute for Science and Technology (KAIST) news release on EurekAlert describes the situation and the Korean scientists’ most recent research into stretchable electronics,

A research team led by Professor Keon Jae Lee of the Department of Materials Science and Engineering at the Korea Advanced Institute of Science and Technology (KAIST) has developed a hyper-stretchable elastic-composite energy harvesting device called a nanogenerator.

Flexible electronics have come into the market and are enabling new technologies like flexible displays in mobile phone, wearable electronics, and the Internet of Things (IoTs). However, is the degree of flexibility enough for most applications? For many flexible devices, elasticity is a very important issue. For example, wearable/biomedical devices and electronic skins (e-skins) should stretch to conform to arbitrarily curved surfaces and moving body parts such as joints, diaphragms, and tendons. They must be able to withstand the repeated and prolonged mechanical stresses of stretching. In particular, the development of elastic energy devices is regarded as critical to establish power supplies in stretchable applications. Although several researchers have explored diverse stretchable electronics, due to the absence of the appropriate device structures and correspondingly electrodes, researchers have not developed ultra-stretchable and fully-reversible energy conversion devices properly.

Recently, researchers from KAIST and Seoul National University (SNU) have collaborated and demonstrated a facile methodology to obtain a high-performance and hyper-stretchable elastic-composite generator (SEG) using very long silver nanowire-based stretchable electrodes. Their stretchable piezoelectric generator can harvest mechanical energy to produce high power output (~4 V) with large elasticity (~250%) and excellent durability (over 104 cycles). These noteworthy results were achieved by the non-destructive stress- relaxation ability of the unique electrodes as well as the good piezoelectricity of the device components. The new SEG can be applied to a wide-variety of wearable energy-harvesters to transduce biomechanical-stretching energy from the body (or machines) to electrical energy.

Professor Lee said, “This exciting approach introduces an ultra-stretchable piezoelectric generator. It can open avenues for power supplies in universal wearable and biomedical applications as well as self-powered ultra-stretchable electronics.”

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

A Hyper-Stretchable Elastic-Composite Energy Harvester by Chang Kyu Jeong, Jinhwan Lee, Seungyong Han, Jungho Ryu, Geon-Tae Hwang, Dae Yong Park, Jung Hwan Park, Seung Seob Lee, Mynghwan Byun, Seung Hwan Ko, and Keon Jae Lee. Advanced Materials DOI: 10.1002/adma.201500367 30 March 2015Full

This paper is behind a paywall.

The researchers have prepared a short video (22 secs. and silent),

3D printing soft robots and flexible electronics with metal alloys

This research comes from Purdue University (Indiana, US) which seems to be on a publishing binge these days. From an April 7, 2015 news item on Nanowerk,

New research shows how inkjet-printing technology can be used to mass-produce electronic circuits made of liquid-metal alloys for “soft robots” and flexible electronics.

Elastic technologies could make possible a new class of pliable robots and stretchable garments that people might wear to interact with computers or for therapeutic purposes. However, new manufacturing techniques must be developed before soft machines become commercially feasible, said Rebecca Kramer, an assistant professor of mechanical engineering at Purdue University.

“We want to create stretchable electronics that might be compatible with soft machines, such as robots that need to squeeze through small spaces, or wearable technologies that aren’t restrictive of motion,” she said. “Conductors made from liquid metal can stretch and deform without breaking.”

A new potential manufacturing approach focuses on harnessing inkjet printing to create devices made of liquid alloys.

“This process now allows us to print flexible and stretchable conductors onto anything, including elastic materials and fabrics,” Kramer said.

An April 7, 2015 Purdue University news release (also on EurekAlert) by Emil Venere, which originated the news item, expands on the theme,

A research paper about the method will appear on April 18 [2015] in the journal Advanced Materials. The paper generally introduces the method, called mechanically sintered gallium-indium nanoparticles, and describes research leading up to the project. It was authored by postdoctoral researcher John William Boley, graduate student Edward L. White and Kramer.

A printable ink is made by dispersing the liquid metal in a non-metallic solvent using ultrasound, which breaks up the bulk liquid metal into nanoparticles. This nanoparticle-filled ink is compatible with inkjet printing.

“Liquid metal in its native form is not inkjet-able,” Kramer said. “So what we do is create liquid metal nanoparticles that are small enough to pass through an inkjet nozzle. Sonicating liquid metal in a carrier solvent, such as ethanol, both creates the nanoparticles and disperses them in the solvent. Then we can print the ink onto any substrate. The ethanol evaporates away so we are just left with liquid metal nanoparticles on a surface.”

After printing, the nanoparticles must be rejoined by applying light pressure, which renders the material conductive. This step is necessary because the liquid-metal nanoparticles are initially coated with oxidized gallium, which acts as a skin that prevents electrical conductivity.

“But it’s a fragile skin, so when you apply pressure it breaks the skin and everything coalesces into one uniform film,” Kramer said. “We can do this either by stamping or by dragging something across the surface, such as the sharp edge of a silicon tip.”

The approach makes it possible to select which portions to activate depending on particular designs, suggesting that a blank film might be manufactured for a multitude of potential applications.

“We selectively activate what electronics we want to turn on by applying pressure to just those areas,” said Kramer, who this year was awarded an Early Career Development award from the National Science Foundation, which supports research to determine how to best develop the liquid-metal ink.

The process could make it possible to rapidly mass-produce large quantities of the film.

Future research will explore how the interaction between the ink and the surface being printed on might be conducive to the production of specific types of devices.

“For example, how do the nanoparticles orient themselves on hydrophobic versus hydrophilic surfaces? How can we formulate the ink and exploit its interaction with a surface to enable self-assembly of the particles?” she said.

The researchers also will study and model how individual particles rupture when pressure is applied, providing information that could allow the manufacture of ultrathin traces and new types of sensors.

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

Nanoparticles: Mechanically Sintered Gallium–Indium Nanoparticles by John William Boley, Edward L. White and Rebecca K. Kramer. Advanced Materials Volume 27, Issue 14, page 2270, April 8, 2015 DOI: 10.1002/adma.201570094 Article first published online: 7 APR 2015

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

Evolution-in-materio and unconventional computing

Training materials such as carbon nanotubes to imitate electronic circuits? Welcome to the world of evolution-in-materio and unconventional computing. From an April 7, 2015 news item on ScienceDaily,

As we approach the miniaturization limits of conventional electronics, alternatives to silicon-based transistors — the building blocks of the multitude of electronic devices we’ve come to rely on — are being hotly pursued.

Inspired by the way living organisms have evolved in nature to perform complex tasks with remarkable ease, a group of researchers from Durham University in the U.K. and the University of São Paulo-USP in Brazil is exploring similar “evolutionary” methods to create information processing devices.

An April 7, 2015 American Institute of Physics (AIP) news release on EurekAlert, which originated the news item, delves into the research itself and the emerging field to which it belongs,

In the Journal of Applied Physics, from AIP Publishing, the group describes using single-walled carbon nanotube composites (SWCNTs) as a material in “unconventional” computing. By studying the mechanical and electrical properties of the materials, they discovered a correlation between SWCNT concentration/viscosity/conductivity and the computational capability of the composite.

“Instead of creating circuits from arrays of discrete components (transistors in digital electronics), our work takes a random disordered material and then ‘trains’ the material to produce a desired output,” said Mark K. Massey, research associate, School of Engineering and Computing Sciences at Durham University.

This emerging field of research is known as “evolution-in-materio,” a term coined by Julian Miller at the University of York in the U.K. What exactly is it? An interdisciplinary field blends together materials science, engineering and computer science. Although still in its early stages, the concept has already shown that by using an approach similar to natural evolution, materials can be trained to mimic electronic circuits–without needing to design the material structure in a specific way.

“The material we use in our work is a mixture of carbon nanotubes and polymer, which creates a complex electrical structure,” explained Massey. “When voltages (stimuli) are applied at points of the material, its electrical properties change. When the correct signals are applied to the material, it can be trained or ‘evolved’ to perform a useful function.”

While the group doesn’t expect to see their method compete with high-speed silicon computers, it could turn out to be a complementary technology. “With more research, it could lead to new techniques for making electronics devices,” he noted. The approach may find applications within the realm of “analog signal processing or low-power, low-cost devices in the future.”

Beyond pursuing the current methodology of evolution-in-materio, the next stage of the group’s research will be to investigate evolving devices as part of the material fabrication “hardware-in-the-loop” evolution. “This exciting approach could lead to further enhancements in the field of evolvable electronics,” said Massey.

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

Computing with carbon nanotubes: Optimization of threshold logic gates using disordered nanotube/polymer composites by using disordered nanotube/polymer composites by M. K. Massey, A. Kotsialos, F. Qaiser, D. A. Zeze, C. Pearson, D. Volpati, L. Bowen, and M. C. Petty. J. Appl. Phys. 117, 134903 (2015); http://dx.doi.org/10.1063/1.4915343

This paper appears to be open access.

Also, the researchers have produced a video,

Credit: Mark Massey/Durham University

Final comment, I am gobsmacked and fascinated.

A more complex memristor: from two terminals to three for brain-like computing

Researchers have developed a more complex memristor device than has been the case according to an April 6, 2015 Northwestern University news release (also on EurekAlert),

Researchers are always searching for improved technologies, but the most efficient computer possible already exists. It can learn and adapt without needing to be programmed or updated. It has nearly limitless memory, is difficult to crash, and works at extremely fast speeds. It’s not a Mac or a PC; it’s the human brain. And scientists around the world want to mimic its abilities.

Both academic and industrial laboratories are working to develop computers that operate more like the human brain. Instead of operating like a conventional, digital system, these new devices could potentially function more like a network of neurons.

“Computers are very impressive in many ways, but they’re not equal to the mind,” said Mark Hersam, the Bette and Neison Harris Chair in Teaching Excellence in Northwestern University’s McCormick School of Engineering. “Neurons can achieve very complicated computation with very low power consumption compared to a digital computer.”

A team of Northwestern researchers, including Hersam, has accomplished a new step forward in electronics that could bring brain-like computing closer to reality. The team’s work advances memory resistors, or “memristors,” which are resistors in a circuit that “remember” how much current has flowed through them.

“Memristors could be used as a memory element in an integrated circuit or computer,” Hersam said. “Unlike other memories that exist today in modern electronics, memristors are stable and remember their state even if you lose power.”

Current computers use random access memory (RAM), which moves very quickly as a user works but does not retain unsaved data if power is lost. Flash drives, on the other hand, store information when they are not powered but work much slower. Memristors could provide a memory that is the best of both worlds: fast and reliable. But there’s a problem: memristors are two-terminal electronic devices, which can only control one voltage channel. Hersam wanted to transform it into a three-terminal device, allowing it to be used in more complex electronic circuits and systems.

The memristor is of some interest to a number of other parties prominent amongst them, the University of Michigan’s Professor Wei Lu and HP (Hewlett Packard) Labs, both of whom are mentioned in one of my more recent memristor pieces, a June 26, 2014 post.

Getting back to Northwestern,

Hersam and his team met this challenge by using single-layer molybdenum disulfide (MoS2), an atomically thin, two-dimensional nanomaterial semiconductor. Much like the way fibers are arranged in wood, atoms are arranged in a certain direction–called “grains”–within a material. The sheet of MoS2 that Hersam used has a well-defined grain boundary, which is the interface where two different grains come together.

“Because the atoms are not in the same orientation, there are unsatisfied chemical bonds at that interface,” Hersam explained. “These grain boundaries influence the flow of current, so they can serve as a means of tuning resistance.”

When a large electric field is applied, the grain boundary literally moves, causing a change in resistance. By using MoS2 with this grain boundary defect instead of the typical metal-oxide-metal memristor structure, the team presented a novel three-terminal memristive device that is widely tunable with a gate electrode.

“With a memristor that can be tuned with a third electrode, we have the possibility to realize a function you could not previously achieve,” Hersam said. “A three-terminal memristor has been proposed as a means of realizing brain-like computing. We are now actively exploring this possibility in the laboratory.”

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

Gate-tunable memristive phenomena mediated by grain boundaries in single-layer MoS2 by Vinod K. Sangwan, Deep Jariwala, In Soo Kim, Kan-Sheng Chen, Tobin J. Marks, Lincoln J. Lauhon, & Mark C. Hersam. Nature Nanotechnology (2015) doi:10.1038/nnano.2015.56 Published online 06 April 2015

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

Dexter Johnson has written about this latest memristor development in an April 9, 2015 posting on his Nanoclast blog (on the IEEE [Institute for Electrical and Electronics Engineers] website) where he notes this (Note: A link has been removed),

The memristor seems to generate fairly polarized debate, especially here on this website in the comments on stories covering the technology. The controversy seems to fall along the lines that the device that HP Labs’ Stan Williams and Greg Snider developed back in 2008 doesn’t exactly line up with the original theory of the memristor proposed by Leon Chua back in 1971.

It seems the ‘debate’ has evolved from issues about how the memristor is categorized. I wonder if there’s still discussion about whether or not HP Labs is attempting to develop a patent thicket of sorts.

Combining the best qualities of batteries and supercapacitors at the University of California at Los Angeles (UCLA)

There’s a reason why I’ve been feeling impatient about batteries and supercapacitors according to an April 2, 2015 news item on Nanowerk,

The dramatic rise of smartphones, tablets, laptops and other personal and portable electronics has brought battery technology to the forefront of electronics research. Even as devices have improved by leaps and bounds, the slow pace of battery development has held back technological progress.

Now, researchers at UCLA’s California NanoSystems Institute have successfully combined two nanomaterials to create a new energy storage medium that combines the best qualities of batteries and supercapacitors.

An April 1, 2015 UCLA news release, which originated the news item, describes the challenge and how the scientists addressed it (Note: A link has been removed),

Supercapacitors are electrochemical components that can charge in seconds rather than hours and can be used for 1 million recharge cycles. Unlike batteries, however, they do not store enough power to run our computers and smartphones.

The new hybrid supercapacitor stores large amounts of energy, recharges quickly and can last for more than 10,000 recharge cycles. The CNSI scientists also created a microsupercapacitor that is small enough to fit in wearable or implantable devices. Just one-fifth the thickness of a sheet of paper, it is capable of holding more than twice as much charge as a typical thin-film lithium battery.

The study, led by Richard Kaner, distinguished professor of chemistry and biochemistry and materials science and engineering, and Maher El-Kady, a postdoctoral scholar, was published in the Proceedings of the National Academy of Sciences.

“The microsupercapacitor is a new evolving configuration, a very small rechargeable power source with a much higher capacity than previous lithium thin-film microbatteries,” El-Kady said.

The new components combine laser-scribed graphene, or LSG — a material that can hold an electrical charge, is very conductive, and charges and recharges very quickly — with manganese dioxide, which is currently used in alkaline batteries because it holds a lot of charge and is cheap and plentiful. They can be fabricated without the need for extreme temperatures or the expensive “dry rooms” required to produce today’s supercapacitors.

“Let’s say you wanted to put a small amount of electrical current into an adhesive bandage for drug release or healing assistance technology,” Kaner said. “The microsupercapacitor is so thin you could put it inside the bandage to supply the current. You could also recharge it quickly and use it for a very long time.”

The researchers found that the supercapacitor could quickly store electrical charge generated by a solar cell during the day, hold the charge until evening and then power an LED overnight, showing promise for off-grid street lighting.

“The LSG–manganese-dioxide capacitors can store as much electrical charge as a lead acid battery, yet can be recharged in seconds, and they store about six times the capacity of state-of-the-art commercially available supercapacitors,” Kaner said. “This scalable approach for fabricating compact, reliable, energy-dense supercapacitors shows a great deal of promise in real-world applications, and we’re very excited about the possibilities for greatly improving personal electronics technology in the near future.”

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

Engineering three-dimensional hybrid supercapacitors and microsupercapacitors for high-performance integrated energy storage by Maher F. El-Kady, Melanie Ihns, Mengping Li, Jee Youn Hwang, Mir F. Mousavi, Lindsay Chaney, Andrew T. Lech, and Richard B. Kaner. Published online before print March 23, 2015, doi: 10.1073/pnas.1420398112 PNAS March 23, 2015

This paper is behind a paywall.

One last bit, Dexter Johnson in an April 3, 2015 post on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website) provides some insight into the research,

The story of graphene in supercapacitors can be represented by the old adage: its greatest strength is its greatest weakness. Of course, the name of the game in supercapacitor energy density is surface area. The greater the surface area, the greater number of ions you can store on the electrodes. While graphene has a theoretical surface area of 2630 square meters per gram, this density is only possible with a single, standalone graphene sheet.

But you can’t actually use a standalone sheet for the electrode of a supercapacitor because it will result in a very low volumetric capacitance. ….

So, while the 2-D characteristic of graphene may limit its usable surface area for supercapacitors, it does offer a way to make supercapacitors with small dimensions, something that would be impossible with activated carbon.

It is this strength that the CNSI researchers are aiming to exploit in their supercapacitor, which is small enough to be used as a wearable or implantable device. …

I recommend reading Dexter’s post in its entirety.

Water is key component to making sub-10nm semiconducting wires

An April 6, 2015 news item on phys.org announces a new technique for making nanowires,

Water is the key component in a Rice University process to reliably create patterns of metallic and semiconducting wires less than 10 nanometers wide.

The technique by the Rice lab of chemist James Tour builds upon its discovery that the meniscus – the curvy surface of water at its edge – can be an effective mask to make nanowires.

The Rice team of Tour and graduate students Vera Abramova and Alexander Slesarev have now made nanowires between 6 and 16 nanometers wide from silicon, silicon dioxide, gold, chromium, tungsten, titanium, titanium dioxide and aluminum. They have also made crossbar structures of conducting nanowires from one or more of the materials.

An April 6, 2015 Rice University news release (also on EurekAlert), which originated the news item, explains why this could have an impact on the semiconductor industry and provides a few more details about the process,

The process is promising for the semiconductor industry as it seeks to make circuits ever smaller. State-of-the-art integrated circuit fabrication allows for signal wires that approach 10 nanometers, visible only with powerful microscopes. These are the paths that connect the billions of transistors in modern electronic devices.

“This could have huge ramifications for chip production since the wires are easily made to sub-10-nanometer sizes,” Tour said of the Rice process. “There’s no other way in the world to do this en masse on a surface.”

Current approaches to making such tiny wires take several paths. Lithography, the standard method for etching integrated circuits, is approaching the physical limits of its ability to shrink them further. Bulk synthesis of semiconducting and metallic nanowires is also possible, but the wires are difficult to position in integrated circuits.

Water’s tendency to adhere to surfaces went from an annoyance to an advantage when the Rice researchers found they could use it as a mask to make patterns. The water molecules gather wherever a raised pattern joins the target material and forms a curved meniscus created by the surface tension of water.

The meniscus-mask process involves adding and then removing materials in a sequence that ultimately leaves a meniscus covering the wire and climbing the sidewall of a sacrificial metal mask that, when etched away, leaves the nanowire standing alone.

Tour said the process should work with modern fabrication technology with no modifications to existing equipment and minimal changes in fabrication protocols. No new tools or materials are needed.

The researchers have provided an image,

These nanowires were created at Rice University through a process called meniscus-mask lithography. From left, they’re made of silicon, silicon dioxide, gold, chromium, tungsten, titanium, titanium dioxide and aluminum. The scale bar is 1 micron for all images. (Credit: Tour Group/Rice University)

These nanowires were created at Rice University through a process called meniscus-mask lithography. From left, they’re made of silicon, silicon dioxide, gold, chromium, tungsten, titanium, titanium dioxide and aluminum. The scale bar is 1 micron for all images. (Credit: Tour Group/Rice University)

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

Meniscus-Mask Lithography for Fabrication of Narrow Nanowires by Vera V. Abramova, Alexander S Slesarev, and James M. Tour. Nano Lett., Just Accepted Manuscript DOI: 10.1021/nl504716u Publication Date (Web): March 31, 2015
Copyright © 2015 American Chemical Society

The paper is freely available but you do need to register on the site for open access.

Tel Aviv University and the quest for super-slim, bendable displays

It’s beginning to seem like the quest for the Holy Grail. That is, the search for an object more myth than fact, but researchers at Tel Aviv University (TAU) believe they are on the right track to develop a slim, flexible screen according to a March 30, 2015 news item on Nanowerk (Note: A link has been removed),

From smartphones and tablets to computer monitors and interactive TV screens, electronic displays are everywhere. As the demand for instant, constant communication grows, so too does the urgency for more convenient portable devices — especially devices, like computer displays, that can be easily rolled up and put away, rather than requiring a flat surface for storage and transportation.

A new Tel Aviv University study, published recently in Nature Nanotechnology (“Light-emitting self-assembled peptide nucleic acids exhibit both stacking interactions and Watson–Crick base pairing”), suggests that a novel DNA-peptide structure can be used to produce thin, transparent, and flexible screens. The research, conducted by Prof. Ehud Gazit and doctoral student Or Berger of the Department of Molecular Microbiology and Biotechnology at TAU’s Faculty of Life Sciences, in collaboration with Dr. Yuval Ebenstein and Prof. Fernando Patolsky of the School of Chemistry at TAU’s Faculty of Exact Sciences, harnesses bionanotechnology to emit a full range of colors in one pliable pixel layer — as opposed to the several rigid layers that constitute today’s screens.

A March 30, 2015 American Friends of Tel Aviv University news release, which originated the news item, describes the material’s advantages and how the researchers developed it,

“Our material is light, organic, and environmentally friendly,” said Prof. Gazit. “It is flexible, and a single layer emits the same range of light that requires several layers today. By using only one layer, you can minimize production costs dramatically, which will lead to lower prices for consumers as well.”

For the purpose of the study, a part of Berger’s Ph.D. thesis, the researchers tested different combinations of peptides: short protein fragments, embedded with DNA elements which facilitate the self-assembly of a unique molecular architecture.

Peptides and DNA are two of the most basic building blocks of life. Each cell of every life form is composed of such building blocks. In the field of bionanotechnology, scientists utilize these building blocks to develop novel technologies with properties not available for inorganic materials such as plastic and metal.

“Our lab has been working on peptide nanotechnology for over a decade, but DNA nanotechnology is a distinct and fascinating field as well. When I started my doctoral studies, I wanted to try and converge the two approaches,” said Berger. “In this study, we focused on PNA — peptide nucleic acid, a synthetic hybrid molecule of peptides and DNA. We designed and synthesized different PNA sequences, and tried to build nano-metric architectures with them.”

Using methods such as electron microscopy and X-ray crystallography, the researchers discovered that three of the molecules they synthesized could self-assemble, in a few minutes, into ordered structures. The structures resembled the natural double-helix form of DNA, but also exhibited peptide characteristics. This resulted in a very unique molecular arrangement that reflects the duality of the new material.

“Once we discovered the DNA-like organization, we tested the ability of the structures to bind to DNA-specific fluorescent dyes,” said Berger. “To our surprise, the control sample, with no added dye, emitted the same fluorescence as the variable. This proved that the organic structure is itself naturally fluorescent.”

The structures were found to emit light in every color, as opposed to other fluorescent materials that shine only in one specific color. Moreover, light emission was observed also in response to electric voltage — which make it a perfect candidate for opto-electronic devices like display screens.

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

Light-emitting self-assembled peptide nucleic acids exhibit both stacking interactions and Watson–Crick base pairing by Or Berger, Lihi Adler-Abramovich, Michal Levy-Sakin, Assaf Grunwald, Yael Liebes-Peer, Mor Bachar, Ludmila Buzhansky, Estelle Mossou, V. Trevor Forsyth, Tal Schwartz, Yuval Ebenstein, Felix Frolow, Linda J. W. Shimon, Fernando Patolsky, & Ehud Gazit. Nature Nanotechnology (2015) doi:10.1038/nnano.2015.27 Published online 16 March 2015

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

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.

Cells as capacitors and resistors concept is key to smart bandages

Bandages that can detect bedsores as they are forming are a distinct possibility with advances in flexible electronics and miniaturization according to researchers at the University of California at Berkeley and the University of California at San Francisco. From a March 17, 2015 University of California at Berkeley news release by Sarah Yang (also on EurekAlert),

Engineers at the University of California, Berkeley, are developing a new type of bandage that does far more than stanch the bleeding from a paper cut or scraped knee. Thanks to advances in flexible electronics, the researchers, in collaboration with colleagues at UC San Francisco, have created a new “smart bandage” that uses electrical currents to detect early tissue damage from pressure ulcers, or bedsores, before they can be seen by human eyes – and while recovery is still possible.

“We set out to create a type of bandage that could detect bedsores as they are forming, before the damage reaches the surface of the skin,” said Michel Maharbiz, a UC Berkeley associate professor of electrical engineering and computer sciences and head of the smart-bandage project. “We can imagine this being carried by a nurse for spot-checking target areas on a patient, or it could be incorporated into a wound dressing to regularly monitor how it’s healing.”

The researchers exploited the electrical changes that occur when a healthy cell starts dying. They tested the thin, non-invasive bandage on the skin of rats and found that the device was able to detect varying degrees of tissue damage consistently across multiple animals.

Bed sores are a big problem now and I imagine that as the population ages and more people find themselves in ill health, the problem will increase (from the news release),

Tackling a growing health problem

The findings, to be published Tuesday, March 17, in the journal Nature Communications, could provide a major boost to efforts to stem a health problem that affects an estimated 2.5 million U.S. residents at an annual cost of $11 billion.

Pressure ulcers, or bedsores, are injuries that can result after prolonged pressure cuts off adequate blood supply to the skin. Areas that cover bony parts of the body, such as the heels, hips and tailbone, are common sites for bedsores. Patients who are bedridden or otherwise lack mobility are most at risk.

“By the time you see signs of a bedsore on the surface of the skin, it’s usually too late,” said Dr. Michael Harrison, a professor of surgery at UCSF and a co-investigator of the study. “This bandage could provide an easy early-warning system that would allow intervention before the injury is permanent. If you can detect bedsores early on, the solution is easy. Just take the pressure off.”

Bedsores are associated with deadly septic infections, and recent research has shown that odds of a hospital patient dying are 2.8 times higher when they have pressure ulcers. The growing prevalence of diabetes and obesity has increased the risk factors for bedsores.

“The genius of this device is that it’s looking at the electrical properties of the tissue to assess damage. We currently have no other way to do that in clinical practice,” said Harrison. “It’s tackling a big problem that many people have been trying to solve in the last 50 years. As a clinician and someone who has struggled with this clinical problem, this bandage is great.”

The electrical components and their role in detecting bed sores is fascinating (from the news release),

Cells as capacitors and resistors

The researchers printed an array of dozens of electrodes onto a thin, flexible film. They discharged a very small current between the electrodes to create a spatial map of the underlying tissue based upon the flow of electricity at different frequencies, a technique called impedance spectroscopy.

The researchers pointed out that a cell’s membrane is relatively impermeable when functioning properly, thus acting like an insulator to the cell’s conductive contents and drawing the comparison to a capacitor. As a cell starts to die, the integrity of the cell wall starts to break down, allowing electrical signals to leak through, much like a resistor.

“Our device is a comprehensive demonstration that tissue health in a living organism can be locally mapped using impedance spectroscopy,” said study lead author Sarah Swisher, a Ph.D. candidate in electrical engineering and computer sciences at UC Berkeley.

To mimic a pressure wound, the researchers gently squeezed the bare skin of rats between two magnets. They left the magnets in place for one or three hours while the rats resumed normal activity. The resumption of blood flow after the magnets were removed caused inflammation and oxidative damage that accelerated cell death. The smart bandage was used to collect data once a day for at least three days to track the progress of the wounds.

The smart bandage was able to detect changes in electrical resistance consistent with increased membrane permeability, a mark of a dying cell. Not surprisingly, one hour of pressure produced mild, reversible tissue damage while three hours of pressure produced more serious, permanent injury.

Promising future

“One of the things that makes this work novel is that we took a comprehensive approach to understanding how the technique could be used to observe developing wounds in complex tissue,” said Swisher. “In the past, people have used impedance spectroscopy for cell cultures or relatively simple measurements in tissue. What makes this unique is extending that to detect and extract useful information from wounds developing in the body. That’s a big leap.”

Maharbiz said the outlook for this and other smart bandage research is bright.

“As technology gets more and more miniaturized, and as we learn more and more about the responses the body has to disease and injury, we’re able to build bandages that are very intelligent,” he said. “You can imagine a future where the bandage you or a physician puts on could actually report a lot of interesting information that could be used to improve patient care.”

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

Impedance sensing device enables early detection of pressure ulcers in vivo by Sarah L. Swisher, Monica C. Lin, Amy Liao, Elisabeth J. Leeflang, Yasser Khan, Felippe J. Pavinatto, Kaylee Mann, Agne Naujokas, David Young, Shuvo Roy, Michael R. Harrison, Ana Claudia Arias, Vivek Subramanian, & Michel M. Maharbiz. Nature Communications 6, Article number: 6575 doi:10.1038/ncomms7575 Published 17 March 2015

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

Finally, one of the researchers describes the work in this 1 min. 31 secs. video,

Two Irelands-US research initiative: UNITE

Happy St. Patrick’s Day on March 17, 2015! Researchers, building on an earlier collaborative effort (FOCUS), have announced a new US-Ireland initiative, from a March 9, 2015 news item on Nanowerk,

A three-year US-Ireland collaborative scientific project aims to reduce power consumption and increase battery life in mobile devices. Researchers will explore new semiconducting materials in the miniaturisation of transistors which are essential to all portable devices.

Leading researchers from the Republic of Ireland (Tyndall National Institute & Dublin City University), Northern Ireland (Queens University Belfast) and the US (University of Texas at Dallas) – each funded by their respective government agencies – are collaborating to develop ultra-efficient electronic materials through the UNITE project: Understanding the Nature of Interfaces in Two-Dimensional Electronic Devices.

A March 9, 2015 (?) Tyndall National Institute press release, which originated the news item, details the project, the researchers, and the hoped for applications,

UNITE will create and test the properties of atomically-thin, 2-dimensional layers of semiconductors called, Transition Metal Dichalcogenides or TMD’s for short. These layers are 100,000 times smaller than the smallest thing the human eye can see. The properties these materials have displayed to date suggest that they could facilitate extremely efficient power usage and high performance computing.

Tyndall’s lead researcher Dr. Paul Hurley explains that, “materials that we are currently reliant on, such as silicon, are soon expected to reach the limit of their performance. If we want to continue to increase performance, while maintaining or even reducing power consumption, it is important to explore these new TMD materials.”

The application of these materials in transistors could prolong the battery charge life of portable devices and phones, as well as having applications in larger more power intensive operations like data storage and server centres. This will have obvious environmental benefits through the reduction of electrical energy consumed by information and communication technologies as well as benefitting consumers.

UNITE builds on a previous highly successful US-Ireland collaborative project between these academic research partners called FOCUS. The success of this project played a role in demonstrating why funders should back the new project, including training for five graduate students in the USA and Ireland, as well as student exchanges between the Institutes, which will provide a broader scientific and cultural experience for the graduates involved.

The press release goes on to describe FOCUS, the researchers’ prior collaborative project,

UNITE builds on a previous highly successful US-Ireland collaborative project between these academic research partners called FOCUS. The success of this project played a role in demonstrating why funders should back the new project, including training for five graduate students in the USA and Ireland, as well as student exchanges between the Institutes, which will provide a broader scientific and cultural experience for the graduates involved.

A March 13, 2015 (?) Tyndall National Institute press release describes both an event to celebrate the success enjoyed by FOCUS and gives specifics about the achievements,

FOCUS, a US-Ireland collaborative project will be presented as a research success highlight to An Taoiseach Enda Kenny on St. Patrick’s Day along with industry and academic leaders, at a Science Foundation Ireland (SFI) event in Washington DC. The event is to celebrate the SFI St. Patrick’s Day Science Medal Award and is an important occasion on the St. Patrick’s Day schedule in the USA.

Funded under the US-Ireland R&D Partnership Programme, FOCUS (Future Oxides and Channel Materials for Ultimate Scaling) linked researchers in Tyndall National Institute (Dr Paul Hurley), Dublin City University (Prof. Greg Hughes), Queen’s University Belfast (Dr David McNeill) and the University of Texas at Dallas (Prof. Robert Wallace).

Billions of silicon-based transistors are crammed onto a single chip and used in billions of electronic devices around the world such as computers, laptops and mobile phones. The FOCUS project group investigated if it was possible to use alternative materials to silicon in the active channels of transistors to improve their energy efficiency and battery life.

The consortium explored using Germanium and Indium-Gallium-Arsenide in combination with high dielectric constant oxides as a viable alternative to silicon. Their research was able to improve the electronic properties of these alternative semiconductor/oxide interfaces to the level needed for practical device applications and the outcomes of their research have now moved to industry for practical application.

The key achievements from the project include:

  • Strong collaboration with Intel USA and Intel Ireland resulting in Paul Hurley receiving the Intel Outstanding Researcher Award in 2012
  • Presentation of the project findings at the annual Intel European Research and Innovation Conference
  • 3 Postdocs trained and 5 PhDs awarded in areas of strong interest to semiconductor manufacturers
  • 35 journal papers published
  • 2011 article on InGaAs surface treatment optimisation listed as one of the top 10 most cited articles in the Journal of Applied Physics in 2012
  • 10 invited presentations at key scientific conferences
  • University research partnership established between Tyndall National Institute and University of Texas at Dallas
  • Project highlighted in Irish press, The Times of India and The Irish Voice
  • Visit by the Consul General of Ireland to University of Texas at Dallas
  • Numerous students and staff exchanges between all partner institutions

Good luck to the UNITE project!