Tag Archives: nanowires

Atomic force microscope with nanowire sensors

Measuring the size and direction of forces may become reality with a nanotechnology-enabled atomic force microscope designed by Swiss scientists, according to an Oct. 17, 2016 news item on phys.org,

A new type of atomic force microscope (AFM) uses nanowires as tiny sensors. Unlike standard AFM, the device with a nanowire sensor enables measurements of both the size and direction of forces. Physicists at the University of Basel and at the EPF Lausanne have described these results in the recent issue of Nature Nanotechnology.

A nanowire sensor measures size and direction of forces (Image: University of Basel, Department of Physics)

A nanowire sensor measures size and direction of forces (Image: University of Basel, Department of Physics)

An Oct. 17, 2016 University of Basel press release (also on EurekAlert), which originated the news item, expands on the theme,

Nanowires are extremely tiny filamentary crystals which are built-up molecule by molecule from various materials and which are now being very actively studied by scientists all around the world because of their exceptional properties.

The wires normally have a diameter of 100 nanometers and therefore possess only about one thousandth of a hair thickness. Because of this tiny dimension, they have a very large surface in comparison to their volume. This fact, their small mass and flawless crystal lattice make them very attractive in a variety of nanometer-scale sensing applications, including as sensors of biological and chemical samples, and as pressure or charge sensors.

Measurement of direction and size

The team of Argovia Professor Martino Poggio from the Swiss Nanoscience Institute (SNI) and the Department of Physics at the University of Basel has now demonstrated that nanowires can also be used as force sensors in atomic force microscopes. Based on their special mechanical properties, nanowires vibrate along two perpendicular axes at nearly the same frequency. When they are integrated into an AFM, the researchers can measure changes in the perpendicular vibrations caused by different forces. Essentially, they use the nanowires like tiny mechanical compasses that point out both the direction and size of the surrounding forces.

Image of the two-dimensional force field

The scientists from Basel describe how they imaged a patterned sample surface using a nanowire sensor. Together with colleagues from the EPF Lausanne, who grew the nanowires, they mapped the two-dimensional force field above the sample surface using their nanowire “compass”. As a proof-of-principle, they also mapped out test force fields produced by tiny electrodes.

The most challenging technical aspect of the experiments was the realization of an apparatus that could simultaneously scan a nanowire above a surface and monitor its vibration along two perpendicular directions. With their study, the scientists have demonstrated a new type of AFM that could extend the technique’s numerous applications even further.

AFM – today widely used

The development of AFM 30 years ago was honored with the conferment of the Kavli-Prize [2016 Kavli Prize in Nanoscience] beginning of September this year. Professor Christoph Gerber of the SNI and Department of Physics at the University of Basel is one of the awardees, who has substantially contributed to the wide use of AFM in different fields, including solid-state physics, materials science, biology, and medicine.

The various different types of AFM are most often carried out using cantilevers made from crystalline Si as the mechanical sensor. “Moving to much smaller nanowire sensors may now allow for even further improvements on an already amazingly successful technique”, Martino Poggio comments his approach.

I featured an interview article with Christoph Gerber and Gerd Binnig about their shared Kavli prize and about inventing the AFM in a Sept. 20, 2016 posting.

As for the latest innovation, here’s a link to and a citation for the paper,

Vectorial scanning force microscopy using a nanowire sensor by Nicola Rossi, Floris R. Braakman, Davide Cadeddu, Denis Vasyukov, Gözde Tütüncüoglu, Anna Fontcuberta i Morral, & Martino Poggio. Nature Nanotechnology (2016) doi:10.1038/nnano.2016.189 Published online 17 October 2016

This paper is behind a paywall.

Small, soft, and electrically functional: an injectable biomaterial

This development could be looked at as a form of synthetic biology without the genetic engineering. From a July 1, 2016 news item on ScienceDaily,

Ideally, injectable or implantable medical devices should not only be small and electrically functional, they should be soft, like the body tissues with which they interact. Scientists from two UChicago labs set out to see if they could design a material with all three of those properties.

The material they came up with, published online June 27, 2016, in Nature Materials, forms the basis of an ingenious light-activated injectable device that could eventually be used to stimulate nerve cells and manipulate the behavior of muscles and organs.

“Most traditional materials for implants are very rigid and bulky, especially if you want to do electrical stimulation,” said Bozhi Tian, an assistant professor in chemistry whose lab collaborated with that of neuroscientist Francisco Bezanilla on the research.

The new material, in contrast, is soft and tiny — particles just a few micrometers in diameter (far less than the width of a human hair) that disperse easily in a saline solution so they can be injected. The particles also degrade naturally inside the body after a few months, so no surgery would be needed to remove them.

A July 1, 2016 University of Chicago news release (also on EurekAlert) by , which originated the news item, provides more detail,

Each particle is built of two types of silicon that together form a structure full of nano-scale pores, like a tiny sponge. And like a sponge, it is squishy — a hundred to a thousand times less rigid than the familiar crystalline silicon used in transistors and solar cells. “It is comparable to the rigidity of the collagen fibers in our bodies,” said Yuanwen Jiang, Tian’s graduate student. “So we’re creating a material that matches the rigidity of real tissue.”

The material constitutes half of an electrical device that creates itself spontaneously when one of the silicon particles is injected into a cell culture, or, eventually, a human body. The particle attaches to a cell, making an interface with the cell’s plasma membrane. Those two elements together — cell membrane plus particle — form a unit that generates current when light is shined on the silicon particle.

“You don’t need to inject the entire device; you just need to inject one component,” João L. Carvalho-de-Souza , Bezanilla’s postdoc said. “This single particle connection with the cell membrane allows sufficient generation of current that could be used to stimulate the cell and change its activity. After you achieve your therapeutic goal, the material degrades naturally. And if you want to do therapy again, you do another injection.”

The scientists built the particles using a process they call nano-casting. They fabricate a silicon dioxide mold composed of tiny channels — “nano-wires” — about seven nanometers in diameter (less than 10,000 times smaller than the width of a human hair) connected by much smaller “micro-bridges.” Into the mold they inject silane gas, which fills the pores and channels and decomposes into silicon.

And this is where things get particularly cunning. The scientists exploit the fact the smaller an object is, the more the atoms on its surface dominate its reactions to what is around it. The micro-bridges are minute, so most of their atoms are on the surface. These interact with oxygen that is present in the silicon dioxide mold, creating micro-bridges made of oxidized silicon gleaned from materials at hand. The much larger nano-wires have proportionately fewer surface atoms, are much less interactive, and remain mostly pure silicon. [I have a note regarding ‘micro’ and ‘nano’ later in this posting.]

“This is the beauty of nanoscience,” Jiang said. “It allows you to engineer chemical compositions just by manipulating the size of things.”

Web-like nanostructure

Finally, the mold is dissolved. What remains is a web-like structure of silicon nano-wires connected by micro-bridges of oxidized silicon that can absorb water and help increase the structure’s softness. The pure silicon retains its ability to absorb light.

Transmission electron microscopy image shows an ordered nanowire array. The 100-nanometer scale bar is 1,000 times narrower than a hair. Courtesy of Tian Lab

Transmission electron microscopy image shows an ordered nanowire array. The 100-nanometer scale bar is 1,000 times narrower than a hair. Courtesy of
Tian Lab

The scientists have added the particles onto neurons in culture in the lab, shone light on the particles, and seen current flow into the neurons which activates the cells. The next step is to see what happens in living animals. They are particularly interested in stimulating nerves in the peripheral nervous system that connect to organs. These nerves are relatively close to the surface of the body, so near-infra-red wavelength light can reach them through the skin.

Tian imagines using the light-activated devices to engineer human tissue and create artificial organs to replace damaged ones. Currently, scientists can make engineered organs with the correct form but not the ideal function.

To get a lab-built organ to function properly, they will need to be able to manipulate individual cells in the engineered tissue. The injectable device would allow a scientist to do that, tweaking an individual cell using a tightly focused beam of light like a mechanic reaching into an engine and turning a single bolt. The possibility of doing this kind of synthetic biology without genetic engineering [emphasis mine] is enticing.

“No one wants their genetics to be altered,” Tian said. “It can be risky. There’s a need for a non-genetic system that can still manipulate cell behavior. This could be that kind of system.”

Tian’s graduate student Yuanwen Jiang did the material development and characterization on the project. The biological part of the collaboration was done in the lab of Francisco Bezanilla, the Lillian Eichelberger Cannon Professor of Biochemistry and Molecular Biology, by postdoc João L. Carvalho-de-Souza. They were, said Tian, the “heroes” of the work.

I was a little puzzled about the use of the word ‘micro’ in a context suggesting it was smaller than something measured at the nanoscale. Dr. Tian very kindly cleared up my confusion with this response in a July 4, 2016 email,

In fact, the definition of ‘micro’ and ’nano’ have been quite ambiguous in literature. For example, microporous materials (e.g., zeolite) usually refer to materials with pore sizes of less than 2 nm — this is defined based on IUPAC [International Union of Pure and Applied Chemistry] definition (http://goldbook.iupac.org/M03853.html). We used ‘micro-bridges’ because they come from the ‘micropores’ in the original template.

Thank you Dr. Tian for that very clear reply and Steve Koppes for forwarding my request to Dr. Tian!

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

Heterogeneous silicon mesostructures for lipid-supported bioelectric interfaces by Yuanwen Jiang, João L. Carvalho-de-Souza, Raymond C. S. Wong, Zhiqiang Luo, Dieter Isheim, Xiaobing Zuo, Alan W. Nicholls, Il Woong Jung, Jiping Yue, Di-Jia Liu, Yucai Wang, Vincent De Andrade, Xianghui Xiao, Luizetta Navrazhnykh, Dara E. Weiss, Xiaoyang Wu, David N. Seidman, Francisco Bezanilla, & Bozhi Tian. Nature Materials (2016)  doi:10.1038/nmat4673 Published online 27 June 2016

This paper is behind a paywall.

I gather animal testing will be the next step as they continue to develop this exciting technology. Good luck!

Observing nanostructures in attosecond time

German scientists have observed a phenomenon (light-matter interaction) that exists for attoseconds. (For anyone unfamiliar with that scale, micro = a millionth, nano = a billionth, pico = a trillionth, femto = a quadrillionth, and atto = a quintillionth.)  A May 31, 2016 news item on Nanowerk announces the work (Note: A link has been removed),

Physicists of the Laboratory for Attosecond Physics at the Max Planck Institute of Quantum Optics and the Ludwig-Maximilians-Universität Munich in collaboration with scientists from the Friedrich-Alexander-Universität Erlangen-Nürnberg have observed a light-matter phenomenon in nano-optics, which lasts only attoseconds (“Attosecond nanoscale near-field sampling”).

Here’s an illustration of the work,

When laser light interacts with a nanoneedle (yellow), electromagnetic near-fields are formed at its surface. A second laser pulse (purple) emits an electron (green) from the needle, permitting to characterize the near-fields. Image: Christian Hackenberger

When laser light interacts with a nanoneedle (yellow), electromagnetic near-fields are formed at its surface. A second laser pulse (purple) emits an electron (green) from the needle, permitting to characterize the near-fields.
Image: Christian Hackenberger

A May 31, 2016 Max Planck Institute of Quantum Optics press release (also on EurekAlert) by Thorsten Naeser, which originated the news item, describes the phenomenon and the work in more detail,

The interaction between light and matter is of key importance in nature, the most prominent example being photosynthesis. Light-matter interactions have also been used extensively in technology, and will continue to be important in electronics of the future. A technology that could transfer and save data encoded on light waves would be 100.000-times faster than current systems. A light-matter interaction which could pave the way to such light-driven electronics has been investigated by scientists from the Laboratory for Attosecond Physics (LAP) at the Ludwig-Maximilians-Universität (LMU) and the Max Planck Institute of Quantum Optics (MPQ), in collaboration with colleagues from the Chair for Laser Physics at the Friedrich-Alexander-Universität Erlangen-Nürnberg. The researchers sent intense laser pulses onto a tiny nanowire made of gold. The ultrashort laser pulses excited vibrations of the freely moving electrons in the metal. This resulted in electromagnetic ‘near-fields’ at the surface of the wire. The near-fields oscillated with a shift of a few hundred attoseconds with respect to the exciting laser field (one attosecond is a billionth of a billionth of a second). This shift was measured using attosecond light pulses which the scientists subsequently sent onto the nanowire.

When light illuminates metals, it can result in curious things in the microcosm at the surface. The electromagnetic field of the light excites vibrations of the electrons in the metal. This interaction causes the formation of ‘near-fields’ – electromagnetic fields localized close to the surface of the metal.

How near-fields behave under the influence of light has now been investigated by an international team of physicists at the Laboratory for Attosecond Physics of the Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics in close collaboration with scientists of the Chair for Laser Physics at the Friedrich-Alexander-Universität Erlangen-Nürnberg.

The researchers sent strong infrared laser pulses onto a gold nanowire. These laser pulses are so short that they are composed of only a few oscillations of the light field. When the light illuminated the nanowire it excited collective vibrations of the conducting electrons surrounding the gold atoms. Through these electron motions, near-fields were created at the surface of the wire.

The physicists wanted to study the timing of the near-fields with respect to the light fields. To do this they sent a second light pulse with an extremely short duration of just a couple of hundred attoseconds onto the nanostructure shortly after the first light pulse. The second flash released individual electrons from the nanowire. When these electrons reached the surface, they were accelerated by the near-fields and detected. Analysis of the electrons showed that the near-fields were oscillating with a time shift of about 250 attoseconds with respect to the incident light, and that they were leading in their vibrations. In other words: the near-field vibrations reached their maximum amplitude 250 attoseconds earlier than the vibrations of the light field.

“Fields and surface waves at nanostructures are of central importance for the development of lightwave-electronics. With the demonstrated technique they can now be sharply resolved.”, explained Prof. Matthias Kling, the leader of the team carrying out the experiments in Munich.

The experiments pave the way towards more complex studies of light-matter interaction in metals that are of interest in nano-optics and the light-driven electronics of the future. Such electronics would work at the frequencies of light. Light oscillates a million billion times per second, i.e. with petahertz frequencies – about 100.000 times faster than electronics available at the moment. The ultimate limit of data processing could be reached.

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

Attosecond nanoscale near-field sampling by B. Förg, J. Schötz, F. Süßmann, M. Förster, M. Krüger, B. Ahn, W. A. Okell, K. Wintersperger, S. Zherebtsov, A. Guggenmos, V. Pervak, A. Kessel, S. A. Trushin, A. M. Azzeer, M. I. Stockman, D. Kim, F. Krausz, P. Hommelhoff, & M. F. Kling.  Nature Communications 7, Article number: 11717  doi:10.1038/ncomms11717 Published 31 May 2016

This paper is open access.

Getting too hot? Strap on your personal cooling unit

Individual cooling units for firefighters, foundry workers, and others working in hot conditions are still in the future but if Pennsylvania State University (Penn State) researchers have their way that future is a lot closer than it was. From an April 29, 2016 news item on Nanotechnology Now,

Firefighters entering burning buildings, athletes competing in the broiling sun and workers in foundries may eventually be able to carry their own, lightweight cooling units with them, thanks to a nanowire array that cools, according to Penn State materials researchers.

An April 28, 2016 Penn State news release by A’ndrea Elyse Messer, which originated the news item, describes some of the concepts and details some of the technology,

“Most electrocaloric ceramic materials contain lead,” said Qing Wang, professor of materials science and engineering. “We try not to use lead. Conventional cooling systems use coolants that can be environmentally problematic as well. Our nanowire array can cool without these problems.”

Electrocaloric materials are nanostructured materials that show a reversible temperature change under an applied electric field. Previously available electrocaloric materials were single crystals, bulk ceramics or ceramic thin films that could cool, but are limited because they are rigid, fragile and have poor processability. Ferroelectric polymers also can cool, but the electric field needed to induce cooling is above the safety limit for humans.

Wang and his team looked at creating a nanowire material that was flexible, easily manufactured and environmentally friendly and could cool with an electric field safe for human use. Such a material might one day be incorporated into firefighting gear, athletic uniforms or other wearables. …

Their vertically aligned ferroelectric barium strontium titanate nanowire array can cool about 5.5 degrees Fahrenheit using 36 volts, an electric field level safe for humans. A 500 gram battery pack about the size of an IPad could power the material for about two hours.

The researchers grow the material in two stages. First, titanium dioxide nanowires are grown on fluorine doped tin oxide coated glass. The researchers use a template so all the nanowires grow perpendicular to the glass’ surface and to the same height. Then the researchers infuse barium and strontium ions into the titanium dioxide nanowires.

The researchers apply a nanosheet of silver to the array to serve as an electrode.

They can move this nanowire forest from the glass substrate to any substrate they want — including clothing fabric — using a sticky tape.

“This low voltage is good enough for modest exercise and the material is flexible,” said Wang. “Now we need to design a system that can cool a person and remove the heat generated in cooling from the immediate area.”

This solid state personal cooling system may one day become the norm because it does not require regeneration of coolants with ozone depletion and global warming potentials and could be lightweight and flexible.

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

Toward Wearable Cooling Devices: Highly Flexible Electrocaloric Ba0.67Sr0.33TiO3 Nanowire Arrays by Guangzu Zhang, Xiaoshan Zhang, Houbing Huang, Jianjun Wang, Qi Li, Long-Qing Chen, and Qing Wang. Advanced Materials DOI: 10.1002/adma.201506118 Article first published online: 27 APR 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

One final comment, I’m trying to imagine a sport where an athlete would willingly wear any material that adds weight. Isn’t an athlete’s objective is to have lightweight clothing and footwear so nothing impedes performance?

Listening to bacteria for superior organic nanowires

Researchers at Michigan State University (MSU; US) claim to have  discovered organic nanowires that are superior to the engineered kind according to a March 24, 2016 news item on ScienceDaily,

A microbial protein fiber discovered by a Michigan State University scientist transports charges at rates high enough to be applied in humanmade nanotechnologies.

The discovery, featured in the current issue of Scientific Reports, describes the high-speed protein fiber produced by uranium-reducing Geobacter bacteria. The fibers are hair-like protein filaments called “pili” that have the unique property of transporting charges at speeds of 1 billion electrons per second.

A March 24, 2016 MSU news release, which originated the news item, provides more information,

“This microbial nanowire is made of but a single peptide subunit,” said Gemma Reguera, lead author and MSU microbiologist. “Being made of protein, these organic nanowires are biodegradable and biocompatible. This discovery thus opens many applications in nanoelectronics such as the development of medical sensors and electronic devices that can be interfaced with human tissues.”

Since existing nanotechnologies incorporate exotic metals into their designs, the cost of organic nanowires is much more cost effective as well, she added.

How the nanowires function in nature is comparable to breathing. Bacterial cells, like humans, have to breathe. The process of respiration involves moving electrons out of an organism. Geobacter bacteria use the protein nanowires to bind and breathe metal-containing minerals such as iron oxides and soluble toxic metals such as uranium. The toxins are mineralized on the nanowires’ surface, preventing the metals from permeating the cell.

Reguera’s team purified their protein fibers, which are about 2 nanometers in diameter. Using the same toolset of nanotechnologists, the scientists were able to measure the high velocities at which the proteins were passing electrons.

“They are like power lines at the nanoscale,” Reguera said. “This also is the first study to show the ability of electrons to travel such long distances — more than a 1,000 times what’s been previously proven — along proteins.”

The researchers also identified metal traps on the surface of the protein nanowires that bind uranium with great affinity and could potentially trap other metals. These findings could provide the basis for systems that integrate protein nanowires to mine gold and other precious metals, scrubbers that can be deployed to immobilize uranium at remediation sites and more.

Reguera’s nanowires also can be modified to seek out other materials in which to help them breathe.

“The Geobacter cells are making these protein fibers naturally to breathe certain metals. We can use genetic engineering to tune the electronic and biochemical properties of the nanowires and enable new functionalities. We also can mimic the natural manufacturing process in the lab to mass-produce them in inexpensive and environmentally friendly processes,” Reguera said. “This contrasts dramatically with the manufacturing of humanmade inorganic nanowires, which involve high temperatures, toxic solvents, vacuums and specialized equipment.”

This discovery came from truly listening to bacteria, Reguera said.

“The protein is getting the credit, but we can’t forget to thank the bacteria that invented this,” she said. “It’s always wise to go back and ask bacteria what else they can teach us. In a way, we are eavesdropping on microbial conversations. It’s like listening to our elders, learning from their wisdom and taking it further.”

Asking what else bacteria can teach us? That’s a lovely thought and  different from the still common ‘let’s wipe them all out’ approach to bacteria. It suggests scientific research that is more amenable to sharing the planet with all forms of life.

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

Thermally activated charge transport in microbial protein nanowires by Sanela Lampa-Pastirk, Joshua P. Veazey, Kathleen A. Walsh, Gustavo T. Feliciano, Rebecca J. Steidl, Stuart H. Tessmer, & Gemma Reguera. Scientific Reports 6, Article number: 23517 (2016) doi:10.1038/srep23517 Published online: 24 March 2016

This paper is open access.

Korean researchers fabricate cross-shaped memristors

I’ve been a bit late getting this Korean research concerning memristors into a posting. A Jan. 30, 2016 news item on Nanotechnology Now announces a new means of fabricating memristors,

Along with the fast development of modern information technology, charge-based memories, such as DRAM and flash memory, are being aggressively scaled down to meet the current trend of small size devices. A memory device with high density, faster speed, and low power consumption is desired to satisfy Moore’s law in the next few decades. Among the candidates of next-generation memory devices, cross-bar-shaped non-volatile resistive memory (memristor) is one of the most attractive solutions for its non-volatility, faster access speed, ultra-high density and easier fabrication process.

Conventional memristors are usually fabricated through conventional optical, imprint, and e-beam lithographic approaches. However, to meet Moore’s law, the assembly of memristors comprised of 1-dimensional (1D) nanowires must be demonstrated to achieve cell dimensions beyond limit of state-of-art lithographic techniques, thus allowing one to fully exploit the scaling potential of high density memory array.

Prof. Tae-Woo Lee (Dept. of Materials Science and Engineering) and his research team have developed a rapid printing technology for high density and scalable memristor array composed of cross-bar-shaped metal nanowires. The research team, which consists of Prof. Tae-Woo Lee, research professor Wentao Xu, and doctoral student Yeongjun Lee at POSTECH [Pohang University of Science and Technology], Korea, published their findings in Advanced Materials.

A Jan. 28, 2016 POSTECH news release, which originated the news item, expands on the theme,

They applied an emerging technique, electrohydrohynamic nanowire printing (e-NW printing), which directly prints highly-aligned nanowire array on a large scale into the fabrication of microminiature memristors, with cross-bar-shaped conductive Cu nanowires jointed with a nanometer-scale CuxO layer. The metal-oxide-metal structure resistive memory device exhibited excellent electrical performance with reproducible resistive switching behavior.

This simple and fast fabrication process avoids conventional vacuum techniques to significantly reduce the industrial-production cost and time. This method paved the way to the future down-scaling of electronic circuits, since 1D conductors represent a logical way to extreme scaling of data processing devices in the single-digit nanometer scale.

They also succeeded in printing memristor array with various shapes, such as parallel lines with adjustable pitch, grids, and waves which can offer a future stretchable memory for integration into textile to serve as a basic building block for smart fabrics and wearable electronics.

“This technology reduces lead time and cost remarkably compared with existing manufacturing methods of cross-bar-shaped nanowire memory and simplifies its method of construction,” said Prof. Lee. “In particular, this technology will be used as a source technology to realize smart fabric, wearable computers, and textile electronic devices.”

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

[Nanowires:] Simple, Inexpensive, and Rapid Approach to Fabricate Cross-Shaped Memristors Using an Inorganic-Nanowire-Digital-Alignment Technique and a One-Step Reduction Process by Wentao Xu, Yeongjun Lee, Sung-Yong Min, Cheolmin Park, andTae-Woo Lee. Advanced Materials Volume 28, Issue 3 January 20, 2016 Page 591  DOI: 10.1002/adma.201503153 Article first published online: 20 NOV 2015

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

This paper is behind a paywall.

Better neuroprostheses for brain diseases and mental illneses

I don’t often get news releases from Sweden but I do on occasion and, sometimes, they even come in their original Swedish versions. In this case, Lund University sent me an English language version about their latest work making brain implants (neural prostheses) safer and effective. From a Sept. 29, 2015 Lund University news release (also on EurekAlert),

Neurons thrive and grow in a new type of nanowire material developed by researchers in Nanophysics and Ophthalmology at Lund University in Sweden. In time, the results might improve both neural and retinal implants, and reduce the risk of them losing their effectiveness over time, which is currently a problem

By implanting electrodes in the brain tissue one can stimulate or capture signals from different areas of the brain. These types of brain implants, or neuro-prostheses as they are sometimes called, are used to treat Parkinson’s disease and other neurological diseases.

They are currently being tested in other areas, such as depression, severe cases of autism, obsessive-compulsive disorders and paralysis. Another research track is to determine whether retinal implants are able to replace light-sensitive cells that die in cases of Retinitis Pigmentosa and other eye diseases.

However, there are severe drawbacks associated with today’s implants. One problem is that the body interprets the implants as foreign objects, resulting in an encapsulation of the electrode, which in turn leads to loss of signal.

One of the researchers explains the approach adopted by the research team (from the news release),

“Our nanowire structure prevents the cells that usually encapsulate the electrodes – glial cells – from doing so”, says Christelle Prinz, researcher in Nanophysics at Lund University in Sweden, who developed this technique together with Maria Thereza Perez, a researcher in Ophthalmology.

“I was very pleasantly surprised by these results. In previous in-vitro experiments, the glial cells usually attach strongly to the electrodes”, she says.

To avoid this, the researchers have developed a small substrate where regions of super thin nanowires are combined with flat regions. While neurons grow and extend processes on the nanowires, the glial cells primarily occupy the flat regions in between.

“The different types of cells continue to interact. This is necessary for the neurons to survive because the glial cells provide them with important molecules.”

So far, tests have only been done with cultured cells (in vitro) but hopefully they will soon be able to continue with experiments in vivo.

The substrate is made from the semiconductor material gallium phosphide where each outgrowing nanowire has a diameter of only 80 nanometres (billionths of a metre).

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

Support of Neuronal Growth Over Glial Growth and Guidance of Optic Nerve Axons by Vertical Nanowire Arrays by Gaëlle Piret, Maria-Thereza Perez, and Christelle N. Prinz. ACS Appl. Mater. Interfaces, 2015, 7 (34), pp 18944–18948 DOI: 10.1021/acsami.5b03798 Publication Date (Web): August 11, 2015

Copyright © 2015 American Chemical Society

This paper appears to be open access as I was able to link to the PDF version.

LEDs (light-emitting diodes) that need less energy and give better light

A June 24, 2015 University of Copenhagen Niels Bohr Institute press release (also on EurekAlert), announces research that could lead to a brighter future (pun intended),

The researchers [from the Niels Bohr Institute] studied nanowires using X-ray microscopy and with this method they can pinpoint exactly how the nanowire should be designed to give the best properties. …

Nanowires are very small – about 2 micrometers high (1 micrometer is a thousandth of a millimetre) and 10-500 nanometers in diameter (1 nanometer is a thousandth of a micrometer). Nanowires for LEDs are made up of an inner core of gallium nitride (GaN) and a layer of indium-gallium-nitride (InGaN) on the outside, both of which are semiconducting materials.

“The light in such a diode is dependent on the mechanical strain that exists between the two materials and the strain is very dependent on how the two layers are in contact with each other. We have examined a number of nanowires using X-ray microscopy and even though the nanowires should in principle be identical, we can see that they are different and have very different structure,” explains Robert Feidenhans’l, professor and head of the Niels Bohr Institute at the University of Copenhagen.

Surprisingly efficient

The studies were performed using nanoscale X-ray microscopy in the electron synchrotron at DESY in Hamburg, Germany. The method is usually very time consuming and the results are often limited to very few or even a single study subject. But here researchers have managed to measure a series of upright nanowires all at once using a special design of a nanofocused X-ray without destroying the nanowires in the process.

“We measured 20 nanowires and when we saw the images, we were very surprised because you could clearly see the details of each nanowire. You can see the structure of both the inner core and the outer layer. If there are defects in the structure or if they are slightly bent, they do not function as well. So we can identify exactly which nanowires are the best and have the most efficient core/shell structure,” explains Tomas Stankevic, a PhD student in the research group ‘Neutron and X-ray Scattering’ at the Niels Bohr Institute at the University of Copenhagen.

The nanowires are produced by a company in Sweden and this new information can be used to tweak the layer structure in the nanowires. Professor Robert Feidenhans’l explains that there is great potential in such nanowires. They will provide a more natural light in LEDs and they will use much less power. In addition, they could be used in smart phones, televisions and many forms of lighting.

The researchers expect that things could go very quickly and that they may already be in use within five years.

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

Fast Strain Mapping of Nanowire Light-Emitting Diodes Using Nanofocused X-ray Beams by Tomaš Stankevič, Emelie Hilner, Frank Seiboth, Rafal Ciechonski, Giuliano Vescovi, Olga Kryliouk, Ulf Johansson, Lars Samuelson, Gerd Wellenreuther, Gerald Falkenberg, Robert Feidenhans’l, and Anders Mikkelsen.
ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b01291
Publication Date (Web): June 19, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Sensing smoke with nanoscale sensors

A Feb. 17, 2015 news item on Nanowerk notes that current smoke sensors are ultra-violet light detectors in the context of research about developing better ones,

Researchers at the University of Surrey’s [UK] Advanced Technology Institute manipulated zinc oxide, producing nanowires from this readily available material to create a ultra-violet light detector which is 10,000 times more sensitive to UV light than a traditional zinc oxide detector.

A Feb. 17, 2015 University of Surrey press release (also on EurekAlert), which originated the news item, provides more detail about the work and the theory (Note: Links have been removed),

Currently, photoelectric smoke sensors detect larger smoke particles found in dense smoke, but are not as sensitive to small particles of smoke from rapidly burning fires.

Researchers believe that this new material could increase sensitivity and allow the sensor to detect distinct particles emitted at the early stages of fires, paving the way for specialist sensors that can be deployed in a number of applications.

“UV light detectors made from zinc oxide have been used widely for some time but we have taken the material a step further to massively increase its performance,” said Professor Ravi Silva, co-author of the study and head of the Advanced Technology Institute. “Essentially, we transformed zinc oxide from a flat film to a structure with bristle-like nanowires, increasing surface area and therefore increasing sensitivity and reaction speed.”

The team predict that the applications for this material could be far-reaching. From fire and gas detection to air pollution monitoring, they believe the sensor could also be incorporated into personal electronic devices – such as phones and tablets – to increase speed, with a response time 1,000 times faster than traditional zinc oxide detectors.

“This is a great example of a bespoke, designer nanomaterial that is adaptable to personal needs, yet still affordable. Due to the way in which this material is manufactured, it is ideally suited for use in future flexible electronics – a hugely exciting area,” added Professor Silva.

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

On-chip Fabrication of High Performance Nanostructured ZnO UV Detectors by Mohammad R. Alenezi, Simon J. Henley, & S. R. P. Silva. Scientific Reports 5, Article number: 8516 doi:10.1038/srep08516 Published 17 February 2015

This paper is open access.

Shrinky Dinks* instrumental for new nanowires technique

Shrinky Dinks, a material used for children’s arts and crafts projects, has proved instrumental for developing a new technique to close the gap between nanowires. From a July 1, 2014 news item on Nanowerk (Note: A link has been removed),

How do you put a puzzle together when the pieces are too tiny to pick up? Shrink the distance between them.

Engineers at the University of Illinois at Urbana-Champaign are using Shrinky Dinks, plastic that shrinks under high heat, to close the gap between nanowires in an array to make them useful for high-performance electronics applications. The group published its technique in the journal Nano Letters (“Assembly and Densification of Nanowire Arrays via Shrinkage”).

A July 1, 2014 University of Illinois at Urbana-Champaign news release, which originated the news item, provides more details about the new technique,

Nanowires are extremely fast, efficient semiconductors, but to be useful for electronics applications, they need to be packed together in dense arrays. Researchers have struggled to find a way to put large numbers of nanowires together so that they are aligned in the same direction and only one layer thick.

“Chemists have already done a brilliant job in making nanowires exhibit very high performance. We just don’t have a way to put them into a material that we can handle,” said study leader SungWoo Nam, a professor of mechanical science and engineering at the U. of I. “With the shrinking approach, people can make nanowires and nanotubes using any method they like and use the shrinking action to compact them into a higher density.”

The researchers place the nanowires on the Shrinky Dinks plastic as they would for any other substrate, but then shrink it to bring the wires much closer together. This allows them to create very dense arrays of nanowires in a simple, flexible and very controllable way.

The shrinking method has the added bonus of bringing the nanowires into alignment as they increase in density. Nam’s group demonstrated how even wires more than 30 degrees off-kilter can be brought into perfect alignment with their neighbors after shrinking.

“There’s assembly happening at the same time as the density increases,” Nam said, “so even if the wires are assembled in a disoriented direction we can still use this approach.”

The plastic is clamped before baking so that it only shrinks in one direction, so that the wires pack together but do not buckle. Clamping in different places could direct the arrays into interesting formations, according to Nam. The researchers also can control how densely the wires pack by varying the length of time the plastic is heated. They also are exploring using lasers to precisely shrink the plastic in specific patterns.

Nam first had the idea for using Shrinky Dinks plastic to assemble nanomaterials after seeing a microfluidics device that used channels made of shrinking plastic. He realized that the high degree of shrinking and the low cost of plastic could have a huge impact on nanowire assembly and processing for applications.

“I’m interested in this concept of synthesizing new materials that are assembled from nanoscale building blocks,” Nam said. “You can create new functions. For example, experiments have shown that film made of packed nanowires has properties that differ quite a bit from a crystal thin film.”

One application the group is now exploring is a thin film solar cell, made of densely packed nanowires, that could harvest energy from light much more efficiently than traditional thin-film solar cells.

I have featured the Shrinky Dinks product and its use for nanoscale fabrication before in an Aug. 16, 2010 posting which featured this reply from the lead researcher for that project on nanopatterning,

ETA Aug.17.10: I also contacted Teri W. Odom, professor at Northwestern University about why they use Slinky Dinks in their work. She very kindly responded with this:

Part of what we are interested in is the development of low-cost nanofabrication tools that can create macroscale areas of nanoscale patterns in a single step. For a variety of reasons, this end-product is hard to obtain—even though we and others have chipped away at this problem for years.

As an example, to achieve smaller and smaller separations between patterns, either expensive, top-down serial tools (such as electron beam lithography or scanning probe techniques) or bottom-up assembly methods need to be used. However, the former cannot easily create large areas of patterns, and the latter cannot readily control the separations of patterns.

We needed a way to obtain nanopatterns separated by specific distances on-demand. Here is where the Shrinky Dinks material comes in. My student had read a paper (published in 2007 in Lab on a Chip) about how this material was used to make microscale patterns starting from a pattern printed using a laser printer. I imagine his thought was: if this material could be used for microscale patterns, why not for nanoscale ones? It would be cheap, and it’s easy to order.

So, we combined this substrate with our new molding method—solvent assisted nanoscale embossing (SANE)—and could now heat the material to shrink the spacing between patterns. And thus, in some sense, we made available to any lab some of the capabilities of the billion-dollar nanofabrication industry for less than one-hundred dollars.

Getting back to this latest use of Shrinky Dinks, here’s a link to and a citation for the ‘nanowires’ research paper,

Assembly and Densification of Nanowire Arrays via Shrinkage by Jaehoon Bang, Jonghyun Choi, Fan Xia, Sun Sang Kwon, Ali Ashraf, Won Il Park, and SungWoo Nam. Nano Lett., 2014, 14 (6), pp 3304–3308 DOI: 10.1021/nl500709p Publication Date (Web): May 16, 2014
Copyright © 2014 American Chemical Society

This paper is behind a paywall.

* ‘dinks’ in headline changed to ‘Dinks’ on July 2, 2014 at 1150 hours PDT.