Quantum Dots ~ “On the Move” ~ Illuminating Applications for photovoltaic cells, computers and drug delivery


The quantum dots used by the researchers are particles of semi-conducting material just a few nanometres wide, and are the subject of great interest because of their potential for use in photovoltaic cells or computers.

“The great thing about these particles is that they absorb light and emit it in a different colour,” explains research leader Lukas Kapitein. “We use that characteristic to follow their movements through the cell with a microscope.”

But to do so, the quantum dots had to be inserted into the cell. Most current techniques result in dots that are inside microscopic vesicles surrounded by a membrane, but this prevents them from moving freely.

However, the researchers succeeded directly delivering the particles into cultured cells by applying a strong electromagnetic field that created transient openings in the cell membrane.

In their article (“Probing cytoskeletal modulation of passive and active intracellular dynamics using nanobody-functionalized quantum dots”), they describe how this electroporation process allowed them to insert the quantum dots inside the cell.

The various transport processes that can be Sstudied using quantum dots

The various transport processes that can be Sstudied using quantum dots. Cyan: rapid diffusion. Red: slow diffusion in an actin network. Green: active transport by motor proteins. (Image: Anna Vinokurova)

Extremely bright

Once inserted, the quantum dots begin to move under the influence of diffusion. Kapitein: “Since Einstein, we have known that the movement of visible particles can provide information about the characteristics of the solution in which they move.

“Previous research has shown that particles move fairly slowly inside the cell, which indicates that the cytoplasm is a viscous fluid. But because our particles are extremely bright, we could film them at high speed, and we observed that many particles also make much faster movements that had been invisible until now.

“We recorded the movements at 400 frames per minute, more than 10 times faster than normal video. At that measurement speed, we observed that some quantum dots do in fact move very slowly, but others can be very fast.”

Kapitein is especially interested in the spatial distribution between the slow and fast quantum dots: at the edges of the cell, the fluid seems to be very viscous, but deeper in the cell he observed much faster particles.

Kapitein: “We have shown that the slow movement occurs because the particles are caught in a dynamic network of protein tubules called actin filaments, which are more common near the cell membrane. So the particles have to move through the holes in that network.”

Motor proteins

In addition to studying this passive transport process, the researchers have developed a technique for actively moving the quantum dots by binding them to a variety of specific motor proteins. 
These motor proteins move along microtubuli, the other filaments in the cytoskeleton, and are responsible for transport within the cell.

This allowed them to study how this transport is influenced by the dense layout of the actin network near the cell membrane. They observed that this differs for different types of motor protein, because they move along different types of microtubuli.

Kapitein: “Active and passive transport are both very important for the functioning of the cell, so several different physics models have been proposed for transport within the cell. Our results show that such physical models must take the spatial variations in the cellular composition into consideration as well.”

Source: Utrecht University

PNNL: ‘Composing and De-Composing’ with designer molecules at the nano scale for better Batteries/ Energy Storage 



Designed at Pacific Northwest National Laboratory, the device lets scientists add designer molecules to an extremely well-defined electrochemical cell. They can then characterize the electrode-electrolyte interface while the cell is charged and discharged at technologically relevant conditions. (Image: Mike Perkins, PNNL

Whether inside your laptop computer or storing energy outside wind farms, we need high-capacity, long-lasting, and safe batteries. In batteries, as in any electrochemical device, critical processes happen where the electrolyte and active material meet at the solid electrode.

However, determining what happens at the meeting point has been difficult because in addition to active molecules, interfaces often contain numerous inactive components.

Led by Laboratory Fellow Dr. Julia Laskin, scientists at Pacific Northwest National Laboratory have now found a way to carefully design technologically important interfaces by soft landing active molecules onto a small solid-state electrochemical cell. 

They packed the electrolyte into a solid membrane, deposited active ions on top, and characterized the cell using traditional electrochemical techniques. The device they built allows them to study key reactions in real time in controlled gaseous environments (PNAS, “In Situ Solid-State Electrochemistry of Mass-Selected Ions at Well-Defined Electrode-Electrolyte Interfaces”).

“To increase performance, we need to study what takes place inside batteries or fuel cells— understand processes at the interface in real time as the reactions are happening,” said Dr. Venkateshkumar Prabhakaran, first author of the study.

The device provides a way to understand the basic breakdown reactions, material build-up, and other processes at the electrode surface during operation. Being able to gather this dynamic information is vital to building better batteries, fuel cells, and other energy devices. 
It also matters in improving the efficiency of industrial processes through electrocatalysis. “We are doing fundamental research on state-of-the-art technologically relevant interfaces,” said Laskin.

Methods

At PNNL, scientists designed an electrochemical device to study the electrode-electrolyte interface in real time. The device uses a solid ionic-liquid membrane, in vacuum or other well-controlled environments, that has transport properties similar to a liquid electrolyte.

The solid membrane lets the team modify the electrolyte interface using ion soft-landing techniques. With soft landing, they place well-characterized active molecules at the interface. These molecules include catalytic metal clusters and redox-active “molecular battery” species capable of holding large numbers of electrons—potential candidates for boosting battery capacity.

In an exciting new twist, scientists can also add molecular fragments to the cell. They create the fragment ions by “smashing” precursor molecules in the gas phase. These gas-phase fragments may then be selected and added to the membrane. The result is a well-defined film that you can’t typically make in solution. “This gives us access to a broad range of species that aren’t stable under normal conditions and enables us to understand the contribution of individual building blocks to the overall activity of parent molecules,” said Dr. Grant Johnson, a PNNL chemist and member of the team.

When the soft-landed clusters diffuse through the extremely thin membrane and reach the electrode surface of the newly designed device, the team has a detailed and precisely defined active species they can examine using several electrochemical and spectroscopic techniques. Once at the interface, the team can study how the active molecules change the transport of electrons, increasing capacity or depleting it, for example.

What’s Next? 

The researchers are using the device to study how soft-landed noble metal clusters modify carbon dioxide to upgrade this common pollutant to more valuable chemical feedstocks.

Source: Pacific Northwest National Laboratory

MIT: Making tumor cells more vulnerable with Tethered Nanoparticles


MIT researchers have devised a way to make tumor cells more susceptible to certain types of cancer treatment by coating the cells with nanoparticles before delivering drugs.

By tethering hundreds of nanoparticles to the surfaces of tumor cells in the presence of a mechanical force, the researchers made the cells much more vulnerable to attack by a drug that triggers cancer cells to commit suicide.

It appears that the tethered nanoparticles increase the forces exerted on the cells by flowing blood, which makes the cells more likely to die.

“When you attach many particles to the membranes of these cells, and then expose them to forces that mimic those in the human body, like blood flow, these therapeutics become more effective. It’s a way of amplifying the forces on the cells using polymeric materials,” says Michael Mitchell, a postdoc at MIT’s Koch Institute for Integrative Cancer Research and the lead author of the study.

In tests in mice, the researchers found that the tethered nanoparticles made the cell-suicide-inducing drug 50 percent more effective, and this combination eliminated up to 90 percent of tumor cells in the mice.

Robert Langer, the David H. Koch Institute Professor at MIT, is the senior author of the paper, which appears in the March 20 issue of Nature Communications (“Polymeric mechanical amplifiers of immune cytokine-mediated apoptosis”)

Tethering hundreds of nanoparticles to the surfaces of tumor cells

By tethering hundreds of nanoparticles to the surfaces of tumor cells in the presence of a mechanical force, an MIT team made the cells much more vulnerable to attack by a drug that triggers cancer cells to commit suicide. (Image: Second Bay Studios)

Enhancing cell death

In addition to studying tumors’ abnormal genetic and biochemical traits, scientists and engineers in recent years have examined how tumors’ physical characteristics contribute to disease progression. Solid tumors exploit physical forces, such as their increased stiffness and altered blood flow, to enhance their survival and growth. Forces exerted by flowing blood and fluid in soft tissues also affect the behavior of cancer and a variety of host cells.

In the new study, the MIT team set out to determine whether physical forces such as those exerted by blood flow might influence how tumors respond to drug treatment. They focused on an experimental drug known as TRAIL, which is a protein expressed on different cells of the immune system. TRAIL is a member of a family of tumor necrosis factors that bind to death receptors on cell membranes, sending them a signal that stimulates apoptosis, or programmed cell death.

Initial experiments revealed that tumor cells became more susceptible to this drug after being exposed to shear forces from physiological fluids. “Under these flow conditions, more tumor cells began to die in the presence of the therapeutic,” Mitchell says.

That led the researchers to hypothesize that they could make cells even more susceptible to the treatment by increasing the forces acting on them. One way to do that is to attach tiny particles to the cell surfaces. Acting like balls on a string, the tethered particles batter and tug at the tumor cell surface as blood flows by, making the cells more susceptible to the cell death signal from the drug.

The particles, which can be injected into the bloodstream, are made of biodegradable polymers known as PLGA. These particles are coated with another polymer, PEG, that is tagged with a ligand or antibody specific to proteins found on tumor cell surfaces, which allows them to be tethered onto the surface.

In tests in mice, the researchers found that attaching particles to tumor cells and then treating them with TRAIL killed metastatic tumor cells in the bloodstream and also reduced the progression of solid tumors in mice. The researchers tested particles ranging from 100 nanometers to 1 micrometer and found that the largest ones were more effective. Also, as greater numbers of particles were tethered to the surface, more cells died.

The effect of the treatment appears to be specific to tumor cells and does not induce apoptosis in healthy cells, the researchers say.

Michael King, a professor of biomedical engineering at Cornell University who was not involved in the research, described the approach as very creative.

“I’ve never seen another study where anyone tried to use particles attached to the cell surfaces to mechanically amplify the cells’ drug sensitivity,” says King, adding that this approach may also be applicable to other drugs.

Forced interactions

The researchers believe that the particles may enhance TRAIL’s effects by compressing the shroud of molecules that usually surrounds tumor cells, making it easier for the drug to interact with receptors on the cell surface that turn on the cell death pathway.

“When you expose cells to forces and then these particles are coming down on the cell, they could be flattening all these molecules on the surface. Then the receptor can come in better contact with TRAIL to induce tumor cell death,” Mitchell says.

The MIT team is now exploring the possibility of using this approach in combination with other drugs that stimulate an immune response, such as drugs that induce a “cytokine storm” — a large release of signaling chemicals that attracts many immune cells to the site to destroy the tumor.

“We’re very interested in combined approaches where you can hit tumor cells with many immune-based therapies and then exploit physical forces that these cells are exposed to, as a new way to kill them,” Mitchell says.

Source: By Anne Trafton, MIT

Storing solar energy -in ‘liquid form’ ~ Video



Researchers at Chalmers University of Technology in Sweden have demonstrated efficient solar energy storage in a chemical liquid. The stored energy can be transported and then released as heat whenever needed. 

The research is now presented on the cover of the scientific journal Energy & Environmental Science (“Exploring the potential of a hybrid device combining solar water heating and molecular solar thermal energy storage”).

Many consider the sun the energy source of the future. But one challenge is that it is difficult to store solar energy and deliver the energy ‘on demand’.

A research team from Chalmers University of Technology in Gothenburg, Sweden, has shown that it is possible to convert the solar energy directly into energy stored in the bonds of a chemical fluid – a so-called molecular solar thermal system. 

The liquid chemical makes it possible to store and transport the stored solar energy and release it on demand, with full recovery of the storage medium. The process is based on the organic compound norbornadiene that upon exposure to light converts into quadricyclane.

‘The technique means that that we can store the solar energy in chemical bonds and release the energy as heat whenever we need it.’ says Professor Kasper Moth-Poulsen, who is leading the research team. ‘Combining the chemical energy storage with water heating solar panels enables a conversion of more than 80 percent of the incoming sunlight.’

Wallenberg Academy Fellow Kasper Moth-Poulsen, Chalmers University of Technology, is developing a promising new concept using artificial molecules that can capture, store and release solar energy, so that it can be used when the sun is not shining.

The research project was initiated at Chalmers more than six years ago and the research team contributed in 2013 to a first conceptual demonstration. 

At the time, the solar energy conversion efficiency was 0.01 percent and the expensive element ruthenium played a major role in the compound. Now, four years later, the system stores 1.1 percent of the incoming sunlight as latent chemical energy – an improvement of a factor of 100. 

Also, ruthenium has been replaced by much cheaper carbon-based elements.

‘We saw an opportunity to develop molecules that make the process much more efficient,’ says Moth-Poulsen. ‘At the same time, we are demonstrating a robust system that can sustain more than 140 energy storage and release cycles with negligible degradation.’

Source: Chalmers University of Technology

New nanosensor of Silk could speed development of new infrastructure; Aerospace and Consumer Materials 



Silk nanosensor could speed development of new infrastructure, aerospace and consumer materials (Middle) Mechanophore-labeled silk fiber fluoresces in response to damage or stress. (Right) Control sample without the mechanophore. (Image: Chelsea Davis and Jeremiah Woodcock/NIST)

Posted: Mar 17, 2017

Consumers want fuel-efficient vehicles and high-performance sporting goods, municipalities want weather-resistant bridges, and manufacturers want more efficient ways to make reliable cars and aircraft. 
What’s needed are new lightweight, energy-saving composites that won’t crack or break even after prolonged exposure to environmental or structural stress. 

To help make that possible, researchers working at the National Institute of Standards and Technology (NIST) have developed a way to embed a nanoscale damage-sensing probe into a lightweight composite made of epoxy and silk.

The probe, known as a mechanophore, could speed up product testing and potentially reduce the amount of time and materials needed for the development of many kinds of new composites.

The NIST team created their probe from a dye known as rhodamine spirolactam (RS), which changes from a dark state to a light state in reaction to an applied force. In this experiment, the molecule was attached to silk fibers contained inside an epoxy-based composite. 

As more and more force was applied to the composite, the stress and strain activated the RS, causing it to fluoresce when excited with a laser. Although the change was not visible to the naked eye, a red laser and a microscope built and designed by NIST were used to take photos inside the composite, showing even the most minute breaks and fissures to its interior, and revealing points where the fiber had fractured.

The results were published today in the journal Advanced Materials Interfaces (“Observation of Interfacial Damage in a Silk-Epoxy Composite, Using a Simple Mechanoresponsive Fluorescent Probe”).

The materials used in the design of composites are diverse. In nature, composites such as crab shell or elephant tusk (bone) are made of proteins and polysaccharides. In this study, epoxy was combined with silk filaments prepared by Professor Fritz Vollrath’s group at Oxford University using Bombyx mori silk worms. Fiber-reinforcedpolymer composites such as the one used in this study combine the most beneficial aspects of the main components–the strength of the fiber and the toughness of the polymer.

What all composites have in common, though, is the presence of an interface where the components meet. The resilience of that interface is critical to a composite’s ability to withstand damage. Interfaces that are thin but flexible are often favored by designers and manufacturers, but it is very challenging to measure the interfacial properties in a composite.

“There have long been ways to measure the macroscopic properties of composites,” said researcher Jeffrey Gilman, who led the team doing the work at NIST. “But for decades the challenge has been to determine what was happening inside, at the interface.”

One option is optical imaging. However, conventional methods for optical imaging are only able to record images at scales as small as 200-400 nanometers. Some interfaces are only 10 to 100 nanometers in thickness, making such techniques somewhat ineffective for imaging the interphase in composites. 

By installing the RS probe at the interface, the researchers were able to “see” damage exclusively at the interface using optical microscopy.

The NIST research team is planning to expand their research to explore how such probes could be used in other kinds of composites as well. They also would like to use such sensors to enhance the capability of these composites to withstand extreme cold and heat. 
There’s a tremendous demand for composites that can withstand prolonged exposure to water, too, especially for use in building more resilient infrastructure components such as bridges and giant blades for wind turbines.

The research team plans to continue searching for more ways that damage sensors such as the one in this study could be used to improve standards for existing composites and create new standards for the composites of the future, ensuring that those materials are safe, strong and reliable.

“We now have a damage sensor to help optimize the composite for different applications,” Gilman said. “If you attempt a design change, you can figure out if the change you made improved the interface of a composite, or weakened it.”

Source: National Institute of Standards and Technology (NIST)

Science in 360°: Say ‘hello’ to HERMAN, The Nanoparticle Robot: Video


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Published on Mar 7, 2017
Science in 360°: Say hello to HERMAN, a robot that accelerates the synthesis of nanoparticles for a wide range of cool applications such as biosensors, smart window coatings, and display technologies. HERMAN (aka High-throughput Experimentation Robot for the Multiplexed Automation of Nanochemistry) is a one-of-a-kind robot at Berkeley Lab’s Molecular Foundry that brings parallel processing and an extreme level of precision to the materials discovery process.

Using Nanotechnology to Control the formation of ice on surfaces


Ice id46132

Control of ice growth kinetics. (A) Hexagonal ice composed by two basal facets (c-axis) and six prism facets (a-axis). (B) Random and aligned orientations of c-axes were found on trapezoid-shaped microgrooves (TMG) and V-shaped microgrooves (VMG) surfaces, respectively. (C) Ice embryos appear on the side walls, the edges, and the valleys of groove on TMG surfaces, resulting in different orientations of ice crystals. On the other hand, an ice embryo forms only at the valley of grooves on the VMG surface, leading to the confined ice orientation. Scale bars are 15 µm. (Reprinted with permission by American Chemical Society) (click on image to enlarge)

In recent years, researchers working on de-icing and anti-icing strategies have been inspired by biology and nanotechnology to develop nanocoatings and other nanostructured surfaces.

Researchers now have demonstrated the ability to spatially control frost nucleation (ice formation from water vapor) and to manipulate ice crystal growth kinetics.”The spatial control of icing in the condensation-freezing process and through the coating of hydrophilic materials has been demonstrated before,” Ming-Chang Lu, Associate Professor in the Department of Mechanical Engineering at National Chiao Tung University said, “However, the ice nucleation control and the confinement of ice crystal growth direction through manipulating roughness scale have not been reported in the literature.”

In previous work, Lu and his team demonstrated that heterogeneous nucleation of condensation could be spatially controlled by manipulating roughness scale (Advanced Functional Materials, “Spatial Control of Heterogeneous Nucleation on the Superhydrophobic Nanowire Array”).

 

ricedeicerga-052416Read more About Nanotechnology and Deicing

Rice University: Graphene Nano-Ribbons Demonstrate Deicing Capabilities: Dr. James Tour

 

 

 

 

This motivated them to further explore whether the same control could be achieved in the icing process.Indeed, as they recently have reported in ACS Nano (“Control of Ice Formation”), they found that a surface’s anti-icing (preventing ice formation) and deicing performances could be promoted through the control of nucleation and the confinement of the ice crystal growth direction.The scientists achieved control of nucleation and the confinement of the crystal growth kinetics by manipulating local free energy barrier for nucleation.Moreover, the growth kinetics of ice can also be altered by adjusting the shape of the microgroove of the surface: Ice stacked along the direction of the V-shaped microgroove, whereas it grew in random directions on the trapezoid-shaped microgroove.As the researchers demonstrate in their paper, the spatial control of frost formation and the confinement of ice-growing kinetics improved the anti-icing and deicing performances.”We have shown that ice formation and ice crystal growth could be manipulated by tailoring surface roughness scale,” notes Lu.

 

“We believe that our results could be potentially applied to alleviate the icing issues in many industrial systems, such as, power transmission system, telecommunication system, heat exchangers, aircraft, etc.”In this work, the team systematically investigated – under an environmental scanning electron microscope (ESEM) – frosting and deicing processes on a plain silicon surface, a silicon nanowire (SiNW) array-coated surface, and V-shaped and trapezoid-shaped microgroove patterned surfaces.Nucleation is the first step of the phase transition during freezing. The team’s goal is to gain complete control of the ice formation process including nucleation, crystal growth, and ice spreading.”The results we demonstrated were on a Si surface and on a laboratory chip; in my opinion, the future directions are to explore whether the phenomena could be realized on other materials and on a larger system,” concludes Lu. “The ultimate goal is to have fully controls of icing and deicing processes. Therefore, it could be applied to alleviate the adverse effect caused by global warming, e.g., the loss of ice sheets.”

Original Post by Micheal Berger

Drug combination delivered by nanoparticles may help in melanoma treatment


Melenoma 170314140859_1_540x360Gavin Robertson, professor of pharmacology, pathology, dermatology, and surgery; director of the Penn State Melanoma and Skin Cancer Center and member of Penn State Cancer Institute, works with associates in the Melanoma Center.
Credit: Penn State College of Medicine

Summary: The first of a new class of medication that delivers a combination of drugs by nanoparticle may keep melanoma from becoming resistant to treatment, according to Penn State College of Medicine researchers.

CelePlum-777 combines a special ratio of the drugs Celecoxib, an anti-inflammatory, and Plumbagin, a toxin. By combining the drugs, the cells have difficulty overcoming the effect of having more than one active ingredient.

Celecoxib and Plumbagin work together to kill melanoma cells when used in a specific ratio. Researchers used microscopic particles called nanoparticles to deliver the drugs directly to the cancer cells. These particles are several hundred times smaller than the width of a hair and can be loaded with medications.

“Loading multiple drugs into nanoparticles is one innovative approach to deliver multiple cancer drugs to a particular site where they need to act and have them released at that optimal cancer cell killing ratio,” said Raghavendra Gowda, assistant professor of pharmacology, who is the lead author on the study. “Another advantage is that by combining the drugs, lower concentrations of each that are more effective and less toxic can be used.”

Celecoxib and Plumbagin cannot be taken by mouth because the drugs do not enter the body well this way and cannot be used together in the ratio needed because of toxicity.

CelePlum-777 can be injected intravenously without toxicity. Because of its small size, it also accumulates inside the tumors where it then releases the drugs to kill the cancer cells. Researchers report their results in the journals Molecular Cancer Therapeutics and Cancer Letters.

“This drug is the first of a new class, loaded with multiple agents to more effectively kill melanoma cells, that has potential to reduce the possibility of resistance development,” said senior author Gavin Robertson, professor of pharmacology, pathology, dermatology, and surgery; director of the Penn State Melanoma and Skin Cancer Center and member of Penn State Cancer Institute. “There is no drug like it in the clinic today and it is likely that the next breakthrough in melanoma treatment will come from a drug like this one.”

The researchers showed the results of CelePlum-777 on killing cancer cells growing in culture dishes and in tumors growing in mice following intravenous injection. The drug prevented tumor development in mice with no detectable side effects and also prevented proteins from enabling uncontrolled cancer cell growth.

More research is required by the Food and Drug Administration before CelePlum-777 can be tested in humans through clinical trials. Penn State has patented this discovery and licensed it to Cipher Pharmaceuticals, which will perform the next series of FDA-required tests.


Story Source:

Materials provided by Penn State College of Medicine. Note: Content may be edited for style and length.

Gold foil discovery could lead to wearable technology – Flexibility is the Key


goldfoildiscAn example of a gold foil peeled from single crystal silicon. Credit: Reprinted with permission from Naveen Mahenderkar et al., Science [355]:[1203] (2017).

Some day, your smartphone might completely conform to your wrist, and when it does, it might be covered in pure gold, thanks to researchers at Missouri University of Science and Technology.

Writing in the March 17 issue of the journal Science, the Missouri S&T researchers say they have developed a way to “grow” thin layers of gold on single crystal wafers of silicon, remove the gold foils, and use them as substrates on which to grow other electronic materials.

wearable-textiles-100616-0414_powdes_ti_f1The research team’s discovery could revolutionize wearable or “flexible” technology research, greatly improving the versatility of such electronics in the future.

According to lead researcher Dr. Jay A. Switzer, the majority of research into wearable technology has been done using polymer substrates, or substrates made up of multiple crystals. “And then they put some typically organic semiconductor on there that ends up being flexible, but you lose the order that (silicon) has,” says Switzer, Donald L. Castleman/FCR Endowed Professor of Discovery in Chemistry at S&T.

Because the polymer substrates are made up of multiple crystals, they have what are called , says Switzer. These grain boundaries can greatly limit the performance of an electronic device.

“Say you’re making a solar cell or an LED,” he says. “In a semiconductor, you have electrons and you have holes, which are the opposite of electrons. They can combine at grain boundaries and give off heat. And then you end up losing the light that you get out of an LED, or the current or voltage that you might get out of a solar cell.”

Most electronics on the market are made of silicon because it’s “relatively cheap, but also highly ordered,” Switzer says.

“99.99 percent of electronics are made out of silicon, and there’s a reason – it works great,” he says. “It’s a single crystal, and the atoms are perfectly aligned. But, when you have a single crystal like that, typically, it’s not flexible.”

By starting with single crystal silicon and growing gold foils on it, Switzer is able to keep the high order of silicon on the foil. But because the foil is gold, it’s also highly durable and flexible.

“We bent it 4,000 times, and basically the resistance didn’t change,” he says.

The gold foils are also essentially transparent because they are so thin. According to Switzer, his team has peeled foils as thin as seven nanometers.

Switzer says the challenge his research team faced was not in growing gold on the single crystal silicon, but getting it to peel off as such a thin layer of foil. Gold typically bonds very well to silicon.

“So we came up with this trick where we could photo-electrochemically oxidize the silicon,” Switzer says. “And the gold just slides off.”

Photoelectrochemical oxidation is the process by which light enables a semiconductor material, in this case silicon, to promote a catalytic oxidation reaction.

Switzer says thousands of gold foils—or foils of any number of other metals—can be made from a single crystal wafer of .

The research team’s discovery can be considered a “happy accident.” Switzer says they were looking for a cheap way to make single crystals when they discovered this process.

“This is something that I think a lot of people who are interested in working with highly ordered materials like single crystals would appreciate making really easily,” he says. “Besides making flexible devices, it’s just going to open up a field for anybody who wants to work with .”

Explore further: ‘Nanospears’ could lead to better solar cells, lasers, lighting

More information: Naveen K. Mahenderkar et al. Epitaxial lift-off of electrodeposited single-crystal gold foils for flexible electronics, Science (2017). DOI: 10.1126/science.aam5830

Read more at: https://phys.org/news/2017-03-gold-foil-discovery-wearable-technology.html#jCp

Read more at: https://phys.org/news/2017-03-gold-foil-discovery-wearable-technology.html#jCp

Third-Generation Solar Cells using Metalorganic Perovskites Challenges silicon based Solar Cells


nanotubefilmAn illustration of a perovskite solar cell. Credit: Photo by Aalto University / University of Uppsala / EPFL

Five years ago, the world started to talk about third-generation solar cells that challenged the traditional silicon cells with a cheaper and simpler manufacturing process that used less energy.

Methylammonium lead iodide is a metal-organic material in the perovskite crystal structure that captures light efficiently and conducts electricity well—both important qualities in . However, the lifetime of solar cells made of metalorganic perovskites has proven to be very short compared to cells made of .

Now researchers from Aalto University, Uppsala University and École polytechnique fédérale de Lausanne (EPFL) in Switzerland have managed to improve the long term stability of solar cells made of perovskite using “random network” nanotube films developed under the leadership of Professor Esko Kauppinen at Aalto University. Random network nanotube films are films composed of single-walled carbon nanotubes that in an electron microscope image look like spaghetti on a plate.

‘In a traditional perovskite solar cell, the hole conductor layer consists of organic material and, on top of it, a thin layer of gold that easily starts to disintegrate and diffuse through the whole solar cell structure. We replaced the gold and also part of the organic material with films made of carbon nanotubes and achieved good cell stability in 60 degrees and full one sun illumination conditions‘, explains Kerttu Aitola, who defended her doctoral dissertation at Aalto University and now works as a researcher at Uppsala University

In the study, thick black films with conductivity as high as possible were used in the back contact of the solar cell where light does not need to get through. According to Aitola, nanotube films can also be made transparent and thin, which would make it possible to use them as the front contact of the cell, in other words as the contact that lets light through.

‘The solar cells were prepared in Uppsala and the long-term stability measurement was carried out at EPFL. The leader of the solar cell group at EPFL is Professor Michael Grätzel, who was awarded the Millennium Prize 2010 for dye-sensitised solar cells, on which the are also partly based on’, says Aitola.

Nanotube film may resolve longevity problem of challenger solar cells
Cross-section of the solar cell in an electron microscope image. The fluff seen in the front of the image is composed of bundles of nanotubes that have become half-loose when the samples have been prepared for imaging. Credit: Photo by Aalto University / University of Uppsala / EPFL

 

The lifetime of solar cells made of silicon is 20-30 years and their industrial production is very efficient. Still, alternatives are needed as reducing the silicon dioxide in sand to silicon consumes a huge amount of energy. It is estimated that a needs two or three years to produce the energy that was used to manufacture it, whereas a perovskite solar cell would only need two or three months to do it.

‘In addition, the silicon used in solar cells must be extremely pure’, says Aitola.

‘Perovskite solar cell is also interesting because its efficiency, in other words how efficiently it converts sunlight energy into electrical energy, has very quickly reached the level of silicon solar cells. That is why so much research is conducted on perovskite solar cells globally.’

The alternative solar cells are even more interesting because of their various application areas. Flexible solar cells have until now been manufactured on conductive plastic. Compared with the conductive layer of plastic, the flexibility of nanotube films is superior and the raw materials are cheaper. Thanks to their flexibility, solar cells could be produced using the roll-to-roll processing method known from the paper industry.

‘Light and would be easy to integrate in buildings and you could also hang them in windows by yourself’, says Aitola.

Explore further: New way to make low-cost solar cell technology

More information: Kerttu Aitola et al, High Temperature-Stable Perovskite Solar Cell Based on Low-Cost Carbon Nanotube Hole Contact, Advanced Materials (2017). DOI: 10.1002/adma.201606398