NEWS FROM THE WORLD OF MATERIALS

Materials in Focus

First images of atomic spin captured 
(Ohio University)
In a new study, researchers present the first images of spin in action. They used a custom-built microscope with an iron-coated tip to manipulate cobalt atoms on a plate of manganese. Through scanning tunneling microscopy, the team repositioned individual cobalt atoms on a surface that changed the direction of the electrons' spin. Images captured showed that the atoms appeared as a single protrusion if the spin direction was upward, and as double protrusions with equal heights when the spin direction was downward. [Nature Nanotechnology]

Sign flips and spin fluctuations in iron high-Tc superconductors 
(Science)
In superconductors, the key process that allows current to travel without resistance is the formation of electron pairs that move as a single quantum state. The mechanism of pairing in the high-temperature (high-Tc) cuprate superconductors is still elusive, so the recent discovery of iron-based superconductors sparked the hope that comparison with the cuprates would lead to a better understanding of pairing in both materials. Researchers now report the experimental determination of the pairing symmetry in FeSe_xTe_1–x. Combined with the recent observation of a spin fluctuation resonance in this material similar to that seen in the cuprates, a compelling hypothesis has emerged that these high-Tc superconductors share a common pairing mechanism. [Science]

Smart sensors use VO₂ grown epitaxially on Si 
(North Carolina State University)
Researchers report vanadium oxide "smart sensors" integrated directly on a silicon chip. This was made possible by growing VO₂ thin films on Si using "domain matching epitaxy". They have explored the mechanisms of how such vanadium oxide sensors work in conjunction with the silicon chips to which they are attached, which yields the ability to improve the reliability of these smart sensors, and account for variable conditions the sensors may be exposed to. Specifically, they report the semiconductor to metal transition (SMT) characteristics of vanadium dioxide grown epitaxially on a Si (001) that is the basis of its sensing properties. [Appl. Phys. Lett.]

Trapped ions detect yoctonewtons force 
(Nature News)
By pushing a cluster of just 60 ions with a tiny electric field, researchers have measured the most minuscule force ever. The result, measuring mere yoctonewtons (10^–24 newtons), beats previous record lows by several orders of magnitude. Previously, researchers were able to successfully measure around an attonewton (10^–18 N) of force by giving small pushes to microscopic paddles or wires and then watching them vibrate. These systems work well, but are limited by factors such as their relatively large size. The new technique eschews the paddle-type systems in favor of just 60 beryllium-9 ions. [Arxiv]

Energy Focus

Fuel cell runs on water and air 
(Highlights in Chemical Technology)
A fuel cell that produces power using only water and a warm breeze has been developed by researchers.In the new cell, water is oxidized catalytically to molecular oxygen, protons and electrons at the anode, while the reverse reaction takes place at the cathode. As in normal fuel cells, the cathode and anode are separated by a polymer electrolyte membrane which allows the protons to cross to the cathode while the electrons are forced to make their way through a wire, creating a current. The water that forms at the cathode is evaporated by the air flow, keeping the water concentration gradient between the two electrodes, which acts as the driving force for the reaction. Unlike other fuel cells no change in enthalpy occurs as water reacts to form water. This means that typically minor contributions, such as changes in entropy, become key factors in the energy output. [Energy Environ. Sci.]

Nano Focus

Seeing Moiré in graphene 
(PhysOrg.com)
Researchers have demonstrated that atomic scale moiré patterns can be used to measure how sheets of graphene are stacked and reveal areas of strain. They created graphene on the surface of a silicon carbide substrate by heating one side so that only carbon, in the form of multilayer sheets of graphene, was left. Using a custom-built scanning tunneling microscope, they were able to peer through the topmost layers of graphene to the layers beneath. This process, which the group dubbed atomic moir interferometry, enabled them to image the patterns created by the stacked graphene layers, which in turn allowed the group to model how the hexagonal lattices of the individual graphene layers were stacked in relation to one another. [Physical Review B]

Measuring wettability with sub-nanometer resolution 
(Massachusetts Institute of Technology)
Wettability is crucial to a wide variety of processes. Until now, the only way to quantify this important characteristic of a material's surface has been to measure the shapes of the droplets that form on it, and this method has very limited resolution. But a team of researchers has found a way to obtain images using atomic force microscopy (AFM) that improves the resolution of such measurements by a factor of 10,000 or more, allowing for unprecedented precision in determining the details of the interactions between liquids and solid surfaces. In addition, the new method can be used to study curved, textured or complex solid surfaces, something that could not be done previously. [Nature Nanotechnology]

Nanosculptors could help focus light on silicon chips 
(New Scientist)

Credit: IBM

Researchers have sculpted a 1:180 billion scale model of the Matterhorn, the 4478-metre-tall Alpine peak on the Swiss-Italian border. The team carved the minute mountain using a technique they have developed for making high-density computer storage. They found they could evaporate material from a surface by heating a punching needle to 330 °C and using it as a kind of chisel. They carved their microscopic Matterhorn from a glassy organic material whose molecules are held together by hydrogen bonds, forces of attraction between partially positive hydrogen ions in one molecule and electron-rich oxygen ions in another. [Science]

Atomic force microscopy of cells using a nanowire cantilever 
(Lawrence Berkeley National Lab)
The core of AFM imaging is a cantilever with a sharp tip that deflects as it encounters undulations across a surface. Due to a minimum force required for imaging, conventional AFM cantilevers can deform or even tear apart living cells and other biological materials. Scientists have now developed nanowire cantilevers whose gentle touch could help discern the workings of living cells and other soft materials in their natural, liquid environment. Used in combination with a new detection mechanism, this new imaging tool is sensitive enough to investigate soft materials without the limitations present in other cantilevers. [Phys. Rev. Lett.]

Bio Focus

Nanoparticles protect bone marrow during radiation cancer therapy 
(Albert Einstein College of Medicine of Yeshiva University)
Melanin-covered nanoparticles could protect bone marrow from the harmful effects of radiation therapy. Radiation therapy is used to kill cancer cells and shrink tumors. But because radiation also damages normal cells, doctors must limit the dose. Melanin, the naturally occurring pigment that gives skin and hair its color, helps shield the skin from the damaging effects of sunlight and has been shown to protect against radiation. Researchers created "melanin nanoparticles" by coating 20 nanometers diameter silica particles with several layers of melanin pigment that they synthesized in their laboratory. The researchers found that these particles successfully lodged in bone marrow after being injected into mice. Then, in a series of experiments, they investigated whether their nanoparticles would protect the bone marrow of mice treated with two types of radiation. [International Journal of Radiation Oncology*Biology*Physics]

Image in Focus 

  

Nano PacMan made of copper oxide
Scanning electron microscope image of a copper oxide cluster, 3.5 microns in diameter, prepared by evaporation and condensation over an alumina substrate. The smiley nose and eye are present in the original SEM image, which has only been color-enhanced.
Credit: Elisabetta Comini, University of Brescia, Italy

(One of three First Place winners of the Science as Art competition at the 2010 MRS Spring Meeting)

[We invite you to submit your images to the Editor for possible inclusion in this feature]

Industry Focus

Process Advances to Accelerate 3D Manufacturing Readiness Reported at MRS Spring Meeting
With a focus on providing cost-effective and reliable solutions to speed manufacturing readiness of 3D technology options, experts from SEMATECH's 3D interconnect program based at the College of Nanoscale Science and Engineering's (CNSE) Albany NanoTech Complex outlined new developments in wafer bonding, copper removal, and wafer thinning at the 2010 Materials Research Society (MRS) Spring Meeting on April 5-9 in San Francisco, CA. 3D integration offers the promise of higher performance, higher density, higher functionality, smaller form factor, and potential cost reduction. In this emerging field, new and improved technologies and integration schemes will be necessary to realize 3D's potential as a manufacturable and affordable path to sustaining semiconductor productivity growth. At the MRS Meeting, SEMATECH researchers described several practical 3D integration achievements – applicable across various 3D processes – in areas such as high-aspect ratio TSVs, wafer bonding, and thinning of interconnect test structures.

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