Nanotechnology will play an important role in future space missions. Nanosensors, dramatically improved high-performance materials, or highly efficient propulsion systems are but a few examples (read more: “Nanotechnology in Space“). One particularly important issue is the protection of satellites from electrostatic discharge (ESD).
In space, the external insulating surfaces accumulate electrostatic charge as a result of exposure to space plasma, including high flux of charged particles especially at geosynchronous earth orbit (GEO). If that charge accumulation suddenly discharges it may damage the electronics of the spacecraft. The space industry therefore has a strong requirement to develop a flexible ESD protection layer for the exterior cover of satellites.
A study conducted by nanotechnology researchers at Tel Aviv University together with scientists from the space environment department at Soreq NRC, explores carbon nanotube-polyimide (CNT-PI) composite materials as a flexible alternative for the currently used indium tin oxide (ITO) coating, which is brittle and suffers from severe degradation of the electrical conductance due to fracture of the coating upon bending. “We developed electrically conducting and flexible CNT-PI films specifically for space applications using polymer solution infiltration into CVD-grown entangled CNT sheets with cup-stacked nanostructure,” Yael Hanein, a professor at Tel Aviv University and Director of the university’s Center for Nanoscience and Nanotechnology, tells Nanowerk. “This fabrication process prevents CNT agglomeration and degradation of the CNT properties that are common in dispersion-based processes.
Schematic illustration of CNT-PI film fabrication process: (a) ∼9 µm thick CNT sheet is first grown by CVD on a prepatterned Si substrate. (b) PI (PMDA-ODA monomer) is then infiltrated into the CNT sheet. (i) Type 1 samples were cast by ∼9 µm thick PI layer (up to the dotted line). (ii) Type 2 samples were prepared with excess of PI layer (∼15 µm thick). (c) Finally, free-standing CNT-PI film is mechanically peeled off the substrate. (Reprinted with permission by American Chemical Society)
The team has published its findings in the November 3, 2014 online edition of ACS Applied Materials & Interfaces (“Reinforced Carbon Nanotubes as Electrically Conducting and Flexible Films for Space Applications”). “We specifically explored the electrical conducting mechanism of CNT-PI composites, given that we sought a simple method to control CNT distribution within a polymer matrix, while protecting the CNT properties,” says Nurit Atar, a PhD candidate and first author of the paper.
“We found that the conductivity of the CNT sheet was preserved in spite of the insulative PI infiltration. This implies that the electrical current was enabled through the original entangled CNT network that was not interrupted by the insulative PI. This proves that the polymer solution did not penetrate into the interface at the CNT junctions and so the original continuum of ohmic contacts between adjacent CNTs was preserved.” CNT-PI composites were produced before by dispersion of CNT powder in polymer matrices. Since CNTs are insoluble and tend to agglomerate as bundles, sonication and functionalization are commonly used to improve homogeneity. These incorporation techniques often result in severe degradation of the original CNT properties (e.g., electrical, thermal, and mechanical characteristics). The preparation method used by the Israeli team is based on PI infiltration into CVD-grown CNT sheets, enabling preservation of the original CNT sheet conductivity with no degradation related to the insulating PI matrix. Hence, higher electrical conductivity can be easily reached, e.g., by controlling the CNT growth process (CVD) to form denser CNT sheets with higher conductivities. “Another advantage of the technique presented in our recent paper is the compatibility with patterning of CNT along the composites, which is not facilitated by the dispersion technique,” Atar points out.
(a) Top view HRSEM image of an as-grown entangled CNT sheet. (b) TEM image of a typical cup-stacked CNT. (c) Optical microscope image of a patterned, free-standing CNT-PI film with area of 1 × 1.5 cm2 and 10 µm thickness. (d) AFM phase image of the top surface of a CNT-PI film. Inset: Optical microscope image of a free-standing CNT-PI nanocomposite film (17 µm thick, 0.5 × 3.5 cm2 area) wrapped around a glass tube (7 mm diameter). (Reprinted with permission by American Chemical Society)
As electrically conducting films, the CNT-PI composites can prevent electrostatic charge accumulation on the exterior of satellites. Particularly, the researchers found that their CNT-PI films are durable in space environment hazards such as high vacuum, thermal cycling, and ionizing radiation. The team’s current work focuses on improving the stability of the CNT-PI film to atomic oxygen, which is dominant at low earth orbit space environment. The challenge is to introduce inorganic nanoparticles into the polymer matrix to create a self-passivation layer when exposed to atomic oxygen.
Shape has a pervasive but often overlooked impact on how natural systems are ordered. At the same time, entropy (the probabilistic measure of the degree of energy delocalization in a system) – while often misunderstood as the state of a system’s disorder – and emergence (the sometimes controversial observance of macroscopic behaviors not seen in isolated systems of a few constituents) are two areas of research that have long received, and are likely to continue receiving, significant scientific attention. Now, materials science and chemical engineering researchers working with computer simulations of colloidal suspensions of hard nanoparticles at University of Michigan, Ann Arbor have linked entropy and emergence through a little-understood property they refer to as shape entropy – an emergent, entropic effect – unrelated to geometric entropy or topological entropy – that differs from and competes with intrinsic shape properties that arise from both the shape geometry and the material itself and affect surface, chemical and other intrinsic properties.
According to the researchers, shape entropy directly affects system structure through directional entropic forces (DEFs) that align neighboring particles and thereby optimize local packing density. Interestingly, the scientists demonstrate that shape entropy drives the emergence of DEFs in a wide class of soft matter systems as particles adopt local dense packing configurations when crowded and drives the phase behavior of systems of anisotropic shapes into complex crystals, liquid crystals and even ordered but non-periodic structures called quasicrystals through these DEFs. (Anisotropy refers to a difference in a material’s physical or mechanical properties – absorbance, refractive index, conductivity, tensile strength, and so on – when measured along different axes.)
Prof. Sharon C. Glotzer discussed the paper that she, lead author and Research Investigator Dr. Greg van Anders and their co-authors published in Proceedings of the National Academy of Sciences, noting that one of the fundamental issues they faced was the historical problem of linking microscopic mechanisms with macroscopic emergent behavior. “This is a difficult problem that was really, to our knowledge, only brought into sharp contrast for physical systems by Philip Warren Anderson in his 1972 essay More is Different1 – and really, the title says it all,” van Anders tells Phys.org. (Anderson is a physicist and Nobel laureate who in his essay addressed emergent phenomena and the limitations of reductionism.) “We’re interested in the type of systems that are dominated by entropy – meaning that their behavior originates from effects of the system as whole,” Glotzer points out. “In a way, we’re grappling with the problem of how things that operate with basic rules can produce complicated behavior.” For Glotzer and her team, the rules are shapes, and the behavior takes the form of complex crystals. “It’s very important to understand shape effects in nanosystems,” she adds, “because nanoparticles tend to have a natural shape to them because of how they grow.”
In addressing this problem, the scientists – in addition to isolating shape entropy in model systems – had to precisely delineate between and correlate the relative influences of shape entropy and intrinsic shape effects. This can be formidable: While the intrinsic shape of a cell or nanoparticle affects a range of other intrinsic properties, such as its surface and chemical characteristics, shape entropy is an effect that emerges from the geometry of the shape itself in the context of other shapes crowded around it. “Intrinsic shape effects are conceptually straightforward because they’re forces that originate from van der Waals, Coulomb, and other electrostatic and other forces, though in practice they may not be easy to measure experimentally,” Glotzer explains. “However, comparing intrinsic shape effects to shape entropy is a bit like comparing apples and oranges: there are many ways to characterize shapes, but forces aren’t typically one of them.” Moreover, research has historically focused on shape effects in specific systems, so a general solution was elusive, and there were no rules specifying the types of systems where shape effects might be seen.
Not surprisingly, then, a significant obstacle was quantitatively demonstrating that shape drives the phase behavior of systems of anisotropic particles upon crowding through directional entropic forces. “Our main problem here was trying to understand how there could be a local mechanism for global ordering that acts through entropy – which is a global construct,” Glotzer says. “It took us a while to realize that other investigators had already been asking this question for systems containing mixtures of large particles and very small particles.” (The latter, known as depletants, induce assembly or crystallization of larger particles.) “However,” she continues, “it was more challenging to determine how to pose and interpret this question mathematically when all particles are the same.” Glotzer adds that the technique van Anders and the rest of her team used to understand these systems – the potential of mean force and torque (PMFT), a treatment of isotropic entropic forces first given in 1949 by Jan de Boer2 at the Institute for Theoretical Physics, University of Amsterdam – is in many ways rather basic. Nevertheless, and somewhat remarkably, PMFT provided them with the key by allowing them to quantify directional entropic forces between anisotropic particles at arbitrary density. (PMFT is related to the potential of mean force, or PMF, an earlier approach that – unlike PMFT – has no concept of relative orientation between particles, and regarding shapes would only provide insight into radial, but not angular, dependence.)
The paper also address the relationships between shape entropy, self-assembly and packing behavior. (Self-assembly refers to thermodynamically stable or metastable phases that arise from systems maximizing their generalized entropy through spontaneous self-assembly in the presence of energetic and volumetric constraints, such as temperature and pressure; or through directed self-assembly due to other constraints, such as electromagnetic fields.) “Once we had determined how to measure the directional entropic forces,” van Anders explains, “the entropy/self-assembly connection became evident: On the systems we studied, the forces we were able to measure between particles were exactly in the range they should be to contribute to self-assembly (several kBT), which is on the order of intrinsic interactions between nanoparticles and on the scale of temperature-induced random motion.” (The metric kBT is the product of the Boltzmann constant, k, and the temperature, T, used in physics as a scaling factor for energy values or as a unit of energy in molecular-scale systems.)
That said, the scientists were able to use directional entropic forces to draw a distinction between self-assembly and packing behavior. “This was puzzling: For a long time, global density packing arguments have been used to predict assembly behavior in a range of systems,” Glotzer continues. “However, in the last few years – especially as researchers began looking more seriously at the anisotropic shapes being fabricated in the lab – these packing arguments started failing. Around the same time my group wrote a paper that showed that the assembled behavior can often be predicted by looking at the structure of a dense fluid of particles that hasn’t yet assembled.” The researchers realized that the forces they were seeing in their calculations were coming from local dense packing that happens in the fluid and the assembled systems. This showed that self-assembly and packing behavior were related, but not by global dense packing.
An important implication of understanding how shape entropy drives both self-assembly and packing despite their observable differences, Glotzer points out, is that there is growing interest in making ordered materials for various optical, electronic and other applications. “We’ve shown that, in general, it’s possible to use shape to control the structure of these materials,” she explains. “Now that we understand why particles are doing what they do when they form these materials, it becomes much easier to determine how to design them to generate desired materials rather than just going by trial-and-error.”
Another dramatic realization was that shape entropy drives the phase behavior of systems of anisotropic shapes through directional entropic forces. “We already knew from prior work in my group that you can quite often predict what crystal structure will form by looking at the fluid and the particle shape,” Glotzer tells Phys.org. “The problem for us was identifying what caused particles to arrange into the local structures they did in the fluid, and to show that they had the same sort of structure when they assembled.” Van Anders adds that the scientists were able to find the forces that induced and kept the particles in their preferred structures. “When they turned out to be in the right range we knew that we had it right.”
To date, the researchers have conducted their simulation studies only on idealized model systems. “Still,” says Glotzer, “our simulations capture what we believe to be the most important features of real colloidal systems.” Indeed, a growing number of published experimental studies now report the same structures her team predicted, and no counter-results have yet been observed. “We’re working closely with collaborators to leverage existing experimental techniques that will allow us to measure the strength of these forces and compare them with our predictions.” One such approach is measuring directional entropic forces in the lab by using confocal microscopy to determine the location and orientation of particles in assembling systems.
Moreover, Glotzer’s research group is collaborating with several experimental groups to investigate potential approaches to exploiting shape effects in the laboratory. “Now that we understand how local entropic forces work,” she tells Phys.org, “we can begin to think about designing particles so that entropy and internal energy balance in just the right way to yield complex target structures.”
Glotzer and van Anders conclude that “Researchers have been thinking about different kinds of entropy-driven systems since the 1930s, and since the 1950s have done a lot of work in systems in so-called depletant mixtures – but to our knowledge most people tend to think of those systems as having little to do with densely crowded, single-particle systems. Our work helps to tie these different lines of research together – and we hope that the decades of work done by the community in trying to understand depletant systems can help us get a deeper understanding of pure, dense systems, so that we can narrow our search for interesting new materials.”
We are all familiar with the hassles that accompany air travel. We shuffle through long lines, remove our shoes, and carry liquids in regulation-sized tubes. And even after all the effort, we still wonder if these procedures are making us any safer. Now a new type of security detection that uses terahertz radiation is looking to prove its promise. Able to detect explosives, chemical agents, and dangerous biological substances from safe distances, devices using terahertz waves could make public spaces more secure than ever.
But current terahertz sources are large, multi-component systems that sometimes require complex vacuum systems, external pump lasers and even cryogenic cooling. The unwieldy devices are heavy, expensive, and hard to transport, operate and maintain.
“A single-component solution capable of room temperature and widely tunable operation is highly desirable to enable next-generation terahertz systems,” said Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science at Northwestern Univ.’s McCormick School of Engineering and Applied Science.
Director of Northwestern’s Center for Quantum Devices, Razeghi and her team have been working to develop such a device. In a recent paper in Applied Physics Letters, they demonstrate a room temperature, highly tunable, high-power terahertz source. Based on nonlinear mixing in quantum cascade lasers, the source can emit up to 1.9 mW of power and has a wide frequency coverage of 1 to 4.6 terahertz. By designing a multi-section, sampled-grating distribution feedback and distributed Bragg reflector waveguide, Razeghi and her team were also able to give the device a tuning range of 2.6 to 4.2 terahertz at room temperature.
The device has applications in medical and deep space imaging as well as security screening.
“I am very excited about these results,” Razeghi said. “No one would believe any of this was possible, even a couple years ago.”
Conventional treatment seeks to eradicate cancer cells by drugs and therapy delivered from outside the cell, which may also affect (and potentially harm) nearby normal cells.
In contrast to conventional cancer therapy, a University of Cincinnati team has developed several novel designs for iron-oxide based nanoparticles that detect, diagnose and destroy cancer cells using photo-thermal therapy (PTT). PTT uses the nanoparticles to focus light-induced heat energy only within the tumor, harming no adjacent normal cells.
The results of the UC work will be presented at the Materials Research Society Conference in Boston Nov. 30-Dec. 5 by Andrew Dunn, doctoral student in materials science engineering in UC’s College of Engineering and Applied Science. Working with Dunn in this study are Donglu Shi, professor of materials science engineering in UC’s College of Engineering and Applied Science; David Mast, associate professor of physics in UC’s McMicken College of Arts and Sciences; and Giovanni Pauletti, associate professor in the James L. Winkle College of Pharmacy.
The UC study used the living cells of mice to successfully test the efficacy of their two-sided nanoparticle designs (one side for cell targeting and the other for treatment delivery) in combination with the PTT. However, the U.S. Food and Drug Administration has now approved the use of iron-oxide nanoparticles in humans. That means the photo-thermal effect of iron-oxide nanoparticles may show, in the next decade, a strong promise in human cancer therapy, likely with localized tumors.
How the nanoparticles work with photothermal therapy
With this technology, a low-power laser beam is directed at the tumor where a small amount of magnetic iron-oxide nanoparticles are present, either by injecting the particles directly into the tumor or injecting them into the blood stream whereby the particles find and bind to the abnormal cancer cells via cell-specific targeting.
Sufficient heat is then generated locally by the laser light, raising the tumor temperature rapidly to above 43 degrees Celsius, and thereby burning the abnormal cancer cells. This particular PTT treatment does not involve any medicine, but only generates local heat within the tumor, therefore posing much less side effects than the traditional chemo or radiation therapies.
“This treatment is much more ideal because it goes straight to the cancer cell,” says Shi. “The nanomaterials enter only the abnormal cells, illuminating those cells and then doing whatever it is you have designed them to do. In this case, it is to heat up hot enough to burn and kill the cancer cells, but not harm the surrounding normal cells.”
Shi added that physicians are often frustrated with the current conventional means for early imaging of cancer cells through Medical Resonance Imaging or Computerized Tomography scans because the tumors are usually stage three or four before they can be detected. He stated, “With nanomaterial technology, we can detect the tumor early and kill it on sight at the same time.”
Each tumor has a corresponding protein that is cancer specific called a tumor specific ligand or an antibody antigen reaction that only has expression for that specific cancer such as breast or prostate cancer.
Scientists identify this certain bio-marker that is specific to a certain tumor, then conjugates this bio-marker on the surface of the nanocarrier that only has the expression for that specific kind of cancer cell.
It then only targets the abnormal cancer cell, not normal, healthy cells, and because it is so small it can break the membrane and enter that conjugated cancer cell and release the PTT.
The nanotech carriers go into the body through a vein in the blood stream, seek the abnormal cancer cells, find the bio-marker or cancer cells and attach to those cells and unlock their florescent particles so they can be detected by a photon laser-light.
The laser-light heats the nanoparticles to at least 43 degrees Celsius to kill the cancer cells, ultimately leaving all the other cells in the body unharmed.
Potential DIY cancer treatment
The procedure can ultimately be carried out by the patient following training to direct a small laser light device to the affected area for a specified amount of time two to three times a day. This method can ultimately improve the success rate, as well as cut costs to the patient. This gives “point and shoot” a whole new meaning.
Future research in nanoparticle PTT will look at toxicity, biodegradability and compatibility issues. Shi said that the team is currently looking for other diverse biodegradable materials to use for the carriers such as plant chlorophylls like those in cabbage that are both edible and photothermal. This material is biocompatible and biodegradable and can potentially stay in the tumor cells until its job is finished, then dissolve and be passed out through the digestive system.
Paper-based touch pad. (a) Schematic view of a paper-based touch pad. (b) Working principle of the paper-based touchpad. (c) Fabrication of the paper-based touchpad involving direct writing silver nanowire ink, flashlight sintering and tape coating. (d) The schematic of the direct writing equipment. (Reprinted with permission by American Chemical Society)
“Paper electronics have been extensively studied in the past years but a printing protocol has yet to be developed,” Anming Hu, an assistant professor at the University of Tennessee, Knoxville, tells Nanowerk. “Here, we wanted to develop a way to print it directly on a variety of paper to make a sensor that could respond to touch or specific molecules, such as glucose.” “We also proposed a simplified theoretical model to elucidate the capacitive operating of touch pads, which closely approximated empirical data,” notes Hu. Hu and his collaborators developed a technique that uses a 2D programmed printing machine with postdeposition sintering using a camera flash light to harden the deposited silver nanowire ink. The researchers point out that the resulting paper-based touchpads produced by direct writing with silver nanowire inks offer several distinct advantages over existing counterparts including:
low-cost and disposable;
rapid sintering of nanowires through surface plasmonic excitation, typically requiring 3 flash pulses and less than 20 seconds using a commercial camera flash;
ultrathin and ultralight: less than 0.1 mm thickness with printing and inkjet paper substrates and less than 60 mg for a single keypad on printing paper; and
flexible and robust: the device responded to touch even when curved, folded and unfolded 15 times, and rolled and unrolled 5,000 times.
Four keypad touch pad in (a) untouched state, (b) touching with a single finger, (c) touching with two fingers. (d) Folded touch pad, (e) touch pad after 15 folding cycles, (f) unfolded touch pad with two fingers touching, (g) touch pad functioning on a curved surface. (Reprinted with permission by American Chemical Society) (click on image to enlarge)
The team is now working on printable biosensors and energy devices with paper-based or polymer-based substrates. “We hope that we can integrate micro-sized batteries into a sensor and form a stand-alone microsystem,” says Hu.
Researchers at Nano-Meta Technologies Inc. (NMTI) in the Purdue Research Park have shown how to overcome key limitations of a material that could enable the magnetic storage industry to achieve data-recording densities far beyond today’s computers.
The new technology could make it possible to record data on an unprecedented small scale using tiny “nanoantennas” and to increase the amount of data that can be stored on a standard magnetic disk by 10 to 100 times.
The storage industry’s technology strategy, called heat-assisted magnetic recording (HAMR), hinges on the design of the nanoantenna, or near-field transducer (NFT), said Urcan Guler, chief scientist at Nano-Meta Technologies.
HAMR harnesses “plasmonics,” a technology that uses clouds of electrons called surface plasmons to manipulate and control light. However, some of the plasmonic NFTs under development rely on the use of metals such as gold and silver, which are not mechanically robust and present a challenge in fabrication and long-term reliability of the HAMR recording head.
Researchers from Nano-Meta Technologies and Purdue Univ. are working to replace gold with titanium nitride. The material offers high strength and durability at high temperatures, and its use as a nanoantenna paves the way for next-generation recording systems, said Vladimir M. Shalaev, scientific director of nanophotonics at Purdue’s Birck Nanotechnology Center and a distinguished professor of electrical and computer engineering.
The researchers have modified the physical properties of titanium nitride, tailoring it for HAMR.
A team from Nano-Meta Technologies and Purdue has authored an article on the need to develop new materials as alternatives to gold and silver for various plasmonic applications, using HAMR as an example. The article was published online in Faraday Discussions.
The technology could make it possible to circumvent the disk-storage-capacity limits imposed by conventional magnetic recording materials.Normally, lenses cannot focus light smaller than the wavelength of the light itself, which is hundreds of nanometers across. However, nanoantennas allow light to be focused into spots far smaller than the wavelength of light, making it possible to increase the storage capacity of the medium.
Industry has been reluctant to adopt titanium nitride for potential new plasmonic applications because making nanoantennas out of conventional titanium nitride leads to excessive “self-heating” through absorption of the input laser light, hindering performance. Common titanium nitride also undergoes oxidation reactions at high temperatures that degrade its optical properties, said Ernesto Marinero, a professor in Purdue’s School of Materials Engineering who is an expert in magnetic recording and joined the university after a long career in the storage industry.
To address both problems, the researchers have modified titanium nitride to significantly reduce its intrinsic light absorption, thereby paving the pathway to overcome the self-heating roadblock. Furthermore, the researchers also have solved the oxidation problem by protecting the material with an ultrathin coating that prevents oxidation without affecting the material’s optical properties.
HAMR uses a laser to illuminate a nanoantenna, a tiny structure with the ideal shape and size for “optimum light coupling” to produce the required spot size onto the recording medium. The antenna couples electromagnetic energy into a small spot, creating heat that allows a magnetic head to write the ones and zeroes required for data storage onto a spinning disk. HAMR allows the use of recording materials with superior magnetic properties to guarantee the stability of the nanoscale ones and zeroes of future computer drives.
Graduate student Rakesh Gupta takes a thin film sample out of a biochar solution.
Credit: Image courtesy of South Dakota State University
Energy storage devices and computer screens may seem worlds apart, but they’re not.
When associate professor Qi Hua Fan of the South Dakota State University electrical engineering and computer science department set out to make a less expensive supercapacitor for storing renewable energy, he developed a new plasma technology that will streamline the production of display screens.
For his work on thin film and plasma technologies, Fan was named researcher of the year for the Jerome J. Lohr College of Engineering. His research at the Center for Advanced Photovoltaics focuses on nanostructured materials used for photovoltaics, energy storage and displays.
Making electrodes for supercapacitors
Last spring Fan received a proof-of-concept grant from the Department of Energy through the North Central Regional Sun Grant Center to determine if biochar, a byproduct of the a process that converts plants materials into biofuel, could be used in place of expensive activated carbon to make electrodes for supercapacitors
Sun Grant promotes collaboration among researchers from land-grant institutions, government agencies and the private sector to develop and commercialize renewable, bio-based energy technologies. The proof-of-concept grants allow researchers to advance promising research to the next level of toward product development and commercialization.
“The amount of charge stored in a capacitor depends on the surface area,” Fan explained, “and the biochar nanoparticles can create an extremely large surface area which can then hold more charge.”
He deposits the biochar on a substrate using a patent-pending electrochemical process he developed and licensed to Applied Nanofilms LLC, in Brookings, South Dakota. Applied Nanofilms and Wintek, a company that makes flat panel displays for notebooks and touch screens in Ann Arbor, Michigan, provided matching funds.
Through this project, Fan developed a faster way of treating the biochar particles using a new technology called plasma activation. “Treating means you use plasma to change the material surface, such as creating pores,” Fan said.
The plasma treatment activates the biochar in five minutes and at room temperature, Fan explained. Conventional chemical activation takes several hours to complete and must be done at high temperatures — approximately 1,760 degrees Fahrenheit.
“This saves energy and is much more efficient,” Fan said. In this project, he has been collaborating with assistant professor Zhengrong Gu in the agricultural and biosystems engineering department, whose research focuses on energy storage materials and devices. They plan to use these promising results to apply for federal funding.
Applying plasma process to displays
The technique that treats biochar electrodes for supercapacitors can also be used in making displays, explained Fan, who was a research scientist at Wintek more than 10 years ago. Since last fall, Fan has been collaborating with Wintek on ways of producing more efficient, better performing materials, such as silicon and carbon thin films, for the company’s displays.
“Plasma processing is a very critical technology in modern optoelectronic materials and devices,” Fan explained. The high-energy plasma can deposit highly transparent and conductive thin films, create high quality semiconductors, and pattern micro- or nano-scale devices, thus making the display images brighter and clearer.
Fan will work with Wintek to develop a prototype plasma system. The activation method has the potential to improve production efficiency, saving time and energy, he noted.
Watch how ordinary tap water beads on cement and stone after being treated with SurfaPore C, a nanotechnology material that does not alter the physical appearance of the surface. Simply place with a brush. More info on http://www.nanophos.com
Scientists at the Canadian Light Source are on the forefront of battery technology using cheaper materials with higher energy and better recharging rates that make them ideal for electric vehicles (EVs).
The switch from conventional internal combustion engines to EVs is well underway. However, limited mileage of current EVs due to the confined energy storage capability of available battery systems is a major reason why these vehicles are not more common on the road.
A group of researchers from the CLS and Western Univ. have made significant strides in addressing the rechargeability and reaction kinetics of sodium-air batteries. They believe understanding sodium-air battery systems and the chemical composition and charging behavior will contribute to manufacturing more road-worthy batteries for EVs.
Schematic diagram of sodium-air (Na-Air) batteries based on porous carbon electrodes. Image: Canadian Light Source
“Metal-air cells use different chemistry from conventional lithium-ion batteries, making them more suited to compete with gasoline,” said Dr. Xueliang (Andy) Sun, Canada Research Chair from Western’s Dept. of Mechanical and Materials Engineering. “Development of new rechargeable battery systems with higher energy density will increase the EVs mileage and make them more practical for everyday use.
“On the other side, higher energy density battery systems will pave the road for renewable energy sources in order to decrease emissions and climate change consequences,” said Sun.
During their experiments, researchers looked at different “discharge products” from the sodium-air batteries under various physicochemical conditions. Products such as sodium peroxide and sodium superoxide are produced. Understanding these discharge products is critically important to the charging cycle of the battery cell, since various oxides exhibit different charging potentials.
The experiments were conducted using the powerful x-rays of the CLS VLS-PGM beamline.
“We took advantage of the high brightness and high-energy resolution of the photoemission endstation, using a surface sensitive technique to identify the different states of the sodium oxides,” said Dr. Xiaoyu Cui, CLS staff scientist. “We could also monitor the change in the chemical composition of the products by changing the kinetic parameters of the cell. The conclusive data from the CLS helped us confirm our hypothesis.”
According to the researchers, only a few studies have ever addressed sodium-air battery systems, with limited understanding behind the chemistry of the cell. Their work was published in Energy and Environmental Science and the authors believe the findings of the study contribute to better understanding the chemistry behind sodium-air cells which, in turn, will result in improved recharging rates and energy efficiencies.
“Although lots of research has been done to develop rechargeable, high energy metal-air battery cells during the past decade, there is still a long road ahead to achieve a practical high-energy battery system that can meet the demand for our current EVs,” said Sun. “We are working to develop novel materials for different battery systems to increase the energy density and lifecycle.
“Metal-air batteries are less expensive compared with other battery systems such as lithium-ion. Specifically, sodium-air batteries are very cost effective since the materials can easily be supplied from natural resources – sodium and oxygen being among the most abundant elements on earth.”
A potential path to identify imperfections and improve the quality of nanomaterials for use in next-generation solar cells has emerged from a collaboration of University of Oregon and industry researchers.
To increase light-harvesting efficiency of solar cells beyond silicon’s limit of about 29 percent, manufacturers have used layers of chemically synthesized semiconductor nanocrystals. Properties of quantum dots that are produced are manipulated by controlling the synthetic process and surface chemical structure.
This process, however, creates imperfections at the surface-forming trap states that limit device performance. Until recently, improvements in production quality have relied on feedback provided by traditional characterization techniques that probe average properties of large numbers of quantum dots.
“We want to use these materials in real devices, but they are not yet optimized,” said co-author Christian F. Gervasi, a UO doctoral student.
In their study, detailed in the Journal of Physical Chemistry Letters, researchers investigated electronic states of lead sulfide nanocrystals. By using a specially designed scanning tunneling microscope, researchers created atomic-scale maps of the density of states in individual nanocrystals. This allowed them to pinpoint the energies and localization of charge traps associated with defects in the nanocrystal surface structure that are detrimental to electron propagation.
The microscope was designed in the lab of co-author George V. Nazin, a professor in the UO Department of Chemistry and Biochemistry. Its use was described in a previous paper in the same journal, in which Nazin’s lab members were able to visualize the internal structures of electronic waves trapped by external electrostatic charges in carbon nanotubes.
“This technology is really cool,” said Peter Palomaki, senior scientist for Voxtel Nanophotonics and co-author on the new paper. “When you really dig down into the science at a very fundamental level, this problem has always been an open-ended question. This paper is just the tip of the iceberg in terms of being able to understand what’s going on.”
The insight, he said, should help manufacturers tweak their synthesis of nanocrystals used in a variety of electronic devices. Co-author Thomas Allen, also a senior scientist at Voxtel, agreed. The project began after Allen heard Gervasi and Nazin discussing the microscope’s capabilities.
“We wanted to see what the microscope could accomplish, and it turns out that it gives us a lot of information about the trap states and the depths of trap states in our quantum dots,” said Allen, who joined Voxtel after completing the Industrial Internship Program in the UO’s Materials Science Institute. “The information will help us fine-tune the ligand chemistry to make better devices for photovoltaics, detectors and sensors.”
The trap states seen by the microscope in this project may explain why nanoparticle-based solar cells have not yet been commercialized, Nazin said.
“Nanoparticles are not always stable. It is a fundamental problem. When you synthesize something at this scale you don’t necessarily get the same structure for all of the quantum dots. Working at the atomic scale can produce large variations in the electronic states. Our tool allows us to see these states directly and allow us to provide feedback on the materials.”