The Design of Future Nano-Electronic  Circuits – Free Flowing Electrons in Graphene 



Electrons flowing like liquid in graphene start a new wave of physics – University of Manchester 

A new understanding of the physics of conductive materials has been uncovered by scientists observing the unusual movement of electrons in graphene.

Graphene is many times more conductive than copper thanks, in part, to its two-dimensional structure. In most metals, conductivity is limited by crystal imperfections which cause electrons to frequently scatter like billiard balls when they move through the material.


Now, observations in experiments at the National Graphene Institute have provided essential understanding as to the peculiar behaviour of electron flows in graphene, which need to be considered in the design of future nanoelectronic circuits.

In some high-quality materials, like graphene, electrons can travel micron distances without scattering, improving the conductivity by orders of magnitude. This so-called ballistic regime, imposes the maximum possible conductance for any normal metal, which is defined by the Landauer-Buttiker formalism.

Appearing today in Nature Physics (“Superballistic flow of viscous electron fluid through graphene constrictions”), researchers at The University of Manchester, in collaboration with theoretical physicists led by Professor Marco Polini and Professor Leonid Levitov, show that Landauer’s fundamental limit can be breached in graphene. Even more fascinating is the mechanism responsible for this.

Last year, a new field in solid-state physics termed ‘electron hydrodynamics’ generated huge scientific interest. Three different experiments, including one performed by The University of Manchester, demonstrated that at certain temperatures, electrons collide with each other so frequently they start to flow collectively like a viscous fluid.

The new research demonstrates that this viscous fluid is even more conductive than ballistic electrons. 

The result is rather counter-intuitive, since typically scattering events act to lower the conductivity of a material, because they inhibit movement within the crystal. However, when electrons collide with each other, they start working together and ease current flow.

This happens because some electrons remain near the crystal edges, where momentum dissipation is highest, and move rather slowly. At the same time, they protect neighbouring electrons from colliding with those regions. Consequently, some electrons become super-ballistic as they are guided through the channel by their friends.

Sir Andre Geim said: “We know from school that additional disorder always creates extra electrical resistance. In our case, disorder induced by electron scattering actually reduces rather than increase resistance. This is unique and quite counterintuitive: Electrons when make up a liquid start propagating faster than if they were free, like in vacuum”.

The researchers measured the resistance of graphene constrictions, and found it decreases upon increasing temperature, in contrast to the usual metallic behaviour expected for doped graphene.

By studying how the resistance across the constrictions changes with temperature, the scientists revealed a new physical quantity which they called the viscous conductance. The measurements allowed them to determine electron viscosity to such a high precision that the extracted values showed remarkable quantitative agreement with theory.


Source: University of Manchester

Army COE Creates New Energy Efficient ‘Graphene Oxide’ Water Filter at Commercial Scale



The Army Corps of Engineers have successfully created a usable prototype of a new type of water filter.

The membranes are made of a mixture of chitosan, a material commonly found in shrimp shells, and a new synthetic chemical known as “graphene oxide”. Graphene oxide is a highly researched chemical worldwide.

  According to the Army Corps, one problem encountered by scientists working with graphene oxide is not being able to synthesize the material on a scale that can be put to use.

“One of the major breakthroughs that we’ve had here is that with our casting process, we’re not limited by size,” explains Luke Gurtowski, a research chemical engineer working on the membranes.


These filters have been found to effectively remove a number of different contaminants commonly found in water.

Dr. Christopher Griggs is the research scientist in charge of overseeing development of the new membranes.

Dr. Griggs told us, “Anybody who’s experienced water shortages or has been concerned about their water quality, or any type of contaminants in the water, this type of technology certainly works to address that.”

Another challenged faced by conventional water filtering methods is maintaining high energy efficiency.

“It requires a lot of energy for the net driving pressure to force the water through the membrane,” Dr. Griggs explains. “…we’re going to have to look to new materials to try to get those efficiency gains, and so graphene oxide is a very promising candidate for that.”

The Engineer Research and Development Center currently has two patents associated with the new filters and hopes to apply them for both civil and military purposes in the near future. 

Metal-free nanoparticle could expand MRI use, tumor detection



What might sound like the set-up to a joke actually has a clinical answer: Both groups can face health risks when injected with metal-containing agents sometimes needed to enhance the color contrast — and diagnostic value — of MRIs.

But a new metal-free nanoparticle developed by the University of Nebraska-Lincoln and MIT could help circumvent these health- and age-related barriers to the powerful diagnostic tool, which physicians use to investigate or confirm a broad range of medical issues.

The team’s nanoparticle contains a non-metallic molecule that enhances MRI contrast to help distinguish among bodily tissue, a task typically performed by contrast agents containing gadolinium or other metals (ACS Central Science, “Nitroxide-Based Macromolecular Contrast Agents with Unprecedented Transverse Relaxivity and Stability for Magnetic Resonance Imaging of Tumors”).

It also survived long enough to congregate around tumors in mice, suggesting the nanoparticle could help detect cancers as well as its metallic counterparts while eliminating concerns about the long-term accumulation of metal in the body.


MRIs of a mouse before (first and third rows) and 20 hours after being injected with a low dose (second row) and high dose (fourth row) of a new metal-free contrast agent developed by Nebraska and MIT. The yellow arrow indicates the location of a tumor. (click on image to enlarge)

Contrast in styles

The molecules residing in the team’s nanoparticle belong to a family known as the nitroxides, which are among the most promising alternatives to the metallic agents often injected into patients prior to undergoing MRIs.

But antioxidants in the body typically begin breaking down nitroxides within minutes, limiting how long they can enhance the contrast of an MRI. And the team’s molecule of interest — a so-called organic radical — has just a single electron, a fact that normally inhibits how much contrast it can produce.

Gadolinium and other metals possess multiple electrons that help them influence how the magnetic waves produced by an MRI interact with water molecules in tissue. This magnetic influence, or relaxivity, ultimately dictates the strength of contrast signals that get converted into the familiar multicolored MRIs.

So Nebraska chemist Andrzej Rajca began collaborating with colleagues at MIT to design a metal-free nanoparticle that would exhibit stability and relaxivity comparable to gadolinium’s. Rajca previously designed a nitroxide that, when embedded within relatively small nanoparticles, displayed a relaxivity several times greater than its predecessors.

This time around, MIT researchers incorporated Rajca’s nitroxide into a large nanoparticle known as a brush-arm star polymer. The process involved assembling polymers into a spherical structure with a water-attracting core and water-repelling shell, then squeezing multitudes of nitroxide molecules between that core and shell.

The team found that packing so many nitroxides into such tight quarters effectively multiplied their individual relaxivity values, resulting in a nanoparticle with a relaxivity about 40 times higher than a typical nitroxide.

“You don’t need much of the (new) contrast agent to see a good image,” said Rajca, Charles Bessey Professor of chemistry.

The nanoparticle’s polymer shell also helped slow the advance of the disruptive antioxidants enough to prolong the nitroxides’ lifespan from roughly two hours to 20. By injecting mice with their agent, the researchers showed that the nanoparticle’s longevity and large size allow it to reach tumors and differentiate them from normal tissue. Even in doses larger than those typically needed for MRIs, the team’s contrast agent showed no signs of toxicity in human cells or mice.

Source: University of Nebraska-Lincoln

Harnessing the Functionality and ‘Power’ of Perovskites for Better Solar and LED’s



Originally a mineral, the perovskite used in today’s technology is quite different from the rock found in the Earth mantle. 

A “perovskite structure” uses a different combination of atoms but keep the general 3-dimensional structure originally observed in the mineral, which possesses superb optoelectronic properties such as strong light absorption and facilitated charge transport. These advantages qualify the perovskite structure as particularly suited for the design of electronic devices, from solar cells to lights.

The accelerating progress in perovskite technology over the past few years suggest new perovskite-based devices will soon outperform current technology in the energy sector. 

The Energy Materials and Surface Sciences Unit at OIST led by Prof. Yabing Qi is at the forefront of this development, with now two new scientific publications focusing on the improvement of perovskite solar cells and a cheaper and smarter way to produce emerging perovskite-based LED lights.

An extra layer in a solar cell “sandwich”

Perovskite-based solar cells is a rising technology forecast to replace the classic photovoltaic cells currently dominating the industry. 




In just seven years of development, the efficiency of perovskite solar cells increased to almost rival – and is expected to soon overtake – commercial photovoltaic cells, but the perovskite structure still plagued by a short lifespan due to stability issues. 


OIST
scientists have made constant baby steps in improving the cells stability, identifying the degradations factors and providing solutions towards better solar cell architecture.

The new finding, reported in the Journal of Physical Chemistry B (“Engineering Interface Structure to Improve Efficiency and Stability of Organometal Halide Perovskite Solar Cells”), suggests interactions between components of the solar cell itself are responsible for the rapid degradation of the device. 

More precisely, the titanium oxide layer extracting electrons made available through solar energy – effectively creating an electric current – causes unwanted deterioration of the neighboring perovskite layer. 

Imagine the solar cell as a multi-layered club sandwich: if not properly assembled, fresh and juicy vegetables in contact with the bread slices will make the bread very soggy in a matter of hours. 

But if you add a layer of ham or turkey between the vegetables and the bread, then your sandwich stays crisp all day in the lunchroom refrigerator.


A perovskite-based layer includes many layers, including for example the electrodes on both sides, and the perovskite in the middle. The addition of a polystyrene layer in-between prevents the titanium oxide layer to deteriorate the perovskite, but does not affect the overall power conversion efficiency. (© American Chemical Society)

This is exactly what the OIST researchers achieved: they inserted in the solar cell an additional layer made from a polymer to prevent direct contact between the titanium oxide and the perovskite layers. 
This polymer layer is insulating but very thin, which means it lets the electron current tunnel through yet does not diminish the overall efficiency of the solar cell, while efficiently protecting the perovskite structure.

“We added a very thin sheet, only a few nanometers wide, of polystyrene between the perovskite layer and the titanium oxide layer,” explained Dr. Longbin Qiu. 

“Electrons can still tunnel cross this new layer and it does not affect the light absorption of the cell. This way, we were able to extend the lifetime of the cell four-fold without loss in energy conversion efficiency”.

The lifespan of the new perovskite device was extended to over 250 hours – still not enough to compete with commercial photovoltaic cells regarding stability, but an important step forward toward fully functional perovskite solar cells.

Manufacturing LED lights from gasses

The bipolar electronic properties of the perovskite structure not only confer them the ability to generate electricity from solar energy but also can convert electricity into vivid light. Light-Emitting Diode – LED – technology, omnipresent in our daily life from laptop and smartphone screens to car lights and ceiling tubes, currently relies on semi-conductors that are difficult and expensive to manufacture. Perovskite LEDs are envisaged to become the new industry standard in the near future due to the lower cost and their efficiency to convert power into light. Moreover, by changing the atomic composition in the perovskite structure, perovskite LED can be easily tuned to emit specific colors.

The manufacturing of these perovskite LEDs is currently based on dipping or covering the targeted surface with liquid chemicals, a process which is difficult to setup, limited to small areas and with low consistency between samples. To overcome this issue, OIST researchers reported in the Journal of Physical Chemistry Letters (“Methylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor Deposition”) the first perovskite LED assembled with gasses, a process called chemical vapor deposition or CVD.

“Chemical vapor deposition is already compatible with the industry, so in principle it would be easy to use this technology to produce LEDs,” commented Prof. Yabing Qi. “The second advantage in using CVD is a much lower variation from batch to batch compared to liquid-based techniques. Finally, the last point is scalability: CVD can achieve a uniform surface over very large areas”.

Like the solar cell, the perovskite LED also comprises many layers working in synergy. First, an indium tin oxide glass sheet and a polymer layer allow electrons into the LED. The chemicals required for the perovskite layer – lead bromide and methylammonium bromide – are then successively bound to the sample using CVD, in which the sample is exposed to gasses in order to convert to perovskite instead of typically solution-coating processes with liquid. In this process, the perovskite layer is composed of nanometer-small grains, whose sizes play a critical role in the efficiency of the device. Finally, the last step involves the deposition of two additional layers and a gold electrode, forming a complete LED structure. The LED can even form specific patterns using lithography during the manufacturing process.

Perovskite LED fabrication


Top: the perovskite LED sits in a furnace, where the Methylammonium Bromide (MABr) in gaseous form will be introduced into the system and deposit on the LED surface. Bottom left: a glass-based LED, glowing green when electricity is applied. Bottom right: size and shapes of the perovskite grains on the surface of the LED. (© American Chemical Society)

“With large grains, the surface of the LED is rough and less efficient in emitting light. The smaller the grain size, the higher the efficiency and the brighter the light,” explained Dr. Lingqiang Meng. “By changing the assembly temperature, we can now control the growth process and the size of the grains for the best efficiency”.

Controlling the grain size is not the only challenge for this first-of-its-kind assembling technique of LED lights.

“Perovskite is great, but the choice in the adjacent layers is really important too,” added Dr. Luis K. Ono. “To achieve high electricity-to-light conversion rates, every layer should be working in harmony with the others.”

The result is a flexible, thick film-like LED with a customizable pattern. The luminance, or brightness, currently reaches 560 cd/m2, while a typical computer screen emits 100 to 1000 cd/m2 and a ceiling fluorescent tube around 12,000 cd/m2.

Perovskite-LED


This large perovskite-LED was produced using chemical vapor deposition and connect to a 5V current, illuminating through an OIST pattern etched on the surface. (© American Chemical Society)

“Our next step is to improve the luminance a thousand-fold or more,” concluded Dr. Meng. “In addition, we have achieved a CVD-based LED emitting green light but we are now trying to repeat the process with different combinations of perovskite to obtain a vivid blue or red light”.

Source: By Wilko Duprez, Okinawa Institute of Technology

Rice University (NEWT) / China team use phage-enhanced nanoparticles to kill bacteria that foul water treatment systems


Clusters of nanoparticles with phage viruses attached find and kill Escherichia coli bacteria in a lab test at Rice University. 

Abstract:
Magnetic nanoparticle clusters have the power to punch through biofilms to reach bacteria that can foul water treatment systems, according to scientists at Rice University and the University of Science and Technology of China.
Magnetized viruses attack harmful bacteria: Rice, China team uses phage-enhanced nanoparticles to kill bacteria that foul water treatment systems.

Researchers at Rice and the University of Science and Technology of China have developed a combination of antibacterial phages and magnetic nanoparticle clusters that infect and destroy bacteria that are usually protected by biofilms in water treatment systems. (Credit: Alvarez Group/Rice University)

The nanoclusters developed through Rice’s Nanotechnology-Enabled Water Treatment (NEWT) Engineering Research Center carry bacteriophages – viruses that infect and propagate in bacteria – and deliver them to targets that generally resist chemical disinfection.

Without the pull of a magnetic host, these “phages” disperse in solution, largely fail to penetrate biofilms and allow bacteria to grow in solution and even corrode metal, a costly problem for water distribution systems.

The Rice lab of environmental engineer Pedro Alvarez and colleagues in China developed and tested clusters that immobilize the phages. A weak magnetic field draws them into biofilms to their targets.

The research is detailed in the Royal Society of Chemistry’s Environmental Science: Nano.
“This novel approach, which arises from the convergence of nanotechnology and virology, has a great potential to treat difficult-to-eradicate biofilms in an effective manner that does not generate harmful disinfection byproducts,” Alvarez said.

Biofilms can be beneficial in some wastewater treatment or industrial fermentation reactors owing to their enhanced reaction rates and resistance to exogenous stresses, said Rice graduate student and co-lead author Pingfeng Yu. “However, biofilms can be very harmful in water distribution and storage systems since they can shelter pathogenic microorganisms that pose significant public health concerns and may also contribute to corrosion and associated economic losses,” he said.

The lab used phages that are polyvalent – able to attack more than one type of bacteria – to target lab-grown films that contained strains of Escherichia coli associated with infectious diseases and Pseudomonas aeruginosa, which is prone to antibiotic resistance.

The phages were combined with nanoclusters of carbon, sulfur and iron oxide that were further modified with amino groups. The amino coating prompted the phages to bond with the clusters head-first, which left their infectious tails exposed and able to infect bacteria.

The researchers used a relatively weak magnetic field to push the nanoclusters into the film and disrupt it. Images showed they effectively killed E. coli and P. aeruginosa over around 90 percent of the film in a test 96-well plate versus less than 40 percent in a plate with phages alone.

The researchers noted bacteria may still develop resistance to phages, but the ability to quickly disrupt biofilms would make that more difficult. Alvarez said the lab is working on phage “cocktails” that would combine multiple types of phages and/or antibiotics with the particles to inhibit resistance.

Graduate student Ling-Li Li of the University of Science and Technology of China, Hefei, is co-lead author of the paper. Co-authors are graduate student Sheng-Song Yu and Han-Qing Yu, a professor at the University of Science and Technology of China, and graduate student Xifan Wang and temporary research scientist Jacques Mathieu of Rice.


The National Science Foundation and its Rice-based NEWT Engineering Research Center supported the research.

UC Berkeley Labs: A Semiconductor That Can Beat the Heat



Berkeley Lab, UC Berkeley scientists discover unique thermoelectric properties in cesium tin iodide

JULY 31, 2017

A newly discovered collective rattling effect in a type of crystalline semiconductor blocks most heat transfer while preserving high electrical conductivity – a rare pairing that scientists say could reduce heat buildup in electronic devices and turbine engines, among other possible applications.

A team led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) discovered these exotic traits in a class of materials known as halide perovskites, which are also considered promising candidates for next-generation solar panels, nanoscale lasers, electronic cooling, and electronic displays.

These interrelated thermal and electrical (or “thermoelectric”) properties were found in nanoscale wires of cesium tin iodide (CsSnI3). The material was observed to have one of the lowest levels of heat conductivity among materials with a continuous crystalline structure.


Image – Rattling structures of halide perovskites: cesium tin iodide (left) and cesium lead iodide (right). (Credit: Berkeley Lab/UC Berkeley)

This so-called single-crystal material can also be more easily produced in large quantities than typical thermoelectric materials, such as silicon-germanium, researchers said.

“Its properties originate from the crystal structure itself. It’s an atomic sort of phenomenon,” said Woochul Lee, a postdoctoral researcher at Berkeley Lab who was the lead author of the study, published the week of July 31 in the Proceedings of the National Academy of Sciences journal. These are the first published results relating to the thermoelectric performance of this single crystal material.

Researchers earlier thought that the material’s thermal properties were the product of “caged” atoms rattling around within the material’s crystalline structure, as had been observed in some other materials. Such rattling can serve to disrupt heat transfer in a material.

“We initially thought it was atoms of cesium, a heavy element, moving around in the material,” said Peidong Yang, a senior faculty scientist at Berkeley Lab’s Materials Sciences Division who led the study.

Jeffrey Grossman, a researcher at the Massachusetts Institute of Technology, then performed some theory work and computerized simulations that helped to explain what the team had observed. 

Researchers also used Berkeley Lab’s Molecular Foundry, which specializes in nanoscale research, in the study.

“We believe there is essentially a rattling mechanism, not just with the cesium. It’s the overall structure that’s rattling; it’s a collective rattling,” Yang said. “The rattling mechanism is associated with the crystal structure itself,” and is not the product of a collection of tiny crystal cages. “It is group atomic motion,” he added.

Within the material’s crystal structure, the distance between atoms is shrinking and growing in a collective way that prevents heat from easily flowing through.

But because the material is composed of an orderly, single-crystal structure, electrical current can still flow through it despite this collective rattling. Picture its electrical conductivity is like a submarine traveling smoothly in calm underwater currents, while its thermal conductivity is like a sailboat tossed about in heavy seas at the surface.

Yang said two major applications for thermoelectric materials are in cooling, and in converting heat into electrical current. For this particular cesium tin iodide material, cooling applications such as a coating to help cool electronic camera sensors may be easier to achieve than heat-to-electrical conversion, he said.

A challenge is that the material is highly reactive to air and water, so it requires a protective coating or encapsulation to function in a device.

Cesium tin iodide was first discovered as a semiconductor material decades ago, and only in recent years has it been rediscovered for its other unique traits, Yang said. “It turns out to be an amazing gold mine of physical properties,” he noted.


SEM images of suspended micro-island devices. Individual AIHP NW is suspended between two membranes. (Credit: Berkeley Lab/UC Berkeley)

To measure the thermal conductivity of the material, researchers bridged two islands of an anchoring material with a cesium tin iodide nanowire. The nanowire was connected at either end to micro-islands that functioned as both a heater and a thermometer. 
Researchers heated one of the islands and precisely measured how the nanowire transported heat to the other island.

They also performed scanning electron microscopy to precisely measure the dimensions of the nanowire. They used these dimensions to provide an exacting measure of the material’s thermal conductivity. The team repeated the experiment with several different nanowire materials and multiple nanowire samples to compare thermoelectric properties and verify the thermal conductivity measurements.

“A next step is to alloy this (cesium tin iodide) material,” Lee said. “This may improve the thermoelectric properties.”

Also, just as computer chip manufacturers implant a succession of elements into silicon wafers to improve their electronic properties – a process known as “doping” – scientists hope to use similar techniques to more fully exploit the thermoelectric traits of this semiconductor material. This is relatively unexplored territory for this class of materials, Yang said.

The research team also included other scientists from Berkeley Lab’s Materials Sciences Division and the Molecular Foundry, the Kavli Energy NanoScience Institute at UC Berkeley and Berkeley Lab, and UC Berkeley’s Department of Chemistry.

The Molecular Foundry is a DOE Office of Science User Facility that provides free access to state-of-the-art equipment and multidisciplinary expertise in nanoscale science to visiting scientists from all over the world.

This work was supported by the Department of Energy’s Office of Basic Energy Sciences.
More information about Peidong Yang’s research group: http://nanowires.berkeley.edu/.

###
Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel Prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit http://www.lbl.gov.
DOE’s 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 science.energy.gov.

Breakthrough in thin electrically conducting sheets paves way for smaller electronic devices



Through nanotechnology, physicists Dr Raymond McQuaid, Dr Amit Kumar and Professor Marty Gregg from Queen’s University’s School of Mathematics and Physics, have created unique 2-D sheets, called domain walls, which exist within crystalline materials.

The sheets are almost as thin as the wonder-material graphene, at just a few atomic layers. However, they can do something that graphene can’t – they can appear, disappear or move around within the crystal, without permanently altering the crystal itself.

This means that in future, even smaller electronic devices could be created, as electronic circuits could constantly reconfigure themselves to perform a number of tasks, rather than just having a sole function.
Professor Marty Gregg explains: “Almost all aspects of modern life such as communication, healthcare, finance and entertainment rely on microelectronic devices. 

The demand for more powerful, smaller technology keeps growing, meaning that the tiniest devices are now composed of just a few atoms – a tiny fraction of the width of human hair.”


Breakthrough in thin electrically conducting sheets paves way for smaller electronic devices Credit: Queen’s University Belfast

“As things currently stand, it will become impossible to make these devices any smaller – we will simply run out of space. This is a huge problem for the computing industry and new, radical, disruptive technologies are needed. One solution is to make electronic circuits more ‘flexible’ so that they can exist at one moment for one purpose, but can be completely reconfigured the next moment for another purpose.”

The team’s findings, which have been published in Nature Communications, pave the way for a completely new way of data processing.

Professor Gregg says: “Our research suggests the possibility to “etch-a-sketch” nanoscale electrical connections, where patterns of electrically conducting wires can be drawn and then wiped away again as often as required.

“In this way, complete electronic circuits could be created and then dynamically reconfigured when needed to carry out a different role, overturning the paradigm that electronic circuits need be fixed components of hardware, typically designed with a dedicated purpose in mind.”


Breakthrough in thin electrically conducting sheets paves way for smaller electronic devices Credit: Queen’s University Belfast

There are two key hurdles to overcome when creating these 2-D sheets, long straight walls need to be created. These need to effectively conduct electricity and mimic the behavior of real metallic wires. It is also essential to be able to choose exactly where and when the domain walls appear and to reposition or delete them.

 Through the research, the Queen’s researchers have discovered some solutions to the hurdles. Their research proves that long conducting sheets can be created by squeezing the crystal at precisely the location they are required, using a targeted acupuncture-like approach with a sharp needle. The sheets can then be moved around within the crystal using applied electric fields to position them.

Dr Raymond McQuaid, a recently appointed lecturer in the School of Mathematics and Physics at Queen’s University, added: “Our team has demonstrated for the first time that copper-chlorine boracite crystals can have straight conducting walls that are hundreds of microns in length and yet only nanometres thick. 

The key is that, when a needle is pressed into the crystal surface, a jigsaw puzzle-like pattern of structural variants, called “domains”, develops around the contact point. The different pieces of the pattern fit together in a unique way with the result that the conducting walls are found along certain boundaries where they meet.

“We have also shown that these walls can then be moved using applied electric fields, therefore suggesting compatibility with more conventional voltage operated devices. Taken together, these two results are a promising sign for the potential use of conducting walls in reconfigurable nano-electronics.”

 

More information: Raymond G.P. McQuaid et al. Injection and controlled motion of conducting domain walls in improper ferroelectric Cu-Cl boracite, Nature Communications (2017). DOI: 10.1038/ncomms15105

Provided by: Queen’s University Belfast

NREL: Semiconducting Single-Walled Carbon Nanotubes in Solar Energy Harvesting


National Renewable Energy Laboratory, Golden, Colorado 

Semiconducting single-walled carbon nanotubes (s-SWCNTs) represent a tunable model one-dimensional system with exceptional optical and electronic properties. 

High-throughput separation and purification strategies have enabled the integration of s-SWCNTs into a number of optoelectronic applications, including photovoltaics (PVs). In this Perspective, we discuss the fundamental underpinnings of two model PV interfaces involving s-SWCNTs. 

We first discuss s-SWCNT–fullerene heterojunctions where exciton dissociation at the donor–acceptor interface drives solar energy conversion. Next, we discuss charge extraction at the interface between s-SWCNTs and a photoexcited perovskite active layer. 

In each case, the use of highly enriched semiconducting SWCNT samples enables fundamental insights into the thermodynamic and kinetic mechanisms that drive the efficient conversion of solar photons into long-lived separated charges. 

These model systems help to establish design rules for next-generation PV devices containing well-defined organic semiconductor layers and help to frame a number of important outstanding questions that can guide future studies.

New chemical method could revolutionize Graphene: U of Illinois – Chicago




“The distinction of our chemistry will enable integration of graphene with almost anything, while retaining its properties.”

University of Illinois at Chicago scientists have discovered a new chemical method that enables graphene to be incorporated into a wide range of applications while maintaining its ultra-fast electronics.

 

Graphene, a lightweight, thin, flexible material, can be used to enhance the strength and speed of computer display screens, electric/photonics circuits, solar cells and various medical, chemical and industrial processes, among other things. It is comprised of a single layer of carbon atoms bonded together in a repeating pattern of hexagons.

 

Isolated for the first time 15 years ago by a physics professor at the University of Manchester in England, it is so thin that it is considered two-dimensional and thought to be the strongest material on the planet.

 

Vikas Berry, associate professor and department head of chemical engineering, and colleagues used a chemical process to attach nanomaterials on graphene without changing the properties and the arrangement of the carbon atoms in graphene. 





By doing so, the UIC scientists retained graphene’s electron-mobility, which is essential in high-speed electronics.

 

The addition of the plasmonic silver nanoparticles to graphene also increased the material’s ability to boost the efficiency of graphene-based solar cells by 11 fold, Berry said.

Instead of adding molecules to the individual carbon atoms of graphene, Berry’s new method adds metal atoms, such as chromium or molybdenum, to the six atoms of a benzoid ring. 

Unlike carbon-centered bonds, this bond is delocalized, which keeps the carbon atoms’ arrangement undistorted and planar, so that the graphene retains its unique properties of electrical conduction.

 

The new chemical method of annexing nanomaterials on graphene will revolutionize graphene technology by expanding the scope of its applications, Berry said.

 

“It’s been a challenge to interface graphene with other nano-systems because graphene lacks an anchoring chemistry,” he said. “And if graphene’s chemistry is changed to add anchors, it loses its superior properties. 

The distinction of our chemistry will enable integration of graphene with almost anything, while retaining its properties.

 We envision that our work will motivate a worldwide move towards ‘ring-centered’ chemistries to interface graphene with other systems.”

 

Source and top image: University of Illinois at Chicago

Solar paint offers endless energy from water vapor: Breakthrough by RMIT Researchers


Credit: CC0 Public Domain


Researchers have developed a solar paint that can absorb water vapour and split it to generate hydrogen – the cleanest source of energy.

The paint contains a newly developed compound that acts like silica gel, which is used in sachets to absorb moisture and keep food, medicines and electronics fresh and dry.

But unlike silica gel, the new material, synthetic molybdenum-sulphide, also acts as a semi-conductor and catalyses the splitting of water atoms into hydrogen and oxygen.

Lead researcher Dr Torben Daeneke, from RMIT University in Melbourne, Australia, said: “We found that mixing the compound with titanium oxide particles leads to a sunlight-absorbing paint that produces hydrogen fuel from solar energy and moist air.

“Titanium oxide is the white pigment that is already commonly used in wall paint, meaning that the simple addition of the new material can convert a brick wall into energy harvesting and fuel production real estate.

“Our new development has a big range of advantages,” he said. “There’s no need for clean or filtered water to feed the system. Any place that has water vapour in the air, even remote areas far from water, can produce fuel.”

 

His colleague, Distinguished Professor Kourosh Kalantar-zadeh, said hydrogen was the cleanest source of energy and could be used in fuel cells as well as conventional combustion engines as an alternative to fossil fuels.

“This system can also be used in very dry but hot climates near oceans. The sea water is evaporated by the hot sunlight and the vapour can then be absorbed to produce fuel.

“This is an extraordinary concept – making fuel from the sun and water vapour in the air.”

 

More information: Torben Daeneke et al, Surface Water Dependent Properties of Sulfur-Rich Molybdenum Sulfides: 
Electrolyteless Gas Phase Water Splitting, ACS Nano (2017). DOI: 10.1021/acsnano.7b01632
Provided by: RMIT University