2D MXenes...

Helper two-dimensional metal-carbide layers could improve perovskite solar cell stability and help make these complex solar cells a viable green energy option. Credit: iStock Milos-Muller

Topics: Condensed Matter Physics, Green Tech, Materials Science, Metamaterials, Nanotechnology, Solar Power

With the reality of climate change looming, the importance of realistic green energy sources is higher than ever. Solar cells are one promising avenue, as they can convert readily available visible and ultraviolet energy into usable electricity. In particular, perovskite materials sandwiched between other support layers have demonstrated impressive power conversion efficiencies. Current challenges reside in optimizing perovskite/support layer interfaces, which can directly impact power conversion and cell degradation. Researchers Antonio Agresti et al. under the direction of Aldo Di Carlo at the University of Rome Tor Vergata in Italy have investigated how cells containing two-dimensional titanium-carbide MXene support layers could improve perovskite solar cell performance.

To obtain good power conversion within a perovskite solar cell, all layers and layer interfaces within the cell must have good compatibility. Typical cells contain the active perovskite material sandwiched between two charge transport layers, which are then adjacent to their corresponding electrodes. Support layers may also be added. Charge mobility, energy barriers, interface energy alignment, and interfacial vacancies all impact compatibility and subsequent cell performance and stability. Thus, engineering well-suited interfaces with the cell is paramount to cell success and long-term stability, an important criterion for potential commercialization.

Two-dimensional buffer materials could help to modify and promote useful interface interactions. MXenes, a growing class of two-dimensional transitional metal carbides, nitrides, and carbonitrides, have shown impressive electronic properties that are easily tuned via surface modification. For example, the band gap of an MXene can be modified by changing the surface termination group from an oxygen atom to a hydroxide molecule. Additionally, MXene composition impacts the overall material performance. This type of fine-tuning allows impressive control over MXene properties and makes them ideal for interface adjustments.

Two-dimensional MXenes improve perovskite solar cell efficiency
Amanda Carr, Physics World

#P4TC: MXenes...August 24, 2015

Conjuring Ray Palmer...

MIT engineers have devised a way to create 3D nanoscale objects by patterning a larger structure with a laser and then shrinking it. This image shows a complex structure prior to shrinking. Courtesy: Daniel Oran

Topics: 3D Printing, Materials Science, Metamaterials, Nanotechnology, Science Fiction

A new 3D nanofabrication technique called Implosion Fabrication could be used to create a wide variety of nano- and microstructures not previously possible. The technique, which can print 3D objects of nearly any shape by patterning a polymer scaffold with a laser and then shrinking the structure to a thousandth of its original volume, might be used to make novel optical metamaterials and electronics devices.

Shrinking hydrogel scaffold

Most existing nanofabrication techniques are limited in what they can produce. Direct laser writing methods, for example, can produce 2D patterns but not 3D ones, which need to be built up a layer at a time – a process that is difficult and slow. Lithography, one of the oldest nanofabrication techniques, can again only print 2D layers on patterned surfaces.

The apropos cultural reference that absolutely dates me!

Image Source: Wikipedia link below

Raymond "Ray" Palmer, is a physicist and professor at Ivy University in the fictional city of Ivy Town, somewhere in New England, specializing in matter compression as a means to fight overpopulation, famine and other world problems. Using a mass of white dwarf star matter he finds after it lands on Earth, Palmer fashions a lens that enables him to shrink any object to any degree he wishes. Compression destabilizes an object's molecular structure, however, causing it to explode. Source: Wikipedia

It's also the epitome of escapist fiction, since a white dwarf in real life is kind of dense.

Imploding hydrogel shrinks objects to the nanoscale, Belle Dumé, Physics World

Nanoglue...

Illustrations of frequency-dependent toughening in a polymer-metal-nanoglue-ceramic composite. Credit: Rensselaer Polytechnic Institute

Topics: Materials Science, Metamaterials, Nanotechnology

In a discovery that could pave the way for new materials and applications, materials scientists at Rensselaer Polytechnic Institute have found that oscillating loads at certain frequencies can lead to several-fold increases in the strength of composites with an interface that is modified by a molecular layer of "nanoglue."

A newly published article in Nature Communications reports the unexpected discovery of the effects of loading frequency on the fracture energy of a multilayer composite involving a "nanoglue," the use of which was also pioneered at Rensselaer.

"Unearthing, understanding, and manipulating nanoscale phenomena at interfaces during dynamic stimuli is a key to designing new materials with novel responses for applications," said Ganpati Ramanath, the John Tod Horton Professor of Materials Science and Engineering at Rensselaer and the lead author on the study. "Our work demonstrates that introducing a nanoglue layer at an interface of a layered composite can lead to large mechanical toughening at certain loading frequencies."

Nanoglue can make composites several times tougher during dynamic loading,
Matthew Kwan et al. Nature Communications, Phys.org

Flexible Ferroelectrics...

A scanning electron microscopy image of flexible haloimidazole crystals, which were found to show both ferroelectric and piezoelectric properties. (Image by Seungbum Hong/Argonne National Laboratory.)

Topics: Condensed Matter Physics, Nanotechnology, Materials Science, Metamaterials, Solid State Physics

Until recently, “flexible ferroelectrics” could have been thought of as the same type of oxymoronic phrase. However, thanks to a new discovery by the U.S. Department of Energy’s (DOE) Argonne National Laboratory in collaboration with researchers at Northwestern University, scientists have pioneered a new class of materials with advanced functionalities that moves the idea from the realm of irony into reality.

Ferroelectrics are a useful type of material that is found in capacitors that are used in sensors, as well as computer memory and RFID cards. Their special properties originate from the fact that they contain charged regions polarized in a specific orientation, which can be controlled with an external electric field. But they’ve also had a big drawback as engineers try to use them in new inventions.

“Ferroelectric materials are known for being quite brittle, and so it has always been a big challenge to make them mechanically flexible,” said Argonne nanoscientist Seungbum Hong, who helped to lead the research. “Because ferroelectricity and this kind of flexibility are relatively rare properties to see on their own, to have both ferroelectricity and flexibility in this new material is basically unprecedented.”

Argonne National Laboratory: Flexible ferroelectrics bring two material worlds together

Squeezing Below The Quantum Limit...

NIST researchers applied a special form of microwave light to cool a microscopic aluminum drum to an energy level below the generally accepted limit, to just one fifth of a single quantum of energy. Having a diameter of 20 micrometers and a thickness of 100 nanometers, the drum beat 10 million times per second while its range of motion fell to nearly zero.

Credit: Teufel/NIST

Topics: Metamaterials, Nanotechnology, Quantum Computer, Quantum Mechanics

Physicists at the National Institute of Standards and Technology (NIST) have cooled a mechanical object to a temperature lower than previously thought possible, below the so-called “quantum limit.”

The new NIST theory and experiments, described in the Jan. 12, 2017, issue of Nature, showed that a microscopic mechanical drum—a vibrating aluminum membrane—could be cooled to less than one-fifth of a single quantum, or packet of energy, lower than ordinarily predicted by quantum physics. The new technique theoretically could be used to cool objects to absolute zero, the temperature at which matter is devoid of nearly all energy and motion, NIST scientists said.

“The colder you can get the drum, the better it is for any application,” said NIST physicist John Teufel, who led the experiment. “Sensors would become more sensitive. You can store information longer. If you were using it in a quantum computer, then you would compute without distortion, and you would actually get the answer you want.”

NIST Physicists ‘Squeeze’ Light to Cool Microscopic Drum Below Quantum Limit
Laura Ost

Electrospinning...

A schematic diagram of a needleless twisted wire electrospinning setup showing the main components in the system. The polymer solution is fed to the top of twisted wire that acts as the spinneret. The fibers are collected on the cylindrical collector around the wire. Courtesy Nanotechnology

Topics: Materials Science, Metamaterials, Nanotechnology

Electrospinning works by ejecting liquid through a needle at the end of a cone. By applying an electric field, interaction between the charges in the liquid and the field provides the tensile force that would be exerted by spindles and reels in conventional spinning. Meanwhile the surface tension of the liquid – if it is sufficient – stops the ejected liquid breaking up into droplets. The result is long, extremely narrow fibres. While the textile industry has used the process since the 1930s, its potential for producing fibres with nanoscale diameters only came to light in the 1990s.

Like any other spun yarn, electrospun nanofibres can be woven, and the resulting nanoporous fabric can have huge advantages. Porous materials allow diffusion of molecules – useful for a number of applications, among them drug delivery. In 2006 Pattama Taepaiboon, Uracha Rungsardthong and Pitt Supaphol in Thailand were first to publish on the potential of electrospun hydrogel polymers for drug delivery through the skin. Their study of drug-loaded poly(vinyl alcohol) (PVA) electrospun mats not only showed that the chemical integrity of the drugs was unimpeded by electrospinning, but provided insights into the effect of drug solubility on the morphology of mat formed, as well as on the drug release characteristics. Ten years later use of electrospun mats for drug delivery remains a hot topic of research.

Nanotechweb: Electrospinning forms a common thread in new technologies Anna Demming

3D Acoustic Holograms...

The researchers designed a hologram that projects sound waves with an amplitude pattern shaped like the letter "A". The top images show the simulated field patterns of the amplitude of sound waves at three representative depths. The bottom row shows the actual experimental amplitudes recorded in an anechoic chamber. (Courtesy: Scientific Reports 6 35437)

Topics: Acoustic Physics, Electromagnetism, Holograms, Metamaterials

Researchers in the US have created a printed array of metamaterials that can produce passive 3D acoustic holograms from a simple sound source, such as a single speaker. The device is made up of 3D-printed Lego-like blocks that can be put together in different configurations. The researchers say that their method is cheaper and simpler than other techniques and that they expect it to "open a new realm of holographic acoustic wave manipulation".

A visual hologram manipulates electromagnetic waves in the visible part of the spectrum to create a 3D image. Because sound also travels in waves, it should be possible to create complex 3D fields of sound – acoustic holograms – in a similar way. While visual holograms can be made with physical structures that diffract light, it isn't so easy with sound due to a lack of materials with the required acoustic properties. Generally, acoustic holograms use a transducer array controlled by complex phase shifting electronics.

Physics World: Building-block metamaterials shape 3D acoustic holograms
Michael Allen is a science writer based in Bristol, UK

Self-Healing Tribofilm...

Image Source: insideHPC

Topics: Materials Science, Metamaterials, Science, Research

Fans of Superman surely recall how the Man of Steel used immense heat and pressure generated by his bare hands to form a diamond out of a lump of coal.

The tribologists — scientists who study friction, wear, and lubrication — and computational materials scientists at the U.S. Department of Energy's (DOE's) Argonne National Laboratory will probably never be mistaken for superheroes. However, they recently applied the same principles and discovered a revolutionary diamond-like film of their own that is generated by the heat and pressure of an automotive engine.

The discovery of this ultra-durable, self-lubricating tribofilm — a film that forms between moving surfaces — was first reported yesterday in the journal Nature. It could have profound implications for the efficiency and durability of future engines and other moving metal parts that can be made to develop self-healing, diamond-like carbon (DLC) tribofilms.

"This is a very unique discovery, and one that was a little unexpected," said Ali Erdemir, the Argonne Distinguished Fellow who leads the team. "We have developed many types of diamond-like carbon coatings of our own, but we've never found one that generates itself by breaking down the molecules of the lubricating oil and can actually regenerate the tribofilm as it is worn away."

ANL: Argonne discovery yields self-healing diamond-like carbon, Greg Cunningham

Nano Oasis...

Researchers have accidentally created nanorods that can absorb water at low humidity and expel it as the humidity increases.

Topics: Carbon Nanotubes, Materials Science, Metamaterials, Nanotechnology

Learning from your mistakes is a key life lesson, and it's one that researchers at Pacific Northwest National Laboratory (PNNL) can attest to. After unintentionally creating carbon-rich nanorods, the team realized its accidental invention behaves weirdly with water, demonstrating a 20-year old theory and potentially paving the way to low-energy water harvesting systems and sweat-removing fabrics.

The researchers note that ordinarily materials will absorb more water as the humidity in the air around them increases. But between 50 and 80 percent relative humidity, these nanorods will actually do the opposite and expel water, a behavior they say is not shared by any other material. Below that range, they behave as normal, so the process is reversible by lowering the humidity again.

"Our unusual material behaves a bit like a sponge; it wrings itself out halfway before it's fully saturated with water," says David Lao, PNNL research associate and creator of the material.

These nanorods were created by mistake while trying to fabricate magnetic nanowires, and the researchers decided to give the accidents a closer look. On examining them with a vapor analysis instrument, Satish Nune, one of the authors of the research paper, noticed that the structures were actually losing weight as the humidity increased.

Gizmag:
Scientists accidentally create nanorods that harvest water from the air, Michael Irving

Out Of This World...

Orbits of inner planets are shown as large circles in this computer-generated snapshot of actual known objects as of July 20, 2002. Green dots represent asteroids in the main belt between Mars and Jupiter. Red dots are asteroids that stray out of the main belt and pose a small but known possible risk of hitting Earth.

Credit: MPC, CBAT, Harvard CfA, IAU

Source: Space.com

Topics: Asteroids, Astrophysics, Geophysics, Metamaterials, Quasicrystals

Naturally formed quasicrystals—crystal-like solids with supposedly impossible symmetries—are among the rarest structures on Earth. Only two have ever been found.

A team led by Paul Asimow (MS '93, PhD '97), professor of geology and geochemistry at Caltech, may have uncovered one of the reasons for that scarcity, demonstrating in laboratory experiments that quasicrystals could arise from collisions between rocky bodies in the asteroid belt with unusual chemical compositions.

A paper on their findings was published on June 13 in the advance online edition of the Proceedings of the National Academy of Sciences.

At an atomic level, crystals are both ordered and periodic, meaning that they have a defined geometric structure, with that structure repeating itself over and over. To grow such a repeating structure without the original organization breaking down, the crystal can only exhibit one of four types of rotational symmetry: two-fold, three-fold, four-fold, or six-fold.

The number refers to how many times an object will look exactly the same within a full 360-degree rotation about an axis. For example, an object with two-fold symmetry appears the same twice, or every 180 degrees; an object with three-fold symmetry appears the same three times, or every 120 degrees; and an object with four-fold symmetry appears the same four times, or every 90 degrees.

Phys.org:
Natural quasicrystals may be the result of collisions between objects in the asteroid belt
Robert Perkins

Changeling...

Image courtesy of Ilsa van Meerbeek
The material is capable o both withstanding heavy loads or deforming under them as needed.

Topics: Materials Science, Metamaterials, Robotics

For all the discussion surrounding artificial intelligence and robots recently, the stiff, dull metal exterior of robots has only recently begun to evolve. While human-like robots, with silicon skin, can simulate emotions but robots with the shape-shifting ability of the Transformers have yet to hit the market. However, Prof. Robert Shepherd, mechanical and aerospace engineering, is developing a material that could soon bring that to reality.

Shepherd and his team at Organic Robotics Lab is working on a metal-rubber composite by harnessing the strength of a metallic alloy and the flexibility of a soft silicone foam. The material can withstanding heavy loads or deform under them upon command. The only requirement for switching between these properties is a change in temperature.

Cornell Daily Sun:
Cornell Researchers Create New Material Capable of Shifting States, Arnav Ghosh

Snapology...

Image Source: Harvard, John A. Paulson School of Engineering and Applied Science

Topics: 3D Objects, Architectural Engineering, Materials Science, Metamaterials

"A house that could fit in a backpack or a wall that could become a window with the flick of a switch" are just two fantastical objects that could be made from a new self-folding metamaterial – according to its inventors at Harvard University in the US. Inspired by origami, the material will pop up and fold down on command, and can change both its shape and stiffness. Other possible applications for the new material include retractable roofs and medical implants.

The metamaterial was developed by a team led by Katia Bertoldi, James Weaver and Chuck Hoberman. It was inspired by "snapology", which is a type of origami that uses modular units of folded paper to create larger objects. In the new approach, each unit cell is an extruded rhombus that has inflatable air pockets along three of its edges (see video). When an air pocket is pressurized, it causes an edge of the unit cell to try to fold flat. By pressurizing different combinations of pockets, the shape of the unit cell itself can be changed.

Physics World: Origami-inspired metamaterial changes shape and stiffness on command
Hamish Johnston

Metamorphosis...

Image credit: rexboggs5 via flickr | http://bit.ly/1SECwxD
Rights information: http://bit.ly/1haBUhX

Topics: Engineering, Materials Science, Metamaterials, Research, Robotics

(Inside Science) -- By using fluids similar to Silly Putty that can behave as both liquids and solids, researchers say they have created fluid robots that might one day perform tasks that conventional machines cannot.

Conventional robots are made of rigid parts that are vulnerable to bumps, scrapes, twists and falls. In contrast, researchers worldwide are increasingly developing robots made from soft, elastic plastic and rubber that are inspired by worms, starfish and octopuses. These soft robots can resist many of the kinds of damage, and can squirm past many of the obstacles, that can impede hard robots.

However, even soft robots and the living organisms they are inspired by are limited by their solidity — for example, they remain vulnerable to cutting. Instead, researcher Ido Bachelet of Bar-Ilan University in Israel and his colleagues have now created what they call fluid robots that they say could operate better than solid robots in chaotic, hostile environments. They detailed their findings online Jan. 22 in the journal Artificial Life.

Inside Science: Researchers Are Developing Shape-Shifting Fluid Robots
Charles Q. Choi

Sole Power...

Image GIF source: MIT Technology Review

Topics: Economy, Jobs, Materials Science, Metamaterials, STEM

Considering the obesity rate in the country and the FitBit craze, this could be a win-win for all of us.

Children have been harnessing energy from their steps ever since 1992, when L.A. Gear introduced sneakers that light up. For most adults, however, the ambient energy created by the simple act of walking is forever lost. Considering that the average person takes around 216 million steps in a lifetime, it’s a significant waste.

Inventor Laurence Kemball-Cook hopes to harness the lost energy at two points of contact: the shoe and the floor. In 2009, Kemball-Cook founded Pavegen, a company whose floor tiles can capture the power of footsteps. The technology uses compression to skim a tiny fraction of the energy created when a human steps on the tile. It’s been installed in more than 100 projects around the world, including a football stadium in Rio de Janeiro and a terminal in Heathrow Airport. The energy is stored in batteries inside the tiles, where it can then be used to power lighting, advertisements, and way-finding solutions, which guide people through an environment via directional arrows.

Now Kemball-Cook and his R&D team have turned their attention to the shoe itself, hoping to apply the same principles used in the tiles as a way to harness personal energy. “The idea is that the energy source would be readily available to the shoe wearer,” explains Kemball-Cook, who has been in discussions with major footwear manufacturers such as Nike and Reebok about ways the technology could be incorporated into consumer products. “You could walk from work and charge your phone en route instead of waiting to use a charger at home. Runners could charge their music players during a jog.”

MIT Technology Review: The Quest to Make Your Shoe a Power Source, Simon Parkin

Beauty...

Image Source: NIST

Topics: Condensed Matter Physics, Lasers, Materials Science, Metamaterials, Quantum Mechanics

Physicists at JILA have made their "quantum crystal" of ultracold molecules more valuable than ever by packing about five times more molecules into it. The denser crystal will help scientists unlock the secrets of magnets and other, more exotic materials.

The crystal is actually a gas of particles trapped in 3-D formation by laser beams. The trap, called an optical lattice, has wells—local regions of low energy—like an egg carton made of light. The researchers maneuvered a single molecule into each well, successfully filling about 25 percent of the crystal. The structure has an advantage over a real crystal, as it is made of scientifically interesting molecules that normally would not crystallize.

Described in the Nov. 6, 2015, issue of Science,* the JILA crystal is useful for studying correlations among the molecules' "spins," or rotations, a quantum behavior related to magnetism. The denser crystal will enable scientists to study and model complex effects such as how spin correlations or entanglement—a quantum link between the properties of separated particles—spread through a large system. Scientists might use these effects, for example, to make novel materials for electronics or other applications.

NIST:
It’s a Beauty: JILA’s Quantum Crystal is Now More Valuable, Laura Ost

Wearing Well...

The world’s first stretchable and conformable thin-film transistor (TFT) driven LED display laminated into textiles developed by Holst Centre, imec and CSMT.

Topics: Consumer Electronics, Humor, Materials Science, Metamaterials, Thin Films

Okay, I've got a wearable device on my wrist that's synced to my smart phone. I often forget to put it on. I input my mass; it monitors the steps I take per day (goal of 10,000) and how long and how "deep" my sleep was. I'm often disappointed.

I could see this catching on with the young initially. As with Facebook and all other social media platforms, they'll exit as soon as the "oldsters" start wearing their favorite duds. Youngsters really should calm down...you're sounding like us.

Researchers from Holst Centre (set up by TNO and imec), imec and CMST, imec’s associated lab at Ghent University, have demonstrated the world’s first stretchable and conformable thin-film transistor (TFT) driven LED display laminated into textiles. This paves the way to wearable displays in clothing providing users with feedback.

Wearable devices such as healthcare monitors and activity trackers are now a part of everyday life for many people. Today’s wearables are separate devices that users must remember to wear. The next step forward will be to integrate these devices into our clothing. Doing so will make wearable devices less obtrusive and more comfortable, encouraging people to use them more regularly and, hence, increasing the quality of data collected. A key step towards realizing wearable devices in clothing is creating displays that can be integrated into textiles to allow interaction with the wearer.

Solid State Technology: Turning clothing into information displays

Now You Don't...

Credit: NSF

Topics: Applied Physics, Optics, Invisibility, Metamaterials, Transformative Optics

Andrea Alù, an engineering professor at the University of Texas at Austin, has an amazing job description: he makes things invisible. Alù is a leading innovator in metamaterials, artificial materials with properties that allow electromagnetic waves to wrap around them. Those include radio waves--creating the possibility of more efficient antennas--and, at a very small scale, even the light waves that our eyes perceive. That light-bending technology could allow for the creation of microscopes with drastically improved performance. For his work, the National Science Foundation presented Alù with its 2015 Alan T. Waterman Award, which recognizes outstanding young researchers.

National Science Foundation: Andrea Alù makes small things invisible--and that could mean big things for technology

MXenes...

Add caption

Topics: Condensed Matter Physics, Green Energy, Green Tech, Materials Science, Metamaterials, Nanotechnology

Otherwise known as Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes), the title of the actual paper, and quoting the article (link below): "A technique for fusing different elements in layers to make a uniform and stable composite with predictable properties could open up routes to faster, smaller and more efficient energy storage devices, supercapacitors and wear-resistant and tough armored materials, according to a team at Drexel University in Philadelphia, Pennsylvania, USA. Babak Anasori and his colleagues at Drexel and Linköping University, Sweden, have demonstrated how to sandwich together two-dimensional sheets of molybdenum, titanium and carbon that would otherwise not stick together."

Abstract

The higher the chemical diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, density functional theory (DFT) is used to predict the existence of two new families of 2D ordered, carbides (MXenes), M′₂M″C₂ and M′₂M″₂C₃, where M′ and M″ are two different early transition metals. In these solids, M′ layers sandwich M″ carbide layers. By synthesizing Mo₂TiC₂T_x, Mo₂Ti₂C₃MT_x, and Cr₂TiC₂T_x (where T is a surface termination), we validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2D flakes’ chemical and electrochemical properties. The latter was proven by showing quite different electrochemical behavior of Mo₂TiC₂T_x and Ti₃C₂T_x. This work further expands the family of 2D materials, offering additional choices of structures, chemistries, and ultimately useful properties.

Materials Today: Metal sandwich solution, David Bradley

Dumbbells and Detection Techniques...

Figure 1: Nano-objects with varying curvatures, Nature

ARGONNE, Ill. – Like snowflakes, nanoparticles come in a wide variety of shapes and sizes. The geometry of a nanoparticle is often as influential as its chemical makeup in determining how it behaves, from its catalytic properties to its potential as a semiconductor component. 

Thanks to a new study from the U.S. Department of Energy’s (DOE) Argonne National Laboratory, researchers are closer to understanding the process by which nanoparticles made of more than one material – called heterostructured nanoparticles – form. This process, known as heterogeneous nucleation, is the same mechanism by which beads of condensation form on a windowpane.

Heterostructured nanoparticles can be used as catalysts and in advanced energy conversion and storage systems. Typically, these nanoparticles are created from tiny “seeds” of one material, on top of which another material is grown. In this study, the Argonne researchers noticed that the differences in the atomic arrangements of the two materials have a big impact on the shape of the resulting nanoparticle. [1]

ARGONNE, Ill. ― A team of researchers from the U.S. Department of Energy's Argonne National Laboratory and Ohio University have devised a powerful technique that simultaneously resolves the chemical characterization and topography of nanoscale materials down to the height of a single atom.

The technique combines synchrotron X-rays (SX) and scanning tunneling microscopy (STM). In experiments, the researchers used SX as a probe and a nanofabricated smart tip of a STM as a detector.

Using this technique, researchers detected the chemical fingerprint of individual nickel clusters on a copper surface at a two-nanometer (nm) lateral resolution, and at the ultimate single atom height sensitivity. By varying the photon energy, the researchers used the difference in photoabsorption cross sections for nickel and the copper substrate to chemically image a single-nickel nanocluster - thus opening the door to new opportunities for chemical imaging of nanoscale materials. Until now, a spatial limit of about only 10-nm was attainable, and the researchers would simultaneously sample a large sample area. The researchers have improved the spatial resolution to 2 nm. [2]

Argonne National Laboratories:
1. Atomic 'mismatch' creates nano 'dumbbells', Jared Sagoff
2. Powerful new technique simultaneously determines nanomaterials' chemical makeup, topography, Angela Hardin

3D Topological Insulator...

Purdue University's Yang Xu inspects devices made from topological insulators under a microscope before electrical measurements are made on the samples. (Courtesy: Purdue University/Ting-fung Chung)

Researchers in the US say that they have made the best 3D topological insulator to date. The material is called bismuth antimony tellurium selenide (BiSbTeSe2) and could be of fundamental importance for testing a number of condensed-matter and particle-physics theories. The material could also find use in spintronics devices and be used to build robust topological quantum bits (qubits) for quantum computers.

Topological insulators are materials that are electrical insulators in the bulk but can conduct electricity on their surface via special surface electronic states. "Most topological insulators made to date have not been completely insulating in the bulk, because of impurities (unintentionally introduced during material synthesis or processing) that doped the bulk and made it conducting," explains Yong Chen of Purdue University, who led the research. "Our topological insulator appears not to conduct at all in the bulk but does so only at its surface."

The researchers worked this out by measuring how thin flakes of BiSbTeSe2 of various thicknesses conducted electricity. They found that the conductance of different samples was almost independent of their thicknesses. Such behaviour is completely different to that seen in normal 3D materials, in which conductance is proportional to sample thickness.

Physics World: New 3D topological insulator is the nearest to perfection yet
#P4TC: Hopping To Open Bandgap