Tag Archives: nanowires

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.

Solar cells and copper sprouts

First, Washington University in St. Louis (WUSTL; located in Missouri, US) announced a discovery about solar cells, then, the university announced a commitment to increase solar output by Fall 2014. Whether these two announcements are linked by some larger policy or strategy is not clear to me but it’s certainly an interesting confluence of events.

An April 26, 2014 news item on Azonano describes the researchers’ discovery,

By looking at a piece of material in cross section, Washington University in St. Louis engineer Parag Banerjee, PhD, and his team discovered how copper sprouts grass-like nanowires that could one day be made into solar cells.

Banerjee, assistant professor of materials science and an expert in working with nanomaterials, Fei Wu, graduate research assistant, and Yoon Myung, PhD, a postdoctoral research associate, also took a step toward making solar cells and more cost-effective.

An April 21, 2014 WUSTL news release by Beth Miller, which originated the news item, describes the research in some detail,

Banerjee and his team worked with copper foil, a simple material similar to household aluminum foil. When most metals are heated, they form a thick metal oxide film. However, a few metals, such as copper, iron and zinc, grow grass-like structures known as nanowires, which are long, cylindrical structures a few hundred nanometers wide by many microns tall. They set out to determine how the nanowires grow.

“Other researchers look at these wires from the top down,” Banerjee says. “We wanted to do something different, so we broke our sample and looked at it from the side view to see if we got different information, and we did.”

The team used Raman spectroscopy, a technique that uses light from a laser beam to interact with molecular vibrations or other movements. They found an underlying thick film made up of two different copper oxides (CuO and Cu2O) that had narrow, vertical columns of grains running through them. In between these columns, they found grain boundaries that acted as arteries through which the copper from the underlying layer was being pushed through when heat was applied, creating the nanowires.

“We’re now playing with this ionic transport mechanism, turning it on and off and seeing if we can get some different forms of wires,” says Banerjee, who runs the Laboratory for Emerging and Applied Nanomaterials (L.E.A.N.).

Like solar cells, the nanowires are single crystal in structure, or a continuous piece of material with no grain boundaries, Banerjee says.

“If we could take these and study some of the basic optical and electronic properties, we could potentially make solar cells,” he says. “In terms of optical properties, copper oxides are well-positioned to become a solar energy harvesting material.”

This work may be useful in other applications according to the news release,

The find may also benefit other engineers who want to use single crystal oxides in scientific research. Manufacturing single crystal Cu2O for research is very expensive, Banerjee says, costing up to about $1,500 for one crystal.

“But if you can live with this form that’s a long wire instead of a small crystal, you can really use it to study basic scientific phenomena,” Banerjee says.

Banerjee’s team also is looking for other uses for the nanowires, including acting as a semiconductor between two materials, as a photocatalyst, a photovoltaic or an electrode for splitting water.

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

Unravelling transient phases during thermal oxidation of copper for dense CuO nanowire growth by Fei Wu, Yoon Myunga and Parag Banerjee.  CrystEngComm, 2014,16, 3264-3267. DOI: 10.1039/C4CE00275J First published online 26 Feb 2014

This article is behind a paywall.

Shortly after the research announcement, WUSTL made this ‘solar’ announcement via an April 29, 2014 news release by Neil Schoenherr,

Washington University in St. Louis is moving forward with a bold and impactful plan to increase solar output on all campuses by 1,150 percent over current levels by this fall. The project demonstrates the university’s commitment to sustainable operations and to reducing its environmental impact in the St. Louis region and beyond.

This spring and early summer, the university will add a total of 379 kilowatts (kw) of solar on university-owned property throughout the region. Prior to this installation, the university had 33 kw that were installed as demonstration projects.

I suspect the two announcements reflect synchronicity or, perhaps, my tendency to see and develop patterns.

Ahoy me hearties! A new theory for Damascus steel

I hope I got that right. It’s been a long time since I’ve seen a pirate movie but talk of Damascus steel meant that I had to have at least one movie pirate-type phrase in this piece.

I first came across Damascus steel outside the pirate movie domain in 2007 about the time that researchers declared blades made of Damascus steel sported carbon nanotubes giving  the blades their legendary qualities. From a Nov. 16, 2006 National Geographic article by Mason Inman,

New studies of Damascus swords are revealing that the legendary blades contain nanowires, carbon nanotubes, and other extremely small, intricate structures that might explain their unique features.

Damascus swords, first made in the eighth century A.D., are renowned for their complex surface patterns and sharpness. According to legend, the blades can cut a piece of silk in half as it falls to the ground and maintain their edge after cleaving through stone, metal, or even other swords.

Now studies of the swords’ molecular structure are uncovering the tiny structures that may explain these properties.

Peter Paufler, a crystallographer at Technical University in Dresden, Germany, and his colleagues had previously found tiny nanowires and nanotubes when they used an electron microscope to examine samples from a Damascus blade made in the 17th century.

It seems that while researchers were able to answer some questions about the blade’s qualities, researchers in China believe they may have answered the question about the blade’s unique patterns, from a March 12, 2014 news release on EurekAlert,

Blacksmiths and metallurgists in the West have been puzzled for centuries as to how the unique patterns on the famous Damascus steel blades were formed. Different mechanisms for the formation of the patterns and many methods for making the swords have been suggested and attempted, but none has produced blades with patterns matching those of the Damascus swords in the museums. The debate over the mechanism of formation of the Damascus patterns is still ongoing today. Using modern metallurgical computational software (Thermo-Calc, Stockholm, Sweden), Professor Haiwen Luo of the Central Iron and Steel Research Institute in Beijing, together with his collaborator, have analyzed the relevant published data relevant to the Damascus blades, and present a new explanation that is different from other proposed mechanisms.

Before the development of tanks, guns, and cannons, humans fought with swords, and there was one type of sword in particular that everyone wanted, a Damascus sword. Western Europeans first encountered these swords in the hands of Muslim warriors in Damascus about a thousand years ago. Damascus swords were prized for their strength and sharpness. They were famous for being so sharp that they could cut a silk scarf in half as it fell to ground, something that European swords could not do. Both Mediterranean and European blacksmiths believed that the outstanding strength and sharpness of the swords resulted from their beauty, i.e., the Damascus pattern. This presents as a wavy pattern like a rose and ladder on the surface of Damascus blades, as shown in Fig. 1. It was recorded that blacksmiths in Persia made the best Damascus steel swords by hammering a small cake of Wootz steel, which was a high-quality steel ingot imported from ancient India. The best European blade smiths from the Middle Ages onwards were not able to fabricate similar blades, even though they carefully studied examples made in the East. Damascus blades became even more mysterious when the art of making them actually died out. Despite all the knowledge and technological advances of the 21st century, people are still debating the mechanism through which such beautiful patterns were formed on Damascus blades.

Here’s the figure showing a blade and its pattern,

Caption: This is an example of a Damascus sword with a typical Damascus pattern of Muhammad ladder and rose. Microstructural examination of the blade indicates that rows of cementite particles (in black) form the Damascus patterns[11]. Credit: ©Science China Press

Caption: This is an example of a Damascus sword with a typical Damascus pattern of Muhammad ladder and rose. Microstructural examination of the blade indicates that rows of cementite particles (in black) form the Damascus patterns[11].
Credit: ©Science China Press

The news release goes on,

The compositions and microstructures of many existing Damascus steel blades have been examined previously. Their C contents are within the range of 1 wt.%, and often around 1.6 wt.%. It is also known that the Damascus pattern results from the band-like formation of coarse cementite particles. The high C content leads to a large amount of cementite particles being precipitated during hot hammering. After proper etching, the coarse cementite bands appear white within the dark matrix, such that they form a visible pattern on the surface. After the 1970s, the mechanism for the formation of the Damascus pattern was revisited and debated, particularly by Professors Verhoeven from Iowa State University and Sherby from Stanford University. Sherby and his co-workers[1-4] thought that a coarse cementite network was formed around the large austenite grains, when the Wootz steel cake was cooled slowly in crucibles for several days after melting. Later, the continuous cementite network was broken into spheroidal particles during extensive hammering at relatively low temperatures between cherry (850 °C) and blood red (650 °C), rather than the white heat customarily used by European blacksmiths. Furthermore, Wootz steel cake must be used in the manufacture of genuine Damascus blades. The low-temperature hammering was also a key technology, by which Wootz steels were easily hot deformed without cracking, and finer carbide particles precipitated to make the steel stronger and tougher. However, Verhoeven et al. though that the Damascus pattern was related to the microsegregation of solutes during solidification. They carried out experiments on two genuine Damascus blades during which the carbides were removed completely by dissolution treatment, followed by quenching. It was shown that the planar arrays of carbide particles could be made to return, together with the surface pattern, by thermal cycling, whereas the Sherby mechanism requires the cementite particles formed on the boundaries of the large austenite grains to be retained during deformation. Hence, they argued strongly that the surface patterns formed on genuine Damascus steel blades should result from a type of microsegregation-induced carbide banding that requires thermal cycling[5-10]. In particular, the dendritic segregation of V was considered the most likely reason for carbide banding[11].

However, compositional examinations of some existing Damascus steel blades revealed that many of them contain almost no V or any other carbide-forming elements. Moreover, it is apparent that the ancient craftsmen making Wootz steels had no concept of alloying with particular elements such as V. As Wootz steel cakes have been discovered in many parts of the ancient Indian region, it is unlikely that the iron ores in all those places happened to contain V or other certain types of carbide-forming elements. Therefore, the explanation proposed by Verhoeven et al. is also less than convincing.

Luo et al. adopted a new method to approach this puzzle. Using an advanced metallurgical computational software package (Thermo-Calc), all possible factors, such as the influence of S, P, and V elements on the Fe-C phase diagram, precipitation of V(CN), diffusion of V in austenite, and the dendritic segregation of S and P during solidification were quantified, because they have all been considered as possible prerequisites for forming Damascus patterns. The calculations indicated that V(CN) particles precipitate or dissolve at temperatures much lower than cementite in cases with a low content of V, as is commonly found in Damascus steels (see Fig. 2a). Instead, the sulfide and phosphide could precipitate at the dendritic zone because of the severe segregation during slow solidification. In particular, the remaining P-rich liquid at the end of solidification might transform to a eutectic product of phosphide and cementite (Fig. 2b), which cannot be distinguished from cementite under an optical microscope. The high concentration of P will not be homogenized by diffusion after a short dissolution treatment, such that cementite might re-precipitate in the P-segregated regions. Therefore, the dendritic segregation of P influences the spatial distribution of cementite in Damascus blades and thus, the patterns are formed.

Luo et al. also suggested that their method could be widely employed to tackle other puzzles similar to that of the Damascus patterns, because today’s knowledge is so well developed that reliable theoretical computations are now possible. Although people were capable of making Damascus steel swords containing ultrahigh carbon contents (1 wt.%) a long time ago, it is surprising that almost all modern steels in use contain C contents below 1 wt.%. However, with future developments of knowledge and technology, it is expected that ultrahigh carbon steels. e.g., Wootz steels, will once again find important applications, because the best of the new is often the long-forgotten past.

I want to draw attention to two elements that distinguish this news release, the request from the authors and the bibliographic notes (I don’t recall seeing bibliographies appended to a news release before),

Note from the authors: It would be much appreciated if anyone would like to donate a piece of genuine Damascus blade for our research.

Corresponding Author:

LUO Haiwen
Email: [email protected]

References

1. Sherby O D, Wadsworth J. Damascus Steels. Sci Amer, 1985,252:112-118

2. Wadsworth J, Sherby O D. On the Bulat Damascus steels revisited. Prog Mater Sci, 1980,25:35-68

3. Sherby O D, Wadsworth J. Ancient blacksmiths, the Iron Age, Damascus steels, and modern metallurgy. J of Mater Processing Techno, 2001,117:347-352

4. Wadsworth J, Sherby O D. Response to Verhoeven comments on Damascus steel. Mater Charact, 2001, 47: 163

5. Verhoeven J D, Pendary A H. Origin of the Damask pattern in Damascus steel blades. Mater Charact, 2001, 47: 423

6. Verhoeven J D, Pendary A H. On the origin of the Damask pattern of Damascus steels. Mater Charact, 2001, 47: 79

7. Verhoeven J D, Baker H H, Peterson D T, et al. Damascus Steel, Part III—The Wadsworth-Sherby mechanism. Mater Charact, 1990, 24:205

8. Verhoeven J D, Pendary A H, Gibson E D. Wootz Damascus steel blades. Mater Charact, 1996, 37: 9

9. Verhoeven J D, Pendary A H. Studies of Damascus steel blades: Part I—Experiments on reconstructed blades. Mater Charact, 1993, 30:175

10. Verhoeven J D, Pendary A H, Berge P M. Studies of Damascus steel blades: Part II—Destruction and reformation of the patterns. Mater Charact, 1993, 30: 187

11. Verhoeven J D, Pendray A. The mystery of the Damascus sword. Muse, 1998, 2: 35

Here’s a link to and a citation for the paper (you will likely need Chinese language skills to read it, although there is an English language abstract on the page),

Theoretic analysis on the mechanism of particular pattern formed on the ancient Damascus steel blades by LUO HaiWen, QIAN Wei, and DONG Han. Chinese Science Bulletin, 2014(9)

I believe the paper is behind a paywall. Finally, I hope the researchers are able to obtain a piece of genuine Damascus steel blade for their studies.

Biology and lithium-air batteries

Firstly, the biology in question is that of viruses and, secondly, research in lithium-air batteries has elicited big interest according to David Chandler’s November 13, 2013 Massachusetts Institute of Technology (MIT) news piece (also on EurekAlert and Nanowerk),

Lithium-air batteries have become a hot research area in recent years: They hold the promise of drastically increasing power per battery weight, which could lead, for example, to electric cars with a much greater driving range. But bringing that promise to reality has faced a number of challenges, ….

Now, MIT researchers have found that adding genetically modified viruses to the production of nanowires — wires that are about the width of a red blood cell, and which can serve as one of a battery’s electrodes — could help solve some of these problems.

Lithium-air batteries can also be referred to as lithiium-oxygen batteries, although Chandler does not choose to mix terms as he goes on to describe the process the researchers developed,

The researchers produced an array of nanowires, each about 80 nanometers across, using a genetically modified virus called M13, which can capture molecules of metals from water and bind them into structural shapes. In this case, wires of manganese oxide — a “favorite material” for a lithium-air battery’s cathode, Belcher says — were actually made by the viruses. But unlike wires “grown” through conventional chemical methods, these virus-built nanowires have a rough, spiky surface, which dramatically increases their surface area.

Belcher, the W.M. Keck Professor of Energy and a member of MIT’s Koch Institute for Integrative Cancer Research, explains that this process of biosynthesis is “really similar to how an abalone grows its shell” — in that case, by collecting calcium from seawater and depositing it into a solid, linked structure.

The increase in surface area produced by this method can provide “a big advantage,” Belcher says, in lithium-air batteries’ rate of charging and discharging. But the process also has other potential advantages, she says: Unlike conventional fabrication methods, which involve energy-intensive high temperatures and hazardous chemicals, this process can be carried out at room temperature using a water-based process.

Also, rather than isolated wires, the viruses naturally produce a three-dimensional structure of cross-linked wires, which provides greater stability for an electrode.

A final part of the process is the addition of a small amount of a metal, such as palladium, which greatly increases the electrical conductivity of the nanowires and allows them to catalyze reactions that take place during charging and discharging. Other groups have tried to produce such batteries using pure or highly concentrated metals as the electrodes, but this new process drastically lowers how much of the expensive material is needed.

Altogether, these modifications have the potential to produce a battery that could provide two to three times greater energy density — the amount of energy that can be stored for a given weight — than today’s best lithium-ion batteries, a closely related technology that is today’s top contender, the researchers say.

MIT has produced a video highlighting the researchers’ work (this runs longer than most of the materials I embed here at approximately 11 mins. 25 secs.),

For those who want to know more about this intriguing and speculative work,

Biologically enhanced cathode design for improved capacity and cycle life for lithium-oxygen batteries by Dahyun Oh, Jifa Qi, Yi-Chun Lu, Yong Zhang, Yang Shao-Horn, & Angela M. Belcher. Nature Communications 4, Article number: 2756 doi:10.1038/ncomms3756 Published 13 November 2013

This article is behind a paywall.

ETA Nov. 15, 2013: Dexter Johnson offers more context and information, including commercialization issues, about lithium-air batteries and lithium-ion batteries in his Nov. 14, 2013 posting on the Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website).

Proteins which cause Alzheimer’s disease can be used to grow functionalized nanowires

This is the first time I’ve ever heard of anything good resulting from Alzheimer’s Disease (even if it’s tangential). From the May 24, 2013 news item on ScienceDaily,

Prof. Sakaguchi and his team in Graduate School of Science, Hokkaido University,jointly with MANA PI Prof. Kohei Uosaki and a research group from the University of California, Santa Barbara, have successfully developed a new technique for efficiently creating functionalized nanowires for the first time ever.

The group focused on the natural propensity of amyloid peptides, molecules which are thought to cause Alzheimer’s disease, to self-assemble into nanowires in an aqueous solution and controlled this molecular property to achieve their feat.

The May 23, 2013 National Institute for Materials press release, which originated the news item, offers insight into why functionalized nanowires are devoutly desired,

Functionalized nanowires are extremely important in the construction of nanodevices because they hold promise for use as integrated circuits and for the generation of novel properties, such as conductivity, catalysts and optical properties which are derived from their fine structure. However, some have remarked on the technical and financial limitations of the microfabrication technology required to create these structures. Meanwhile, molecular self-organization and functionalization have attracted attention in the field of next-generation nanotechnology development. Amyloid peptides, which are thought to cause Alzheimer’s disease, possess the ability to self-assemble into highly stable nanowires in an aqueous solution. Focusing on this, the research team became the first to successfully develop a new method for efficiently creating a multifunctional nanowire by controlling this molecular property.

The team designed a new peptide called SCAP, or structure-controllable amyloid peptide, terminated with a three-amino-acid-residue cap. By combining multiple SCAPs with different caps, the team found that self-organization is highly controlled at the molecular level. Using this new control method, the team formed a molecular nanowire with the largest aspect ratio ever achieved. In addition, they made modifications using various functional molecules including metals, semiconductors and biomolecules that successfully produced an extremely high quality functionalized nanowire. Going forward, this method is expected to contribute significantly to the development of new nanodevices through its application to a wide range of functional nanomaterials with self-organizing properties.

You can find the published paper here,

Formation of Functionalized Nanowires by Control of Self-Assembly Using Multiple Modified Amyloid Peptides by Hiroki Sakai, Ken Watanabe, Yuya Asanomi, Yumiko Kobayashi, Yoshiro Chuman, Lihong Shi, Takuya Masuda, Thomas Wyttenbach, Michael T. Bowers, Kohei Uosaki, & Kazuyasu Sakaguchi1. Advanced Functional Materials. doi: 10.1002/adfm.201300577 Article first published online: 23 APR 2013

The study is behind a paywall.

I have written about nanowires before and, in keeping with today’s theme of peculiar relationships  (Alzheimer’s disease), prior to this, the most unusual nanowire item I’ve come across had to do with growing them to the sounds  of music. From the Nanotech Mysteries (wiki), Scientists get musical page (Note: Footnotes have been removed),

After testing Deep Purple’s ‘Smoke on the Water‘, Chopin’s ‘Nocturne Opus 9 no. 1‘, Josh Abraham’s ‘Addicted to Bass‘, Rammstein’s ‘Das Model‘, and Abba’s ‘Dancing Queen‘, David Parlevliet found that music can be used to grow nanowires but they will be kinky.

Scientists want to grow straight nanowires and one of the popular methods is to “[blast] a voltage through silane gas to produce a plasma that pulses on and off at 1000 times a second. Over time the process enables molecules from the gas to deposit on a glass slide in the form of a mesh of crystalline silicon nanowires.”

Parlevliet, a PhD student at Murdoch University in Perth, Australia, plugged in a music player instead of a pulse generator usually used for this purpose and observed the results. While there are no current applications for kinky nanowires, the Deep Purple music created the densest mesh. Rammstein’s music grew nanowires the least successfully. In his presentation to the Australian Research Council Nanotechnology Network Symposium in March 2008, Parlevliet concluded that music could become more important for growing nanowires if applications can be found for the kinky ones.

Integrated artificial photosynthesis nanosystem, a first for Lawrence Berkeley National Laboratory

There’s such a thing as too much information and not enough knowledge, a condition I’m currently suffering from with regard to artificial photosynthesis. Before expanding on that theme, here’s the latest about artificial photosynthesis from a May 16, 2013 Lawrence Berkeley National Laboratory news release (also available on EurekAlert),

In the wake of the sobering news that atmospheric carbon dioxide is now at its highest level in at least three million years, an important advance in the race to develop carbon-neutral renewable energy sources has been achieved. Scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have reported the first fully integrated nanosystem for artificial photosynthesis. While “artificial leaf” is the popular term for such a system, the key to this success was an “artificial forest.”

Here’s a more detailed description of the system, from the news release,

“Similar to the chloroplasts in green plants that carry out photosynthesis, our artificial photosynthetic system is composed of two semiconductor light absorbers, an interfacial layer for charge transport, and spatially separated co-catalysts,” says Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division, who led this research. “To facilitate solar water- splitting in our system, we synthesized tree-like nanowire  heterostructures, consisting of silicon trunks and titanium oxide branches. Visually, arrays of these nanostructures very much resemble an artificial forest.”

… Artificial photosynthesis, in which solar energy is directly converted into chemical fuels, is regarded as one of the most promising of solar technologies. A major challenge for artificial photosynthesis is to produce hydrogen cheaply enough to compete with fossil fuels. Meeting this challenge requires an integrated system that can efficiently absorb sunlight and produce charge-carriers to drive separate water reduction and oxidation half-reactions.

More specifically,

“In natural photosynthesis the energy of absorbed sunlight produces energized charge-carriers that execute chemical reactions in separate regions of the chloroplast,” Yang says. “We’ve integrated our nanowire nanoscale heterostructure into a functional system that mimics the integration in chloroplasts and provides a conceptual blueprint for better solar-to-fuel conversion efficiencies in the future.”

When sunlight is absorbed by pigment molecules in a chloroplast, an energized electron is generated that moves from molecule to molecule through a transport chain until ultimately it drives the conversion of carbon dioxide into carbohydrate sugars. This electron transport chain is called a “Z-scheme” because the pattern of movement resembles the letter Z on its side. Yang and his colleagues also use a Z-scheme in their system only they deploy two Earth abundant and stable semiconductors – silicon and titanium oxide – loaded with co-catalysts and with an ohmic contact inserted between them. Silicon was used for the hydrogen-generating photocathode and titanium oxide for the oxygen-generating photoanode. The tree-like architecture was used to maximize the system’s performance. Like trees in a real forest, the dense arrays of artificial nanowire trees suppress sunlight reflection and provide more surface area for fuel producing reactions.

“Upon illumination photo-excited electron−hole pairs are generated in silicon and titanium oxide, which absorb different regions of the solar spectrum,” Yang says. “The photo-generated electrons in the silicon nanowires migrate to the surface and reduce protons to generate hydrogen while the photo-generated holes in the titanium oxide nanowires oxidize water to evolve  oxygen molecules. The majority charge carriers from both semiconductors recombine at the ohmic contact, completing the relay of the Z-scheme, similar to that of natural photosynthesis.”

Under simulated sunlight, this integrated nanowire-based artificial photosynthesis system achieved a 0.12-percent solar-to-fuel conversion efficiency. Although comparable to some natural photosynthetic conversion efficiencies, this rate will have to be substantially improved for commercial use. [emphasis mine] However, the modular design of this system allows for newly discovered individual components to be readily incorporated to improve its performance. For example, Yang notes that the photocurrent output from the system’s silicon cathodes and titanium oxide anodes do not match, and that the lower photocurrent output from the anodes is limiting the system’s overall performance.

“We have some good ideas to develop stable photoanodes with better performance than titanium oxide,” Yang says. “We’re confident that we will be able to replace titanium oxide anodes in the near future and push the energy conversion efficiency up into single digit percentages.”

Now I can discuss my confusion, which stems from my May 24, 2013 posting about work done at the Argonne National Laboratory,

… Researchers still have a long way to go before they will be able to create devices that match the light harvesting efficiency of a plant.

One reason for this shortcoming, Tiede [Argonne biochemist David Tiede] explained, is that artificial photosynthesis experiments have not been able to replicate the molecular matrix that contains the chromophores. “The level that we are at with artificial photosynthesis is that we can make the pigments and stick them together, but we cannot duplicate any of the external environment,” he said.  “The next step is to build in this framework, and then these kinds of quantum effects may become more apparent.”

Because the moment when the quantum effect occurs is so short-lived – less than a trillionth of a second – scientists will have a hard time ascertaining biological and physical rationales for their existence in the first place. [emphasis mine]

It’s not clear to me whether or not the folks at the Berkeley Lab bypassed the ‘problem’ described by Tiede or solved it to achieve solar-to-fuel conversion rates comparable to natural photosynthesis conversions. As I noted, too much information/not enough knowledge.

Pousse-café nanowires

If you grow a nanowire made up of three elements on a graphene substrate, you get a surprise. At least, that’s what the research team at the University of Illinois received. From the Apr. 23, 2013 news release on EurekAlert,

Nanowires, tiny strings of semiconductor material, have great potential for applications in transistors, solar cells, lasers, sensors and more.

“Nanowires are really the major building blocks of future nano-devices,” said postdoctoral researcher Parsian Mohseni, first author of the study. “Nanowires are components that can be used, based on what material you grow them out of, for any functional electronics application.”

Li’s group uses a method called van der Waals epitaxy to grow nanowires from the bottom up on a flat substrate of semiconductor materials, such as silicon. The nanowires are made of a class of materials called III-V (three-five), compound semiconductors that hold particular promise for applications involving light, such as solar cells or lasers.

The group previously reported growing III-V nanowires on silicon. While silicon is the most widely used material in devices, it has a number of shortcomings. Now, the group has grown nanowires of the material indium gallium arsenide (InGaAs) on a sheet of graphene, a 1-atom-thick sheet of carbon with exceptional physical and conductive properties.

“One of the reasons we want to grow on graphene is to stay away from thick and expensive substrates,” Mohseni said. “About 80 percent of the manufacturing cost of a conventional solar cell comes from the substrate itself. We’ve done away with that by just using graphene. Not only are there inherent cost benefits, we’re also introducing functionality that a typical substrate doesn’t have.”

The researchers pump gases containing gallium, indium and arsenic into a chamber with a graphene sheet. The nanowires self-assemble, growing by themselves into a dense carpet of vertical wires across the surface of the graphene. Other groups have grown nanowires on graphene with compound semiconductors that only have two elements, but by using three elements, the Illinois group made a unique finding: The InGaAs wires grown on graphene spontaneously segregate into an indium arsenide (InAs) core with an InGaAs shell around the outside of the wire. [emphasis mine]

“This is unexpected,” Li [professor Xiuling Li] said. “A lot of devices require a core-shell architecture. Normally you grow the core in one growth condition and change conditions to grow the shell on the outside. This is spontaneous, done in one step. The other good thing is that since it’s a spontaneous segregation, it produces a perfect interface.”

The group plans to make solar cells amongst other items with this new type of nanowire. You can find the whole story (Apr. 23, 2013 news item) on ScienceDaily along with a link to and citation for the researchers’ paper.

This story reminded me of a cocktail that’s fascinated me for years, a pousse-café,

Downloaded from http://www.scienceofdrink.com/2010/10/18/pousse-cafe-and-some-modern-derivatives/langswitch_lang/en/

Downloaded from http://www.scienceofdrink.com/2010/10/18/pousse-cafe-and-some-modern-derivatives/langswitch_lang/en/

The layers are not self-assembling as are the nanowires. Making this drink requires knowledge of the various weights of the liqueurs you are using and some care. You can find some recipes for modern pousse-cafés at the Science of Drink here. I believe this site has been translated from another language so you may find some unusual grammatical structures.

Have a lovely weekend.

Beginner’s guide to carbon nanotubes and nanowires

There’s a very nice Apr. 11, 2013  introductory article by David L. Chandler for the Massachusetts Institute of Technology (MIT) news office) about carbon and other nanotubes and nanowires,

The initial discovery of carbon nanotubes — tiny tubes of pure carbon, essentially sheets of graphene rolled up unto a cylinder — is generally credited to a paper published in 1991 by the Japanese physicist Sumio Ijima (although some forms of carbon nanotubes had been observed earlier). Almost immediately, there was an explosion of interest in this exotic form of a commonplace material. Nanowires — solid crystalline fibers, rather than hollow tubes — gained similar prominence a few years later.

Due to their extreme slenderness, both nanotubes and nanowires are essentially one-dimensional. “They are quasi-one-dimensional materials,” says MIT associate professor of materials science and engineering Silvija Gradečak: “Two of their dimensions are on the nanometer scale.” This one-dimensionality confers distinctive electrical and optical properties.

For one thing, it means that the electrons and photons within these nanowires experience “quantum confinement effects,” Gradečak says. And yet, unlike other materials that produce such quantum effects, such as quantum dots, nanowires’ length makes it possible for them to connect with other macroscopic devices and the outside world.

The structure of a nanowire is so simple that there’s no room for defects, and electrons pass through unimpeded, Gradečak explains. This sidesteps a major problem with typical crystalline semiconductors, such as those made from a wafer of silicon: There are always defects in those structures, and those defects interfere with the passage of electrons.

H/T Nanowerk Apr. 11, 2013 news item. There’s more to read at the MIT website and I recommend this as a good beginner’s piece since the focus is entirely on what carbon nanotubes and nanowires are , how they are formed, and which distinctive properties are theirs. You can find some of this information in the odd paragraph of a news release touting the latest research but I’m very excited to find this much explanatory material in one place.

Another very good explanatory piece, this one focused on carbon nanotubes and risk, is a video produced by Dr. Andrew Maynard for his Risk Bites series. I featured and embedded it in my Mar. 15, 2013 posting. titled, The long, the short, the straight, and the curved of them: all about carbon nanotubes.  You can also find the video in Andrew’s Mar. 14, 2013 posting on his 2020 Science blog where he also writes about the then recently released information from the US National Institute of Occupational Health and Safety on carbon nanotubes and toxicity.

2.5M Euros for Ireland’s John Boland and his memristive nanowires

The announcement makes no mention of the memristor or neuromorphic engineering but those are the areas in which  John Boland works and the reason for his 2.5M Euro research award. From the Ap. 3, 2013 news item on Nanowerk,

Professor John Boland, Director of CRANN, the SFI-funded [Science Foundation of Ireland] nanoscience institute based at Trinity College Dublin, and a Professor in the School of Chemistry has been awarded a €2.5 million research grant by the European Research Council (ERC). This is the second only Advanced ERC grant ever awarded in Physical Sciences in Ireland.

The Award will see Professor Boland and his team continue world-leading research into how nanowire networks can lead to a range of smart materials, sensors and digital memory applications. The research could result in computer networks that mimic the functions of the human brain and vastly improve on current computer capabilities such as facial recognition.

The University of Dublin’s Trinity College CRANN (Centre for Research on Adaptive Nanostructures and Nanodevices) April 3, 2013 news release, which originated the news item,  provides details about Boland’s proposed nanowire network,

Nanowires are spaghetti like structures, made of materials such as copper or silicon. They are just a few atoms thick and can be readily engineered into tangled networks of nanowires. Researchers worldwide are investigating the possibility that nanowires hold the future of energy production (solar cells) and could deliver the next generation of computers.

Professor Boland has discovered that exposing a random network of nanowires to stimuli like electricity, light and chemicals, generates chemical reaction at the junctions where the nanowires cross. By controlling the stimuli, it is possible to harness these reactions to manipulate the connectivity within the network. This could eventually allow computations that mimic the functions of the nerves in the human brain – particularly the development of associative memory functions which could lead to significant advances in areas such as facial recognition.

Commenting Professor John Boland said, “This funding from the European Research Council allows me to continue my work to deliver the next generation of computing, which differs from the traditional digital approach.  The human brain is neurologically advanced and exploits connectivity that is controlled by electrical and chemical signals. My research will create nanowire networks that have the potential to mimic aspects of the neurological functions of the human brain, which may revolutionise the performance of current day computers.   It could be truly ground-breaking.”

It’s only in the news release’s accompanying video that the memristor and neuromorphic engineering are mentioned,

I have written many times about the memristor, most recently in a Feb. 26, 2013 posting titled, How to use a memristor to create an artificial brain, where I noted a proposed ‘blueprint’ for an artificial brain. A contested concept, the memristor has attracted critical commentary as noted in a Mar. 19, 2013 comment added to the ‘blueprint’  post,

A Sceptic says:

….

Before talking about blueprints, one has to consider that the dynamic state equations describing so-called non-volatile memristors are in conflict with fundamentals of physics. These problems are discussed in:

“Fundamental Issues and Problems in the Realization of Memristors” by P. Meuffels and R. Soni (http://arxiv.org/abs/1207.7319)

“On the physical properties of memristive, memcapacitive, and meminductive systems” by M. Di Ventra and Y. V. Pershin (http://arxiv.org/abs/1302.7063)

Carbon Management Canada announces research for an affordable CO2 nanosensor

Researchers at the University of Toronto (Ontario) and St. Francis Xavier University (Nova Scotia) have received funding from Carbon Management Canada (a Network Centre for Excellence [NCE]) to develop an ultra-sensitive and affordable CO2 nanosensor. From the Feb. 4, 2013 news item on Nanowerk,

Researchers at the Universities of Toronto and St. Francis Xavier are developing an affordable, energy efficient and ultra-sensitive nano-sensor that has the potential to detect even one molecule of carbon dioxide (CO2).

Current sensors used to detect CO2 at surface sites are either very expensive or they use a lot of energy. And they’re not as accurate as they could be. Improving the accuracy of measuring and monitoring stored CO2 is seen as key to winning public acceptance of carbon capture and storage as a greenhouse gas mitigation method.

With funding from Carbon Management Canada (CMC), Dr. Harry Ruda of the Centre for Nanotechnology at the University of Toronto and Dr. David Risk of St. Francis Xavier are working on single nanowire transistors that should have unprecedented sensitivity for detecting CO2 emissions.

The Carbon Management Canada (CMC) Feb. 4, 2013 news release, which originated the news item, provides  details about the funding and reasons for the research,

CMC, a national network that supports game-changing research to reduce CO2 emissions in the fossil energy industry as well as from other large stationary emitters, is providing Ruda and his team $350,000 over three years. [emphasis mine] The grant is part of CMC’s third round of funding which saw the network award $3.75 million to Canadian researchers working on eight different projects.

The sensor technology needed to monitor and validate the amount of CO2 being emitted has not kept pace with the development of other technologies required for carbon capture and storage (CCS), says Ruda.

“This is especially true when it comes to surface monitoring verification and accounting (MVA),” he says. “Improving MVA is essential to meet the potential of carbon capture and storage.”

And that’s where the ultra-sensitive sensor comes in. “It’s good for sounding the alarm but it’s also good from a regulatory point of view because you want to able to tell people to keep things to a certain level and you need sensors to ensure accurate monitoring of industrial and subsurface environments,” Ruda says.

Given CMC’s vision for ‘game-changing research to reduce carbon emissions’, it bears noting that this organization is located in Calgary (the street address ‘EEEL 403, 2500 University Drive NW Calgary‘ as per my search today [Feb.4.13] on Google [https://www.google.ca/search?q=CMC+address+Calgary&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a] suggests the University of Calgary houses the organization). Calgary is the home of the Canadian fossil fuel industry and a centre boasting many US-based fossil fuel-based companies due to its size and relative proximity to the Alberta oil sands (aka, Athabaska oil sands). From the Wikipedia essay (Note: Links and footnotes have been removed),

The Athabasca oil sands or Athabasca tar sands are large deposits of bitumen or extremely heavy crude oil, located in northeastern Alberta, Canada – roughly centred on the boomtown of Fort McMurray. These oil sands, hosted in the McMurray Formation, consist of a mixture of crude bitumen (a semi-solid form of crude oil), silica sand, clay minerals, and water. The Athabasca deposit is the largest known reservoir of crude bitumen in the world and the largest of three major oil sands deposits in Alberta, along with the nearby Peace River and Cold Lake deposits.

Together, these oil sand deposits lie under 141,000 square kilometres (54,000 sq mi) of boreal forest and muskeg (peat bogs) and contain about 1.7 trillion barrels (270×109 m3) of bitumen in-place, comparable in magnitude to the world’s total proven reserves of conventional petroleum. Although the former CEO of Shell Canada, Clive Mather, estimated Canada’s reserves to be 2 trillion barrels (320 km3) or more, the International Energy Agency (IEA) lists Canada’s reserves as being 178 billion barrels (2.83×1010 m3).

As for locating a carbon management organization in Calgary, it does make sense of a sort. Here’s a somewhat calmer description of Carbon Management Canada on the website’s About CMC page,

Carbon Management Canada CMC-NCE [Network Centre for Escellence] is a national network of academic researchers working with experts in the fossil energy industry, government, and the not-for-profit sector. Together, we are developing the technologies, the knowledge and the human capacity to radically reduce carbon dioxide emissions in the fossil energy industry and other large stationary emitters.

Carbon emissions and the growing global concern about its effects present a unique opportunity for innovation and collaboration, especially in the fossil energy industry. Rapidly increasing global complexity demands robust, responsive innovation that can only develop in a highly collaborative context involving industry, scientists, policy makers, politicians and industry leaders in concert with an informed, supportive public.

Carbon Management Canada is the national body charged with harnessing the collective energy of this diverse group in order to push forward an ambitious agenda of innovation and commercialization to bring research from the lab into the world of practice.

Funding

Funding for CMC was provided through the federal Networks of Centres of Excellence ($25 million) and the Province of Alberta through Alberta Environment ($25 million). Industry has also provided $5.7 million in contributions.

The Network has over 160 investigators at 27 Canadian academic institutions and close to 300 graduate and postdoctoral students working on research projects. CMC currently has invested $22 million in 44 research projects.

Our Themes

CMC is an interdisciplinary network with scientists working in fields that range from engineering to nanotechnology to geoscience to business to political science and communications. These investigators work in 4 themes: Recovery, Processing and Capture; Enabling and Emerging Technologies; Secure Carbon Storage; and Accelerating Appropriate Deployment of Low Carbon Emission Technologies.

Given that CMC is largely government-funded, it seems odd (almost as if they don’t want anyone to know) that the website does not feature a street address. In addition to trying  a web search, you can find the information on the last page of the 2012 annual/financial report. One final note, the chair of CMC’s board is Gordon Lambert who is also Vice President, Sustainable Development, Suncor Energy. From Suncor’s About Us webpage,

n 1967, we pioneered commercial development of Canada’s oil sands — one of the largest petroleum resource basins in the world. Since then, Suncor has grown to become a globally competitive integrated energy company with a balanced portfolio of high-quality assets, a strong balance sheet and significant growth prospects. Across our operations, we intend to achieve production of one million barrels of oil equivalent per day.

Then, there’s this on the company’s home page,

We create energy for a better world

Suncor’s vision is to be trusted stewards of valuable natural resources. Guided by our values, we will lead the way to deliver economic prosperity, improved social well-being and a healthy environment for today and tomorrow.

The difficulty I’m highlighting is the number of competing interests. Governments which are dependent on industry for producing jobs and tax dollars are also funding ‘carbon management’. The fossil fuel-dependent industry make a great deal money from fossil fuels and doesn’t have much incentive to explore carbon management as that costs money and doesn’t add to profit. Regardless of how enlightened any individuals within that industry may be they have a fundamental problem similar to an asthmatic who’s being poisoned by the medication they need to breathe. Do you get immediate relief from the medication, i.e., breathe, or do you refuse the medication which causes damage years in the future and continue struggling for air?

All of these institutions (CMC, Suncor, etc.) would have more credibility if they addressed the difficulties rather than ignoring them.