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Utah Fast Elec engineeringm

University of Utah engineers have discovered a new kind of 2D semiconducting material for electronics that opens the door for much speedier computers and smartphones that also consume a lot less power.

The semiconductor, made of the elements tin and oxygen, or tin monoxide (SnO), is a layer of 2D material only one atom thick, allowing electrical charges to move through it much faster than conventional 3D materials such as silicon. This material could be used in transistors, the lifeblood of all such as computer processors and graphics processors in desktop computers and mobile devices. The material was discovered by a team led by University of Utah materials science and engineering associate professor Ashutosh Tiwari.

A paper describing the research was published online Monday, Feb. 15, 2016 in the journal, Advanced Electronic Materials. The paper, which also will be the cover story on the printed version of the journal, was co-authored by University of Utah materials science and engineering doctoral students K. J. Saji and Kun Tian, and Michael Snure of the Wright-Patterson Air Force Research Lab near Dayton, Ohio.

Transistors and other components used in electronic devices are currently made of 3D materials such as silicon and consist of multiple layers on a glass substrate. But the downside to 3D materials is that electrons bounce around inside the layers in all directions.

The benefit of 2D materials, which is an exciting new research field that has opened up only about five years ago, is that the material is made of one layer the thickness of just one or two atoms. Consequently, the electrons “can only move in one layer so it’s much faster,” says Tiwari.

Engineering material magic
University of Utah materials science and engineering associate professor Ashutosh Tiwari stands in his lab where he and his team have discovered a new 2-D semiconducting material made of tin and oxygen. This new material allows electrical …more

While researchers in this field have recently discovered new types of 2D material such as graphene, molybdenun disulfide and borophene, they have been that only allow the movement of N-type, or negative, electrons. In order to create an electronic device, however, you need semiconductor material that allows the movement of both negative electrons and positive charges known as “holes.” The tin monoxide material discovered by Tiwari and his team is the first stable P-type 2D ever in existence.

“Now we have everything—we have P-type 2D semiconductors and N-type 2D semiconductors,” he says. “Now things will move forward much more quickly.”

Now that Tiwari and his team have discovered this new 2D material, it can lead to the manufacturing of transistors that are even smaller and faster than those in use today. A computer processor is comprised of billions of transistors, and the more packed into a single chip, the more powerful the processor can become.

Transistors made with Tiwari’s semiconducting material could lead to computers and smartphones that are more than 100 times faster than regular devices. And because the electrons move through one layer instead of bouncing around in a 3D material, there will be less friction, meaning the processors will not get as hot as normal computer chips. They also will require much less power to run, a boon for mobile electronics that have to run on battery power. Tiwari says this could be especially important for medical devices such as electronic implants that will run longer on a single battery charge.

“The field is very hot right now, and people are very interested in it,” Tiwari says. “So in two or three years we should see at least some prototype device.”

Explore further: Semiconductor miniaturisation with 2D nanolattices

anticounterf ink 021116Researchers have demonstrated that transparent ink containing gold, silver, and magnetic nanoparticles can be easily screen-printed onto various types of paper, with the nanoparticles being so small that they seep into the paper’s pores. Although invisible to the naked eye, the nanoparticles can be detected by the unique ways that they scatter light and by their magnetic properties. Since the combination of optical and magnetic signatures is extremely difficult to replicate, the nanoparticles have the potential to be an ideal anti-counterfeiting technology.

The researchers, Carlos Campos-Cuerva, Maciej Zieba, and coauthors at the University of Zaragoza in Zaragoza, Spain, and CIBER-BBN in Madrid, Spain, have published a paper on the anti-counterfeiting nanoparticle ink in a recent issue of Nanotechnology.

“We believe that it would be interesting to sell to different manufacturers their own personalized ink providing a specific combination of signals,” coauthor Manuel Arruebo at the University of Zaragoza and CIBER-BBN told Phys.org. “The nanoparticle-containing ink could then be used to mark a wide variety of supports including paper (documents, labels of wine, or drug packaging), plastic (bank or identity cards), textiles (luxury clothing or bags), and so on.”

Whereas previous methods of using nanoparticles as an anti-counterfeiting measure often require expensive, sophisticated equipment, the is much simpler. The researchers attached the nanoparticles to the paper by standard screen-printing of transparent ink, and then authenticated the samples using commercially available optical and magnetic sensors.

“We demonstrated that the combination of nanomaterials providing different optical and on the same printed support is possible, and the resulting combined signals can be used to obtain a user-configurable label, providing a high degree of security in anti-counterfeiting applications using simple commercially available sensors at a low cost,” Arruebo said.

anticounterfeiting nanoparticles
An SEM micrograph of paper printed with nanoparticle-based ink, with the nanoparticles circled in red. Credit: Campos-Cuerva, et al. ©2016 IOP Publishing

Although the nanoparticle ink is easy for the researchers to fabricate, attempting to replicate these authentication signals would be extremely difficult for a forger because the signals arise from the highly specific physical and chemical characteristics of the nanoparticles. Replicating the exact type, size, shape, and surface coating requires highly precise fabrication methods and an understanding of the correlation between the signals and these characteristics.

Making replication even more complicated is the fact that the combined optical and are printed on top of each other in the same spot, and this overlap creates an even more complex signal. Another advantage of the new technique is that the nanoparticles are able to withstand extreme temperatures and humidity under accelerated weathering conditions.

One of the greatest applications of the technology may be to prevent forgery of pharmaceutical drugs. Counterfeit medicine—which includes drugs that have incorrect or no active ingredients, as well as drugs that are intentionally mislabeled—is a growing problem throughout the world. The researchers plan to pursue such applications as well as further increase the security of the technology in future work.

“We plan to add more physical signals to the same tag by combining which could provide optical, magnetic, and electrical signals, etc., on the same printed spot,” Arruebo said.

Explore further: Upconverting nanoparticle inks: Invisible QR codes tackle counterfeit bank notes

More information: Carlos Campos-Cuerva, et al. “Screen-printed nanoparticles as anti-counterfeiting tags.” Nanotechnology. DOI: 10.1088/0957-4484/27/9/095702

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Lithium Batt Metal 23d9926Rechargeable lithium metal batteries have been known for four decades to offer energy storage capabilities far superior to today’s workhorse lithium-ion technology that powers our smartphones and laptops. But these batteries are not in common use today because, when recharged, they spontaneously grow treelike bumps called dendrites on the surface of the negative electrode.

Over many hours of operation, these dendrites grow to span the space between the negative and positive electrode, causing short-circuiting and a potential safety hazard.

Current technology focuses on managing these dendrites by putting up a mechanically strong barrier, normally a ceramic separator, between the negative and the positive electrodes to restrict the movement of the dendrite. The relative non-conductivity and brittleness of such barriers, however, means the battery must be operated at high temperature and are prone to failure when the barrier cracks.

But a Cornell team, led by chemical and biomolecular engineering professor Lynden Archer and graduate student Snehashis Choudhury, proposed in a recent study that by designing nanostructured membranes with pore dimensions below a critical value, it is possible to stop growth of dendrites in lithium batteries at room temperature.

“The problem with ceramics is that this brute-force solution compromises conductivity,” said Archer, the William C. Hooey Director and James A. Friend Family Distinguished Professor of Engineering and director of the Robert Frederick Smith School of Chemical and Biomolecular Engineering.

“This means that batteries that use ceramics must be operated at very high temperatures — 300 to 400 degrees Celsius [572 to 752 degrees Fahrenheit], in some cases,” Archer said. “And the obvious challenge that brings is, how do I put that in my iPhone?”

You don’t, of course, but with the technology that the Archer group has put forth, creating a highly efficient lithium metal battery for a cellphone or other device could be reality in the not-too-distant future.

Archer credits Choudhury with identifying the polymer polyethylene oxide as particularly promising. The idea was to take advantage of “hairy” nanoparticles, created by grafting polyethylene oxide onto silica to form nanoscale organic hybrid materials (NOHMs), materials Archer and his colleagues have been studying for several years, to create nanoporous membranes.

To screen out dendrites, the nanoparticle-tethered PEO is cross-linked with another polymer, polypropylene oxide, to yield mechanically robust membranes that are easily infiltrated with liquid electrolytes. This produces structures with good conductivity at room temperature while still preventing dendrite growth.

“Instead of a ‘wall’ to block the dendrites’ proliferation, the membranes provided a porous media through which the ions pass, with the pore-gaps being small enough to restrict dendrite penetration,” Choudhury said. “With this nanostructured electrolyte, we have created materials with good mechanical strength and good ionic conductivity at room temperature.”

Archer’s group plotted the performance of its crosslinked nanoparticles against other materials from previously published work and determined “with this membrane design, we are able to suppress dendrite growth more efficiently that anything else in the field. That’s a major accomplishment,” Archer said.

One of the best things about this discovery, Archer said, is that it’s a “drop-in solution,” meaning battery technology wouldn’t have to be radically altered to incorporate it.

“The membrane can be incorporated with batteries in a variety of form factors, since it’s like a paint — and we can paint the surface of electrodes of any shape,” Choudhury added.

This solution also opens the door for other applications, Archer said.

“The structures that Snehashis has created can be as effective with batteries based on other metals, such as sodium and aluminum, that are more earth-abundant and less expensive than lithium and also limited by dendrites,” Archer said.

The group’s paper, “A highly reversible room-temperature lithium metal battery based on crosslinked hairy nanoparticles,” was published Dec. 4 in Nature Communications. All four group members, including doctoral students Rahul Mangal and Akanksha Agrawal, contributed to the paper.

The Archer group’s work was supported by the National Science Foundation’s Division of Materials Research and by a grant from the King Abdullah University of Science and Technology in Saudi Arabia. The research made use of the Cornell High Energy Synchrotron Source, which also is supported by the NSF.


Story Source:

The above post is reprinted from materials provided by Cornell University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Snehashis Choudhury, Rahul Mangal, Akanksha Agrawal, Lynden A. Archer. A highly reversible room-temperature lithium metal battery based on crosslinked hairy nanoparticles. Nature Communications, 2015; 6: 10101 DOI: 10.1038/ncomms10101

Lithium Batt Micro Org 160204151102_1_540x360Lithium Battery Catalyst Found to Harm Key Soil Microorganism

University of Wisconsin-Madison

The material at the heart of the lithium ion batteries that power electric vehicles, laptop computers and smartphones has been shown to impair a key soil bacterium, according to new research published online in the journal Chemistry of Materials.

The study by researchers at the University of Wisconsin-Madison and the University of Minnesota is an early signal that the growing use of the new nanoscale materials used in the rechargeable batteries that power portable electronics and electric and hybrid vehicles may have untold environmental consequences.

Researchers led by UW-Madison chemistry Professor Robert J. Hamers explored the effects of the compound nickel manganese cobalt oxide (NMC), an emerging material manufactured in the form of nanoparticles that is being rapidly incorporated into lithium ion battery technology, on the common soil and sediment bacterium Shewanella oneidensis.

Lithium Batt Micro Org 160204151102_1_540x360

Shewanella oneidensis is a ubiquitous, globally distributed soil bacterium. In nature, the microbe thrives on metal ions, converting them to metals like iron that serve as nutrients for other microbes. The bacterium was shown to be harmed by the compound nickel manganese cobalt oxide, which is produced in nanoparticle form and is the material poised to become the dominant material in the lithium ion batteries that will power portable electronics and electric vehicles.
Credit: Illustration by Marushchenko/University of Minnesota

“As far as we know, this is the first study that’s looked at the environmental impact of these materials,” says Hamers, who collaborated with the laboratories of University of Minnesota chemist Christy Haynes and UW-Madison soil scientist Joel Pedersen to perform the new work.

NMC and other mixed metal oxides manufactured at the nanoscale are poised to become the dominant materials used to store energy for portable electronics and electric vehicles. The materials, notes Hamers, are cheap and effective.

“Nickel is dirt cheap. It’s pretty good at energy storage. It is also toxic. So is cobalt,” Hamers says of the components of the metal compound that, when made in the form of nanoparticles, becomes an efficient cathode material in a battery, and one that recharges much more efficiently than a conventional battery due to its nanoscale properties.

Hamers, Haynes and Pedersen tested the effects of NMC on a hardy soil bacterium known for its ability to convert metal ions to nutrients. Ubiquitous in the environment and found worldwide, Shewanella oneidensis, says Haynes, is “particularly relevant for studies of potentially metal-releasing engineered nanomaterials. You can imagine Shewanella both as a toxicity indicator species and as a potential bioremediator.”

Subjected to the particles released by degrading NMC, the bacterium exhibited inhibited growth and respiration. “At the nanoscale, NMC dissolves incongruently,” says Haynes, releasing more nickel and cobalt than manganese. “We want to dig into this further and figure out how these ions impact bacterial gene expression, but that work is still underway.”

Haynes adds that “it is not reasonable to generalize the results from one bacterial strain to an entire ecosystem, but this may be the first ‘red flag’ that leads us to consider this more broadly.”

The group, which conducted the study under the auspices of the National Science Foundation-funded Center for Sustainable Nanotechnology at UW-Madison, also plans to study the effects of NMC on higher organisms.

According to Hamers, the big challenge will be keeping old lithium ion batteries out of landfills, where they will ultimately break down and may release their constituent materials into the environment.

“There is a really good national infrastructure for recycling lead batteries,” he says. “However, as we move toward these cheaper materials there is no longer a strong economic force for recycling. But even if the economic drivers are such that you can use these new engineered materials, the idea is to keep them out of the landfills. There is going to be 75 to 80 pounds of these mixed metal oxides in the cathodes of an electric vehicle.”

Hamers argues that there are ways for industry to minimize the potential environmental effects of useful materials such as coatings, “the M&M strategy,” but the ultimate goal is to design new environmentally benign materials that are just as technologically effective.


Story Source:

The above post is reprinted from materials provided by University of Wisconsin-Madison. The original item was written by Terry Devitt. Note: Materials may be edited for content and length.


Journal Reference:

  1. Mimi N. Hang, Ian L. Gunsolus, Hunter Wayland, Eric S Melby, Arielle C. Mensch, Katie R Hurley, Joel A. Pedersen, Christy L. Haynes, Robert J Hamers. Impact of Nanoscale Lithium Nickel Manganese Cobalt Oxide (NMC) on the Bacterium Shewanella oneidensis MR-1. Chemistry of Materials, 2016; DOI: 10.1021/acs.chemmater.5b04505

 

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Note to Readers: A lot of you have Commented or E-mailed with a common question about this article, “Who is the new start-up company?” (developing the anti-counterfeiting technology based on Quantum Dots). For more information about the Company, its History, Founders and Technologies visit: Quantum Materials Corporation: Symbol: QTMM

BTW … In a recent press release they just released: Quantum Materials Corp to launch Quantum Dot Production in China with Joint Venture Partner GTG, who has committed $20 Million US in investment.”

Cheers! Team GNT

 

3D Printed Auto 020516 XMODULE3-1-e1454538456427

Even with all the promise offered by additive manufacturing (AM), some people are still wary of the potential pitfalls exposed by the technology. Leaving the notion of 3D printed guns, hearts and electronics aside, there are very real concerns about how intellectual property (IP) will fare in a digital manufacturing world, or how any single company can protect sales of 3D printed objects. Piracy is often seen as only a 3D scanner and printer away.

 

QD AM Mfg 020516 LEDA new start-up Nano-materials company may have the solution to some of these concerns. The company is in the business of manufacturing, among other things, quantum dots. These tiny structures are constructed from semiconductor Nano-materials, and can be embedded within 3D printed objects. A partnership with the Institute for Critical Technology and Applied Science and the Design, Research, and Education for Additive Manufacturing Systems (DREAMS) Laboratory at Virginia Tech has resulted in a method of using quantum dots to act as a sort of fingerprint for objects built using AM.

“The remarkable number of variations of semiconductor Nano-materials properties that can be manufactured, coupled with Virginia Tech’s anti-counterfeiting process design, combine to offer corporations extreme flexibility in designing physical cryptography systems to thwart counterfeiters. As 3D printing and additive manufacturing technology advances, its ubiquity allows for the easy pirating of protected designs.” (VP for research and development)

The quantum dots work to foil counterfeiters by creating a unique signature for each item that is only known to the company producing that item. This will allow for rapid recognition of counterfeit items without requiring destructive testing methods.

Additionally, the company offers a number of semiconductor Nano-materials that further increase security. If you are familiar with computing, the addition of unique materials improves security strength in a similar way as moving from 128-bit to 256-bit encryption, according to the company.

With the recent boom in medical AM, both for rapid prototyping and end-use, this type of security can offer companies some assurance that they’ll see a return on investment for all the hard work put in to designing new devices. The use of quantum dots should also reassure other manufacturers who are on the fence about the use of AM that their patents will be upheld by more than a piece of paper and a handshake.

3D Printing I 020516 3d_printing

The specter of counterfeit products is always a concern for any company that relies on other facilities to actually manufacture and assemble their products. From fake Rolex watches to fake iPhones to fake Louis Vuitton purses, large companies often spend millions to protect their intellectual property from criminals who copy and sell fake products to often unsuspecting consumers.

While it can be easy to be anti-corporate and turn a blind eye to this kind of theft, especially when the companies are large and extremely profitable, their concern goes far beyond the potential loss of profits. The fact is, most counterfeit products are vastly inferior to the real thing, and if a consumer doesn’t know that they are purchasing a fake then the company not only has a lost sale, but their reputation will take a hit based on something that they didn’t even produce.

Even as 3D printing continues to grow into a valid and profitable alternative manufacturing method to injection molding or large-scale mass production, there are still companies that see the threat of counterfeiting as a reason to stall the adoption of 3D printing technology. Realistically there is not much that can be done about pirated 3D models and individuals using home 3D printers to make fake products. Combating individual piracy has been woefully ineffective for the entertainment industry, and probably only encouraged more users to download electronic files illegally. It stands to reason that going after individual pirates will work just as well if the 3D printing industry makes an attempt to over-regulate and control the flow of 3D printable files.

DRM on 3D printable files is probably not going to be an effective deterrent.

DRM on 3D printable files is probably not going to be an effective deterrent.

Many of the solutions that are being floated as counter-counterfeiting measures don’t really seem especially feasible or sustainable. Adding DRM (digital rights management) or unlock code requirements to 3D files may slow down some users, but just as with DRM efforts on movies and video games, if someone can put a lock on something, someone can take that same lock off and teach others how to do it as well. These efforts may work in the short term, as the pool of users who are capable of breaking DRM on 3D printable files is smaller, and there isn’t really an outlet to disperse those illegal files yet. But as the industry grows it is going to be harder and harder for companies to control their intellectual property using these methods. I’m not really sure that there is much to be done on this end of the industry. Besides, there is an even greater counterfeiting problem brewing on the manufacturing side of the industry and it is far more important than individual piracy ever could be.

Counterfeit bolts.

Counterfeit bolts.

As with fake mass-produced consumer goods, mass-produced industrial parts are also counterfeited quite frequently. It may be more interesting to talk about fake purses, but a greater threat is products like fake screws, bolts, fittings and individual components. Many of the parts that are used to build our homes, businesses, vehicles and personal electronics use mass-produced components that manufacturers simply purchase in extremely large quantities. And all of those parts are held to very strict manufacturing guidelines that dictate how they can be used, what their maximum stress tolerances are and how they can be expected to perform.

When these types of components are forged, they are rarely made with the same quality of materials and often don’t even come close to performing as required. If these fake parts find their way unknowingly into the hands of manufacturers, who design products with these components’ manufacturing guidelines in mind, then the results could be catastrophic. There have been instances of airplanes and automobiles that have crashed due to the failure of lower quality, counterfeit parts. Buildings and homes are also at risk due to poor quality and counterfeited construction materials being used. It may seem odd, but cheaply made products that do not pass strict regulations are a huge business and lives can be lost to it.

3D printed Nike shoes with embedded InfraStructs.

3D printed Nike shoes with embedded InfraStructs.

With 3D printed components becoming more common, and eventually expected to be extremely common, counterfeit parts will pose a real risk. Using DRM, even if it was effective on a small scale, to prevent machines from making unauthorized parts is not going to matter when these parts can simply be 3D scanned and reproduced without the need for the original 3D model. The methods that need to be developed to combat this type of industrial counterfeiting will need to work in ways that DRM never will and identify the specific physical object as authentic. There are a few different methods that are currently being proposed, with varying probabilities of success.

The most likely option will be including RFID tags on 3D printed components that will identify an object as the real thing. The idea is that any part that doesn’t have an embedded RFID device in it — and they can easily be made small enough to easily be inserted inside of a 3D printed part — will automatically be identified as fake. The downside of this method is price, as the RFID tags themselves would be costly, as would the labor involved in inserting them. Testing for tags will also require specialized equipment that adds more cost to the authentication process. It is possible that a 3D printable material that would act as a tag called InfraStructs could be developed, but that would mean developing multiple materials that will be RFID reactive, which will be quite costly on the development side.

Subsurface fingerprinting with InfraTrac.

Subsurface fingerprinting with InfraTrac.

Another authentication option would be chemically tagging materials that can be detected with a handheld spectrometer. There are multiple companies providing these types of materials, but the most promising is a technique developed by InfraTrac. The Maryland-based company has developed a chemical that can be discreetly added to virtually anything without altering the chemical makeup of the material. For instance, parts can be 3D printed with a small subsurface “fingerprint” hidden in a discrete location. That mark alone would be printed with the material that has been treated with the chemical, and would easily identify the part as genuine. The material could also be printed as a single layer of the print with no mark, and no risk of altering the integrity of the part. Of course again this comes with it the need for specialized equipment in the form of the spectrometer and an actual machine that can 3D print with the standard material and the second, tagged material.

3D Printing II Heart 020516 maxresdefault

3D Printed Model of a Human Heart

One thing is very clear, there is a desire for additive manufacturing to be developed as an alternative to other mass production methods. That means the companies looking to use 3D printing to manufacture parts, and the 3D printing industry itself, are going to need to address the problem sooner rather than later. Determining which of these options is the ideal solution will not be an easy choice, as they both bring with them additional costs and challenges, but doing nothing simply isn’t an option.

 

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Nanowires 020316 bf8802f7297fd2bfea985c26d0b9a636_w1440

California is committed to 33 percent energy from renewable resources by 2020. With that deadline fast approaching, researchers across the state are busy exploring options.

Solar energy is attractive but for widespread adoption, it requires transformation into a storable form. This week in ACS Central Science, researchers report that nanowires made from multiple metal oxides could put solar ahead in this race.

One way to harness solar power for broader use is through photoelectrochemical (PEC) water splitting that provides hydrogen for fuel cells. Many materials that can perform the reaction exist, but most of these candidates suffer from issues, ranging from efficiency to stability and cost.

Peidong Yang and colleagues designed a system where nanowires from one of the most commonly used materials (TiO2) acts as a “host” for “guest” nanoparticles from another oxide called BiVO4. BiVO4 is a newly introduced material that is among the best ones for absorbing light and performing the water splitting reaction, but does not carry charge well while TiO2 is stable, cheap and an efficient charge carrier but does not absorb light well.

Together with a unique studded nanowire architecture, the new system works better than either material alone.

The authors state their approach can be used to improve the efficiencies of other photoconversion materials.

Synopsis

We report the use of Ta:TiO2|BiVO4 as a photoanode for use in solar water splitting cells. This host−guest system makes use of the favorable band alignment between the two semiconductors. The nanowire architecture allows for simultaneously high light absorption and carrier collection for efficient solar water oxidation.

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Metal oxides that absorb visible light are attractive for use as photoanodes in photoelectrosynthetic cells. However, their performance is often limited by poor charge carrier transport. We show that this problem can be addressed by using separate materials for light absorption and carrier transport. Here, we report a Ta:TiO2|BiVO4 nanowire photoanode, in which BiVO4 acts as a visible light-absorber and Ta:TiO2 acts as a high surface area electron conductor. Electrochemical and spectroscopic measurements provide experimental evidence for the type II band alignment necessary for favorable electron transfer from BiVO4 to TiO2. The host–guest nanowire architecture presented here allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent density of 2.1 mA/cm2 at 1.23 V vs RHE.

Introduction


Harnessing energy from sunlight is a means of meeting the large global energy demand in a cost-effective and environmentally benign manner. However, to provide constant and stable power on demand, it is necessary to convert sunlight into an energy storage medium.(1) An example of such a method is the production of hydrogen by photoelectrochemical (PEC) water splitting. The direct splitting of water can be achieved using a single semiconductor; however, due to the voltage requirement of the water splitting reaction and the associated kinetic overpotentials, only wide-band-gap materials can perform overall water splitting, limiting the efficiency due to insufficient light absorption.(2) To address this issue, a dual-band-gap z-scheme system can be utilized, with a semiconductor photoanode and photocathode to perform the respective oxidation and reduction reactions.(3) This approach allows for the use of lower-band-gap materials that can absorb complementary portions of the solar spectrum and yield higher solar-to-fuel efficiencies.(4, 5) In this integrated system, the charge flux is matched in both light absorbers of the photoelectrochemical cell. Therefore, the overall performance is determined by the limiting component. In most photoelectrosynthetic cells, this limiting component is the semiconductor photoanode.(6)
Metal oxides have been heavily researched as photoanode materials since few conventional light absorber materials are stable at the highly oxidizing conditions required for water oxidation.(7) However, the most commonly studied binary oxide, TiO2, has a band gap that is too large to absorb sunlight efficiently (∼3.0 eV), consequently limiting its achievable photocurrent.(8) While promising work has recently been done on stabilizing conventional light absorbers such as Si,(9) GaAs,(10) and InP,(11) the photovoltage obtained by these materials thus far has been insufficient to match with smaller-band-gap photocathode materials such as Si and InP in a dual absorber photoelectrosynthetic cell.(12, 13) Additionally, these materials have high production and processing costs. Small-band-gap metal oxides that absorb visible light and can be inexpensively synthesized, such as WO3, Fe2O3, and BiVO4, are alternative materials that hold promise to overcome these limitations.(14-16) Among these metal oxides, BiVO4 has emerged as one of the most promising materials due to its relatively small optical band gap of ∼2.5 eV and its negative conduction band edge (∼0 V versus RHE).(17, 18) Under air mass 1.5 global (AM1.5G) solar illumination, the maximum achievable photocurrent for water oxidation using BiVO4 is ∼7 mA/cm2.(16) However, the water oxidation photocurrent obtained in practice for BiVO4 is substantially lower than this value, mainly due to poor carrier transport properties, with electron diffusion lengths shorter than the film thickness necessary to absorb a substantial fraction of light.(17)
One approach for addressing this problem is to use two separate materials for the tasks of light absorption and carrier transport. To maximize performance, a conductive and high surface area support material (“host”) is used, which is coated with a highly dispersed visible light absorber (“guest”). This architecture allows for efficient use of absorbed photons due to the proximity of the semiconductor liquid junction (SCLJ). This strategy has been employed in dye sensitized (DSSC) and quantum dot sensitized solar cells (QDSSC).(19, 20) Using a host–guest scheme can improve the performance of photoabsorbing materials with poor carrier transport but relies upon appropriate band alignment between the host and guest. Namely, the electron affinity of the host should be larger, to favor electron transfer from guest to host without causing a significant loss in open-circuit voltage.(21) Nanowire arrays provide several advantages for use as the host material as they allow high surface area loading of the guest material, enhanced light scattering for improved absorption, and one-dimensional electron transport to the back electrode.(22) Therefore, nanowire arrays have been used as host materials in DSSCs, QDSSCs, and hybrid perovskite solar cells.(23-25) In photoelectrosynthetic cells, host–guest architectures have been utilized for oxide photoanodes such as Fe2O3|TiSi2,(26) Fe2O3|WO3,(27) Fe2O3|SnO2,(28) and Fe2TiO5|TiO2.(29) For BiVO4, it has been studied primarily with WO3|BiVO4,(30-32) ZnO|BiVO4,(33) and anatase TiO2|BiVO4.(34) While attractive for its electronic transport properties, ZnO is unstable in aqueous environments, and WO3 has the disadvantage of having a relatively positive flatband potential (∼0.4 V vs RHE)(14) resulting in potential energy losses for electrons as they are transferred from BiVO4 to WO3, thereby limiting the photovoltage of the combined system. Performance in the low potential region is critical for obtaining high efficiency in photoelectrosynthetic cells when coupled to typical p-type photocathode materials such as Si or InP.(12, 13) TiO2 is stable in a wide range of pH and has a relatively negative flat band potential (∼0.2 V vs RHE)(7) which does not significantly limit the photovoltage obtainable from BiVO4, while still providing a driving force for electron transfer. While TiO2 has intrinsically low mobility, doping TiO2 with donor type defects could increase the carrier concentration and thus the conductivity. Indeed, niobium and tantalum doped TiO2 have recently been investigated as potential transparent conductive oxide (TCO) materials.(35, 36) A host material with high carrier concentration could also ensure low contact resistance with the guest material.(37)
Using a solid state diffusion approach based on atomic layer deposition (ALD), we have previously demonstrated the ability to controllably and uniformly dope TiO2.(38) In this study we demonstrate a host–guest approach using Ta-doped TiO2 (Ta:TiO2) nanowires as a host and BiVO4 as a guest material. This host–guest nanowire architecture allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent of 2.1 mA/cm2 at 1.23 V vs RHE. We show that the synergistic effect of the host–guest structure results in higher performance than either pure TiO2 or BiVO4. We also experimentally demonstrate thermodynamically favorable band alignment between TiO2 and BiVO4 using spectroscopic and electrochemical methods, and study the band edge electronic structure of the TiO2 and BiVO4 using X-ray absorption and emission spectroscopies.

Article adapted from a American Chemical Society news release. To Read the FULL release, please click on the link provided below.

Publication: TiO2/BiVO4 Nanowire Heterostructure Photoanodes Based on Type II Band Alignment. Resasco, J et al. ACS Central Science (3 February, 2016): Click here to view.

GNT Thumbnail Alt 3 2015-page-001

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Sun Solar 061015 Fusion BBkFITY

Video Interview with Professor Ted Sargent at the University of Toronto

With global climate change on the rise, finding ways to capture renewable energy sources is becoming more urgent. Today, our energy needs are largely being met by fossil fuels, such as oil and coal, but we are rapidly depleting these natural resources, and damaging our environment by burning them for fuel. One sustainable alternative is solar energy. Prof. Ted Sargent, an electrical engineer at the University of Toronto, is working on making a new paint-based solar cell that would be low-cost, lightweight, portable, and efficient, bringing sustainable electricity anywhere that it is needed.

We picture a world in which solar cells are so convenient. They are on a carpet that you can roll out onto your roof, or they are on a decal that you can stick on the side of a streetcar or stick on your car, you can stick on your airplane wing. And they can be kind of adhered to any surface. And they can be used to meet the power needs of that automobile or plane or helicopter or home or tent; and they are ubiquitous.

Unlike fossil fuels, Sargent explains, “the sun is this incredible, vast resource. We get more sun reaching the Earth’s surface everyday than we need to power the world’s energy needs. In fact, in an hour, we get enough to meet our energy needs for a year; it’s that abundant.” To achieve a better solar cell, Prof. Sargent is working at the interface of chemistry, physics, materials science, and electrical engineering to understand the relationships between light and electrons. He is developing a liquid for solar capture that can be applied as a paint, and that can be printed using roll-to-roll processes similar to those used to print newspapers. These paints would absorb sunlight and use it to generate electricity.

Prof. Sargent envisions solar cells that are so minimal that installing one might be as simple as unrolling a sheet onto a rooftop, or applying a decal to a streetcar or phone. “We picture a world in which solar cells are so convenient… They are so little in their consumption of materials that we change the paradigm of solar energy from one that takes planning, major capital investment, to one where it’s all over the place because it’s so compelling and convenient,” says Sargent.

How do you envision the future of energy and power? Let us know in the comments.


Prof. Ted Sargent
Prof. Ted Sargent holds the Canada Research Chair in Nanotechnology at the University of Toronto, where he also serves as Vice Dean for Research for the Faculty of Applied Science and Engineering. He is a Fellow of the Royal Society of Canada, a Fellow of the AAAS “for distinguished contributions to the development of solar cells and light sensors based on solution-processed semiconductors” and a Fellow of the IEEE “for contributions to colloidal quantum dot optoelectronic devices.” He is CTO of InVisage Technologies of Menlo Park, CA; and is a co-founder of Xagenic Inc.

QD Images Scale and Size quantum_dots_c

 

Readers’ Note: Dr. Alivisatos (Berkeley) has been a pioneer of ‘nano-cystals’ and their potential applications. Most recently these ‘crystals’ or Quantum Dots have found their way into commercial application for Display Screens. However the much larger vision for QD’s has significant (“game changing”) implications for: Solar Energy, Bio-Medicine, Drug Theranostics & Delivery, Lighting and Hybrid-Materials (Coatings, Paints, Security Inks as examples).  Enjoy the Video ~ Team GNT

Nanosys scientific co-founder and Director of the Lawerence Berkeley National Lab, Dr. Paul Alivisatos, takes NBC Learn on a tour of Nanosys’ Silicon Valley Quantum Dot manufacturing facility.

The section on Nanosys begins at 2:16 – enjoy!

Watch: NanoSys: Quantum Dot Video

Dr Alivisatos, who recently received the 2016 National Medal of Science, talks with NBC reporter Kate Snow about how this amazing nanotechnology that he helped pioneer is changing the way our TVs work today:

SNOW: When quantum dots of different sizes are grouped together by the billions, they produce vivid colors that have changed the way we look at display screens. The initial research, funded by the NSF, has found its way into many applications, including a nanotechnology company called Nanosys, which produces 25 tons of quantum dot materials every year, enough for approximately 6 million 60 inch TVs.

ALIVISATOS: What we have here is a plastic film that contains inside of it quantum dots, very tiny, tiny crystals made out of semiconductors. It actually contains two sizes of nanoparticle – a very small size that emits a green color and a slightly larger size that emits a red color of light.

SNOW: This film is embedded into tablets, televisions, and laptops to enhance their displays with brilliant color.

ALIVISATOS: One of the things that we’ve learned about vision is that we have receptors in our eyes for green, red and blue colors. And if we want a really high quality display, we need to match the light emission from our display to the receptors in our eyes.

Tour De Ice graphenecomp

Rice University scientists embedded graphene nanoribbon-infused epoxy in a section of helicopter blade to test its ability to remove ice through Joule heating. Credit: Tour Group/Rice University 

A thin coating of graphene nanoribbons in epoxy developed at Rice University has proven effective at melting ice on a helicopter blade.

The coating by the Rice lab of chemist James Tour may be an effective real-time de-icer for aircraft, , transmission lines and other surfaces exposed to winter weather, according to a new paper in the American Chemical Society journal ACS Applied Materials and Interfaces.

In tests, the lab melted centimeter-thick ice from a static helicopter rotor blade in a minus-4-degree Fahrenheit environment. When a small voltage was applied, the coating delivered electrothermal heat – called Joule heating – to the surface, which melted the ice.

The nanoribbons produced commercially by unzipping nanotubes, a process also invented at Rice, are highly conductive. Rather than trying to produce large sheets of expensive graphene, the lab determined years ago that nanoribbons in composites would interconnect and conduct electricity across the material with much lower loadings than traditionally needed.

Previous experiments showed how the nanoribbons in films could be used to de-ice radar domes and even glass, since the films can be transparent to the eye.

Graphene composite may keep wings ice-free
Lab tests at Rice University on a section of a helicopter rotor chilled to minus-4 degrees Fahrenheit show that a thin coat of nanoribbon-infused epoxy can be used as a de-icer. The composite, imbedded between an abrasion shield and the …more

“Applying this composite to wings could save time and money at airports where the glycol-based chemicals now used to de-ice aircraft are also an environmental concern,” Tour said.

In Rice’s lab tests, nanoribbons were no more than 5 percent of the composite. The researchers led by Rice graduate student Abdul-Rahman Raji spread a thin coat of the composite on a segment of rotor blade supplied by a helicopter manufacturer; they then replaced the thermally conductive nickel abrasion sleeve used as a leading edge on . They were able to heat the composite to more than 200 degrees Fahrenheit.

For wings or blades in motion, the thin layer of water that forms first between the heated composite and the surface should be enough to loosen ice and allow it to fall off without having to melt completely, Tour said.

The lab reported that the remained robust in temperatures up to nearly 600 degrees Fahrenheit.

As a bonus, Tour said, the coating may also help protect aircraft from lightning strikes and provide an extra layer of electromagnetic shielding.

Explore further: Researchers create sub-10-nanometer graphene nanoribbon patterns

More information: Abdul-Rahman O. Raji et al. Composites of Graphene Nanoribbon Stacks and Epoxy for Joule Heating and Deicing of Surfaces, ACS Applied Materials & Interfaces (2016). DOI: 10.1021/acsami.5b11131

Nano Weaving RD_COF

There are many different ways to make nano-materials but weaving, the oldest and most enduring method of making fabrics, has not been one of them – until now. An international collaboration led by scientists at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley, has woven the first three-dimensional covalent organic frameworks (COFs) from helical organic threads. The woven COFs display significant advantages in structural flexibility, resiliency and reversibility over previous COFs – materials that are highly prized for their potential to capture and store carbon dioxide then convert it into valuable chemical products.

“We have taken the art of weaving into the atomic and molecular level, giving us a powerful new way of manipulating matter with incredible precision in order to achieve unique and valuable mechanical properties,” says Omar Yaghi, a chemist who holds joint appointments with Berkeley Lab’s Materials Sciences Division and UC Berkeley’s Chemistry Department, and is the co-director of the Kavli Energy NanoScience Institute (Kavli-ENSI).

“Weaving in chemistry has been long sought after and is unknown in biology,” Yaghi says. “However, we have found a way of weaving organic threads that enables us to design and make complex two- and three-dimensional organic extended structures.”

Yaghi is the corresponding author of a paper in Science reporting this new technique. The paper is titled “Weaving of organic threads into a crystalline covalent organic framework.” The lead authors are Yuzhong Liu, Yanhang Ma and Yingbo Zhao. Other co-authors are Xixi Sun, Felipe Gándara, Hiroyasu Furukawa, Zheng Liu, Hanyu Zhu, Chenhui Zhu, Kazutomo Suenaga, Peter Oleynikov, Ahmad Alshammari, Xiang Zhang and Osamu Terasaki.

COFs and their cousin materials, metal organic frameworks (MOFs), are porous three-dimensional crystals with extraordinarily large internal surface areas that can absorb and store enormous quantities of targeted molecules. Invented by Yaghi, COFs and MOFs consist of molecules (organics for COFs and metal-organics for MOFs) that are stitched into large and extended netlike frameworks whose structures are held together by strong chemical bonds. Such frameworks show great promise for, among other applications, carbon sequestration.

Through another technique developed by Yaghi, called “reticular chemistry,” these frameworks can also be embedded with catalysts to carry out desired functions: for example, reducing carbon dioxide into carbon monoxide, which serves as a primary building block for a wide range of chemical products including fuels, pharmaceuticals and plastics.

In this latest study, Yaghi and his collaborators used a copper(I) complex as a template for bringing threads of the organic compound “phenanthroline” into a woven pattern to produce an immine-based framework they dubbed COF-505. Through X-ray and electron diffraction characterizations, the researchers discovered that the copper(I) ions can be reversibly removed or restored to COF-505 without changing its woven structure. Demetalation of the COF resulted in a tenfold increase in its elasticity and remetalation restored the COF to its original stiffness.

“That our system can switch between two states of elasticity reversibly by a simple operation, the first such demonstration in an extended chemical structure, means that cycling between these states can be done repeatedly without degrading or altering the structure,” Yaghi says. “Based on these results, it is easy to imagine the creation of molecular cloths that combine unusual resiliency, strength, flexibility and chemical variability in one material.”

Yaghi says that MOFs can also be woven as can all structures based on netlike frameworks. In addition, these woven structures can also be made as nanoparticles or polymers, which means they can be fabricated into thin films and electronic devices.

“Our weaving technique allows long threads of covalently linked molecules to cross at regular intervals,” Yaghi says. “These crossings serve as points of registry, so that the threads have many degrees of freedom to move away from and back to such points without collapsing the overall structure, a boon to making materials with exceptional mechanical properties and dynamics.”

Source: Lawrence Berkeley National Laboratory


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