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New Method for Building Complex Structures from Quantum Dots Proposed

Edward Sargent, Professor in The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto, has been a busy man of late.

At the end of last month, I wrote on his work in using colloidal quantum dots for multi-junction solar cells.

This month Sargent along with Shana Kelley, a Professor in the Department of Biochemistry at the University of Toronto, are reporting in the journalNature Nanotechnology that they have developed a strategy by which to build complex structures out of varying types of quantum dots. In this case, the structure that they built serves as a kind of antenna for light.

As testament to how multi-disciplinary investigations into nanotechnologies can be, expertise in both semiconductor engineering and DNA had to be combined to realize their results. 

"The credit for this remarkable result actually goes to DNA: its high degree of specificity – its willingness to bind only to a complementary sequence – enabled us to build rationally-engineered, designer structures out of nanomaterials," says Sargent in a article

"The amazing thing is that our antennas built themselves – we coated different classes of nanoparticles with selected sequences of DNA, combined the different families in one beaker, and nature took its course,” adds Sargent. “The result is a beautiful new set of self-assembled materials with exciting properties."

The analogy to an antenna comes from the fact that like a traditional antenna these nano-antennae capture dispersed energy and then concentrate that captured energy to a specific location. According to Sargent, this particular kind of antenna for light is seen in the leaves of trees.

While creating light absorbing antennae from quantum dots is an interesting way to manipulate the material, it would seem that developing a method for building various structures with disparate types of quantum dots would be the more impressive bit of this research.

"What this work shows is that our capacity to manipulate materials at the nanoscale is limited only by human imagination,” says Kelley in the article. “If semiconductor quantum dots are artificial atoms, then we have rationally synthesized artificial molecules from these versatile building blocks."

Opposite Sides of the Atlantic Deliver Alternative Views of Nanotech's Development

This week we get two very different perspectives on the state of nanotechnology and its development.

On the one hand, we have the somewhat jaundiced view from the United Kingdom–based New Scientist, which confesses to a fair amount of skepticism about the mere idea of nanotechnology but wonders why the UK has seemingly dropped off the nanotech map.

On the other hand, we have the United States–based Industry Week, which promises that whatever regulatory problems we see now are merely growing pains in the manifest destiny of nanotech’s ultimate success.

The somewhat more pessimistic Old World view comes from Roger Highfield, the New Scientist editor who penned the publication’s blog piece. He references the travails of UK-based quantum manufacturer Nanoco as evidence of the lack of emphasis on nanotech’s development in the UK.

Highfield also bases much of his perspective on a nearly abandoned piece of research sponsored by the RCUK Nanoscience Programme entitled “Setting the Foundations for New Industries and Opportunities,” which can be found here. Of course, abandoning previous research so you can do it all over again is a popular tradition that seems to plague European Union projects and especially those in the UK

The report, which was put together by an international panel of academics, seems to have ignored the rule for most of these government reports: They ultimately must serve as a pat on the back while urging people to do even more great work.

It does, however, nail one of the key problems with nanotech’s development in the UK (and, one could argue, in the EU as well):

“...the system is top-heavy, with a labyrinth of advisory, consultative, and coordinating committees. These impede decision taking, rather than facilitating it, and create confusion both within the research community and at higher policy levels.”

I am sure that this dependence on consultations and repetitive reports all started innocently enough, but now it seems to have become a systemic problem that will really need to be addressed for there to be forward progress—not only in the UK, but in just about any country that has announced a nanotechnology initiative.

Graphene Enables Invisibility Cloak

Fans of the original "Star Trek" television show surely recall those dastardly Klingons employing a cloaking device that rendered their vessels invisible. Of course, that is science fiction, but in research coming out of the University of Texas at Austin, that capability sounds amusingly similar to a proposed use of graphene in providing an “active, dynamically tunable invisibility cloak.”

The research, which was originally published in the ACS journal Nano, builds on two fields of previous work. The first field is termed “plasmonic cloaking,” which uses metamaterial coatings, and the second is known as “mantle cloaking,” which achieves more or less the same effects as plasmonic cloaking but by using impedance.

"The graphene cloak idea stems from the mantle cloaking concept, which we have proposed at microwaves using frequency-selective surfaces, i.e., properly patterned conducting surfaces that can tailor their effective surface impedance at will," says Andrea Alù, at the University of Texas at Austin, in the Nanowerk article cited above.

Alù adds, "Due to the recent progress in understanding graphene's AC conductivity, we have realized that its unique features of ultrahigh mobility and largely tunable Fermi level may naturally provide the required reactive properties in a single atomic layer. The effective surface impedance of graphene can be tuned in real time, another great advantage of this graphene cloak, which makes dynamically tunable and switchable cloaking operation possible."

While invisible aircraft may leap to mind, the applications for this technology could be in the areas of noninvasive sensors and low-scattering electronic components.

"There is great interest in realizing low-scattering or impedance-matched electronic components, and we believe that the use of this graphene layer may realize this effect in an ultrathin geometry—much thinner than antireflection coatings or other available technology," says Alù.

UK-Based Nanotech Company Threatens to Move Abroad

While cutting-edge research grabs the nanotechnology headlines and a good deal of the focus, much of the groundbreaking bit never finds its way into commercial products.

Sure, research papers always contain a tag promising to revolutionize this or that application, but in the long run this is rarely the case. Remarkably, it turns out that technological obstacles are one of the smallest factors in preventing this kind of research from finding its way into commercial products.

As tired as it may sound, one of the key issues remains the funding gap.

When it comes to the most groundbreaking nanotech research, it’s typically start-ups that lead the way. The reasons are obvious and center around the idea that they are attempting to have their technology transplant that of an established one

Of course, it’s rare that large, established companies conduct expensive research into making their own technologies obsolete. The underlying problem is that large companies have plenty of money for bringing new technologies to market but little motivation to do so, while a start-up has lots of incentive but little cash to see it realized.

Then there is the role of government. Governments around the world have spent billions of dollars over the last decade in building shiny new research facilities and funding “nanotech” research that used to be called solid-state physics or chemistry—but they have blithely allowed the fruits of that funding to rot on the vine.

I suppose all that exciting research is not a complete waste, since some big company will pick up some of it for its particular purposes, whether to augment a technology or possibly simply to keep it off the market.

In any case, one UK-based nanotech start-up has announced that it's mad as hell and it's not going to take it anymore. The Financial Times has a story this week about how Nanoco, a manufacturer of quantum dots, is threatening to move its manufacturing facilities out of the UK and to a country that is more financially supportive, namely either Japan or Singapore. 

Michael Edelman, the chief executive of Nanoco, is quoted in the article as saying, “Ministers talk a good game [about trying to encourage manufacturing], but when you look at the support packages that are available, they are often unsuitable or too thinly spread.” I would tell him to move and be quick about it. Save your company, and then maybe you can worry about saving the UK manufacturing industry.

Do Alternative Memories Need to Meet the 3-Nanometer Test?

Last month, an article in the pages of IEEE Spectrum looked at how alternative memories were getting the so-called carbon nanotube test.

The article describes the work of Stanford researchers, led by H.-S. Philip Wong, in testing the capabilities of two different types of alternative memory to flash, namely resistive random-access memory (RRAM) and phase-change memory (PCM). I myself have covered in this blog Eric Pop's research into PCM.

But in the recent past, those alternative memories that have taken on flash, such as IBM's much ballyhooed Millipede Project, have suffered ignominious ends. 

We are told, however, that flash memory cannot rule the roost forever because of density limits. So alternatives must be found.

With the pressure on, up step RRAM and PCM. And in the article we learn that some companies are planning to introduce PCM and RRAM memories in the near future. With commercial introduction possible so soon, Wong thought it might be worthwhile to see how far the technology can scale. So they went right to the limit, using 1.2-nanometer-wide nanotubes as electrodes.

Ultimately, Wong and his team were able to produce an RRAM cell measuring 6 by 6 nm that was fully operational. Since the memory cell switches with less than 10 microamperes of current and about 10 volts, which meets expectations derived from previous experiments, it serves as a sign that RRAM will scale well, according to Wong.

But while I was reading this I couldn’t help but think about the paper recently presented by Professor Mike Kelly at Cambridge University that claims that structures with dimensions of 3 nm or less cannot be mass-produced. 

Now, drawing a line in the sand of technological progress is a risky—and rarely rewarding—exercise. But Kelly would seem to have presented some pretty plausible reasons for why he drew that line.

I wonder how seriously the companies that are nearing the introduction of some kind of PCM or RRAM products in the coming years are considering this theoretical threshold. Maybe a 3-nm test should be instituted.

A Top-10 Nanotechnology List Worth Reading

My aversion to top-5 or top-10 nanotechnology lists is powerful. However, Nature Nanotechnology has overcome my disgust with the top-10 idea and listed its top-10 most-downloaded articles in the last few weeks. I don’t know if this is a new or an established feature of the publication, but it is the first time I’ve seen it.

At the top of the list is the work done by Angela Belcher and her team at MIT in using viruses to self-assemble carbon nanotubes for use in dye-sensitized solar cells (DSSCs), about which the inventor of DSSCs, Michael Grätzel, remarked to me recently, “That’s a real breakthrough—we can learn a lot from her fascinating experiment.”

It’s an interesting list of research and opinion. On the opinion side, I was glad to see the publishers made available for everyone with or without a subscription a take on the toxicity of nanoparticles entitled The dose makes the poison“ that mirrors some of my own thoughts on the topic.

While some of the research I have covered, I have not reported a majority of the research listed on the pages of this blog. I have, however, recently highlighted some of the other work of the lead researchers, such as MIT researcher Michael Strano.

The most intriguing of the studies I have not covered are the Dutch-Swiss research into “Single-Molecule Transport Across an Individual Biomimetic Nuclear Pore Complex” (which in my defense was only published last week) and the South Korean and Japanese paper “Roll-to-Roll Production of 30-Inch Graphene Films for Transparent Electrodes.”

As I said, this is the first time I’ve seen this feature in Nature, so I will need to check back again and look to see if they offer it on some of their other journals, such as Nature Photonics and Nature Materials.

Harvesting Visible and Invisible Light in PVs with Colloidal Quantum Dots

The promise of multijunction solar cells made from colloidal quantum dots (CQDs) has been discussed as a hopeful prospect for collecting a broad spectrum of light from the sun. If achieved, it would make possible extremely high energy-conversion rates for photovoltaics (PVs).

One of the leading researchers in the field, Edward H. Sargent, and his research team at the University of Toronto have described a new device architecture that includes “a graded recombination layer to provide a progression of work functions from the hole-accepting electrode in the bottom cell to the electron-accepting electrode in the top cell, allowing matched electron and hole currents to meet and recombine,” as it's described in the most recent online edition of the journal Nature Photonics 

The solar power conversion efficiency for the device, according to the Nature abstract, is 4.2 percent—not quite staggering, since levels of 5 percent have been reported as the state of the art for CQD multijunction PVs.

The breakthrough appears to be in that "graded recombination layer," which serves as an interface between the visible and infrared junction passing electrons between the two layers.

When one considers that tandem CQD solar cells are believed to possess astronomical conversion efficiency rates of 42%, it would seem that the 4.2% achieved by the University of Toronto researchers means there is still room for improvement on the technology.

Nonetheless, Sargent has expressed hope that the technology described in the Nature Photonics paper will make it to market and be integrated into building materials, mobile devices, and automobile parts in the next five years.

In addition to the science, what I find interesting about the story is that this research was in part made possible by a US $10 million grant given to Sargent back in 2008 by King Abdullah University of Science and Technology (KAUST) in Thuwal, Saudi Arabia.

It seems Saudi Arabia is committed to developing solar energy alternatives despite sitting on one of the world’s largest oil reserves.


Russia's Nanotechnology Initiative Goes on a Spending Spree

I have been fascinated by the Russian government’s foray into nanotechnology; it contains intrigue,  hidden complexities, and more than its share of skepticism.

The list of skeptics even extends to the country's political leaders

"[Rusnano] is the kind of instrument that sometimes works and sometimes doesn't work at all," President Dmitry Medvedev said two years ago, calling the company a "large structure that has a lot of money and that still has to understand how to correctly spend it."

Well, it seems that Rusnano has overcome that learning curve and is spending…a lot. Over at TNT Log this week there is a pretty thorough recap of the deals that Rusnano has been involved in to date.

But so fast and furious is the action at this point that there are already new deals here at the end of the week to add to the list. For instance, Rusnano and Toyota Tsusho have signed a memorandum of cooperation in the fields of electronics, organic chemistry, the environment, and automobile manufacturing.

A fair share of the announced deals really only involve MOUs, and the world of business is littered with MOUs that never actually turn into contracts. Nonetheless, is a picture developing from the deals we have seen thus far? 

It’s hard to say for sure, but at least TNT Log characterizes them as being on the riskier side of the investment scale. And well should they be, in my estimation. If you’re going after market segments that will be affected by the enabling technology of nanotech, then you're likely to find yourself in some pretty risky investments.

Carbon Nanotubes Fluoresce at Right Wave Length for Seeing Internal Organs

Researchers at Stanford University have discovered that fluorescent single-walled carbon nanotubes improve on the murky images provided by traditional dyes and deliver detailed and clear images of the internal organs of mice.

Interestingly, the idea of using fluorescent carbon nanotubes to illuminate the internal organs was partly inspired by the use of carbon nanotubes in drug delivery.

"We have already used similar carbon nanotubes to deliver drugs to treat cancer in laboratory testing in mice, but you would like to know where your delivery went, right?" says Hongjie Dai, a Stanford chemistry professor. "With the fluorescent nanotubes, we can do drug delivery and imaging simultaneously—in real time—to evaluate the accuracy of a drug in hitting its target."

The technique, described this month in the journal Proceedings of the National Academy of Sciences, is able to produce such clear images because of the wavelength at which the carbon nanotubes operate.

The problem has been that both the biocompatible dyes used today and biological tissue fluoresce at the same wavelength of below 900 nanometers. This creates a background fluorescence that results in murky images.

But the carbon nanotubes fluoresce at between 1000 and 1400 nm, where the biological tissue is hardly emitting any fluorescence so that there is minimal background noise.

"The nanotubes fluoresce naturally, but they emit in a very oddball region," Dai says. "There are not many things—living or inert—that emit in this region, which is why it has not been explored very much for biological imaging."

While computer tomography and magnetic resonance imaging still rule the roost when it comes to imaging deep tissue, this should push the capabilities and application of fluorescence imaging, which is used mainly in research and requires far simpler machinery.

Piezoelectrics and Thin Films Power Your Mobile With a Press of Your Finger

While the pedantic among us may quibble with phrases like “self-powering portable electronics” and start blathering about the second law of thermodynamics, new research from Australia is pushing the limits of piezoelectric materials for turning pressure into electrical energy for mobile devices.

The researchers have published their work in the journal Advanced Functional Materials after demonstrating a method for combining piezoelectric materials with thin-film technology to produce more easily integrated into mass-production techniques.

"The concept of energy harvesting using piezoelectric nanomaterials has been demonstrated, but the realization of these structures can be complex, and they are poorly suited to mass fabrication,” says Dr. Madhu Bhaskaran, lead coauthor of the research. "Our study focused on thin-film coatings because we believe they hold the only practical possibility of integrating piezoelectrics into existing electronic technology."

When more easily integrated piezoelectric materials are combined with groundbreaking work in reducing the amount of energy consumed by electronic devices like that done by Eric Pop and his team at the University of Illinois at Urbana-Champaign’s Beckman Institute for Advanced Science and Technology, it seems possible that we may be able to run our small electronic devices for longer than a few hours before we have to plug them into an outlet. 



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

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