Flexible, Bendable Digital Storage made Possible by Spray-on (nanoparticle inks) Memory


sprayonmemorDuke University researchers have developed a new ‘spray-on’ digital memory (upper left) that could be used to build programmable electronic devices on flexible materials like paper, plastic or fabric. To demonstrate a simple application of …more

USB flash drives are already common accessories in offices and college campuses. But thanks to the rise in printable electronics, digital storage devices like these may soon be everywhere—including on our groceries, pill bottles and even clothing.

Duke University researchers have brought us closer to a future of low-cost, flexible electronics by creating a new “spray-on” digital memory using only an aerosol jet printer and nanoparticle inks.

The device, which is analogous to a 4-bit flash drive, is the first fully-printed digital memory that would be suitable for practical use in simple electronics such as environmental sensors or RFID tags. And because it is jet-printed at relatively low temperatures, it could be used to build programmable electronic devices on bendable materials like paper, plastic or fabric.

“We have all of the parameters that would allow this to be used for a practical application, and we’ve even done our own little demonstration using LEDs,” said Duke graduate student Matthew Catenacci, who describes the device in a paper published online March 27 in the Journal of Electronic Materials.

At the core of the new device, which is about the size of a postage stamp, is a new copper-nanowire-based printable material that is capable of storing digital information.

“Memory is kind of an abstract thing, but essentially it is a series of ones and zeros which you can use to encode information,” said Benjamin Wiley, an associate professor of chemistry at Duke and an author on the paper.

Most flash drives encode information in series of silicon transistors, which can exist in a charged state, corresponding to a “one,” and an uncharged state, corresponding to a “zero,” Wiley said.

Spray-on memory could enable bendable digital storage
Duke researchers demonstrated their new “spray-on” digital memory by programing a simple circuit to display four LED lights in different patterns. Credit: Duke University

 

 

 

 

 

The new material, made of silica-coated copper nanowires encased in a polymer matrix, encodes information not in states of charge but instead in states of resistance. By applying a small voltage, it can be switched between a state of high resistance, which stops electric current, and a state of low resistance, which allows current to flow.

And, unlike silicon, the nanowires and the polymer can be dissolved in methanol, creating a liquid that can be sprayed through the nozzle of a printer.

“We have developed a way to make the entire device printable from solution, which is what you would want if you wanted to apply it to fabrics, RFID tags, curved and flexible substrates, or substrates that can’t sustain high heat,” Wiley said.

To create the device, Catenacci first used commercially-available gold nanoparticle ink to print a series of gold electrodes onto a glass slide. He then printed the copper-nanowire memory material over the gold electrodes, and finally printed a second series of electrodes, this time in copper.

To demonstrate a simple application, Catenacci connected the device to a circuit containing four LED lights. “Since we have four bits, we could program sixteen different states,” Catenacci said, where each “state” corresponds to a specific pattern of lights. In a real-world application, each of these states could be programmed to correspond to a number, letter, or other display symbol.

Though other research groups have fabricated similar printable memory devices in recent years, this is the first to combine key properties that are necessary for practical use. The write speed, or time it takes to switch back and forth between , is around three microseconds, rivaling the speed of . Their tests indicate that written information may be retained for up to ten years, and the material can be re-written many times without degrading.

While these devices won’t be storing digital photos or music any time soon—their memory capacity is much too small for that—they may be useful in applications where low cost and flexibility are key, the researchers say.

“For example, right now RFID tags just encode a particular produce number, and they are typically used for recording inventory,” Wiley said. “But increasingly people also want to record what environment that product felt—such as, was this medicine always kept at the right temperature? One way these could be used would be to make a smarter RFID tags that could sense their environments and record the state over time.”

Explore further: Nanowire ‘inks’ enable paper-based printable electronics

More information: Matthew J. Catenacci et al, Fully Printed Memristors from Cu–SiO2 Core–Shell Nanowire Composites, Journal of Electronic Materials (2017). DOI: 10.1007/s11664-017-5445-5

 

Duke University: Silver nanowire inks enable paper-based printable electronics



By suspending tiny metal nanoparticles in liquids, Duke University scientists are brewing up conductive ink-jet printer “inks” to print inexpensive, customizable circuit patterns on just about any surface.

Printed electronics, which are already being used on a wide scale in devices such as the anti-theft radio frequency identification (RFID) tags you might find on the back of new DVDs, currently have one major drawback: for the circuits to work, they first have to be heated to melt all the nanoparticles together into a single conductive wire, making it impossible to print circuits on inexpensive plastics or paper.

A new study by Duke researchers shows that tweaking the shape of the nanoparticles in the ink might just eliminate the need for heat.

Silver Nanostructures

Duke University chemists have found that silver nanowire films like these conduct electricity well enough to form functioning circuits without applying high temperatures, enabling printable electronics on heat-sensitive materials like paper or plastic. (Image: Ian Stewart and Benjamin Wiley)

By comparing the conductivity of films made from different shapes of silver nanostructures, the researchers found that electrons zip through films made of silver nanowires much easier than films made from other shapes, like nanospheres or microflakes. In fact, electrons flowed so easily through the nanowire films that they could function in printed circuits without the need to melt them all together.

“The nanowires had a 4,000 times higher conductivity than the more commonly used silver nanoparticles that you would find in printed antennas for RFID tags,” said Benjamin Wiley, assistant professor of chemistry at Duke. “So if you use nanowires, then you don’t have to heat the printed circuits up to such high temperature and you can use cheaper plastics or paper.”

“There is really nothing else I can think of besides these silver nanowires that you can just print and it’s simply conductive, without any post-processing,” Wiley added.

These types of printed electronics could have applications far beyond smart packaging; researchers envision using the technology to make solar cells, printed displays, LEDS, touchscreens, amplifiers, batteries and even some implantable bio-electronic devices. The results appeared online in ACS Applied Materials and Interfaces (“Effect of Morphology on the Electrical Resistivity of Silver Nanostructure Films”).

Silver has become a go-to material for making printed electronics, Wiley said, and a number of studies have recently appeared measuring the conductivity of films with different shapes of silver nanostructures. However, experimental variations make direct comparisons between the shapes difficult, and few reports have linked the conductivity of the films to the total mass of silver used, an important factor when working with a costly material.

“We wanted to eliminate any extra materials from the inks and simply hone in on the amount of silver in the films and the contacts between the nanostructures as the only source of variability,” said Ian Stewart, a recent graduate student in Wiley’s lab and first author on the ACS paper.

Stewart used known recipes to cook up silver nanostructures with different shapes, including nanoparticles, microflakes, and short and long nanowires, and mixed these nanostructures with distilled water to make simple “inks.” He then invented a quick and easy way to make thin films using equipment available in just about any lab — glass slides and double-sided tape.

“We used a hole punch to cut out wells from double-sided tape and stuck these to glass slides,” Stewart said. By adding a precise volume of ink into each tape “well” and then heating the wells — either to relatively low temperature to simply evaporate the water or to higher temperatures to begin melting the structures together — he created a variety of films to test.

The team say they weren’t surprised that the long nanowire films had the highest conductivity. Electrons usually flow easily through individual nanostructures but get stuck when they have to jump from one structure to the next, Wiley explained, and long nanowires greatly reduce the number of times the electrons have to make this “jump”.

But they were surprised at just how drastic the change was. “The resistivity of the long silver nanowire films is several orders of magnitude lower than silver nanoparticles and only 10 times greater than pure silver,” Stewart said.

The team is now experimenting with using aerosol jets to print silver nanowire inks in usable circuits. Wiley says they also want to explore whether silver-coated copper nanowires, which are significantly cheaper to produce than pure silver nanowires, will give the same effect.

Source: Duke University

Scientists uncover navigation system used by cancer, nerve cells


Cancer Nerve System jhfkfffDuke University researchers have found a “roving detection system” on the surface of cells that may point to new ways of treating diseases like cancer, Parkinson’s disease and amyotrophic lateral sclerosis (ALS).

The , which were studied in nematode worms, are able to break through normal tissue boundaries and burrow into other tissues and organs—a crucial step in many normal developmental processes, ranging from embryonic development and wound-healing to the formation of new blood vessels.

But sometimes the process goes awry. Such is the case with metastatic cancer, in which cancer cells spread unchecked from where they originated and form tumors in other parts of the body.

“Cell invasion is one of the most clinically relevant yet least understood aspects of cancer progression,” said David Sherwood, an associate professor of biology at Duke.

 

Cancer Nerve System jhfkfff

Sherwood is leading a team that is investigating the molecular mechanisms that control in both normal development and cancer, using a one-millimeter worm known as C. elegans.

At one point in C. elegans development, a specialized cell called the anchor cell breaches the dense, sheet-like membrane that separate the worm’s uterus from its vulva, opening up the worm’s reproductive tract.

Anchor cells can’t see, so they need some kind of signal to tell them where to break through. In a 2009 study, Sherwood and colleagues discovered that an extracellular cue called netrin orients the anchor cell so that it invades in the right direction.

In a new study appearing Aug. 25 in the Journal of Cell Biology, the team shows how receptors on the invasive cells essentially rove around the cell membrane “hunting” for the missing netrin signal that will guide the cell to the correct location.

The researchers used a video camera attached to a powerful microscope to take time-lapse movies of the slow movement of the C. elegans anchor cell during its invasion.

Their time-lapse analyses reveal that when netrin production is blocked, netrin receptors on the surface of the anchor cell periodically cluster, disperse and reassemble in a different region of the cell membrane. The receptors cluster alongside patches of actin filaments—thin flexible fibers that help cells change shape and form invasive protrusions –- that pop up in ea

“It’s kind of like a missile detection system,” Sherwood said.

Rather than the whole cell having to move around, its receptors move around on the outside of the cell until they get a signal. Once the receptors locate the netrin signal, they stabilize in the region of the that is closest to the source of the signal.

The findings redefine decades-old ideas about how the cell’s navigation system works. “Cells don’t just passively respond to the netrin signal—they’re actively searching for it,” Sherwood said.

Given that netrin has been found to promote cell invasion in some of the most lethal cancers, the findings could lead to new treatment strategies. Disrupting the cell’s netrin detection system, for example, could prevent from finding their way to the bloodstream or the lymphatic system and stop them from metastasizing, or becoming invasive and spreading throughout the body.

“One of the things we’re gearing up to do next are drug screens with our collaborators to see if we can block this detection system during invasion,” Sherwood said.

Scientists have also known for years that netrin plays a key role in wiring the brain and nervous system by guiding developing nerve cells as they grow and form connections.

This means the results could also point to new ways of treating neurological disorders like Parkinson’s and ALS and recovering from spinal cord injuries.

Tinkering with the cell’s netrin detection machinery, for example, may make it possible to encourage damaged cells in the central nervous system—which normally have limited ability to regenerate—to regrow.

Explore further: Scientists unravel mystery of brain cell growth

 

 

 

Investing in Renewable Energy and Efficiency Can Significantly Lower Water Use


QDOTS imagesCAKXSY1K 8The U.S. could dramatically lower the power industry’s draw on strained water supplies by replacing aging power plants with water-smart options such as renewable energy and efficiency, according to a study recently released by the Union of Concerned Scientists-led “Energy and Water in a Warming World” Initiative.

Water-Smart Power: Strengthening the U.S. Electricity System in a Warming World claims the choices the industry makes now will decide how much the energy sector will tax the nation’s threatened water supplies and contribute to climate change in the decades to come.

More than 40 percent of U.S. freshwater withdrawals are used for power plant cooling, the report says. These plants also lose several billion gallons of freshwater every day through evaporation and increasing demand and drought are putting a greater strain on water resources.

Low water levels and high water temperatures also can cause power plants to cut their electricity output in order to avoid overheating or harming local water bodies. Such energy and water collisions can leave customers with little or no electricity or with added costs because their electric supplier has to purchase power from elsewhere, as occurred during the past two summers.

However, low natural gas prices and a rash of retirements of old and uncompetitive coal-fired power plants have prompted significant change in the power industry.

“Our electricity system clearly isn’t able to effectively meet our needs as we battle climate change and face a future of expanding electricity demand and increasing water strain,” said Doug Kenney, director of the Western Water Policy Program at the University of Colorado Law School. “As old plants are retired or retrofitted and new plants are built, we’ve got to untangle our competing demands for water and energy.”

Examining different paths the nation’s electricity production can take in the coming decades, the study says that while utilities’ ongoing shift to natural gas would decrease water use in the coming decades, its ongoing requirements could still harm water-strained areas. This shift to natural gas also would do little to lower the power sector’s carbon emissions.

“In our water-constrained world, a 20-year delay in tackling the problem leaves the power industry unnecessarily vulnerable to drought and exacerbates competition with other water users,” said John Rogers, co-manager of EW3 and a senior energy analyst with UCS’s Climate and Energy Program. “We can bring water use down faster and further, but only by changing how we get our electricity.”

According to the report, strong investments in renewables and energy efficiency could greatly reduce power generation’s water use and carbon emissions. Under such a scenario, water withdrawals would drop by 97 percent from current levels by 2050, with most of that drop within the next 20 years. This approach also would cut carbon emissions by 90 percent from current levels. A renewables path would also be a much cheaper path for consumers, the report found.

“We have a tremendous opportunity before us,” said Robert Jackson, an environmental scientist at Duke University. “By increasing energy efficiency and renewables, we can cut greenhouse gas emissions and water use, improve the quality of our water and air, and save money and lives at the same time. How often do we get a chance like that?”

The study concludes that many short-term options exist to reduce power sector water and climate risks such as prioritizing low-carbon, water-smart energy choices, such as renewable energy and energy efficiency; upgrading power plant cooling systems with technologies that ease local water stress; and instituting integrated resource planning that connects energy and water decision making.

Last month, Coca-Cola announced a new set of environmental goals, including returning 100 percent of the water from its manufacturing facilities back to the environment at a level that supports aquatic life by 2020. On Tuesday, Molson Coors Brewing Company announced that in 2012, its water intensity was seven percent lower than in 2008. Since 2008, the company reduced total water consumption by over 12.6 million hectoliters, equivalent to 504 Olympic swimming pools. Lower than expected volumes made it difficult to reduce water intensity and caused the company to fall short of its 2012 target of 15 percent reduction.