Researchers design superhydrophobic ‘n…

Researchers design superhydrophobic ‘nanoflower’ for biomedical applications

Plant leaves have a natural superpower—they’re designed with water repelling characteristics. Called a superhydrophobic surface, this trait allows leaves to cleanse themselves from dust particles. Inspired by such natural designs, a team of researchers at Texas A&M University has developed an innovative way to control the hydrophobicity of a surface to benefit to the biomedical field.

Researchers in Dr. Akhilesh K. Gaharwar’s lab in the Department of Biomedical Engineering have developed a “lotus effect” by incorporating atomic defects in nanomaterials, which could have widespread applications in the biomedical field including biosensing, lab-on-a-chip, blood-repellent, anti-fouling and self-cleaning applications.

Superhydrophobic materials are used extensively for self-cleaning characteristic of devices. However, current materials require alteration to the chemistry or topography of the surface to work. This limits the use of superhydrophobic materials.

“Designing hydrophobic surfaces and controlling the wetting behavior has long been of great interest, as it plays crucial role in accomplishing self-cleaning ability,” Gaharwar said. “However, there are limited biocompatible approach to control the wetting behavior of the surface as desired in several biomedical and biotechnological applications.”

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Atomic ‘patchwork’ using heteroe…

Atomic ‘patchwork’ using heteroepitaxy for next-generation semiconductor devices

Researchers from Tokyo Metropolitan University have grown atomically thin crystalline layers of transition metal dichalcogenides (TMDCs) with varying composition over space, continuously feeding in different types of TMDC to a growth chamber to tailor changes in properties. Examples include 20-nanometer strips surrounded by TMDCs with atomically straight interfaces and layered structures. They also directly probed the electronic properties of these heterostructures; potential applications include electronics with unparalleled power efficiency.

Semiconductors are indispensable; silicon-based integrated circuits underpin the operation of all things digital, from discrete devices like computers, smartphones and home appliances to control components for every possible industrial application. A broad range of scientific research has been directed to the next steps in semiconductor design, particularly the application of novel materials to engineer more compact, efficient circuitry that leverages the quantum mechanical behavior of materials at the nanometer-length scale. Of special interest are materials with a fundamentally different dimensionality; the most famous example is graphene, a two-dimensional lattice of carbon atoms which is atomically thin.

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A peculiar ground-state phase for 2-D superc…

A peculiar ground-state phase for 2-D superconductors

The application of large enough magnetic fields results in the disruption of superconducting states in materials, even at drastically low temperature, thereby changing them directly into insulators—or so was traditionally thought. Now, scientists at Tokyo Institute of Technology (Tokyo Tech), the University of Tokyo and Tohoku University report curious multi-state transitions of these superconductors in which they change from superconductor to special metal and then to insulator.

Characterized by their zero electrical resistance, or alternatively, their ability to completely expel external magnetic fields, superconductors have fascinating prospects for both fundamental physics and applications for e.g., superconducting coils for magnets. This phenomenon is understood by considering a highly ordered relationship between the electrons of the system .Due to a coherence over the entire system, electrons form bounded pairs and flow without collisions as a collective, resulting in a perfect conducting state without energy dissipation. However, upon introducing a magnetic field, the electrons are no longer able to maintain their coherent relationship, and the superconductivity is lost. For a given temperature, the highest magnetic field under which a material remains superconducting is known as the critical field.

Often these critical points are marked by phase transitions. If the change is abrupt like in the case of melting of ice, it is a first-order transition. If the transition takes place in a gradual and continuous manner by the growth of change-driving fluctuations extending on the entire system, it is called a second-order transition. Studying the transition path of superconductors when subjected to the critical field can yield insights into the quantum processes involved and allows us to design smarter superconductors (SCs) for application to advanced technologies.

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Confirmation of old theory leads to new brea…

Confirmation of old theory leads to new breakthrough in superconductor science

Phase transitions occur when a substance changes from a solid, liquid or gaseous state to a different state—like ice melting or vapor condensing. During these phase transitions, there is a point at which the system can display properties of both states of matter simultaneously. A similar effect occurs when normal metals transition into superconductors—characteristics fluctuate and properties expected to belong to one state carry into the other.

Scientists at Harvard have developed a bismuth-based, two-dimensional superconductor that is only one nanometer thick. By studying fluctuations in this ultra-thin material as it transitions into superconductivity, the scientists gained insight into the processes that drive superconductivity more generally. Because they can carry electric currents with near-zero resistance, as they are improved, superconducting materials will have applications in virtually any technology that uses electricity.

The Harvard scientists used the new technology to experimentally confirm a 23-year-old theory of superconductors developed by scientist Valerii Vinokur from the U.S. Department of Energy’s (DOE) Argonne National Laboratory.

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A new quasi-2D superconductor that bridges a…

A new quasi-2D superconductor that bridges a ferroelectric and an insulator

Researchers at the Zavoisky Physical-Technical Institute and the Southern Scientific Center of RAS, in Russia, have recently fabricated quasi-2-D superconductors at the interface between a ferroelectric Ba0.8Sr0.2TiO3 film and an insulating parent compound of La2CuO4. Their study, presented in a paper published in Physical Review Letters, is the first to achieve superconductivity in a heterostructure consisting of a ferroelectric and an insulator.

The idea of forming a quasi-2-D superconducting layer at the interfacebetween two different compounds has been around for several years. One past study, for instance, tried to achieve this by creating a thin superconducting layer between two insulating oxides (LaAlO3 and SrTiO3) with a critical temperature of 300mK. Other researchers observed the thin superconducting layer in bilayers of an insulator (La2CuO4) and a metal (La1.55Sr0.45CuO4), neither of which is superconducting in isolation.

“Here we put forward the idea that thin charged layer on the interface between ferroelectric and insulator is formed in order to screen the electric field,” Viktor Kabanov and Rinat Mamin, two researchers who carried out the study, told via email. “This thin layer may be conducting or superconducting depending on the properties of the insulator. In order to get a superconducting layer, we chose La2CuO4 – an insulator that becomes a high Tc superconductor when it is doped by carriers.”

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Researchers explain visible light from 2-D l…

Researchers explain visible light from 2-D lead halide perovskites

Researchers drew attention three years ago when they reported that a two-dimensional perovskite—a material with a specific crystal structure—composed of cesium, lead and bromine emitted a strong green light. Crystals that produce light on the green spectrum are desirable because green light, while valuable in itself, can also be relatively easily converted to other forms that emit blue or red light, making it especially important for optical applications ranging from light-emitting devices to sensitive diagnostic tools.

But there was no agreement about how the crystal, CsPb2Br5, produced the green photoluminescence. Several theories emerged, without a definitive answer.

Now, however, researchers from the United States, Mexico and China, led by an electrical engineer from the University of Houston, have reported in the journal Advanced Materials they have used sophisticated optical and high-pressure diamond anvil cell techniques to determine not only the mechanism for the light emission but also how to replicate it.

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Crystal with a twist: scientists grow spiral…

Crystal with a twist: scientists grow spiraling new material

With a simple twist of the fingers, one can create a beautiful spiral from a deck of cards. In the same way, scientists at the University of California, Berkeley, and Lawrence Berkeley National Laboratory (Berkeley Lab) have created new inorganic crystals made of stacks of atomically thin sheets that unexpectedly spiral like a nanoscale card deck.

Their surprising structures, reported in a new study appearing online Wednesday, June 20, in the journal Nature, may yield unique optical, electronic and thermal properties, including superconductivity, the researchers say.

These helical crystals are made of stacked layers of germanium sulfide, a semiconductor material that, like graphene, readily forms sheets that are only a few atoms or even a single atom thick. Such “nanosheets” are usually referred to as “2-D materials.”

“No one expected 2-D materials to grow in such a way. It’s like a surprise gift,” said Jie Yao, an assistant professor of materials science and engineering at UC Berkeley. “We believe that it may bring great opportunities for materials research.”

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Exfoliating 2D materials.


I finally got to try my hand at sample preparation these past 2 weeks. Materials can exhibit striking electronic ​and mechanical properties when stripped to few layers / monolayer. Graphene (single layer graphite) is one popular example, first to be discovered among the family of 2D materials in 2004. But the search for conducting 2D materials has now extended beyond graphene.

I tried to exfoliate a single layer of molybdenum disulfide (MoS2), one type of transition metal dichalcogenides (TMD), under the guidance of my lab colleague. The properties of these TMD in the form of 2D sheets have application in more efficient electronics, semiconductors, solar cells, and touch screen display panels, just to name a few.

Exfoliation in this context is actually applying the material of interest onto a scotch tape, then folding and opening the tape several times until the flakes on it are as thin as possible. Judging with my naked eyes, this usually just means for the flakes to not appear as shiny (for metal compounds) anymore. Then, I will have to transfer the flakes on the Scotch tape to a tiny piece of transparent gel (PDMS gel). The procedure is pretty simple, but the flakes produced are not guaranteed to be thin enough. Through my many trials, I find random thickness of flakes distributed all over the gel under optical microscope. And among them, we need to locate the thinnest of all that could potentially be a monolayer.

Below is the flake that I suspect to be a single layer of MoS2 at different magnification level. ​ ​Can you find it in the last picture?

Here is the relative size of the PDMS gel on which all these flakes lie.

This also happened when I managed to transfer plenty of flakes onto the PDMS gel, while most of the time I do not get enough to choose from when observed under the microscope. After identifying this flake, I had to transfer it onto another substrate (such as a silicon nitride grid), before I can put it into an electron microscope that offer higher resolution through electrons scattering method. The transfer patience takes some patience, as pressing or lifting the gel too quickly may break the hard-found flake. So it is just a lot of going back and forth between the sample preparation table and microscope to get one nice specimen. But it is important to get through this process for us to get to the characterization part, which is where all the fun stuff about science comes in!


Curbing the flammability of epoxy resin

Curbing the flammability of epoxy resin

In a paper to be published in a forthcoming issue of Nano, a team of researchers from Henan University have investigated the flame retardant performance of epoxy resin using a boron nitride nanosheet decorated with cobalt ferrite nanoparticles.

Polymers are widely used in our daily lives due to good physical and chemical stability, corrosion resistance and other superior properties. However, most polymers, due to their organic nature, are inherently flammable which is a potential threat to the safety of human life and property. In order to avoid or reduce the flammability of polymers, it is a good strategy to add flame retardants to the polymers.

Among them, two-dimensional (2-D) layered inorganic nanomateirals (nanosheets), represented by graphene oxide, molybdenum disulfide, and boron nitride nanosheets (BNNS), exhibit excellent flame retardant performance due to their good physical barrier effects. However, the flame retardance is not enough in the use of such 2-D inorganic flame retardants alone, and in particular, the ability to suppress toxic gases and smoke is weak.

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Opposite piezoresistant effects of rhenium d…

Opposite piezoresistant effects of rhenium disulfide in two principle directions

Using optical and electrical measurements, a two-dimensional anisotropic crystal of rhenium disulfide was found to show opposite piezoresistant effects along two principle axes, i.e. positive along one axis and negative along another. Piezoresistance was also reversible; it appeared upon application of a strain, but the relative resistance returned to its original value on strain removal. This novel finding is expected to lead to wide application of rhenium disulfide.

Upon application of mechanical stress such as pressure on crystals and some kinds of ceramics, a surface charge proportional to the applied strain is induced; this phenomenon is called the piezoelectric effect. The piezoelectric effect has been known since the mid-18th century and has found use, for example, in the ignition device of cigarette lighters. Today it is widely applied in sensors, actuators, etc. On the other hand, when mechanical strain is applied to semiconducting materials, some of them show a change in electrical resistance, called the piezoresistive effect. Materials showing the piezoresistive effect are used in pressure sensors, strain sensors etc.

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