Researchers Create Quantum Dots with Single-Atom Precision: Naval Research Center

 

Washington, DC | Posted on June 30th, 2014

Quantum dots are often regarded as artificial atoms because, like real atoms, they confine their electrons to quantized states with discrete energies. But the analogy breaks down quickly, because while real atoms are identical, quantum dots usually comprise hundreds or thousands of atoms – with unavoidable variations in their size and shape and, consequently, in their properties and behavior. External electrostatic gates can be used to reduce these variations. But the more ambitious goal of creating quantum dots with intrinsically perfect fidelity by completely eliminating statistical variations in their size, shape, and arrangement has long remained elusive.

Creating atomically precise quantum dots requires every atom to be placed in a precisely specified location without error. The team assembled the dots atom-by-atom, using a scanning tunneling microscope (STM), and relied on an atomically precise surface template to define a lattice of allowed atom positions. The template was the surface of an InAs crystal, which has a regular pattern of indium vacancies and a low concentration of native indium adatoms adsorbed above the vacancy sites. The adatoms are ionized +1 donors and can be moved with the STM tip by vertical atom manipulation. The team assembled quantum dots consisting of linear chains of N = 6 to 25 indium atoms; the example shown here is a chain of 22 atoms.

This image shows quantized electron states, for quantum numbers n = 1 to 6, of a linear quantum dot consisting of 22 indium atoms positioned on the surface of an InAs crystal.
Image: Stefan Fölsch/PDI

Stefan Fölsch, a physicist at the PDI who led the team, explained that “the ionized indium adatoms form a quantum dot by creating an electrostatic well that confines electrons normally associated with a surface state of the InAs crystal. The quantized states can then be probed and mapped by scanning tunneling spectroscopy measurements of the differential conductance.” These spectra show a series of resonances labeled by the principal quantum number n. Spatial maps reveal the wave functions of these quantized states, which have n lobes and n – 1 nodes along the chain, exactly as expected for a quantum-mechanical electron in a box. For the 22-atom chain example, the states up to n = 6 are shown.

Because the indium atoms are strictly confined to the regular lattice of vacancy sites, every quantum dot with N atoms is essentially identical, with no intrinsic variation in size, shape, or position. This means that quantum dot “molecules” consisting of several coupled chains will reflect the same invariance. Steve Erwin, a physicist at NRL and the team’s theorist, pointed out that “this greatly simplifies the task of creating, protecting, and controlling degenerate states in quantum dot molecules, which is an important prerequisite for many technologies.” In quantum computing, for example, qubits with doubly degenerate ground states offer protection against environmental decoherence.

By combining the invariance of quantum dot molecules with the intrinsic symmetry of the InAs vacancy lattice, the team created degenerate states that are surprisingly resistant to environmental perturbations by defects. In the example shown here, a molecule with perfect three-fold rotational symmetry was first created and its two-fold degenerate state demonstrated experimentally. By intentionally breaking the symmetry, the team found that the degeneracy was progressively removed, completing the demonstration.

The reproducibility and high fidelity offered by these quantum dots makes them excellent candidates for studying fundamental physics that is typically obscured by stochastic variations in size, shape, or position of the chains. Looking forward, the team also anticipates that the elimination of uncontrolled variations in quantum dot architectures will offer many benefits to a broad range of future quantum dot technologies in which fidelity is important.

####

About Naval Research Laboratory

The U.S. Naval Research Laboratory is the Navy’s full-spectrum corporate laboratory, conducting a broadly based multidisciplinary program of scientific research and advanced technological development. The Laboratory, with a total complement of nearly 2,800 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 90 years and continues to meet the complex technological challenges of today’s world. For more information, visit the NRL homepage or join the conversation on Twitter, Facebook, and YouTube.

For more information, please click here

Contacts:
Donna McKinney
donna.mckinney@nrl.navy.mil
202-404-3322

Copyright © Naval Research Laboratory

Quantum Dot Manufacturing Company Secures Technology to 3D Print Quantum Dots for Anti-Counterfeiting

(Re-Posted Article: by Heidi Milkert · June 30, 2014: Original Post in Va. Tech NT News) Quantum mechanics, it’s certainly an intriguing and almost spooky field, but over the next decade or two we will see a major shift in the understanding and utilization of the various applications of quantum physics. One company based in San Marcos, Texas is already working on 3D printing technologies which are within the quantum realm.

Quantum Materials Corporation has been researching and producing quantum dots for several years now. Quantum dots are the tiny little nanocrystals which are produced from semiconductor materials. They are so tiny, that they take on quantum mechanical properties. Today the company announced that they have secured a specific type of quantum dot technology which has been developed by the Institute for Critical Technology and Applied Science and the Design, Research, and Education for Additive Manufacturing Systems (DREAMS) Laboratory at Virginia Tech.

 

The technology is based around a patented process which embeds tiny quantum dots into products during a 3D printing process, so that their manufacturers can detect counterfeits. The quantum dots are embedded in such a way that they create an unclonable signature of sorts. Only the manufacturers of the products which have these signatures embedded, know what they should be, making it easy for them to detect illegal copies. Such a security feature would work well within a variety of markets.

“The remarkable number of variations of semiconductor nanomaterials properties QMC can manufacture, coupled with Virginia Tech’s anti-counterfeiting process design, combine to offer corporations extreme flexibility in designing physical cryptography systems to thwart counterfeiters, “stated David Doderer, Quantum Materials Corporation VP for Research and Development. “As 3D printing and additive manufacturing technology advances, its ubiquity allows for the easy pirating of protected designs. We are pleased to work with Virginia Tech to develop this technology’s security potential in a way that minimizes threats and maximizes 3D printing’s future impact on product design and delivery by protecting and insuring the integrity of manufactured products.”

The security that such a technique offers is quite high. Not only can Quantum Materials Corporation print quantum dots into object, and have those dots emit specific colors, but they can print the dots into an object shaped in several different ways. In addition the company has the ability to use dual emission tetrapod quantum dots to give off two different colors at once. Such technology should easily slow down product counterfeiting, by giving each product a nanoscale signature, that only its manufacturers know exists.

As 3D printing technology expands, we will find ourselves in a world rife with intellectual property theft. This new quantum dot technology could give companies the ability to 3D print their own products, while maintaining the ability to make sure others are not doing the same with their proprietary designs.

Watching nanoscale fluids flow

(Phys.org) —At the nanoscale, where objects are measured in billionths of meters and events transpire in trillionths of seconds, things do not always behave as our experiences with the macro-world might lead us to expect. Water, for example, seems to flow much faster within carbon nanotubes than classical physics says should be possible. Now imagine trying to capture movies of these almost imperceptibly small nanoscale movements.

 

 

Researchers at Caltech now have done just that by applying a new imaging technique called four-dimensional (4D) electron microscopy to the nanofluid dynamics problem. In a paper appearing in the June 27 issue of Science, Ahmed Zewail, the Linus Pauling Professor of Chemistry and professor of physics, and Ulrich Lorenz, a postdoctoral scholar in chemistry, describe how they visualized and monitored the flow of molten lead within a single zinc oxide nanotube in real time and space.

The 4D microscopy technique was developed in the Physical Biology Center for Ultrafast Science and Technology at Caltech, created and directed by Zewail to advance understanding of the fundamental physics of chemical and biological behavior.

This artistic rendering depicts fluid-filled nanotubes changing with time. Caltech researchers used four-dimensional electron microscopy to visualize and monitor the flow of molten lead within single zinc oxide nanotubes in real time and space. Credit: Caltech 

In 4D microscopy, a stream of ultra-fast-moving electrons bombards a sample in a carefully timed manner. Each electron scatters off the sample, producing a still image that represents a single moment, just a femtosecond—or a millionth of a billionth of a second—in duration. Millions of the still images can then be stitched together to produce a digital movie of nanoscale motion.

In the new work, Lorenz and Zewail used single laser pulses to melt the lead cores of individual zinc oxide nanotubes and then, using 4D microscopy, captured how the hot pressurized liquid moved within the tubes—sometimes splitting into multiple segments, producing tiny droplets on the outside of the tube, or causing the tubes to break. Lorenz and Zewail also measured the friction experienced by the liquid in the nanotube.

“These observations are particularly significant because visualizing the behavior of fluids at the nanoscale is essential to our understanding of how materials and biological channels effectively transport liquids,” says Zewail. In 1999, Zewail won the Nobel Prize for his development of femtosecond chemistry.

The paper is titled “Observing liquid flow in nanotubes by 4D electron microscopy.”

Explore further: New microscope captures movements of atoms and molecules

Read more at: http://phys.org/news/2014-06-nanoscale-fluids.html#jCp

 

Graphene quantum dot band-aids disinfect wounds

A growing body of medical nanotechnology research deals with the development of antibacterial applications, ranging from nanotechnology-based approaches for diagnosing superbugs to antimicrobial surface coatings and wound treatment with antibacterial nanomaterials (Read more: “Nanotechnology solutions to combat superbugs“).

 

Especially silver nanomaterials have been used effectively against different bacteria, fungi and viruses (see for instance: “Stamping antibacterial nanoparticles onto wounds“) but also carbon nanomaterials like nanotubes (read more: “antimicrobial coating combines carbon nanotubes and natural materials“) and graphene (see: “Antibacterial paper made from graphene“). In new work, researchers have now designed an antibacterial system combining graphene quantum dots (GQDs) with a low dose of a common medical reagent, hydrogen peroxide H2O2. By using GQDs, a high concentration of H2O2 – which is harmful to healthy tissue and even delays the wound healing – can be avoided for wound disinfection.

With the assist of GQDs, H2O2 with a concentration that is 2~3 order lower than that commonly used, can kill bacterial effectively. “We find that the peroxidase-like activity of GQDs originates from their ability to catalyze the decomposition of H2O2, generating hydroxyl radicals,” Xiaogang Qu, a professor of chemistry at Changchun Institute of Applied Chemistry, tells Nanowerk. “Since the hydroxyl radicals have a higher antibacterial activity, the conversion of H2O2 into hydroxyl radicals improves the antibacterial performance of H2O2 at low level, which makes it possible to avoid the toxicity of H2O2 at high levels in wound disinfection.” Qu and his team have published their findings in the May 28, 2014 online edition of ACS Nano (“Graphene Quantum Dots-Band-Aids Used for Wound Disinfection”).

 

Schematic of the designed system based on GQDs and low level of H2O2 for antibacterial applications. (Image: Dr. Xiaogang Qu, Changchun Institute of Applied Chemistry)

Researchers have already demonstrated that functional inorganic analogues, such as V2O5 and magnetic iron oxide, can be used to assist H2O2 for antibacterial application, i.e. killing bacteria and destroying bacterial biofilms. Qu points out that the V2O5 and magnetic iron oxide were considered to be toxic and inappropriate for the application in vivo unless via elaborate surface functionalization.

“Considering the excellent biocompatibility and high peroxidase-like activity of GQDs, we conducted our work using GQDs to improve the antibacterial activity of H2O2 for the application of wound disinfection.” Qu’s team showed that their system provides antibacterial properties against both Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria in vitro. The researchers also designed band-aids containing graphene quantum dots and found in their experiments that these GQD-Band-Aids showed excellent antibacterial property in vivo with the assistance of low concentrations of H2O2.

“Our results indicate that GQD-Band-Aids have potential use for wound disinfection,” says Qu. A future extension of this work could be the design of biocompatible functional nanoparticles with high peroxidase-like activity to further improve the antibacterial activity of H2O2 at low concentrations.

As Qu notes, the synergy of peroxidase-like activity and other antibacterial mechanism to achieve better effect may be a particular, but promising, challenge in this field.

Copyright © Nanowerk

Precision production: Nanotubes meet Electronics Requirements

Carbon nanotubes have been hailed as one of the materials most likely to usurp silicon in next-generation electronics that will require nanoscale device sizes. But the existing production techniques do not provide carbon nanotubes with the purity and structural specificity that are needed for electronics applications. Now, a collaboration of researchers in China have identified a catalyst that yields carbon nanotubes with a specificity almost 40% greater than previous methods, bringing the prospect of carbon-based nanoelectronic devices closer to reality.

Identical nanotubes can be grown from the new nanocatalysts

“We thought it would be great to get selectivity [the percentage produced with one specific structure] greater than 80%, but we achieved 92%,” says Yan Li, professor at the Beijing National Laboratory for Molecular Science at Peking University in China. The key to their success was a nanocatalyst made from a tungsten-cobalt alloy, which has a unique crystal structure and is very stable even at the high temperatures required for growing carbon nanotubes.

Although carbon nanotubes are already used in applications such as composites, touch panels for smartphones and lithium-ion batteries, it is much more difficult to exploit their electronic properties – mainly because they are highly dependent on the exact nanotube structure. For a start, the structure of a carbon nanotube determines whether it is metallic or semiconducting, and this in turn depends on the “chirality” – essentially a measure of the “twist” in the honeycomb carbon lattice. The chirality also determines the size of the electronic bandgap for semiconducting nanotubes, which means that nanotubes must always have the same structural properties to produce devices with reproducible performance characteristics.

Different groups have tried to separate nanotubes with different chiralities by using an external voltage to burn off the metallic nanotubes, or by dispersing them in a solvent. However, these methods are either limited in their specificity or introduce impurities, which impair the nanotubes’ electronic properties.

The nanotubes synthesized by Li and her team have a chirality described as (12, 6), which means they are metallic – useful for nanowires but not field effect transistors. Li tells nanotechweb.org that using different faces of the catalyst crystal should yield tubes with chirality either (16, 0) or (14, 4), and both these types are semiconducting. What’s more, the bandgap of these types of carbon nanotubes is ideal for electronic applications.

Catalysts feel the heat

Some attempts have already been made to exploit catalyst crystals as templates for growing nanotubes with a specific structure, but until now the proportion of nanotubes with the same chirality was limited to just 55%. “People did not realize that if you use a catalyst as a template you need to make the structure of the catalyst stable,” explains Li.

Li’s background in inorganic chemistry and metals directed her to tungsten, known to have exceedingly high thermal stability. Tungsten itself is not a catalyst so the researchers investigated alloys with cobalt, which is catalytic. “At first we were just trying to find a very stable catalyst, but on the way we found the structure is also very important,” Li tells nanotechweb.org.

Li explains that the atoms are very densely packed in monometallic nanoparticles, which allows a number of different carbon nanotube structures to fit onto the atoms – which in turn lowers the chiral specificity of the tubes grown. “Our new catalyst is an alloy and the crystal structure has very low symmetry. The arrangement is very unique, so only one structure of carbon nanotube can fit on a particular face.”

Next steps

Li’s team collaborated with researchers at the Hong Kong Polytechnic University, the Institute of Physics in China, Shanghai Institute of Applied Physics and the Electron Microscopy Laboratory at Peking University on the current work. They are now trying to design new catalysts to make tubes with different chiralities. They are also still optimizing the process to improve the selectivity. “We think we can now improve it to 98%,” she adds, although this work is still in relatively preliminary stages.

The researchers are also exploring the potential of the approach for bulk synthesis. “The challenge is that we made these nanotubes on a substrate. In bulk the conditions and chemical vapour deposition are different.”

Further details are available in Nature .

Supercapacitors and Li-ion Batteries in one Tidy Device

A team of researchers at Rice University in the US has fabricated 3D nanostructured thin-film electrodes using tantalum oxide nanotubes and “carbon-onion”-coated iron oxide nanoparticles. The thin films appear to be excellent lithium-ion batteries while being good supercapacitors too. The devices might be ideal in next-generation hybrid energy-storage applications, including wearable “smart textiles”.

The heterogeneous nanotubes

 

Electrochemical energy-storage devices such as Li-ion batteries (LIBs) and electrochemical supercapacitors (ECs) are currently the best option for powering portable electronics. Even better would be to combine the two types of device into one multifunctional electrode that combines the high energy density and capacity of Li-ion batteries with the high power density of supercapacitors. Capacitors are devices that store electric charge but ECs can store much more charge thanks to the double layer formed at an electrolyte-electrode interface when voltage is applied.

Until now, researchers have mainly studied carbon materials such as nanotubes and graphene nanoribbons for LIB anodes and ECs. However, they are far from ideal because carbon only has a theoretical storage capability of around 370 mAh/g in LIB anodes and less than 150 F/g in ECs. Transition metal oxides, in particular Fe₂O₃ (which has a high storage capability of 1005 mAh/g in LIB anodes and more than 1340 F/g in ECs), are good alternatives but again there is a problem in that these structures expand and contract too much during the charge/discharge cycles of a battery, which limits their use too. The fact that most transition-metal oxides conduct electricity poorly is also a big drawback.

Carbon-onion coating

One way of restricting the volume changes in these oxides and enhancing their electronic conductivity is to passivate them using a coating made of “carbon onions” (carbon nanoparticles consisting of concentric graphite-like shells).

James Tour and colleagues have now done just this for electrodes made from tantalum oxide nanotubes. The researchers coated the surface of the tubes with Fe₂O₃ nanoparticles, themselves coated with carbon-onions. The carbon-onion layers act as microelectrodes to separate the two different metal oxides and form a nanoscale 3D sandwich structure (see figure). The result is that space-charge layers form at the boundaries between the two oxides that can then store energy thanks to charge separation.

Multifunctional electrode

The 3D nanostructured films are excellent LIBs (800 mAh/cm³) and good supercapacitors too (capable of storing more than 18 mF/cm²). “The fact that the two devices can be assembled onto the same electrode is promising for next-generation hybrid energy storage and delivery,” says team member Yang Yang. “Ta₂O₅ nanotubes and carbon-coated Fe₂O₃ nanoparticles are electrochemically active for both LIBs and supercapacitors and the carbon coating also makes the electrodes more conductive than if the Ta₂O₅ nanotubes were left bare,” he told nanotechweb.org. “The electrode actually becomes multifunctional thanks to us using both materials.”

According to the team, the devices might find use in wearable energy devices, including smart textiles. They might also be ideal as air batteries.

The researchers describe their electrochemical energy storage devices in ACS Nano DOI: 10.1021/nn502341x.

Nanosheet Membranes Give Ultrafast Molecule Separation

The atomically thin, porous graphene membranes represent a new class of ideal molecular sieves, where transport occurs through pores which have a thickness and diameter on the atomic scale. These characteristics make graphene an ideal material for creating a separation membrane because it is durable and yet doesn’t require a lot of energy to push molecules through it.

Simulations point to graphene oxide frameworks’ great potential in water purification and researchers already have used Individual graphene sheets and their functionalized derivatives to remove metal ions and organic pollutants from water (read more: “Nanotechnology water remediation with bulky graphene materials“) and simulations More recently, researchers have begun exploring analogues of graphene, i.e. other two-dimensional (2D) layered materials such as boron and molybdenum oxides (read more: “Two-dimensional nanotechnology materials beyond graphene“). ”

Although tens of novel 2D layered materials are found, the separation membranes made of them are rather scarce, except recently for MoS2 and graphene oxide nanosheets,” Xinsheng Peng, a Professor in the State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering at Zhejiang University, tells Nanowerk. “Like graphene and its derivatives, layered transition-metal dichalcogenides have also desirable mechanical properties and could be assembled into lamellar thin films.

Therefore, they are expected to be used to construct novel high-performance lamellar separation membranes.” In new work, Peng and his collaborators have developed a new separation membrane with 2D layered transition metal dichalcogenides (tungsten disulfide) for size-selective separation of small molecules of about 3 nm. As they reported in ACS Nano (“Ultrafast Molecule Separation through Layered WS2 Nanosheet Membranes”), as-prepared WS2 membranes exhibit 5 times higher water permeance than graphene oxide membranes with similar rejection.

Schematics of the nanostrand-channeled WS2 membrane. (Reprinted with permission by American Chemical Society)

The team assembled their separation membrane from chemically exfoliated WS20 nanosheets by filtration. As prepared, this 300-500 nm thick membrane demonstrates a water permeance of 450 L/m2•h•bar with over 90% rejection for 3 nm molecules (Evans Blue). To further improve the water permeance, they employed ultrathin metal hydroxide nanostrands to create more fluidic channels while keeping the rejection rate of specific molecules unchanged.

This more than doubled the membrane performance to 930 L/m2•h•bar. Peng points out that a well calibrated thickness is crucial for a highly efficient separation membrane to balance water flux and rejection rate: “A too thick membrane has low water flux despite high rejection rate, while a thinner membrane usually presents higher flux but worse rejection and suffers mechanical problems.”

When testing their membranes under pressure, the team found that the as-prepared WS2 membrane linearly depends on pressure, as was expected. The nanostrand-channeled WS2 membrane however displays a rather different pressure-dependent water flux. “At lower pressure range, similar to the as-prepared membranes, the water flux increases linearly with external pressure,” Peng describes the results. “However, at 0.3 MPa, we observed a transition of water flux with respect to pressure. The flux at the external pressure above 0.3 MPa is fitted with a straight line with larger slope.

The transition implies a geometry evolution of the nanochannels during the pressure loading on the channeled membranes beyond 0.3 MPa.” The team speculated that the larger water flux at higher pressure may be attributed to the formation of new fluidic channels. “Our pressure loading-unloading tests suggests that the channels arising from ultrathin nanostrands are cracked between 0.3 and 0.4 MPa,” explains Peng.

“These cracks produce new fluidic nanochannels that further results in water flux 4 times that of the as-prepared WS2 membrane without degradation of the rejection performance.” He notes, though, that the ratio of WS2 suspension and ultrathin nanostrands needs to be carefully adjusted. An excess of nanostrands will result in their overlapping, which produces larger channels in the membranes, leading to worse separation performance.

Overall, the results suggest that WS2 membranes hold promising potential for use in applications for ultrafast small organic molecule separation for water purification. “The development of more 2D-layered materials will also expand the family of 2D-layered material separation membranes,” concludes Peng. “Due to their individual unique surface states in combination with different preparation strategies, these novel membranes will exhibit different water permeation behavior and separation performances. In our opinion, the challenge likely comes from how to model the new 2D-layered materials in a proper way.”

Copyright © Nanowerk

Will Nanotechnology be the Answer for the Next Generation of Lithium-Ion Batteries?

Despite the recently reported battery-flaming problem of lithium-ion batteries (LIBs) in Boeing’s 787 Dreamliners and laptops (in 2006), LIBs are now successfully being used in many sectors. Consumer gadgets, electric cars, medical devices, space and military sectors use LIBs as portable power sources and in the future, spacecraft like James Webb Space Telescope are expected to use LIBs.

The main reason for this rapid domination of LIB technology in various sectors is that it has the highest electrical storage capacity with respect to its weight (one unit of LIB can replace two nickel-hydrogen battery units). Also, LIBs are suitable for applications where both high energy density and power density are required, and in this respect, they are superior to other types of rechargeable batteries such as lead-acid, nickel-cadmium, nickel-metal hydride, nickel-metal batteries, etc.

However, LIBs are required to improve in the following aspects: (i) store more energy and deliver higher power for longer duration of time, (ii) get charged in shorter period of time, (iii) have a longer life-time and (iv) be resistant to fire hazards. Figure 1 depicts the basic LIB Characteristics required for different applications and the respective properties that need to be improved.

Fig. 1: Basic LIB characteristics required for different applications 1,2 (DOD: Depth of Discharge, SOC: State of Charge). (click on image to enlarge)

At present, there is a great deal of interest to upgrade the existing LIBs with improved properties and arrive at a battery technology that would permit smart-storage of electric energy. Futuristic smart electric grids that can provide an uninterruptible power supply to a household for 24 hours can replace the currently used lead acid battery systems by performing better in terms of longer back up time and reduced space requirements.

With the advent of next generation LIBs, electric vehicles are expected to cover longer distances with shorter charging times; mobile phones and laptops are expected to be charged within minutes and last longer.

What Nanotechnology can do to Improve the Performance of LIBs Nanotechnology has the potential to deliver the next generation LIBs with improved performance, durability and safety at an acceptable cost. A typical LIB consists of three main components: an anode (generally made of graphite and other conductive additives), a cathode (generally, a layered transition metal oxide) and electrolyte through which lithium ions shuttles between the cathode and anode during charging and discharging cycles.

On electrodes: The electrodes of LIB, both anode and cathode are made of materials that have the ability to be easily intercalated with lithium ions. The electrodes also should have high electrical conductivity so that the LIB can have high charging rates. Faster intercalation of Li ions can be facilitated by using nanosized materials for electrodes, which offer high surface areas and short diffusion paths, and hence faster storage and delivery of energy. One prominent example is the cathode material of A123 LIBs that use nanosized lithium iron phosphate cathode. Researchers have been trying to increase the electrical conductivity of lithium iron phosphate by doping it with metals.

However, without the need for doping, the conductivity and hence the performance of the cathode material could be improved significantly by using nano-sized lithium iron phosphate. One dimensional vanadium oxide materials, LiCoO2 nanofibers, nanostructured spinels (LiMn2O4) and phosphor-olivines (LiFePO4), etc., are being explored as cathode materials for the next generation LIBs. Similarly, nanosizing the anode materials can make the anode to have short mass and charge pathways (i.e allow easier transport of both lithium ions and electrons) resulting in high reverse capacity and deliver at a faster rate.

Nanostructured materials like silicon nanowires, silicon thin films, carbon nanotubes, graphene, tin-filled carbon nanotubes, tin, germanium, etc., are currently being explored as anode materials for the next generation LIBs.

On electrolyte: Electrolytes in LIB conduct lithium ions to and fro between two electrodes. Using solid electrolytes could render high-energy battery chemistries and better safety (avoids fire hazards) when compared to the conventionally used liquid electrolytes. However, achieving the optimal combination of high lithium-ion conductivity and a broad electrochemical window is a challenge. Also, reduction of interfacial resistance between the solid electrolyte and lithium based anodes also poses a formidable challenge3.

Nanostructuring of solid electrolytes has proven to improve the lithium ion conductivity, for example, when the conventional bulk lithium thiophosphate electrolyte was made nanoporous, it could conduct lithium ions 1000 times faster4. Another example is the nanostructured polymer electrolyte (NPE), which ensures safety. Main advantage of using this benign electrolyte is that it allows the use of lithium metal as anodes (instead of carbon based anodes) and contribute to the increase of energy density of the battery5.

On improving the performance of LIBs: The performance of the LIB is typically measured by its power and energy stored per unit mass or unit volume. The power density of the LIBs can be increased but often at an expense of energy density5. In order to achieve high power density as well as energy density, researchers are using nanotechnology to design electrodes with high surface area and short diffusion paths for ionic transport.

The high surface area provides more sites for lithium ions to make contact allowing greater power density and faster discharging and recharging. Another important parameter known as rate capability, indicates the maximum current output the LIB can provide and it plays an important role in deciding life-cycle of the LIB. In general, higher the rate capability, greater is the power density and longer the cycle-life.

Safety

The demand for the LIBs with increased power/energy density (P/E) ratio is accompanied by the greater safety risk of the battery. Preferably, a P/E ratio of roughly 0.5 along with uncomplicated heat management is proposed for the next generation LIBs. In order to avoid fire hazards, heat generated during the charging and discharging of the battery should be dissipated quickly and non-combustible materials should be used in LIBs.

In case of the LIBs with lithium metal as anodes, the so-called dendrite problem (growth of microscopic fibers of lithium across the electrolyte that leads to short circuits and overheating) remains to be solved. Separators with nanoporous structures can prevent the spreading of dendtrites by acting as a mechanical barrier without hindering the ion-transport during charging and discharging cycles.

Recently, a nanoporous polymer-ceramic composite separator that could prevent the spreading of dendrites has been reported. This novel separator consist of a laminated nanoporous gamma alumina sheet (pore size of 100 nm) sandwiched between macroporous polymer membranes. The nanoporous alumina in this layered composite could effectively impede the proliferation of dendrites and prevent cell failure that are caused by short circuits13. Thermally stable electrolytes, for example, nanoarchitectured plastic crystal polymer electrolytes (N-PCPE) can facilitate the development of safe LIBs.

Owing to its nanoarchitectural structure, N-PCPE is flexible while maintaining high ionic conductance and thermal stability. This makes the material to perform well with high electrochemical stability even in a wrinkled state. As it suffers no internal short-circuit problems even under severely deformed state, N-PCPE can be used in place of currently used flammable carbonate-based liquid electrolytes and polyolefin separator membranes to improve the safety of the LIBs14. In another context, it can be said that nanotechnology, in a way helps to use thermally stable advanced new materials as electrodes.

For example, Li4Ti5O12 spinel, which is a state-of-the-art anode material for LIBs has excellent safety and structural stability during cycling, but suffer from low ionic and electronic conductivities (in bulk form) that hampers the wide-spread use of this material. By making anodes with nanosized Li4Ti5O12 spinel and Li4Ti5O12/carbon nanocomposites, the safety as well as the electrochemical performance of the battery can be improved15. Also, nano-enabled separators with improved stability and low shrinkage properties at high temperatures have proved to improve the safety aspects as well as the performance of the LIBs16.

 For example, separators made of polymeric nanofibers (DuPont™ Energain™ battery separators) can allow automobile LIBs to accelerate quickly but safely due to their excellent stability at high temperatures.

Durability

The cycle life (number of times the LIB can be charged and discharged (one cycle together) by maintaining up to 70-80% of its original capacity) can be improved by the use of nanostructured electrodes.

New nanostructures like mesoporous CNT@TiO2-C nanocable having an inner core of carbon nanotubes encapsulating TiO2 nanoparticles, which are further covered by an outer carbon layer with mesoporous architectures provided superior electrochemical performance as anodes, hence achieving long-term cycling stability at high rates17. A high charge of 122 mA h g-1 even after 2000 cycles at 50 C could be achieved using this material.

Durable high rate LIB anodes, namely, carbon-encapsulated Fe3O4 nanoparticles homogeneously embedded in 2D porous graphitic carbon nanosheets present an excellent cycling performance (a capacity-loss of just 3.47% after 350 cycles at a high rate of 10 C). This is the highest among other conventional as well as nanostructured Fe3O4-based electrodes.

Here, Fe3O4 nanoparticles of size of about 18.2 nm were homogeneously coated with conformal and thin onion-like carbon shells and embedded into 2D carbon nanosheets (thickness <30 nm). The carbon shells prevent the exposure of Fe3O4 nanoparticles to the electrolyte and stabilize the electrode-electrolyte interface18. New 2D and 3D battery designs like forest of nanowires/rods on a thin film electrode and stacked nanorods in a ‘truck bed’ are also being explored to accommodate the volume expansion of new electrode materials and hence improve their stability.

Cost

By the year 2020, the cost of the LIBs for automotive applications are expected to come down by half 19] and almost 70% reduction in the lifetime cost of the LIBs (which brings down the cost of a battery by three times) [20] would be achieved by using nanomaterials (graphene coated silicon) for fabricating the LIB electrodes.

In terms of using high energy electrode materials in a minimal quantity, nanotechnology can help reducing the cost of the next generation LIBs. Also, improvement in the durability (cycle life) of the LIBs using nanostructured components can improve their cost- benefit aspects.

Recent advances in paper-based batteries are attractive for consumer electronics as they enable low cost manufacturing of devices like transistors, smart displays, etc.[21]. Nanotechnology and nanomanufacturing techniques are expected to open up possibilities of low-energy processing methods for fabricating and stacking of the LIB components.

Challenges in Developing Nanoenabled LIBs

Though the LIB technology is about twenty years old now and even with the advent of nanotechnology, it is still a challenge to attain LIBs with optimal combination of energy, reliability, cost and safety[22]. With regard to the anode materials, lithium suffers from the dentrite-formation (leading to an explosion of the battery), high reactivity, etc. Hence, nanostructures of tin, silicon, etc., are being used as new anode materials.

Fig. 2: Challenges in the development of nano-enabled LIBs.

Various strategies like (i) decreasing the particle size to nano-range (ii) employing hollow nanostructures (iii) making nanocomposites or nanocoatings with carbon and/or inert components, etc., are being used to achieve high capacity and stable cycle-life of electrodes.

However, these approaches reduce the overall energy density of the anode material due to the following reasons: (i) low packing -density of nanosized materials (ii) presence of large voids in the hollow structures (iii) increased weight -percentage of added carbon/or inert components. Lately, smartly-designed nanoparticle agglomerates in micron size range are proposed to be used to solve the above said technical drawbacks of using nano-enabled anodes and similar strategies can also be applied for designing efficient nano-sized cathode materials [23,24].

Other challenges such as lowering the high fabrication cost due to energy- consuming synthetic processes, avoiding undesired reactions at electrode/electrolyte interface that arise due to the large surface areas of nanomaterials, preventing the formation of agglomerates during the fabrication process, etc., can be overcome by careful selection of the fabrication procedure.

Commercialization of Nanoenabled LIBs: Current Scenario

LIBs have already penetrated the consumer electronics market and are now making the move into HEV/EV applications and grid-storage applications. By 2018, global market for LIBs is expected to grow strong and reach $24.2 billion. Unlike before, the industry is ready to develop improved LIBs for diverse and new applications, thanks to the growing knowledge on new materials/technologies.

At present, most of the research efforts to develop advanced electrodes, safe electrolytes, etc., employ nanomaterials/nanotechnology routinely. As discussed in the previous section, there are number of challenges that are yet to be met to achieve 100% reliability and the merit of using nanomaterials for next generation LIBs. Especially, in the case of LIBs for electric vehicles, which is considered as a golden ticket for the commercialization LIBs, some startup companies like A123, Ener1, etc., announced bankruptcies in the past few years in spite of receiving huge capital investment and producing batteries with exceptional properties.

Experts note that this downfall cannot be solely attributed to the new nanotech-enabled LIB technology but also to the issue of replacing internal combustion engine in vehicles [25,26]. At present, LIBs consume the 65% of the total cost of an electric vehicle, and hence in order to be cost-completive with gasoline, LIBs with twice the energy storage of state-of-art LIBs at 30 % of cost are required [27].

Thus, the successful commercialization of nano-enabled LIBs for all-electric vehicles depends on various factors as mentioned above. Apart from these automobile applications, nanoenabled LIBs for powering handheld gadgets and for stationary storage applications are more likely to depend on the improvement in the properties of the LIBs, volume production rates) and usage of abundant, low cost, high energy materials.

Conclusion

LIB technology is rapidly emerging as the most advantageous battery chemistry for transportation as well as consumer electronics. Various research efforts on nanotechnology based LIB technology has already led into the production and use of high performance LIBs (Toshiba, A123 Systems, Altair Nano, Next Alternative Inc., etc.) and yet more improvement with respect to the performance, durability and safety aspects, especially for automotive applications are more likely to be achieved in the future.

Acknowledgement

The author would like to thank Dr. Srinivasan Anandan of ARCI for the insightful discussions on the current research trends on LIBs and Dr. C.K. Nisha of CKMNT for her suggestions on enhancing the content of the article.

References 1. Walter Van Schalkwijk, “Advances in Lithium- Ion Batteries”, Springer (2002), ISBN 0-306-47356-9 2. Battery could find use in mobile applications (26 Feb 2014) 3. Liquid and solid electrolytes in lithium-ion batteries 4. Z. Liu, W. Fu, E.A. Payzant, et al., J. Am. Chem. Soc., 135 (2013) 975-978 5. Berkeley Lab’s Solid Electrolyte May Usher in a New Generation of Rechargeable Lithium Batteries For Vehicles 6. G. Kim, S. Jeong, J-H. Shin, et al., ACS Nano, 8 (2014) 1907-1912 13. Z. Tu, Y. Kambe, Y. Lu, et al., Adv. Energy Mater., 4 (2014) 1300654 14. K-Ho Choi, S-Ju Cho, S-H Kim, et al., Adv. Funct. Mater., 24 (2014) 44-52 15. T-F. Yi, L-J. Jiang, J. Shu, et al., J. Phys. Chem. Solids, 71 (2010) 1236 – 1242 16. DuPont Launches Energain™ Separators for High-Performance Lithium Ion Batteries 17. B. Wang, H. Xin, X. Li, et al., Scientific Reports, 4:3729 (2014) 1-7 18. C. He, S. Wu, N. Zhao et al., ACS Nano, 7 (2013) 4459-4469 19. Battery Executives See Price Drops Ahead (Sep 7 2013) 20. Nanostructured Silicon Li-ion Batteries’ Capacity Figures Are In (26 Oct 2012) 21. Nanotechnology researchers fabricate foldable Li-ion batteries (1 Oct 2013) 22. The Future Requires (Better) Batteries ( 11 Nov 2013) 23. A. Magasinki, P. Dixon, B. Hertzberg, et al., Nature Materials, 9 (2010) 353-358 24. W. Wei, D. Chen D, R. Wang., et al., Nanotechnology, 23 (2012) 475401 25. Is There a Future for Nano-Enabled Lithium Ion Batteries in Electric Vehicles? (14 Dec 2010) 26. Why Ener1 Went Bankrupt (27 Jan 2012) 27. Double Energy Density for Lithium-Ion Batteries By I. Sophia Rani, Centre for Knowledge Management of Nanoscience and Technology (CKMNT).

The full article has appeared in the April 2014 issue of “Nanotech Insights” and the above article is an abridged and revised version of the same.

Progress Review of the National Nanotechnology Initiative: Update

This document provides an overview of progress on the implementation and coordination of the 2011 NNI Environmental, Health, and Safety (EHS) Research Strategy that was developed by the Nanoscale Science, Engineering, and Technology Subcommittee’s Nanotechnology Environmental and Health Implications (NEHI) Working Group.

 

Consistent with the adaptive management process described in this strategy, the NEHI Working Group has made significant progress through the use of various evaluation tools to understand the current status of nanotechnology-related EHS (nanoEHS) research and the Federal nanoEHS research investment.

Most notably, the participating agencies reported to the NEHI Working Group examples of ongoing, completed, and anticipated EHS research (from FY 2009 through FY 2012) relevant to implementation of the 2011 NNI EHS Research Strategy.

These examples, described in this document, demonstrate the breadth of activities in all six core research areas of the 2011 NNI EHS Research Strategy: Nanomaterial Measurement Infrastructure, Human Exposure Assessment, Human Health, Environment, Risk Assessment and Risk Management Methods, and Informatics and Modeling. Overall, coordination and implementation of the 2011 NNI EHS Strategy across the NEHI agencies has enabled:

• Development of comprehensive measurement tools that consider the full life cycles of engineered nanomaterials (ENMs) in various media.
• Collection of exposure assessment data and resources to inform workplace exposure control strategies for key classes of ENMs.
• Enhanced understanding of the modes of interaction between ENMs and physiological systems relevant to human biology.
• Improved assessment of transport and transformations of ENMs in various environmental media, biological systems, and over full life cycles.
• Development of principles for establishing robust risk assessment and risk management practices for ENMs and nanotechnology-enabled products that incorporate ENMs, as well as approaches for identifying, characterizing, and communicating risks to all stakeholders.
• Coordination of efforts to enhance data quality, modeling, and simulation capabilities for nanotechnology, towards building a collaborative nanoinformatics infrastructure.

Extensive collaboration and coordination among the NEHI agencies as well as with international organizations is evident by the numerous research examples and by other activities such as co-sponsored workshops and interagency agreements described in this review document. These examples and activities are a small subset of the extensive research efforts at the NEHI agencies. This document addresses the NEHI Working Group’s broader efforts in coordination, implementation, and social outreach in nanoEHS, as identified in the 2011 NNI EHS Research Strategy. As the NNI agencies sustain a robust budget for EHS research, Federal agencies will continue to invest in tools and share information essential to assess and manage potential risks of current and anticipated ENMs and nanotechnology-enabled products throughout their life cycles. The agencies will also continue to engage with the stakeholder community to establish a broad EHS knowledge base in support of regulatory decision making and responsible development of nanotechnology.

 

File Downloads

2014 NNI EHS Progress Review | 1.2 MB

A Look at Water Markets Worldwide

The world market for water and waste water amounted to $533 Billion US$ in 2011. The markets are expected to expand further with high growth rates to $674 Billion US$ by 2015.The market figures are for the whole value chain. The regions, technology and consumer segments differ, as well as profit potentials for single markets and companies.

 

2011 revenues were in excess of US$530 Billion. Broken down by sector:

• Services 60 %,
• Equipment 26 %,
• Chemicals 2 %,
• Others 12 %.
• Bottled and Bulk Water Market exceeds $90 Billion USD
• Water treatment segment has an especially high growth rate.

The drinking water market worldwide is dominated by communal companies, which belong fully or partially to the states, as well as by big multinational corporations. This sector of supply is dominated by about 20,000 companies worldwide. A further concentration into big corporations is expected also in the process of privatization due to high investments and operating costs.

Drinking water markets provide very limited profit potentials (less than 12%), on the other hand it is a long-lasting market with small year fluctuations. Companies and public institutions, that combine drinking water with other utilities like waste water and energy, are fully capable to gain a higher return of more than 15%. The highest growth rates are expected in Asia, especially in China because the state has launched public programs to improve the drinking water situation in the next 5 years.
 

The public drinking water supply has grown with an average annual rate of 9% and high investment in this field is expected. The World Bank has granted an investment of over $450 Billion US$ for the next 10 years. For over one third of the world population, especially Africa, South America and part of Asia, the drinking water is both a quality and supply shortage problem.

Water markets are local markets but to be successful as an international company, a company will need to serve and work in most important markets worldwide. Over the next 50 years – despite the risks cited, there is a sharp increase in the demand for efficient irrigation technologies, seawater desalination and sewage treatment facilities, technical equipment (e.g. pumps, compressors and fittings), filter systems and disinfection procedures.

New technologies and converging technologies (especially in domestic and residential markets) hold the greatest potential for successful disruption in the marketplace.

In the field of waste water, i.e. clarification of waste water, the situation has improved slightly. Worldwide, 14% of all waste water in the year 2013 was purified. At the bottom of this development list are South America and Africa with less than 2% waste water purification.

The most influential factors are population development, increasing demand for food (and thus demand for water), urbanization, germination, pesticides, nitrates and above all resistance to antibiotics in surface water in the industrialized countries.

 
Goals of the Report

 
The study provides a foundation to gain information about trends, opportunities and risks and to evaluate initial situation and further development as well, identifies and evaluates the growth and profit opportunities within the segments of technologies/markets and value chain. It deals with the following technology sectors:

• Drinking water, water desalination
• Water treatment/water purification
• Treatment of waste water in industry and municipality
• Energy in the water industry
• Automation, E-Technique and Services in Water Market
• Emerging membrane technology
• Emerging desalination

The Helmut Kaiser Consultancy has completed a study that researches and valuates the development of the world markets, single consumer sectors and technology segments. The highest growth rates are in sectors mineral and bottled water, this markets are expected to double from 2015. In this sector 8 companies are dominating worldwide with a market share of 20%. The global market for table water will show a stable high growth rate, because of the many looming challenges for public drinking water most notably, low quality and serious supply shortages.

The report is arranged by sectors and can be obtained either completely, or each sector separately. The markets are presented by countries and regions, as well as by market segments. The report also provides an analysis and profiles, (as well as presentation) of the leading water companies (more than 1500) that are quoted on the stock exchange and their factors of success and technology portfolio. This recent study has been completed to help identify the profitable markets and develop a strategy for future strategic market participation.

For more information: The Helmut Kaiser Consultancy Group (www.hkc22.com )

 

 

*** A Note from Genesis Nanotechnology ***

We believe and are firmly committed to our Strategic Vision of how “Nanotechnology” will play an ever increasing role in Water Treatment, Water Filtration, Wastewater Remediation and Desalinization.

If you would like to talk to us about what we are currently developing with our Research Partners OR would like to discuss YOUR ideas, strategies or research with us, please feel free to contact us with your Contact & Profile Information.

Simply go to our website and complete the ‘Contact Form’: http://genesisnanotech.com/contacts/

We look forward to hearing from you!- Team GNT – “Great Things from Small Things!”

Our “One Picture” Business Summary