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Graphene's multi-colored butterflies

Combining black and white graphene can change the electronic properties of the one-atom thick materials, University of Manchester researchers have found.

Writing in Nature Physics, a large international team led by Dr Artem Mishchenko and Sir Andre Geim from The University of Manchester shows that the electronic properties of graphene change dramatically if graphene is placed on top of boron nitride, also known as 'white graphite'.

One of the major challenges for using graphene in electronics applications is the absence of a band gap, which basically means that graphene's electrical conductivity cannot be switched off completely. Whatever researchers tried to do with the material so far, it remained highly electrically conductive.

A new direction that has recently emerged in graphene research is to try to modify graphene's electronic properties by combining it with other similar materials in multilayered stacks. This creates an additional landscape for electrons moving through graphene and, therefore, its electronic properties can change strongly.

The University of Manchester scientists have used capacitance measurements to probe these changes. They found that in combination with a magnetic field this creates numerous replicas of the original graphene spectrum. This phenomenon is known as the Hofstadter butterfly but it is the first time that well developed replica spectra have been observed.

The researchers found a wealth of unexpected physics in this new system. For example, the Hofstadter butterflies turned out to be strongly contorted, very different from the theoretical predictions. This happens because electrons feel not only the landscape but also each other, which modifies the butterfly.
Another phenomenon that the Manchester paper reports is that graphene starts behaving at very low temperatures like a tiny ferromagnet. Usually, the higher the magnetic field, the more magnetic graphene become. The Hofstadter butterfly in Manchester's capacitors leads to an unexpected oscillating behaviour of the ferromagnetism. As new replica spectra emerge and disappear, so does the ferromagnetism.

Dr Mishchenko said: "It is really a new nice electronic system both similar to and different from graphene. We expect many more surprises. Let us first understand what it is and then we start talking about possible applications."

Reference: 
http://phys.org/
doi:10.1038/nphys2979
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About the figure: 
Artistic impressions of Hofstadter butterfly effect in graphene/BN heterostructures exposed to mangetic field. In such heterostructures Moire pattern arises due to mismatch and rotation between atomic lattices of graphene and hexagonal boron nitride. Credit: Columbia University
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MEMS nanoinjector for genetic modification of cells

The ability to transfer a gene or DNA sequence from one animal into the genome of another plays a critical role in a wide range of medical research—including cancer, Alzheimer's disease, and diabetes.

But the traditional method of transferring genetic material into a new cell, called "microinjection," has a serious downside. It involves using a small glass pipette to pump a solution containing DNA into the nucleus of an egg cell, but the extra fluid can cause the cell to swell and destroy it—resulting in a 25 to 40 percent cell death rate.
Now, thanks to the work of researchers Brigham Young University, there's a way to avoid cell death when introducing DNA into egg cells. In Review of Scientific Instruments, the team describes its microelectromechanical system (MEMS) nanoinjector, which was designed to inject DNA into mouse zygotes (single-cell embryos consisting of a fertilized egg).
"Essentially, we use electrical forces to attract and repel DNA—allowing injections to occur with a tiny, electrically conductive lance," explained Brian Jensen, associate professor in the Department of Mechanical Engineering at Brigham Young University. "DNA is attracted to the outside of the lance using positive voltage, and then the lance is inserted into a cell."
The MEMS nanoinjector's lance is incredibly small and no extra fluid is used with this technique, so cells undergo much less stress compared to the traditional microinjection process.
This ability to inject DNA into cells without causing cell death leads to "more efficient injections, which in turn reduces the cost to create a transgenic animal," according to Jensen.
One of the team's most significant findings is that it's possible to use the electrical forces to get DNA into the nucleus of the cell—without having to carefully aim the lance into the pronucleus (the cellular structure containing the cell's DNA). "This may enable future automation of the injections, without requiring manual injection," Jensen says.
It may also mean that injections can be performed in animals with cloudy or opaque embryos. "Such animals, including many interesting larger ones like pigs, would be attractive for a variety of transgenic technologies," said Jensen. "We believe nanoinjection may open new fields of discovery in these animals."
As a next step, Jensen and colleagues are performing injections into cells in a cell culture using an array of lances that can inject hundreds of thousands of cells at once. "We expect the lance array may enable gene therapy using a culture of a patient's own cells," he noted.

Reference: http://phys.org/

About the figure: This SEM (scanning electron microscope) image shows the nanoinjector next to a latex bead the same size as an egg cell. You can see the size of the nanoinjector and its lance compared to a cell.
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Researchers at the GSI Helmholtz Center for Heavy Ion Research, an accelerator laboratory located in Darmstadt, Germany, say they have created and observed several atoms of element 117, which is temporarily named ununseptium.

Element 117 so-called because it is an atom with 117 protons in its nucleus was previously one of the missing items on the periodic table of elements. These super-heavy elements, which include all the elements beyond atomic number 104, are not found naturally on Earth, and thus have to be created synthetically within a laboratory.
Atoms of a new super-heavy element the as-yet-unnamed element 117 have reportedly been created by scientists in Germany, moving it closer to being officially recognized as part of the standard periodic table
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This 3D pen lets you draw in the air

The world's smallest 3D pen can draw solid lines out of thin air - and Kickstarter users want it bad.
You could soon draw your own physical objects with the help of the Lix 3D pen.
It launched just three days ago on Kickstarter and have already raised 15 times their funding goal (and it's still growing).
The user-friendly works by melting plastic, much like a hot glue gun, which then cools as soon as it exits the pen to form solid lines.
The first pens sold to Kickstarter campaign supporters went for just US$70, and are now on sale for US$135.
The Lix pen just needs to be plugged in users, and users will straight away be able to create a range of mind-blowing art and technology applications.

Reference: http://www.sciencealert.com.au/
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A dozen newly discovered images were unearthed from the 1985 computer disks by Carnegie Mellon University's computer club.

The images depict common Warhol subjects including Campbell's soup cans, self-portraits, bananas and Marilyn Monroe, as well as doodles and camera shots of a desktop.
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Facebook found that the emotion in posts is contagious. 
Those who saw positive content were, on average, more positive and less negative with their Facebook activity in the days that followed. The reverse was true for those who were tested with more negative postings in their News Feed.
The company once manipulated nearly 700,000 users' News Feed to test the effects of emotional content.
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New method stabilizes common semiconductors for solar fuels generation

Researchers around the world are trying to develop solar-driven generators that can split water, yielding hydrogen gas that could be used as clean fuel. Such a device requires efficient light-absorbing materials that attract and hold sunlight to drive the chemical reactions involved in water splitting. Semiconductors like silicon and gallium arsenide are excellent light absorbers—as is clear from their widespread use in solar panels. However, these materials rust when submerged in the type of water solutions found in such systems.

Now Caltech researchers at the Joint Center for Artificial Photosynthesis (JCAP) have devised a method for protecting these common semiconductors from corrosion even as the materials continue to absorb light efficiently. The finding paves the way for the use of these materials in solar-fuel generators.

"For the better part of a half century, these materials have been considered off the table for this kind of use," says Nate Lewis, the George L. Argyros Professor and professor of chemistry at Caltech, and the principal investigator on the paper. "But we didn't give up on developing schemes by which we could protect them, and now these technologically important semiconductors are back on the table."

The research, led by Shu Hu, a postdoctoral scholar in chemistry at Caltech, appears in the May 30 issue of the journal Science.

In the type of integrated solar-fuel generator that JCAP is striving to produce, two half-reactions must take place—one involving the oxidation of water to produce oxygen gas; the other involving the reduction of water, yielding hydrogen gas. Each half-reaction requires both a light-absorbing material to serve as the photoelectrode and a catalyst to drive the chemistry. In addition, the two reactions must be physically separated by a barrier to avoid producing an explosive mixture of their products.

Historically, it has been particularly difficult to come up with a light-absorbing material that will robustly carry out the oxidation half-reaction. Researchers have tried, without much success, a variety of materials and numerous techniques for coating the common light-absorbing semiconductors. The problem has been that if the protective layer is too thin, the aqueous solution penetrates through and corrodes the semiconductor. If, on the other hand, the layer is too thick, it prevents corrosion but also blocks the semiconductor from absorbing light and keeps electrons from passing through to reach the catalyst that drives the reaction.

At Caltech, the researchers used a process called atomic layer deposition to form a layer of titanium dioxide (TiO2)—a material found in white paint and many toothpastes and sunscreens—on single crystals of silicon, gallium arsenide, or gallium phosphide. The key was that they used a form of TiO2 known as "leaky TiO2"—because it leaks electricity. First made in the 1990s as a material that might be useful for building computer chips, leaky oxides were rejected as undesirable because of their charge-leaking behavior. However, leaky TiO2 seems to be just what was needed for this solar-fuel generator application. Deposited as a film, ranging in thickness between 4 and 143 nanometers, the TiO2 remained optically transparent on the semiconductor crystals—allowing them to absorb light—and protected them from corrosion but allowed electrons to pass through with minimal resistance.


On top of the TiO2, the researchers deposited 100-nanometer-thick "islands" of an abundant, inexpensive nickel oxide material that successfully catalyzed the oxidation of water to form molecular oxygen.
The work appears to now make a slew of choices available as possible light-absorbing materials for the oxidation side of the water-splitting equation. However, the researchers emphasize, it is not yet known whether the protective coating would work as well if applied using an inexpensive, less-controlled application technique, such as painting or spraying the TiO2 onto a semiconductor. Also, thus far, the Caltech team has only tested the coated semiconductors for a few hundred hours of continuous illumination.

"This is already a record in terms of both efficiency and stability for this field, but we don't yet know whether the system fails over the long term and are trying to ensure that we make something that will last for years over large areas, as opposed to weeks," says Lewis. "That's the next step."


References: 

http://phys.org/
DOI: 10.1126/science.1251428
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New nanowire growth mechanism observed

A mechanism of growth of anisotropic metal oxides that was predicted 20 years ago has been observed for the first time by researchers at the University of Bristol. The work is described in an article published this week in Science.

The fabrication of nanowires of ternary and quaternary functional materials has become an important goal for their application in miniaturized circuits as diodes and transistors, coaxial gates and sensors.

The growth mechanisms are complex however and invariably proceed via a vapour-liquid-solid process which results in nanowires with a tapering morphology. A nanowire that tapers is undesirable for applications, as functionality would vary along the length, and perhaps even vanish, once a critical size was reached.

Dr Simon Hall and Rebecca Boston in the School of Chemistry, along with colleagues in the University of Birmingham and the National Institute for Materials Science in Tsukuba, Japan have successfully grown nanowires of a phase of the superconductor yttrium barium copper oxide that have a constant cross-sectional area.

In doing so, they engineered their syntheses to proceed via the so-called 'microcrucible mechanism' of crystal growth. This mechanism was first proposed to account for the growth of certain macroscopic metal oxide whiskers in 1994, but has never been observed at any length scale until now.

The team achieved the first observation of this growth mechanism by using a high-resolution transmission electron microscope with video capture and an in-situ furnace. This enabled them to directly observe molten nanoparticles of barium carbonate migrating through a porous yttrium and copper-rich matrix, catalysing nanowire outgrowth from nano-sized microcrucibles on reaching the surface.
Dr Simon Hall said: "Nanowires produced in this way will have the same physical properties along their entire length, leading to more uniform current-carrying ability, ferroic behaviour and tensile strength.

"This work could pave the way for the next generation of devices that use new, high-performance functional materials as their key component."

Reference: http://phys.org/

About the figure: Schematic showing the movement of molten barium-rich nanoparticles to the surface of an yttrium- and copper-rich matrix. The transmission electron microscope image confirms that this leads to outgrowth of yttrium barium copper oxide nanowires via the microcrucible mechanism.
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Physicists have demonstrated unlimited heat conduction in graphene

Everyone's favorite super material is now challenging the fundamental laws of heat conduction.

Researchers have proved that the amount of heat graphene conducts changes depending on the length of the sample.
This contradicts Fourier's law, which states thermal conductivity is an intrinsic material property that's independent of size or shape.
The scientists from the Max Planck Institute for Polymer Research and the National University of Singapore found that the longer the patches of graphene, the more heat they could transfer per unit of length. 
They had already predicted the phenomenon using computer simulations and have now verified it in experiments. The results are published in Nature Communications.
"The very concept of thermal conductivity as an intrinsic property does not hold for graphene, at least for patches as large as several micrometers", said Davide Donadio, head of the Max Planck research group, in a press release.
Joseph Fourier was a French physicist who, in the 1800s, came up with the theory that thermal conductivity remained the same no matter what size a material was. Graphene, a two-dimensional layer of carbon atoms, appears to be the first to prove him wrong.
The breakthrough could mean that more material constants might be alterable on the nanoscale, and shows that we really don't know as much as we think we do about the nature of materials.

Reference: http://www.sciencealert.com.au/
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According to the Guardian’s recent article 5 things a successful PhD student would never do, any PhD student who is stressed and overworked is doing it wrong. You can seemingly choose not to get stressed about a PhD, so any problems you experience are essentially self-inflicted.

On the other hand I think these tips can be useful for every students...
The Guardian today published a list of 5 things a successful PhD student would never do. Reaction to this piece has been mixed. Some find it worryingly optimistic, others find it totally unrealistic. As a result, here is a different list of 5 more things a successful PhD student would never do
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"All the survivor genes across different species had some common traits that differentiate them from genes that didn't survive. They are special, not lucky," said study author Daniel W. Bellott, a research scientist at the Whitehead Institute for Biomedical Research, in Cambridge, Mass. "We think that these genes are very important for male development, and are essential for male viability."
Men have lost most of the genes originally included on the Y chromosome during evolution, but those genes essential for survival have persevered. These genes may contribute to differences between men and women with certain diseases, researchers said.
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