“Harvesting Energy from Light” – ORNL: Multimodal imaging shows strain can drive chemistry in a photovoltaic material –


In a thin film of a solar-energy material, molecules in twin domains (modeled in left and right panels) align in opposing orientations within grain boundaries (shown by scanning electron microscopy in the center panel). Strain can change chemical segregation and may be engineered to tune photovoltaic efficiency. Credit: Stephen Jesse/Oak Ridge National Laboratory, U.S. Dept. of Energy (hi-res image)

OAK RIDGE, Tenn., Sept. 25, 2018—A unique combination of imaging tools and atomic-level simulations has allowed a team led by the Department of Energy’s Oak Ridge National Laboratory to solve a longstanding debate about the properties of a promising material that can harvest energy from light.

The researchers used multimodal imaging to “see” nanoscale interactions within a thin film of hybrid organic–inorganic perovskite, a material useful for solar cells.

They determined that the material is ferroelastic, meaning it can form domains of polarized strain to minimize elastic energy. This finding was contrary to previous assumptions that the material is ferroelectric, meaning it can form domains of polarized electric charge to minimize electric energy.

“We found that people were misguided by the mechanical signal in standard electromechanical measurements, resulting in the misinterpretation of ferroelectricity,” said Yongtao Liu of ORNL, whose contribution to the study became a focus of his PhD thesis at the University of Tennessee, Knoxville (UTK).

Olga Ovchinnikova, who directed the experiments at ORNL’s Center for Nanophase Materials Sciences (CNMS), added, “We used multimodal chemical imaging—scanning probe microscopy combined with mass spectrometry and optical spectroscopy—to show that this material is ferroelastic and how the ferroelasticity drives chemical segregation.”

The findings, reported in Nature Materials, revealed that differential strains cause ionized molecules to migrate and segregate within regions of the film, resulting in local chemistry that may affect the transport of electric charge.

The understanding that this unique suite of imaging tools enables allows researchers to better correlate structure and function and fine-tune energy-harvesting films for improved performance.

“We want to predictively make grains of particular sizes and geometries,” Liu said. “The geometry is going to control the strain, and the strain is going to control the local chemistry.”

For their experiment, the researchers made a thin film by spin-casting a perovskite on an indium tin oxide–coated glass substrate. This process created the conductive, transparent surface a photovoltaic device would need—but also generated strain.

To relieve the strain, tiny ferroelastic domains formed. One type of domain was “grains,” which look like what you might see flying over farmland with patches of different crops skewed in relation to one another. Within grains, sub-domains formed, similar to rows of two plant types alternating in a patch of farmland. These adjacent but opposing rows are “twin domains” of segregated chemicals.

The technique that scientists previously used to claim the material was ferroelectric was piezoresponse force microscopy (“piezo” means “pressure), in which the tip of an atomic force microscope (AFM) measures a mechanical displacement due to its coupling with electric polarization—namely, electromechanical displacement. “But you’re not actually measuring the true displacement of the material,” Ovchinnikova warned. “You’re measuring the deflection of this whole ‘diving board’ of the cantilever.” Therefore, the researchers used a new measurement technique to separate cantilever dynamics from displacement of the material due to piezoresponse—the Interferometric Displacement Sensor (IDS) option for the Cypher AFM, developed by co-author Roger Proksch, CEO of Oxford Instruments Asylum Research.

They found the response in this material is from cantilever dynamics alone and is not a true piezoresponse, proving the material is not ferroelectric.

“Our work shows the effect believed due to ferroelectric polarization can be explained by chemical segregation,” Liu said.

The study’s diverse microscopy and spectroscopy measurements provided experimental data to validate atomic-level simulations. The simulations bring predictive insights that could be used to design future materials.

We’re able to do this because of the unique environment at CNMS where we have characterization, theory and synthesis all under one roof,” Ovchinnikova said.

“We didn’t just utilize mass spectrometry because [it] gives you information about local chemistry. We also used optical spectroscopy and simulations to look at the orientation of the molecules, which is important for understanding these materials. Such a cohesive chemical imaging capability at ORNL leverages our functional imaging.”

Collaborations with industry allow ORNL to have unique tools available for scientists, including those that settled the debate about the true nature of the light-harvesting material. For example, an instrument that uses helium ion microscopy (HIM) to remove and ionize molecules was coupled with a secondary ion mass spectroscopy (SIMS) to identify molecules based on their weights.

The HIM-SIMS instrument ZEISS ORION NanoFab was made available to ORNL from developer ZEISS for beta testing and is one of only two such instruments in the world. Similarly, the IDS instrument from Asylum Research, which is a laser Doppler vibrometer, was also made available to ORNL for beta testing and is the only one in existence.

“Oak Ridge National Laboratory researchers are naturally a good fit for working with industry because they possess unique expertise and are able to first use the tools the way they’re meant to,” said Proksch of Asylum. “ORNL has a facility [CNMS] that makes instruments and expertise available to many scientific users who can test tools on different problems and provide strong feedback during beta testing as vendors develop and improve the tools, in this case our new IDS metrological AFM.”

The title of the paper is “Chemical Nature of Ferroelastic Twin Domains in CH3NH3PbI3 Perovskite.”

The research was supported by ORNL’s Laboratory Directed Research and Development Program and conducted at CNMS, a DOE Office of Science User Facility at ORNL.

UT-Battelle manages ORNL for DOE’s Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit https://science.energy.gov/.

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ORNL: Nano-Ribbons may hold Key to ‘on-off’ states for Graphene ~ Applications in Electronics


Graphene Nano RibbonsZigzag+graphene+nanoribbon_9e206c5e-4835-4d17-b6ca-d717724ca971-prv

“Using electrons like photons could provide the basis for a new electronic device that could carry current with virtually no resistance, even at room temperature.”

 

A new way to grow narrow ribbons of graphene, a lightweight and strong structure of single-atom-thick carbon atoms linked into hexagons, may address a shortcoming that has prevented the material from achieving its full potential in electronic applications.

Graphene nanoribbons, mere billionths of a meter wide, exhibit different electronic properties than two-dimensional sheets of the material.   “Confinement changes graphene’s behavior,” said An-Ping Li, a physicist at the Department of Energy’s Oak Ridge National Laboratory. Graphene in sheets is an excellent electrical conductor, but narrowing graphene can turn the material into a semiconductor if the ribbons are made with a specific edge shape.

Previous efforts to make graphene nanoribbons employed a metal substrate that hindered the ribbons’ useful electronic properties.   Now, scientists at ORNL and North Carolina State University report in the journal Nature Communications that they are the first to grow graphene nanoribbons without a metal substrate. Instead, they injected charge carriers that promote a chemical reaction that converts a polymer precursor into a graphene nanoribbon.

At selected sites, this new technique can create interfaces between materials with different electronic properties. Such interfaces are the basis of semiconductor electronic devices from integrated circuits and transistors to light-emitting diodes and solar cells.   “Graphene is wonderful, but it has limits,” said Li.

“In wide sheets, it doesn’t have an energy gap–an energy range in a solid where no electronic states can exist. That means you cannot turn it on or off.”   When a voltage is applied to a sheet of graphene in a device, electrons flow freely as they do in metals, severely limiting graphene’s application in digital electronics.

GNR 2017 images“When graphene becomes very narrow, it creates an energy gap,” Li said. “The narrower the ribbon is, the wider is the energy gap.”   In very narrow graphene nanoribbons, with a width of a nanometer or even less, how structures terminate at the edge of the ribbon is important too. For example, cutting graphene along the side of a hexagon creates an edge that resembles an armchair; this material can act like a semiconductor. Excising triangles from graphene creates a zigzag edge–and a material with metallic behavior.

To grow graphene nanoribbons with controlled width and edge structure from polymer precursors, previous researchers had used a metal substrate to catalyze a chemical reaction. However, the metal substrate suppresses useful edge states and shrinks the desired band gap.   Li and colleagues set out to get rid of this troublesome metal substrate. At the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL, they used the tip of a scanning tunneling microscope to inject either negative charge carriers (electrons) or positive charge carriers (“holes”) to try to trigger the key chemical reaction. They discovered that only holes triggered it. They were subsequently able to make a ribbon that was only seven carbon atoms wide–less than one nanometer wide–with edges in the armchair conformation.

“We figured out the fundamental mechanism, that is, how charge injection can lower the reaction barrier to promote this chemical reaction,” Li said. Moving the tip along the polymer chain, the researchers could select where they triggered this reaction and convert one hexagon of the graphene lattice at a time.   Next, the researchers will make heterojunctions with different precursor molecules and explore functionalities. They are also eager to see how long electrons can travel in these ribbons before scattering, and will compare it with a graphene nanoribbon made another way and known to conduct electrons extremely well.

Using electrons like photons could provide the basis for a new electronic device that could carry current with virtually no resistance, even at room temperature.

“It’s a way to tailor physical properties for energy applications,” Li said. “This is an excellent example of direct writing. You can direct the transformation process at the molecular or atomic level.” Plus, the process could be scaled up and automated.  

Source and top image: Oak Ridge National Laboratory

Oak Ridge National Laboratory: A NANOTECH WAFER TURNS CARBON DIOXIDE INTO ETHANOL ~ Potential for Future Renewable Energy Storage


ethanol_485TECHNIQUE TO CREATE ALCOHOL FROM THIN AIR HAS APPLICATIONS IN RENEWABLE ENERGY

Now before you conjure up images of “Animal House and John Belushi” … this is NOT the latest Frat House entry into “home brews!” The Researchers at ORNL have found a way to produce a potential fuel and energy storage for renewable energy sources using Nanotechnology – converting carbon dioxide – Alex Rondinone, the lead researcher says, “it’s like pushing combustion backwards– ….”

Ethanol

 

Ethanol’s popularity stems from the fact that it’s a major component of booze, but it has also seen use in recent years as a bio-fuel. Scientists have found a way to take everyone’s least favorite greenhouse gas, carbon dioxide, and mix it with water to create alcohol.

 

A research team at Oak Ridge National Laboratory in Tennessee developed a way to convert carbon dioxide into ethanol--and they did it by accident. Originally, they were hoping to convert carbon dioxide that had been dissolved in water to methanol, a chemical released naturally by volcanic gases and microbes, which can cause blindness in humans if ingested.

But instead of methanol, they discovered they had ethanol, a primary component of gin and also a potential fuel source. Surprised, the team realized that not only was their new material converting the carbon dioxide to ethanol, it needed very little outside support.

The material is a small chip–about a square centimeter in size–covered in spikes, each just a few atoms across. Each spike is constructed out of nitrogen with a carbon sheath and a small sphere of copper embedded in each tip. The chip is dipped into water and carbon dioxide is bubbled in. The copper acts as a small lightning rod, attracting electricity and driving the first steps of the conversion of the carbon dioxide and water into ethanol, before the molecules move to the carbon sheath to finish the process.

Alex Rondinone, the lead researcher, says it’s like pushing combustion backwards–normally ethanol can burn with oxygen to produce carbon dioxide and water, as well as energy. But they’ve managed to reverse the process, supplying carbon dioxide and water, supplying it with electricity, and ending up with ethanol.

 

ethanol-producing nanomaterial

Oak Ridge National Laboratory Nanospikes used to produce ethanol

 

The new material relies on many, many small sphere of copper only a few atoms wide, held up by carbon sheaths surrounding a core of nitrogen. These immeasurably tiny structures handle the entire business of turning carbon dioxide and water into ethanol.

The new nano-structured material allowed the researchers to use widely available materials like copper instead of more expensive options like platinum. In the past, this has hampered the ability to manufacture a material like this at larger scales.

The team hopes that their material, because it’s made from more easily available components, will be able to scale up successfully.

Even though the process probably won’t help much with carbon dioxide in the atmosphere–Rondinone says it would be too energetically costly–he believes there is another way for this process to help meet energy demands.

Rondinone sees an opportunity to help with intermittent power sources like wind and solar. By capturing excess electricity generated by the process and storing it in the form of ethanol, it could be burned later when the wind turbines aren’t spinning or the sun isn’t shining.

Don’t plan on seeing a new Oak Ridge National Laboratory luxury brand of 130 proof liquor on the shelves anytime soon though. Although Rondinone says the ethanol is just like the ethanol you drink, it also contains trace quantities of formate, which is toxic to humans. He cautions, “I would not advise people to drink it without further purification.”

DOE to invest $16M in computational design of new materials for alt and renewable energy, electronics and other fields


DOE_Logo

17 August 2016

The US Department of Energy will invest $16 million over the next four years to accelerate the design of new materials through use of supercomputers.

Two four-year projects—one team led by DOE’s Lawrence Berkeley National Laboratory (Berkeley Lab), the other teamled by DOE’s Oak Ridge National Laboratory (ORNL)—will leverage the labs’ expertise in materials and take advantage of lab supercomputers to develop software for designing fundamentally new functional materials destined to revolutionize applications in alternative and renewable energy, electronics, and a wide range of other fields. The research teams include experts from universities and other national labs.

The new grants—part of DOE’s Computational Materials Sciences (CMS) program launched in 2015 as part of the US Materials Genome Initiative—reflect the enormous recent growth in computing power and the increasing capability of high-performance computers to model and simulate the behavior of matter at the atomic and molecular scales.lawrence-berkeley-national-laboratory

The teams are expected to develop sophisticated and user-friendly open-source software that captures the essential physics of relevant systems and can be used by the broader research community and by industry to accelerate the design of new functional materials.

Berkeley_Lab_Logo_Small 082016The Berkeley Lab team will be led by Steven G. Louie, an internationally recognized expert in materials science and condensed matter physics. A longtime user of NERSC supercomputers, Louie has a dual appointment as Senior Faculty Scientist in the Materials Sciences Division at Berkeley Lab and Professor of Physics at the University of California, Berkeley. Other team members are Jack Deslippe, Jeffrey B. Neaton, Eran Rabani, Feng Wang, Lin-Wang Wang and Chao Yang, Lawrence Berkeley National Laboratory; and partners Daniel Neuhauser, University of California at Los Angeles, and James R. Chelikowsky, University of Texas, Austin.

This investment in the study of excited-state phenomena in energy materials will, in addition to pushing the frontiers of science, have wide-ranging applications in areas such as electronics, photovoltaics, light-emitting diodes, information storage and energy storage. We expect this work to spur major advances in how we produce cleaner energy, how we store it for use, and to improve the efficiency of devices that use energy.

—Steven Louie

ORNL researchers will partner with scientists from national labs and universities to develop software to accurately predict the properties of quantum materials with novel magnetism, optical properties and exotic quantum phases that make them well-suited to energy applications, said Paul Kent of ORNL, director of the Center for Predictive Simulation of Functional Materials, which includes partners from Argonne, Lawrence Livermore, Oak Ridge and Sandia National Laboratories and North Carolina State University and the University of California–Berkeley.ORNL 082016 steamplant_8186871_ver1.0_640_480

Our simulations will rely on current petascale and future exascale capabilities at DOE supercomputing centers. To validate the predictions about material behavior, we’ll conduct experiments and use the facilities of the Advanced Photon Source, Spallation Neutron Source and the Nanoscale Science Research Centers.

—Paul Kent

At Argonne, our expertise in combining state-of-the-art, oxide molecular beam epitaxy growth of new materials with characterization at the Advanced Photon Source and the Center for Nanoscale Materials will enable us to offer new and precise insight into the complex properties important to materials design. We are excited to bring our particular capabilities in materials, as well as expertise in software, to the center so that the labs can comprehensively tackle this challenge.

—Olle Heinonen, Argonne materials scientist

Researchers are expected to make use of the 30-petaflop/s Cori supercomputer now being installed at the National Energy Research Scientific Computing center (NERSC) at Berkeley Lab, the 27-petaflop/s Titan computer at the Oak Ridge Leadership Computing Facility (OLCF) and the 10-petaflop/s Mira computer at Argonne Leadership Computing Facility (ALCF). OLCF, ALCF, and NERSC are all DOE Office of Science User Facilities. One petaflop/s is 1015 or a million times a billion floating-point operations per second.

In addition, a new generation of machines is scheduled for deployment between 2016 and 2019 that will take peak performance as high as 200 petaflops. Ultimately the software produced by these projects is expected to evolve to run on exascale machines, capable of 1000 petaflops and projected for deployment in the mid-2020s.

Research will combine theory and software development with experimental validation, drawing on the resources of multiple DOE Office of Science User Facilities, including the Molecular Foundry and Advanced Light Source at Berkeley Lab, the Center for Nanoscale Materials and the Advanced Photon Source at Argonne National Laboratory (ANL), and the Center for Nanophase Materials Sciences and the Spallation Neutron Source at ORNL, as well as the other Nanoscience Research Centers across the DOE national laboratory complex.

The new research projects will begin in Fiscal Year 2016. Subsequent annual funding will be contingent on available appropriations and project performance.

The two new projects expand the ongoing CMS research effort, which began in FY 2015 with three initial projects, led respectively by ANL, Brookhaven National Laboratory and the University of Southern California.

Is there a “Fourth” State of Water? Oak Ridge National Lab (ORNL) Discovers Bizarre Fourth State of Water ~ P.S. This is Way “Cool” … Should be Featured in the Next Star Trek! (plus Video)


fourth state of water 080116 beryl-1A sample of beryl and an illustration that shows the strange shape water molecules take when found in the mineral’s cage-like channels (Credit: ORNL/Jeff Scovil)

You already know that water can have three states of matter: solid, liquid and gas. But scientists at the Oak Ridge National Lab (ORNL) have discovered that when it’s put under extreme pressure in small spaces, the life-giving liquid can exhibit a strange fourth state known as tunneling.

The water under question was found in super-small six-sided channels in the mineral beryl, which forms the basis for the gems aquamarine and emerald. The channels measure only about five atoms across and function basically as cages that can each trap one water molecule. What the researchers found was that in this incredibly tight space, the water molecule exhibited a characteristic usually only seen at the much smaller quantum level, called tunneling.

Basically, quantum tunneling means that a particle, or in this case a molecule, can overcome a barrier and be on both sides of it at once – or anywhere between. Think of rolling a ball down one side of a hill and up another. The second hill is the barrier and the ball would only have enough energy to climb it to the height from which it was originally dropped. If the second hill was taller, the ball wouldn’t be able to roll over it. That’s classical physics. Quantum physics and the concept of tunneling means the ball could jump to the other side of the hill with ease or even be found inside the hill – or on both sides of the hill at once.

“In classical physics the atom cannot jump over a barrier if it does not have enough energy for this,” ORNL instrument scientist Alexander Kolesnikov tells Gizmag – Kolesnikov is lead author on a paper detailing the discovery published in the April 22 issue of the journal Physical Review Letters. But in the case of the beryl-trapped water his team studied, the water molecules acted according to quantum – not classical – laws of physics.

“This means that the oxygen and hydrogen atoms of the water molecule are ‘delocalized’ and therefore simultaneously present in all six symmetrically equivalent positions in the channel at the same time,” says Kolesnikov. “It’s one of those phenomena that only occur in quantum mechanics and has no parallel in our everyday experience.”

By using neutron-scattering experiments, the researchers were able to see that the water molecules spread themselves into two corrugated rings, one inside the other. At the center of the ring, the hydrogen atom, which is one third of the water molecule, took on six different orientations at one time. “Tunneling among these orientations means the hydrogen atom is not located at one position, but smeared out in a ring shape,” says a report in the online news journal Physics.

“This discovery represents a new fundamental understanding of the behavior of water and the way water utilizes energy,” says ORNL co-author Lawrence Anovitz. “It’s also interesting to think that those water molecules in your aquamarine or emerald ring – blue and green varieties of beryl – are undergoing the same quantum tunneling we’ve seen in our experiments.”

Because the ORNL team discovered this new property of water but not exactly why and how it works, Anovitz also says that the finding is sure to get scientists working to uncover the mechanism that leads to the phenomenon.

Kolesnikov adds that the discovery could have implications wherever water is found in extremely tight spaces such as in cell membranes or inside carbon nanotubes. The following video from ORNL provides more details on the discovery.

ORNL researchers discover a new state of Water Molecule: Video

Oak Ridge National Laboratory: Team Demonstrates large-scale technique to produce Quantum Dots


ORNL 051816 ornldemonstrUsing this 250-gallon reactor, ORNL researchers produced three-fourths of a pound of zinc sulfide quantum dots, shown in the inset. Credit: ORNL

A method to produce significant amounts of semiconducting nanoparticles for light-emitting displays, sensors, solar panels and biomedical applications has gained momentum with a demonstration by researchers at the Department of Energy’s Oak Ridge National Laboratory.

While nanoparticles – a type of quantum dot that is a semiconductor – have many potential applications, high cost and limited availability have been obstacles to their widespread use. That could change, however, because of a scalable ORNL technique outlined in a paper published in Applied Microbiology and Biotechnology.

Unlike conventional inorganic approaches that use expensive precursors, toxic chemicals, high temperatures and high pressures, a team led by ORNL’s Ji-Won Moon used bacteria fed by inexpensive sugar at a temperature of 150 degrees Fahrenheit in 25- and 250-gallon reactors. Ultimately, the team produced about three-fourths of a pound of zinc sulfide nanoparticles – without process optimization, leaving room for even higher yields.

The ORNL biomanufacturing technique is based on a platform technology that can also produce nanometer-size semiconducting materials as well as magnetic, photovoltaic, catalytic and phosphor materials. Unlike most biological synthesis technologies that occur inside the cell, ORNL’s biomanufactured quantum dot synthesis occurs outside of the cells. As a result, the nanomaterials are produced as loose particles that are easy to separate through simple washing and centrifuging.

 

The results are encouraging, according to Moon, who also noted that the ORNL approach reduces production costs by approximately 90 percent compared to other methods.

“Since biomanufacturing can control the quantum dot diameter, it is possible to produce a wide range of specifically tuned semiconducting nanomaterials, making them attractive for a variety of applications that include electronics, displays, solar cells, computer memory, energy storage, printed electronics and bio-imaging,” Moon said.

Successful biomanufacturing of light-emitting or semiconducting nanoparticles requires the ability to control material synthesis at the nanometer scale with sufficiently high reliability, reproducibility and yield to be cost effective. With the ORNL approach, Moon said that goal has been achieved.

Researchers envision their quantum dots being used initially in buffer layers of photovoltaic cells and other thin film-based devices that can benefit from their electro-optical properties as light-emitting materials.

Co-authors of the paper, titled “Manufacturing demonstration of microbially mediated zinc sulfide in pilot-plant scale reactors,” were ORNL’s Tommy Phelps, Curtis Fitzgerald Jr., Randall Lind, James Elkins, Gyoung Gug Jang, Pooran Joshi, Michelle Kidder, Beth Armstrong, Thomas Watkins, Ilia Ivanov and David Graham. Funding for this research was provided by DOE’s Advanced Manufacturing Office and Office of Science.

Explore further: Bacterial method for low-cost, environmentally-friendly synthesis of aqueous soluble quantum dot nanocrystals

More information: Ji-Won Moon et al. Manufacturing demonstration of microbially mediated zinc sulfide nanoparticles in pilot-plant scale reactors, Applied Microbiology and Biotechnology (2016). DOI: 10.1007/s00253-016-7556-y

 

ORNL: Speedy ion conduction in solid electrolytes clears road for advanced energy devices


ORNL Speedy Ion 051016 160505145033_1_540x360An ORNL-led research team found the key to fast ion conduction in a solid electrolyte. Tiny features maximize ion transport pathways, represented by red and green.
Credit: Oak Ridge National Laboratory, U.S. Dept. of Energy

In a rechargeable battery, the electrolyte transports lithium ions from the negative to the positive electrode during discharging. The path of ionic flow reverses during recharging. The organic liquid electrolytes in commercial lithium-ion batteries are flammable and subject to leakage, making their large-scale application potentially problematic. Solid electrolytes, in contrast, overcome these challenges, but their ionic conductivity is typically low.

Now, a team led by the Department of Energy’s Oak Ridge National Laboratory has used state-of-the-art microscopy to identify a previously undetected feature, about 5 billionths of a meter (nanometers) wide, in a solid electrolyte. The work experimentally verifies the importance of that feature to fast ion transport, and corroborates the observations with theory. The new mechanism the researchers report in Advanced Energy Materials points out a new strategy for the design of highly conductive solid electrolytes.

“The solid electrolyte is one of the most important factors in enabling safe, high-power, high-energy, solid-state batteries,” said first author Cheng Ma of ORNL, who conducted most of the study’s experiments. “But currently the low conductivity has limited its applications.”

ORNL’s Miaofang Chi, the senior author, said, “Our work is basic science focused on how we can facilitate ion transport in solids. It is important to the design of fast ion conductors, not only for batteries, but also for other energy devices.” These include supercapacitors and fuel cells.

To directly observe the atomic arrangement in the solid electrolyte, the researchers used aberration-corrected scanning transmission electron microscopy to send electrons through a sample. To observe an extremely small feature in a three-dimensional (3D) material with a method that essentially provides a two-dimensional (2D) projection, they needed a sample of extraordinary thinness. To prepare one, they relied on comprehensive materials processing and characterization capabilities of the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL.

“Usually the transmission electron microscopy specimen is 20 nanometers thick, but Ma developed a method to make the specimen ultra-thin (approximately 5 nanometers),” Chi said. “That was the key because such a thickness is comparable to the size of the hidden feature we finally resolved.”

The researchers examined a prototype system called LLTO, shorthand for its lithium, lanthanum, titanium and oxygen building blocks. LLTO possesses the highest bulk conductivity among oxide systems.

In this material, lithium ions move fastest in the planar 2D pathways resulting from alternating stacks of atomic layers rich in either lanthanum or lithium. The ORNL-led team was the first to see that, without hurting this superior 2D transport, tiny domains, or fine features approximately 5 to 10 nanometers wide, throughout the 3D material provided more directions in which lithium ions could move. The domains looked like sets of shelves stacked at right angles to others. The smaller the shelves, the easier it was for ions to flow in the direction of an applied current.

ORNL’s Yongqiang Cheng and Bobby Sumpter performed molecular dynamics simulations that corroborated the experimental findings.

Previously, scientists looked at the atomic structure of the simplest repeating unit of a crystal–called a unit cell–and rearranged its atoms or introduced different elements to see how they could facilitate ion transport. Unit cells are typically less than 1 nanometer wide. In the material that the ORNL scientists studied for this paper, the unit cell is nearly half a nanometer. The team’s unexpected finding–that fine features, of only a few nanometers and traversing a few unit cells, can maximize the number of ionic transport pathways–provides new perspective.

“The finding adds a new criterion,” Chi said. “This largely overlooked length scale could be the key to fast ionic conduction.”

Researchers will need to consider phenomena on the order of several nanometers when designing materials for fast ion conduction.

Ma agreed. “The prototype material has high ionic conductivity because not only does it maintain unit-cell structure, but also it adds this fine feature, which underpins 3D pathways,” Ma said. “We’re not saying that we shouldn’t be looking at the unit-cell scale. We’re saying that in addition to the unit cell scale, we should also be looking at the scale of several unit cells. Sometimes that outweighs the importance of one unit cell.”

For several decades, when researchers had no explanation for certain material behaviors, they speculated phenomena transcending one unit cell could be at play. But they never saw evidence. “This is the first time we proved it experimentally,” Ma said. “This is a direct observation, so it is the most solid evidence.”


Story Source:

The above post is reprinted from materials provided by DOE/Oak Ridge National Laboratory. Note: Materials may be edited for content and length.


Journal Reference:

  1. Cheng Ma, Yongqiang Cheng, Kai Chen, Juchuan Li, Bobby G. Sumpter, Ce-Wen Nan, Karren L. More, Nancy J. Dudney, Miaofang Chi. Mesoscopic Framework Enables Facile Ionic Transport in Solid Electrolytes for Li Batteries.Advanced Energy Materials, 2016; DOI:10.1002/aenm.201600053

Advanced energy storage material gets unprecedented nanoscale analysis


Advanced Nano Scale Storage 111245_web

OAK RIDGE, Tenn., March 16, 2016 — Researchers at the Department of Energy’s Oak Ridge National Laboratory have combined advanced in-situ microscopy and theoretical calculations to uncover important clues to the properties of a promising next-generation energy storage material for supercapacitors and batteries.

ORNL’s Fluid Interface Reactions, Structures and Transport (FIRST) research team, using scanning probe microscopy made available through the Center for Nanophase Materials Sciences (CNMS) user program, have observed for the first time at the nanoscale and in a liquid environment how ions move and diffuse between layers of a two-dimensional electrode during electrochemical cycling. This migration is critical to understanding how energy is stored in the material, called MXene, and what drives its exceptional energy storage properties.

“We have developed a technique for liquid environments that allows us to track how ions enter the interlayer spaces. There is very little information on how this actually happens,” said Nina Balke, one of a team of researchers working with Drexel University’s Yury Gogotsi in the FIRST Center, a DOE Office of Science Energy Frontier Research Center.

“The energy storage properties have been characterized on a microscopic scale, but no one knows what happens in the active material on the nanoscale in terms of ion insertion and how this affects stresses and strains in the material,” Balke said.

The so-called MXene material — which acts as a two-dimensional electrode that could be fabricated with the flexibility of a sheet of paper — is based on MAX-phase ceramics, which have been studied for decades. Chemical removal of the “A” layer leaves two-dimensional flakes composed of transition metal layers — the “M” — sandwiching carbon or nitrogen layers (the “X”) in the resulting MXene, which physically resembles graphite.

These MXenes, which have exhibited very high capacitance, or ability to store electrical charge, have only recently been explored as an energy storage medium for advanced batteries.

“The interaction and charge transfer of the ion and the MXene layers is very important for its performance as an energy storage medium. The adsorption processes drive interesting phenomena that govern the mechanisms we observed through scanning probe microscopy,” said FIRST researcher Jeremy Come.

The researchers explored how the ions enter the material, how they move once inside the materials and how they interact with the active material. For example, if cations, which are positively charged, are introduced into the negatively charged MXene material, the material contracts, becoming stiffer.

That observation laid the groundwork for the scanning probe microscopy-based nanoscale characterization. The researchers measured the local changes in stiffness when ions enter the material. There is a direct correlation with the diffusion pattern of ions and the stiffness of the material.

Come noted that the ions are inserted into the electrode in a solution.

“Therefore, we need to work in liquid environment to drive the ions within the MXene material. Then we can measure the mechanical properties in-situ at different stages of charge storage, which gives us direct insight about where the ions are stored,” he said.

Until this study the technique had not been done in a liquid environment.

The processes behind ion insertion and the ionic interactions in the electrode material had been out of reach at the nanoscale until the CNMS scanning probe microscopy group’s studies. The experiments underscore the need for in-situ analysis to understand the nanoscale elastic changes in the 2D material in both dry and wet environments and the effect of ion storage on the energy storage material over time.

The researchers’ next steps are to improve the ionic diffusion paths in the material and explore different materials from the MXene family. Ultimately, the team hopes to understand the process’s fundamental mechanism and mechanical properties, which would allow tuning the energy storage as well as improving the material’s performance and lifetime.

ORNL’s FIRST research team also provided additional calculations and simulations based on density functional theory that support the experimental findings. The work was recently published in the Journal Advanced Energy Materials.

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The research team in addition to Balke and Come and Drexel’s Gogotsi included Michael Naguib, Stephen Jesse, Sergei V. Kalinin, Paul R.C. Kent and Yu Xie, all of ORNL.

The FIRST Center is an Energy Frontier Research Center supported by the DOE Office of Science (Basic Energy Sciences). The Center for Nanophase Materials Sciences and the National Energy Research Scientific Computing Center are DOE Office of Science User Facilities.

UT-Battelle manages ORNL for the DOE’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/.

Image: https://www.ornl.gov/sites/default/files/news/images/JCome_MXene.jpg

Image cutline: When a negative bias is applied to a two-dimensional MXene electrode, Li+ ions from the electrolyte migrate in the material via specific channels to the reaction sites, where the electron transfer occurs. Scanning probe microscopy at Oak Ridge National Laboratory has provided the first nanoscale, liquid environment analysis of this energy storage material.

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ORNL (Oak Ridge National Labortory): Researchers Find ‘Greener’ way to Assemble Materials for Solar Applications: “Self-assembly of polymers using surfactants provides huge potential in fabricating nanostructures with molecular-level controllability.”


ORNL Green Solar 100668_webIMAGE: A surfactant template guides the self-assembly of functional polymer structures in an aqueous solution. view more

Credit: Image credit: Oak Ridge National Laboratory, U.S. Dept. of Energy; image by Youngkyu Han and Renee Manning.

OAK RIDGE, Tenn., Oct. 5, 2015–The efficiency of solar cells depends on precise engineering of polymers that assemble into films 1,000 times thinner than a human hair.

Today, formation of that polymer assembly requires solvents that can harm the environment, but scientists at the Department of Energy’s Oak Ridge National Laboratory have found a “greener” way to control the assembly of photovoltaic polymers in water using a surfactant– a detergent-like molecule–as a template. Their findings are reported in Nanoscale, a journal of the Royal Society of Chemistry.

“Self-assembly of polymers using surfactants provides huge potential in fabricating nanostructures with molecular-level controllability,” said senior author Changwoo Do, a researcher at ORNL’s Spallation Neutron Source (SNS).

The researchers used three DOE Office of Science User Facilities–the Center for Nanophase Materials Sciences (CNMS) and SNS at ORNL and the Advanced Photon Source (APS) at Argonne National Laboratory–to synthesize and characterize the polymers.

“Scattering of neutrons and X-rays is a perfect method to investigate these structures,” said Do.

The study demonstrates the value of tracking molecular dynamics with both neutrons and optical probes.

“We would like to create very specific polymer stacking in solution and translate that into thin films where flawless, defect-free polymer assemblies would enable fast transport of electric charges for photovoltaic applications,” said Ilia Ivanov, a researcher at CNMS and a corresponding author with Do. “We demonstrated that this can be accomplished through understanding of kinetic and thermodynamic mechanisms controlling the polymer aggregation.”

The accomplishment creates molecular building blocks for the design of optoelectronic and sensory materials. It entailed design of a semiconducting polymer with a hydrophobic (“water-fearing”) backbone and hydrophilic (“water-loving”) side chains. The water-soluble side-chains could allow “green” processing if the effort produced a polymer that could self-assemble into an organic photovoltaic material. The researchers added the polymer to an aqueous solution containing a surfactant molecule that also has hydrophobic and hydrophilic ends. Depending on temperature and concentration, the surfactant self-assembles into different templates that guide the polymer to pack into different nanoscale shapes–hexagons, spherical micelles and sheets.

In the semiconducting polymer, atoms are organized to share electrons easily. The work provides insight into the different structural phases of the polymer system and the growth of assemblies of repeating shapes to form functional crystals. These crystals form the basis of the photovoltaic thin films that provide power in environments as demanding as deserts and outer space.

“Rationally encoding molecular interactions to rule the molecular geometry and inter-molecular packing order in a solution of conjugated polymers is long desired in optoelectronics and nanotechnology,” said the paper’s first author, postdoctoral fellow Jiahua Zhu. “The development is essentially hindered by the difficulty of in situ characterization.”

In situ, or “on site,” measurements are taken while a phenomenon (such as a change in molecular morphology) is occurring. They contrast with measurements taken after isolating the material from the system where the phenomenon was seen or changing the test conditions under which the phenomenon was first observed. The team developed a test chamber that allows them to use optical probes while changes occur.

Neutrons can probe structures in solutions

Expertise and equipment at SNS, which provides the most intense pulsed neutron beams in the world, made it possible to discover that a functional photovoltaic polymer could self-assemble in an environmentally benign solvent. The efficacy of the neutron scattering was enhanced, in turn, by a technique called selective deuteration, in which specific hydrogen atoms in the polymers are replaced by heavier atoms of deuterium–which has the effect of heightening contrasts in the structure. CNMS has a specialty in the latter technique.

“We needed to be able to see what’s happening to these molecules as they evolve in time from some solution state to some solid state,” author Bobby Sumpter of CNMS said. “This is very difficult to do, but for molecules like polymers and biomolecules, neutrons are some of the best probes you can imagine.” The information they provide guides design of advanced materials.

By combining expertise in topics including neutron scattering, high-throughput data analysis, theory, modeling and simulation, the scientists developed a test chamber for monitoring phase transitions as they happened. It tracks molecules under conditions of changing temperature, pressure, humidity, light, solvent composition and the like, allowing researchers to assess how working materials change over time and aiding efforts to improve their performance.

Scientists place a sample in the chamber and transport it to different instruments for measurements. The chamber has a transparent face to allow entry of laser beams to probe materials. Probing modes–including photons, electrical charge, magnetic spin and calculations aided by high-performance computing–can operate simultaneously to characterize matter under a broad range of conditions. The chamber is designed to make it possible, in the future, to use neutrons and X-rays as additional and complementary probes.

“Incorporation of in situ techniques brings information on kinetic and thermodynamic aspects of materials transformations in solutions and thin films in which structure is measured simultaneously with their changing optoelectronic functionality,” Ivanov said. “It also opens an opportunity to study fully assembled photovoltaic cells as well as metastable structures, which may lead to unique features of future functional materials.”

Whereas the current study examined phase transitions (i.e., metastable states and chemical reactions) at increasing temperatures, the next in situ diagnostics will characterize them at high pressure. Moreover, the researchers will implement neural networks to analyze complex nonlinear processes with multiple feedbacks.

The title of the Nanoscale paper is “Controlling molecular ordering in solution-state conjugated polymers.”

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Zhu, Do and Ivanov led the study. Zhu, Ivanov and Youngkyu Han conducted synchrotron X-ray scattering and optical measurements. Sumpter, Rajeev Kumar and Sean Smith performed theory calculations. Youjun He and Kunlun Hong synthesized the water-soluble polymer. Peter Bonnesen conducted thermal nuclear magnetic resonance analysis on the water-soluble polymer. Do, Han and Greg Smith performed neutron measurement and analysis of the scattering results. This research was conducted at CNMS and SNS, which are DOE Office of Science User Facilities at ORNL. Moreover, the Advanced Photon Source, a DOE Office of Science User Facility at Argonne National Laboratory, was used to perform synchrotron X-ray scattering on the polymer solution. Laboratory Directed Research and Development funds partially supported the work.

UT-Battelle manages ORNL for DOE’s Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit http://science.energy.gov/.

Boosting light-water reactor research


ligh-waterreactorx250Hard on the heels of a five-year funding renewal, modeling and simulation (M&S) technology developed at Los Alamos National Laboratory as part of the Consortium for the Advanced Simulation of Light Water Reactors (CASL) will now be deployed to industry and academia under a new inter-institutional agreement for intellectual property.

This agreement streamlines access to the reactor simulation research tools,” said Kathleen McDonald, software business development executive for the Laboratory, “and with a single contact through UT-Battelle, we have a more transparent release process, the culmination of a lengthy effort on the part of all the code authors,” she said.

CASL is a U.S. Dept. of Energy (DOE) “Energy Innovation Hub” established in 2010 to develop advanced M&S capabilities that serve as a virtual version of existing, operating nuclear reactors. As announced by DOE in January, the hub would receive up to $121.5 million over five years, subject to congressional appropriations. Over the next five years, CASL researchers will focus on extending the M&S technology built during its first phase to include additional nuclear reactor designs, including boiling water reactors and pressurized water reactor-based small modular reactors.

CASL’s Virtual Environment for Reactor Applications (VERA)—essentially a “virtual” reactor—has currently been deployed for testing to CASL’s industrial partners. Created with CASL Funding, VERA consists of CASL Physics Codes and the software that couples CASL Physics Codes to create the computer models to predict and simulate light water reactor (LWR) nuclear power plant operations. VERA is being validated with data from a variety of sources, including operating pressurized water reactors such as the Watts Bar Unit 1 Nuclear Plant in Tennessee, operated by the Tennessee Valley Authority (TVA).

As one of the original founding CASL partners, Los Alamos will continue to play an important role in Phase 2 of CASL. Specifically, Los Alamos has leadership roles in three technical focus areas: Thermal Hydraulics Methods (THM), Fuel, Materials and Chemistry (FMC) and Validation and Modeling Applications (VMA).

Thermal-Hydraulics applications range from fluid-structure interaction to boiling multiphase flows. The Los Alamos-led THM team is targeting a number of industry-defined CASL “challenge problems” related to corrosion, fretting and departure from nucleate boiling.

The Fuel, Materials and Chemistry (FMC) Focus Area aims to develop improved materials performance models for fuel and cladding, and integrate those models via constitutive relations and behavioral models into VERA. In particular, Los Alamos will bring to bear experience in structure-property relations, mechanical deformation and chemical kinetics to address several key aspects of nuclear fuel performance.

The Validation and Modeling Applications (VMA) Focus Area applies the products developed by CASL to address essential industry issues for achieving the CASL objectives of power uprates, lifetime extension and fuel burn up limit increases, while ensuring the fuel performance and safety limits are met. Los Alamos will continue to provide functions that are essential for achieving credible, science-based predictive modeling and simulation capabilities, including verification, validation, calibration through data assimilation, sensitivity analysis, discretization error analysis and control and uncertainty quantification.

The new IIA agreement makes one of the Los Alamos-developed software tools, MAMBA, available for research, subject to agreements through the consortium partners. In addition, the Hydra-TH application is provided under an open-source license in VERA for advanced, scalable single and multiphase computational fluid dynamics simulations.

CASL, which is led by and headquartered at Oak Ridge National Laboratory (ORNL), has created hundreds of technical reports and publications and wide engagement with nuclear reactor technology vendors, utilities, and the advanced computing industry.

Doug Kothe, CASL Director at ORNL, notes that “CASL has benefitted tremendously from the innovative technical contributions and leadership provided by Los Alamos technical staff and is fortunate to have these contributions continuing as CASL moves into its second five-years of execution.”

Source: Los Alamos National Laboratory