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Automating 2-D Material Exfoliation with Suji Park

Posted By Terrance Barkan, Monday, October 19, 2020

Suji Park is a scientific associate in the Electronic Nanomaterials Group at the Center for Functional Nanomaterials (CFN), a U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory. Since joining the CFN in October 2019, she has been designing and building hardware for the automated exfoliation of high-quality atomically thin “flakes” from 3-D bulk materials. When these 2-D material flakes are stacked into layered structures, new electrical, optical, magnetic, and other properties can emerge.

Such 2-D heterostructures could find applications in areas including catalysis, solar energy, and quantum computing. Park received a bachelor’s degree and PhD in materials science and engineering from Pohang University of Science and Technology in South Korea. She then went on to do three postdocs—one at a neutron imaging facility at the Korea Atomic Energy Research Institute, another in Stanford’s Chemical Engineering Department, and a third at the Stanford Institute for Materials and Energy Sciences at SLAC National Accelerator Laboratory.


What characterizes 2-D materials, and why are scientists interested in them?
2-D materials are ultrathin. They are just a few atoms thick—or even just a single atom thick! The most well-known 2-D material is graphene, which is made of sheets of carbon exfoliated from graphite. The different layers of graphite are held together by weak forces, making them easy to detach. This is why we can make 2-D single-layer flakes of graphene. By stacking flakes from different materials, we can create layered structures that are essentially new materials. This lets us tune their mechanical, optical, and electrical properties. There are exciting theoretical predictions for making quantum devices based on 2-D materials, but the bottleneck is actually making these layered materials.

Why is flake fabrication so challenging?
The traditional way to make 2-D materials is through mechanical exfoliation. Adhesives are repeatedly attached to and detached from a bulk crystal so that the fragments get thinner and thinner. When the materials become thin enough, the adhesives are pressed into silicon wafers to transfer the flakes onto the wafer surface. Eventually, you end up with some very small-sized monolayers.

However, the mechanics of this exfoliation process are not very well understood. This process is laborious, has very low reproducibility, and the quality of the flakes strongly depends on who is performing the exfoliation. Because of the lack of understanding, controlling the size, shape, and other parameters of the flakes is quite difficult. People spend a lot of time to get just one perfect flake. Then, they have to repeat this process many times to build complex layered structures.

Graphene was discovered in 2004. Why is our understanding of exfoliation mechanics still limited after all these years?
This has been a question of mine, too. When I began researching mechanical exfoliation, I found that many scientists have simulated how mechanical exfoliation works. However, these results are limited in terms of their applicability to real-world material performance.

Systematic experiments, in which all variables are carefully controlled, are difficult to perform because exfoliation has multiple steps. For example, if I have three possible variables—pressure, temperature, and speed—and I want to find out how speed affects the exfoliation process, I would fix the temperature and pressure and test the process for selected speeds. But for manual exfoliation, it’s not really possible to fix, or even to measure, the peeling speed. You can’t really ask a scientist to peel at a precise speed. This is a limitation of relying on human hands to make materials. Moreover, we lack statistical methods to analyze exfoliated flakes, which are difficult to see and characterize from images.

From an engineering standpoint, reproducibility and reliability are very important. Automation can help by minimizing human engagement. These factors are the motivation behind the automated 2-D material sample preparation system that I’m building to generate consistent, high-quality flakes.

What is involved in building this automated system?
When I joined the CFN, a prototype exfoliator already existed as part of the first generation of a larger automated machine called the QPress, or Quantum Material Press. This exfoliator used a stamp made of a polymer (PDMS) instead of a tape to perform basic robotic motions such as pushing and pulling.

First, I wanted to understand the factors important to mechanical exfoliation. By understanding this process, I can start to control it. I began by studying pressure-sensitive adhesives, which are adhesive tapes that stick to surfaces via applied pressure, and the theoretical background of mechanical exfoliation, step by step. I found that there are factors that we can control, such as pressure, temperature, and dwell time (how long the tape is adhered on a surface). But what is the appropriate amount of pressure? How long do we need to apply that pressure? What kind of pressure application is better—pushing or rolling? Answering such questions is the first step of automation.

To start, I upgraded the QPress exfoliator with functions to quantitatively control the temperature and pressure with various adhesives. With this setup, I could fulfill basic tests for each of these parameters and find specifications required for automation. I also tested the idea of using a roller instead of a stamp to apply pressure, temperature, and rolling speed at the same time. I tried a commercial laminator, and it actually worked! This test opened a new direction for us to consider for the automation process.

More recently, I came up with a new design for a fully automated roll-to-roll (R2R) exfoliator, relying on the knowledge I gained from my early experiments. On the basis of this design, I built a semi-automated R2R exfoliator. With this setup, I can do systematic research to better understand the underlying mechanisms of mechanical exfoliation and find optimized conditions.

As I explained, mechanical exfoliation is simply a combination of two steps: attachment and detachment, or peeling, of adhesives. With the early push-and-pull type of exfoliator, I could focus on the first step. However, the second step is as critical as the first. Using the R2R exfoliator, I want to control and compare important parameters in the detachment process besides temperature, pressure, and rolling speed (or dwell time). One parameter is the peeling speed and angle. For example, if you peel the tape at 45 instead of 90 degrees, the peeling force changes.

How does the R2R exfoliator work?
The R2R exfoliator has several components. A motorized tape unwinder continuously supplies bare pressure-sensitive adhesive tape from a reel. The tape runs over a roller for source material deposition, picking up the source materials. The tape with the source particles is located under a press roller. A sample stage moves to the left, and the roller compresses the source materials at a pressure similar to that of manual exfoliation. After the materials are compressed, we bake the sample using a heating plate installed in the sample stage. Finally, we move the sample stage to the right. The combined motion of a tape rewinder and the sample stage causes the compressed tape to peel off the sample surface. We can control the peeling speed with the sample stage and the peeling angle with an angle adjustment roller.

What excites you most about studying a process that is still not well understood?
Through my research, I am building an entirely new facility with unique capabilities. I am starting from a very basic understanding, progressing step by step. My role is to integrate the incremental findings and complete a big puzzle in my own creative way. It is challenging, but small improvements in understanding fundamental steps in 2-D materials fabrication will allow us to move forward and eventually complete the whole system. This system will help other researchers save time, effort, and research funds and support the creation of new 2-D materials that could be used in our daily lives. Contributing to society in this way makes me feel very good.

Which materials are you using for the tape and which 2-D materials are you exfoliating? Are the 2-D materials limited to those of interest for quantum information science, as the QPress name suggests?
For the purpose of machine development, I am currently using a simple commercial tape, the same that you would use in any office setting. Using commercial tapes is nice because we can easily test different kinds of adhesives. For instance, I am also studying wafer dicing tapes that are used in the semiconductor industry because they leave less residue on the wafer surface after exfoliation.

For 2-D material exfoliation, my current target is graphene because it is the most widely studied. The project team is also trying to produce high-quality flakes from materials for which it is hard to obtain such high quality—for example, very brittle materials. Team member Young-Jae Shin is an expert in 2-D materials. With the commercial laminator, he has been testing molybdenum disulfide and tungsten disulfide, which are more brittle than graphene. I will test these materials with the R2R exfoliator after I finish testing graphene.

Our goal is to help users exfoliate any materials that interest them. The QPress project was initially started with quantum materials in mind, given the recent emphasis on quantum information science research. However, the machine will be available to users who are looking to generate any kind of 2-D materials. Because the machine can run 24 hours a day, it saves a lot of time in generating flakes. Also, we’re planning to make a library-type database of different flakes that users can access for their research.  

You mentioned that the exfoliator will be part of a larger automated machine, the QPress. Are you only working on the exfoliation component?
The final QPress will have robot arms that transfer samples from the exfoliator station to cataloger, stacker, and characterization stations. This workflow will be automated. While my main focus so far has been on making the exfoliator, I’m also working on designing an automated setup for the stacker and figuring out how to combine these different modules. Achieving full automation could be difficult because different tools have different requirements in terms of sample environments, required motions, and physical space. It’s a complicated design issue.

My goals by the end of this year are to complete the fully automated R2R exfoliator, make the R2R exfoliator a functional part of the QPress, and build the first prototype of the automated stacker.

It sounds like building the exfoliator and integrating it into a multicomponent system requires a combination of 2-D materials knowledge and mechanical design expertise. How are you applying your knowledge and experience to this project?
My PhD was in materials science and engineering. For my thesis, I used a synchrotron x-ray microscope to study wetting on polymers. During my postdoc at Stanford, I continued using the synchrotron x-ray microscope to study the fluid dynamics of tear films on soft contact lenses.

When I went to SLAC, I changed my career path. I started studying microstructural changes in solid crystals through ultrafast electron diffraction. I was slightly involved in 2-D material studies, mostly on the experimental side rather than data analysis. Because I was a joint postdoc at Stanford and SLAC, my role was split between maintenance and user support of the electron diffraction facility and my own research. I was frequently involved in the development of new functions at the facility. For example, I designed an upgraded version of a vacuum chamber and manipulator system. So, over the years, I have become used to diving into new areas. As a result, I’m more open-minded and less fearful of taking on new and challenging projects.

Though my field of expertise is not 2-D materials, my unique background in materials science, fluid mechanics, and soft-matter physics and my hands-on experience is very useful in terms of building a facility for 2-D material exfoliation. For example, the adhesives used in mechanical exfoliation are polymers. What I researched during my PhD is the wetting property of polymers, or how they contact liquid surfaces. The exfoliation process is related to wetting but for solid flakes instead of liquids. So, I can apply my expertise related to the mechanics to understand interface phenomena between adhesives and flakes.

What led you to pursue studies in materials science and engineering and a career in scientific research?
I have liked science and math my entire life. Initially, I wanted to be a high school math teacher. But I realized that being a scientist was more aligned with my goal of making a general impact on the world. I chose materials science because materials are the fundamental elements accelerating technology development. I’m very excited to see what 2-D materials emerge from the QPress and how they are applied to new technologies.

Tags:  2D materials  Brookhaven National Laboratory  Energy  Graphene  quantum computing  Suji Park  U.S. Department of Energy 

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New Faculty Member and Group Leader

Posted By Terrance Barkan, Thursday, October 15, 2020
ICFO’s NEST program, supported by Fundació Cellex and Fundació Mir-Puig, allows the institute to offer outstanding opportunities for young scientists aiming to start and lead an independent research group. We are very pleased to announce a new member of the program, Dr F. Pelayo García de Arquer, who will join ICFO as a new faculty member and Group Leader, coming from the University of Toronto. Pelayo will lead a program seeking to reduce the growing CO2 emissions to revert global warming and climate change.

Dr. García de Arquer studied telecommunications engineering, mathematics, and photonics. He earned his PhD from ICFO, during which he investigated how the interaction between nanostructured semiconductors and metals could be manipulated dictating key optoelectronic properties such as absorption, charge transport and doping. He also explored new types of devices where highly energetic electrons in metals could be harnessed for sensing and energy harvesting. He applied his findings to make more efficient photodetectors and solar cells.

Pelayo joined the University of Toronto as a Connaught Postdoctoral Fellow in Bioinspired Ideas for Sustainable Energy. In his postdoctoral work, he expanded his research in the field of clean energy. He explored the use of emerging liquid-processed materials such as perovskites, low dimensional perovskites, quantum dots, and their combination, to control energy transfer at the nanoscale. Soon, he turned his attention to energy storage based on hydrogen and CO2 electroreduction. Pelayo, in this area, advanced in the understanding and performance of catalysts for these reactions, offering new insights into their design considering material transformations, and gas, electron and ion management.

At ICFO, García de Arquer will establish a research program focusing on CO2 Mitigation Accelerated by Photons (CO2MAP). His group will explore the conversion of CO2 into renewable fuels and commodities using clean energy. This has the potential to reduce the massive carbon footprint of existing manufacturing and transport processes. Pelayo’s group will use photon-based spectroscopies to shed light on the reaction mechanisms and catalyst reconstruction processes that drive CO2 electroreduction at high conversion rates. Combined with modeling, his group will use these insights to enable the informed design of catalysts and systems that achieve the selectivity, activity, energy efficiency and stability needed for this technology to make a significant impact in the global effort to revert climate change.

Tags:  energy  environment  F. Pelayo García de Arquer  Graphene  ICFO  University of Toronto 

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Easy-to-make, ultra-low power electronics could charge out of thin air

Posted By Terrance Barkan, Wednesday, October 14, 2020
Researchers have developed a new approach to printed electronics which allows ultra-low power electronic devices that could recharge from ambient light or radiofrequency noise. The approach paves the way for low-cost printed electronics that could be seamlessly embedded in everyday objects and environments.

Electronics that consume tiny amounts of power are key for the development of the Internet of Things, in which everyday objects are connected to the internet. Many emerging technologies, from wearables to healthcare devices to smart homes and smart cities, need cost-effective transistors and electronic circuits that can function with minimal energy use.

Printed electronics are a simple and inexpensive way to manufacture electronics that could pave the way for low-cost electronic devices on unconventional substrates – such as clothes, plastic wrap or paper – and provide everyday objects with ‘intelligence’.

However, these devices need to operate with low energy and power consumption to be useful for real-world applications. Although printing techniques have advanced considerably, power consumption has remained a challenge – the different solutions available were too complex for commercial production.

Now, researchers from the University of Cambridge, working with collaborators from China and Saudi Arabia, have developed an approach for printed electronics that could be used to make low-cost devices that recharge out of thin air. Even the ambient radio signals that surround us would be enough to power them. Their results are published in the journal ACS Nano.

Since the commercial batteries which power many devices have limited lifetimes and negative environmental impacts, researchers are developing electronics that can operate autonomously with ultra-low levels of energy.

The technology developed by the researchers delivers high-performance electronic circuits based on thin-film transistors which are ‘ambipolar’ as they use only one semiconducting material to transport both negative and positive electric charges in their channels, in a region of operation called ‘deep subthreshold’ – a phrase that essentially means that the transistors are operated in a region that is conventionally regarded as their ‘off’ state. The team coined the phrase ‘deep-subthreshold ambipolar’ to refer to unprecedented ultra-low operating voltages and power consumption levels.

If electronic circuits made of these devices were to be powered by a standard AA battery, the researchers say it would be possible that they could run for millions of years uninterrupted.

The team, which included researchers from Soochow University, the Chinese Academy of Sciences, ShanghaiTech University, and King Abdullah University of Science and Technology (KAUST), used printed carbon nanotubes – ultra-thin cylinders of carbon – as an ambipolar semiconductor to achieve the result.

“Thanks to deep-subthreshold ambipolar approach, we created printed electronics that meet the power and voltage requirements of real-world applications, and opened up opportunities for remote sensing and ‘place-and-forget’ devices that can operate without batteries for their entire lifetime,” said co-lead author Luigi Occhipinti from Cambridge’s Department of Engineering. “Crucially, our ultra-low-power printed electronics are simple and cost-effective to manufacture and overcome long-standing hurdles in the field.”

“Our approach to printed electronics could be scaled up to make inexpensive battery-less devices that could harvest energy from the environment, such as sunlight or omnipresent ambient electromagnetic waves, like those created by our mobile phones and wifi stations,” said co-lead author Professor Vincenzo Pecunia from Soochow University. Pecunia is a former PhD student and postdoctoral researcher at Cambridge’s Cavendish Laboratory.

The work paves the way for a new generation of self-powered electronics for biomedical applications, smart homes, infrastructure monitoring, and the exponentially-growing Internet of Things device ecosystem.The research was funded in part by the Engineering and Physical Sciences Research Council (EPSRC).

Tags:  carbon nanotubes  Chinese Academy of Sciences  Energy  Engineering and Physical Sciences Research Council  Graphene  King Abdullah University of Science and Technology  Luigi Occhipinti  Medical  ShanghaiTech University  Soochow University  transistor  University of Cambridge  Vincenzo Pecunia 

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Elkem receives Enova financial support for planning the battery materials industrial plant

Posted By Terrance Barkan, Wednesday, October 14, 2020
Elkem has received NOK 10 million in financial support from Enova to fund the initial planning of the potential large-scale battery materials plant in Norway, named Northern Recharge. The project aims to supply the fast-growing battery industry through a competitive production process and make batteries greener with lower CO2 emissions.

“A positive investment decision requires competitive public support mechanisms and supportive government policies. Elkem is also inviting industrial and financial partners to participate. Securing this initial support from Enova is an important step as we progress towards a final investment decision,” says Elkem’s CEO, Michael Koenig.

Enova is owned by the Norwegian Ministry of Climate and Environment, and supports the development of energy and climate technology, among other responsibilities.

“Batteries will undoubtedly play an important role in a future low-emission society. The production of batteries, however, is energy-consuming, so we need to see production processes that are more energy-efficient in the future, such as the innovative synthetic graphite production technology Elkem has developed. We therefore appreciate the opportunity to support their upcoming initial study, in order to increase the probability that this energy-efficient technology can one day be adopted on a full scale," says Enova's Director of Markets, Øyvind Leistad.

Elkem recently selected Herøya, one of the biggest industrial parks in Norway, as the project site. The company will now continue to progress the Northern Recharge project towards a final investment decision in 2021.

“The market for better and greener batteries is growing fast. We believe Elkem and Norway are uniquely positioned to be among the leaders in this industry,” says vice president for Elkem Battery Materials, Stian Madshus.

“Our Northern Recharge project competitively positions us for large-scale and cost-effective material science solutions for the rapidly developing European battery industry. Elkem brings significant industrial processing experience and by utilising efficient and renewable Norwegian hydropower, our product portfolio developments will be uniquely positioned for today’s EV requirements and tomorrow’s next generation advancements for rapid-charging and longer range. We truly appreciate the support from Enova on our journey towards more sustainable and energy efficient battery materials production,” says Madshus.

The project will produce synthetic graphite and composites, which are the leading anode materials in lithium-ion battery cells. Graphite demand is expected to increase more than ten times from today’s level to 2030. In terms of weight, graphite as an anode material typically represents around 10 percent of the total battery weight. Today, most of both battery cell and graphite production takes place in Asia.

Using Elkem's technology and renewable hydropower, the project can potentially reduce CO2 emissions by more than 90 percent compared to conventional production, while potentially reducing energy consumption by around 50 percent.

Elkem is currently constructing an industrial scale pilot plant for battery graphite in Kristiansand, Norway. Commissioning in early 2021, the pilot aims to conclude processing routes and enhance the product qualification process with customers. This project is supported by Innovation Norway.

Elkem also continues to carry out research on silicon-graphite composite materials for improved battery performance. This year, the company is joining the Hydra and 3beLiEVe research projects on next generation lithium-ion batteries, coordinated by SINTEF and the Austrian Institute of Technology, respectively. Both projects have received funding from the European Union's Horizon 2020 research and innovation programme.

Tags:  Battery  Electric Vehicle  Elkem  Energy  Enova  Environment  Graphene  graphite  Michael Koenig  Norwegian Ministry of Climate and Environment  Øyvind Leistad  Stian Madshus 

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Physicists build circuit that generates clean, limitless power from graphene

Posted By Terrance Barkan, Wednesday, October 7, 2020

A team of University of Arkansas physicists has successfully developed a circuit capable of capturing graphene's thermal motion and converting it into an electrical current.

"An energy-harvesting circuit based on graphene could be incorporated into a chip to provide clean, limitless, low-voltage power for small devices or sensors," said Paul Thibado, professor of physics and lead researcher in the discovery.

The findings, published in the journal Physical Review E, are proof of a theory the physicists developed at the U of A three years ago that freestanding graphene -- a single layer of carbon atoms -- ripples and buckles in a way that holds promise for energy harvesting.

The idea of harvesting energy from graphene is controversial because it refutes physicist Richard Feynman's well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado's team found that at room temperature the thermal motion of graphene does in fact induce an alternating current (AC) in a circuit, an achievement thought to be impossible.

In the 1950s, physicist Léon Brillouin published a landmark paper refuting the idea that adding a single diode, a one-way electrical gate, to a circuit is the solution to harvesting energy from Brownian motion. Knowing this, Thibado's group built their circuit with two diodes for converting AC into a direct current (DC). With the diodes in opposition allowing the current to flow both ways, they provide separate paths through the circuit, producing a pulsing DC current that performs work on a load resistor.

Additionally, they discovered that their design increased the amount of power delivered. "We also found that the on-off, switch-like behavior of the diodes actually amplifies the power delivered, rather than reducing it, as previously thought," said Thibado. "The rate of change in resistance provided by the diodes adds an extra factor to the power."

The team used a relatively new field of physics to prove the diodes increased the circuit's power. "In proving this power enhancement, we drew from the emergent field of stochastic thermodynamics and extended the nearly century-old, celebrated theory of Nyquist," said coauthor Pradeep Kumar, associate professor of physics and coauthor.

According to Kumar, the graphene and circuit share a symbiotic relationship. Though the thermal environment is performing work on the load resistor, the graphene and circuit are at the same temperature and heat does not flow between the two.

That's an important distinction, said Thibado, because a temperature difference between the graphene and circuit, in a circuit producing power, would contradict the second law of thermodynamics. "This means that the second law of thermodynamics is not violated, nor is there any need to argue that 'Maxwell's Demon' is separating hot and cold electrons," Thibado said.

The team also discovered that the relatively slow motion of graphene induces current in the circuit at low frequencies, which is important from a technological perspective because electronics function more efficiently at lower frequencies.

"People may think that current flowing in a resistor causes it to heat up, but the Brownian current does not. In fact, if no current was flowing, the resistor would cool down," Thibado explained. "What we did was reroute the current in the circuit and transform it into something useful."

The team's next objective is to determine if the DC current can be stored in a capacitor for later use, a goal that requires miniaturizing the circuit and patterning it on a silicon wafer, or chip. If millions of these tiny circuits could be built on a 1-millimeter by 1-millimeter chip, they could serve as a low-power battery replacement.

The University of Arkansas holds several patents pending in the U.S. and international markets on the technology and has licensed it for commercial applications through the university's Technology Ventures division. Researchers Surendra Singh, University Professor of physics; ; Hugh Churchill, associate professor of physics; and Jeff Dix, assistant professor of engineering, contributed to the work, which was funded by the Chancellor's Commercialization Fund supported by the Walton Family Charitable Support Foundation.

Tags:  Energy  Graphene  Paul Thibado  Pradeep Kumar  Sensors  University of Arkansas 

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Physicists Build Circuit That Generates Clean, Limitless Power From Graphene

Posted By Terrance Barkan, Monday, October 5, 2020

A team of University of Arkansas physicists has successfully developed a circuit capable of capturing graphene's thermal motion and converting it into an electrical current.

“An energy-harvesting circuit based on graphene could be incorporated into a chip to provide clean, limitless, low-voltage power for small devices or sensors,” said Paul Thibado, professor of physics and lead researcher in the discovery.

The findings, titled "Fluctuation-induced current from freestanding graphene," and published in the journal Physical Review E, are proof of a theory the physicists developed at the U of A three years ago that freestanding graphene — a single layer of carbon atoms — ripples and buckles in a way that holds promise for energy harvesting.

The idea of harvesting energy from graphene is controversial because it refutes physicist Richard Feynman’s well-known assertion that the thermal motion of atoms, known as Brownian motion, cannot do work. Thibado’s team found that at room temperature the thermal motion of graphene does in fact induce an alternating current (AC) in a circuit, an achievement thought to be impossible. 

In the 1950s, physicist Léon Brillouin published a landmark paper refuting the idea that adding a single diode, a one-way electrical gate, to a circuit is the solution to harvesting energy from Brownian motion. Knowing this, Thibado’s group built their circuit with two diodes for converting AC into a direct current (DC). With the diodes in opposition allowing the current to flow both ways, they provide separate paths through the circuit, producing a pulsing DC current that performs work on a load resistor.

Additionally, they discovered that their design increased the amount of power delivered. “We also found that the on-off, switch-like behavior of the diodes actually amplifies the power delivered, rather than reducing it, as previously thought,” said Thibado. “The rate of change in resistance provided by the diodes adds an extra factor to the power.” 

The team used a relatively new field of physics to prove the diodes increased the circuit’s power. “In proving this power enhancement, we drew from the emergent field of stochastic thermodynamics and extended the nearly century-old, celebrated theory of Nyquist,” said coauthor Pradeep Kumar, associate professor of physics and coauthor.  

According to Kumar, the graphene and circuit share a symbiotic relationship. Though the thermal environment is performing work on the load resistor, the graphene and circuit are at the same temperature and heat does not flow between the two.

That’s an important distinction, said Thibado, because a temperature difference between the graphene and circuit, in a circuit producing power, would contradict the second law of thermodynamics. “This means that the second law of thermodynamics is not violated, nor is there any need to argue that ‘Maxwell’s Demon’ is separating hot and cold electrons,” Thibado said.

The team also discovered that the relatively slow motion of graphene induces current in the circuit at low frequencies, which is important from a technological perspective because electronics function more efficiently at lower frequencies. 

“People may think that current flowing in a resistor causes it to heat up, but the Brownian current does not. In fact, if no current was flowing, the resistor would cool down,” Thibado explained. “What we did was reroute the current in the circuit and transform it into something useful.” 

The team’s next objective is to determine if the DC current can be stored in a capacitor for later use, a goal that requires miniaturizing the circuit and patterning it on a silicon wafer, or chip. If millions of these tiny circuits could be built on a 1-millimeter by 1-millimeter chip, they could serve as a low-power battery replacement.

The University of Arkansas holds several patents pending in the U.S. and international markets on the technology and has licensed it for commercial applications through the university’s Technology Ventures division. Researchers Surendra Singh, University Professor of physics; Hugh Churchill, associate professor of physics; and Jeff Dix, assistant professor of engineering, contributed to the work, which was funded by the Chancellor’s Commercialization Fund supported by the Walton Family Charitable Support Foundation.

Tags:  Capacitor  Energy  Graphene  Paul Thibado  Pradeep Kumar  resistor  Sensors  University of Arkansas 

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Investigating high temperature superconductors

Posted By Graphene Council, Wednesday, September 23, 2020
Researchers from the ARC Centre of Excellence in Future Low Energy Electronic Technologies (FLEET) used the Soft X-ray Spectroscopy beamline at the Australian Synchrotron to investigate the structure of a promising high-temperature superconductor, a calcium-doped graphene material.

The FLEET Centre has provided a detailed description of the research, published in The Chemistry of Materials, on their website.

In characterising the material, the investigators wanted to clarify where the calcium went after it was added to a sample consisting of a single layer of graphene on a silicon carbide substrate.

Measurements at the Australian Synchrotron were able to pinpoint that the calcium atoms were located, unexpectedly, near the silicon carbide surface.

Dr Anton Tadich, an instrument scientist on the SXR beamline, member of FLEET and co-author, explained why the Synchrotron was useful in the investigation.

“In order to confirm if a new graphene monolayer formed on the surface, as well as understanding how injected calcium atoms positioned themselves around that newly formed layer, in a process known as intercalation, the research team required an extremely surface-sensitive chemical fingerprinting technique,” said Tadich.

The technique that could provide the information was high resolution x-ray photoelectron spectroscopy (XPS) on the soft X-ray spectroscopy beamline.

Synchrotron-based XPS is a highly surface-sensitive chemical probe, which offers key advantages over its laboratory-based counterpart.

“The ability to 'tune' the x-ray energy for a given element is quite powerful; not only does it maximise the signal from a desired element, at the same time it is possible to enhance the signal from the topmost atomic layers of the sample relative to the bulk; disentangling contributions to the spectrum from different depths.”

The FLEET investigators led by PhD student Jimmy Kotsakidis in the group of Prof Michael Fuhrer and Tadich prepared the intercalated samples in-situ, which were then transferred under vacuum to the XPS chamber.

“The focus quickly turned to the carbon and silicon signal from the top few atomic layers, where all the chemistry was happening,” said Tadich.

“From the carbon signal, we saw a clear signature of the formation of an additional graphene layer.“

Importantly, the silicon spectra revealed that the calcium intercalated underneath the buffer layer, which is a partially-bonded carbon layer on the surface of the silicon carbide. 

“The combined results showed that the intercalation caused the buffer layer to ‘unstitch’ itself from the silicon carbide, lifting it off to form a new layer of graphene!” explained Tadich.

Their finding was contrary to previous studies, which had assumed that the intercalant atoms simply slid in between the original graphene layer and the surface.

The FLEET researchers concluded that the resultant 'bi-layer' graphene, when combined with the presence of the intercalant below it, could result in a form of superconducting graphene with a high transition temperature.

Tags:  Anton Tadich  ARC Centre of Excellence  Australian Synchrotron  Energy  Graphene  Jimmy Kotsakidis  superconductor 

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Energy harvesting goes organic, gets more flexible

Posted By Graphene Council, Thursday, September 17, 2020
Nanogenerators capable of converting mechanical energy into electricity are typically made from metal oxides and lead-based perovskites. But these inorganic materials aren't biocompatible, so the race is on to create natural biocompatible piezoelectric materials for energy harvesting, electronic sensing, and stimulating nerves and muscles.

University College Dublin and University of Texas at Dallas researchers decided to explore peptide-based nanotubes, because they would be an appealing option for use within electronic devices and for energy harvesting applications.

In the Journal of Applied Physics, from AIP Publishing, the group reports using a combination of ultraviolet and ozone exposure to generate a wettability difference and an applied field to create horizontally aligned polarization of nanotubes on flexible substrates with interlocking electrodes.

"The piezoelectric properties of peptide-based materials make them particularly attractive for energy harvesting, because pressing or bending them generates an electric charge," said Sawsan Almohammed, lead author and a postdoctoral researcher at University College Dublin.

There's also an increased demand for organic materials to replace inorganic materials, which tend to be toxic and difficult to make.

"Peptide-based materials are organic, easy to make, and have strong chemical and physical stability," she said.

In the group's approach, the physical alignment of nanotubes is achieved by patterning a wettability difference onto the surface of a flexible substrate. This creates a chemical force that pushes the peptide nanotube solution from the hydrophobic region, which repels water, with a high contact angle to the hydrophilic region, which attracts water, with a low contact angle.

Not only did the researchers improve the alignment of the tubes, which is essential for energy harvesting applications, but they also improved the conductivity of the tubes by making composite structures with graphene oxide.

"It's well known that when two materials with different work functions come into contact with each other, an electric charge flows from low to high work function," Almohammed said. "The main novelty of our work is that controlling the horizontal alignment of the nanotubes by electrical field and wettability-assisted self-assembly improved both the current and voltage output, and further enhancement was achieved by incorporating graphene oxide."

The group's work will enable the use of organic materials, especially peptide-based ones, more widely within electronic devices, sensors, and energy harvesting applications, because two key limitations of peptide nanotubes -- alignment and conductivity -- have been improved.

"We're also exploring how charge transfer processes from bending and electric field applications can enhance Raman spectroscopy-based detection of molecules," Almohammed said. "We hope these two efforts can be combined to create a self-energized biosensor with a wide range of applications, including biological and environmental monitoring, high-contrast imaging, and high-efficiency light-emitting diodes."

Tags:  Energy  Graphene  graphene oxide  LED  Sawsan Almohammed  University College Dublin  University of Texas 

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NETL CHEMIST: LAB’S LOW-COST GRAPHENE TO FUEL ‘REBIRTH’ FOR COAL

Posted By Graphene Council, Wednesday, August 26, 2020
In his long career at NETL, McMahan Gray has experienced more than a few successes.

For example, the award-winning research chemist has made valuable contributions to remove carbon from industrial emissions and extract rare earth elements (REEs) from coal byproducts, wastewater and even acid mine drainage.

Another ground-breaking contribution may be just around the corner. As part of an ongoing research effort, Gray serves on an NETL team that’s writing a new chapter in the long productive history of coal that may revolutionize how the mineral is used in the future.

The team has found that rather than combust coal to produce energy, it can be used in new ways to fuel a transformation in carbon-based, high-tech manufacturing to produce safer cars, faster computers, stronger homes, bridges and highways, and even life-saving biosensors to confirm the presence of disease in the human body.

“We were looking for a rebirth in how coal can be used when we began our project,” said Gray, who has worked at the Lab for 34 years. “I think the rebirth we will see is going to produce sophisticated new uses for coal that have absolutely nothing to do with burning it to produce electricity.”

Gray and his NETL colleagues have developed a patent-pending manufacturing process that converts lignite, bituminous and anthracite ranks of coal into graphene, whose superior strength and optical and electrical conductivity properties make it a game-changing material. (Shi, Fan; Matranga, Christopher; Gray, McMahan; Ji, Tuo., Production of Graphene-structured Products from Coal Using Thermal Molten Salt Process, U.S. Non-provisional Patent No. 16/369,753, 2019).

NETL’s low-cost coal-to-graphene, or C2G, manufacturing process will not only generate a superior material to produce high-value products; it also will create new environmentally friendly uses for one of the nation’s greatest resources — its abundant reserves of coal.

According to Gray, it takes a solid team effort to achieve success. “Teamwork, the leadership of an excellent principal investigation (Matranga) and the outstanding work of my colleagues have enabled us to develop this process so coal can be used in new and innovative ways,” Gray said. 

Discovered in 2004, graphene is only one atomic layer thick, but it’s 100 times stronger than construction steel and 1.6 times more electrically conductive than copper electrical wire. Graphene is a form of carbon. Both graphene and carbon possess the same atoms, but they are arranged in different ways, giving each material its own unique properties. For graphene, those differences produce extraordinary strength.  

However, the high cost of existing supplies of graphene have limited its use. “NETL’s technology reduces the cost of manufacturing graphene by up to tenfold while producing a significantly higher-quality material than what is currently available on the market,” Gray said.

In the future, the team envisions using graphene to build lighter and stronger cars. Gray believes it also can be used to create advanced lightweight body armor for U.S. troops.

Because graphene is one of the lightest, strongest and thinnest materials ever discovered, it makes an ideal additive to improve the mechanical properties and durability of cement and produce battery and electrode materials, 3D printing composites, water- and stain- resistant textiles, catalyst materials and supports, and other items.

NETL also has produced graphene quantum dots — small fluorescent nanoparticles with sheet-like structures — and sent them to the University of Illinois at Urbana-Champaign where they are used to fabricate an advanced type of computer memory chip called a memristor. Recent testing has shown that memristors made with NETL graphene have outperformed those made with conventional materials.

In addition, the project team is collaborating with Ramaco Carbon, a Wyoming-based coal technology company, to take advantage of graphene’s superb electrical conductivity to develop new biosensor products that can quickly confirm the presence of Lyme disease, Zika virus or the amount of medication in a blood sample.

Gray is no stranger to advancing ground-breaking projects.

He led NETL researchers who developed the basic immobilized amine sorbent (BIAS) process to capture carbon dioxide (CO2) from coal-burning power plants. Recognizing that the BIAS approach could do more than capture CO2 from coal combustion, Gray has worked to adapt the technology of sorbents, which are designed to absorb targeted chemical compounds, to remove heavy metals, including lead, from public water supplies and recover valuable rare earth elements (REEs) from acid mine discharges and other sources.

REEs, which are needed to produce high-performance optics and lasers, as well as powerful magnets, superconductors, solar panels and valuable consumers products such as smart phones and computer hard drives, are abundant in nature but are often found in low concentrations and are challenging to extract.

Recently, while working on the coal-to-graphene project, Gray made another exciting discovery that directly benefits his efforts in REE extraction. Gray has found that the water used in the coal-to-graphene process contains REEs in the range of 600 parts per million. “In the field of REE research, that’s a very high extraction rate,” Gray said.

“I call it a ‘double hit,’ which sometimes happens when research on one project produces a positive finding to benefit another project,” said Gray, who received a prestigious R&D 100 award in 2012 for the BIAS technology’s carbon capture application.

Gray is listed as the primary or secondary inventor on 21 patents, and his work has been cited in more than 120 scholarly papers. His other notable honors include the Federal Laboratory Consortium Mid-Atlantic Region Award for Technology Transfer and the Federal Laboratory Consortium National Award for Excellence in Technology Transfer.

He has also received the Hugh Guthrie Award for Innovation as one of NETL’s leading scientists. In 2018, he was awarded a Gold Medal for “Outstanding Contribution to Science (Non-Medical)” from the Federal Executive Board for Excellence in the Government.

The Chemistry Department at the University of Pittsburgh has announced it will present Gray with its 2020 Distinguished Alumni Award for his work advancing innovative technologies while serving as a mentor who has inspired hundreds of students and colleagues.

For Gray, NETL’s revolutionary graphene project rejuvenates coal for high-value uses. “Coal gets a bad rap,” said Gray, who also serves as pastor of Second Baptist Church of Penn Hills near Pittsburgh, Pennsylvania.

“The molecular structure behind coal is amazing. There’s really so much more we can do with coal,” he added.

Tags:  Battery  Biosensor  composites  Energy  Graphene  National Energy Technology Laboratory 

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Oak Ridge National Laboratory, the University of Kentucky, and Penn State University Receive $10M to Develop Coal-Derived Carbon Products

Posted By Graphene Council, Friday, August 21, 2020
Two U.S. Department of Energy (DOE) National Laboratories, the National Energy Technology Laboratory (NETL) and Oak Ridge National Laboratory (ORNL), are working with the University of Kentucky and the Pennsylvania State University to further the research and development of coal-derived carbon fibers.

This research, valued at $10 million, will investigate all aspects of coal-derived carbon fiber production—from computational chemistry and pitch processing to the final spinning and heat treatment process of the fibers. The aim is to produce fibers with superior properties at a lower cost than currently available.

Through this effort, ORNL researchers will work to understand the chemistry and processing conditions required to produce different grades of coal-derived carbon fiber. NETL, ORNL, and the university teams will work closely to diversify U.S. coal use in domestic manufacturing, while making coal and coal-based products more attractive for export.

Because of competition from low-priced natural gas and incentivized renewable energy, the market for coal in the electric power generation sector is decreasing. However, coal-to-products opportunities can develop new markets for coal, which have the potential to offset this decrease.

For example, the market for carbon fibers is estimated to see an annual growth rate of 12 percent through 2024, driven largely by increased use in aerospace and defense applications and in light-weighting of vehicle structures. Additional market growth is also possible in other high-volume applications, such as thermal insulation for buildings and materials for construction and infrastructure.

“NETL’s demonstration of coal-based graphene to reinforce concrete and engineered plastics, along with other examples from the Advanced Coal Processing Program, shows that coal has a major role in the future, beyond electricity generation,” said NETL’s Technology Manager Joseph Stoffa. “We welcome the contributions of ORNL in this endeavor and look forward to the projects these Congressional appropriations will fund.”

The $10 million that ORNL’s Carbon Fiber Technology Facility will receive comes as a part of $30 million in fiscal year 2020 Congressional appropriations to support DOE’s Advanced Coal Processing Program. This program supports the development of technologies that can utilize coal for purposes outside the traditional thermal and metallurgical markets.

Of the $10 million funding, $4.5 million will support University of Kentucky research to determine how coal tar pitch, the carbon fiber precursor, can be tailored and optimized for the specific type of desired fiber. Additionally, $80,000 will go to the Pennsylvania State University for material characterization.

Tags:  carbon fiber  Energy  Graphene  Joseph Stoffa  National Energy Technology Laboratory  Oak Ridge National Laboratory  Pennsylvania State University  University of Kentucky 

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