NEWS FROM THE WORLD OF MATERIALS

Materials in Focus

Redefining electrical current law with the transistor laser 
(University of Illinois)
With the transistor laser, researchers can explore the behavior of photons, electrons and semiconductors. However, harnessing these capabilities hinges on a clear understanding of the physics of the device, and data the transistor laser generated did not fit neatly within established circuit laws governing electrical currents. Kirchhoff's current law states charge input at a node is equal to the charge output. In other words, all the electrical energy going in must go out again. On a basic bipolar transistor, with ports for electrical input and output, the law applies straightforwardly. The transistor laser adds a third port for optical output, emitting light. The unique properties of the transistor laser required researchers of the present study to re-examine and modify the law to account for photon particles as well as electrons, effectively expanding it from a current law to a current-energy law. Simulations based on the modified law accurately fit data collected from the transistor laser. [J. Appl. Phys]

Cleaning AFM probe tip using a grating brush 
(Ultramicroscopy)
Cleaning of atomic force microscope (AFM) tips is crucial for reliable AFM imaging and force measurements. Researchers have now demonstrated that a brush, a calibration grating with supersharp spikes, can be used to mechanically scrub away contaminants by scanning the probe against the spikes at high load at constant-force mode. This allows for removal of organic/inorganic material in a non-destructive and highly efficient manner. In addition, contamination removal and probe study can be completed in a single step. Also, colloidal/particle probes as well as standard AFM tips can be cleaned by thus method. [Ultramicroscopy]

Energy Focus

Nanoholes promise solar power 
(Chemistry World)
Silicon solar cells with arrays of nano-sized holes could outperform their nanowire-based rivals, according to a new study. Nanohole arrays are less fragile and more efficient than nanowires, and can be manufactured using conventional techniques. Nanohole arrays can absorb light even better than nanowire arrays - light that enters the holes will bounce around inside until it is absorbed. In nanowire cells, light is scattered and bounces between nanowires, but the holes seem to do a better job of capturing scattered photons, which increases their energy conversion efficiency. Because the nanohole array is much less fragile than a forest of nanowires, it is also less susceptible to problems associated with broken nanowires, such as recombination of the electrons and positively charged 'holes' that carry current through the device, which boosts the cell's efficiency. [J. Am. Chem. Soc.]

Better platinum catalyst for fuel cells 
(Technology Review)
A new type of catalyst could lead to fuel cells that use a fifth of the platinum they use now. The new material consists of nanoparticles with cores made of a copper-platinum alloy and an outer shell that is mostly platinum. The material is up to five times as efficient as regular platinum. Researchers have revealed the mechanism that makes this catalyst more active than regular platinum. Using x-ray scattering, they discovered that the distance between the platinum atoms that are left on the surface of the nanoparticles is less than the distance in pure platinum nanoparticles. [Nature Chemistry]

Nano Focus

Molecular robots on the rise 
(National Science Foundation)
Recent molecular robotics work has produced so-called DNA walkers, or strings of reprogrammed DNA with 'legs' that enabled them to briefly walk. Now a research team has shown these molecular robotic spiders can in fact move autonomously through a specially-created, two-dimensional landscape. The spiders acted in rudimentary robotic ways, showing they are capable of starting motion, walking for awhile, turning, and stopping. In addition to be incredibly small--about 4 nanometers in diameter--the walkers are also move slowly, covering 100 nanometers in times ranging 30 minutes to a full hour by taking approximately 100 steps. [Nature]

Nanocomposites get in shape 
(Highlights in Chemical Technology)
A material that rapidly heats up and changes shape when connected to a battery has been developed. Researchers blended an electrically conductive network of carbon nanofibers with a shape memory polymer (SMP) - a material that changes from a deformed shape to its original shape induced by a trigger such as a change in temperature. The network of nanofibers enabled the material to heat up very quickly, triggering a change in motion (actuation). [Soft Matter]

Bio Focus

DNA could be backbone of next generation logic chips 
(PhysOrg.com)

In a recent set of experiments, researchers demonstrated that by simply mixing customized snippets of DNA and other molecules, they could create literally billions of identical, tiny, waffle-looking structures. These nanostructures will efficiently self-assemble, and when different light-sensitive molecules are added to the mixture, the waffles exhibit unique and "programmable" properties that can be readily tapped. Using light to excite these molecules, known as chromophores, simple logic gates, or switches, can be created. These nanostructures can then be used as the building blocks for a variety of applications, ranging from the biomedical to the computational. [Small]

Nanotube chip creates bioelectronic link 
(Chemistry World)
A protein coupled with a carbon nanotube has provided a previously unavailable direct biological-to-electronic interface, which its developers hope could lead to brain-controlled prosthetic devices. A group of scientists produced the interface by covering a nanotube in a lipid bilayer that contains ion transporter proteins. The end goal would be to use this kind of system to make a synthetic synaptic junction to transmit signals directly into muscles and tissues. While carbon nanotubes are the right size to integrate with biological molecules, they are usually very hostile to them. Active proteins, like the sodium/potassium ATPase 'biological machine' integrated in the transistor, have therefore not previously been used to control nanoelectronic devices.The scientists came up with the trick of wrapping the nanotube in a lipid bilayer to solve this. [Nano Letters]

Cryo-electron microscope images virus structure with 3.3 Å resolution 
(UCLA)
Researchers report that they have managed to image a virus structure with a resolution of 3.3 angstroms using a cryo-electron microscope. The study demonstrates the great potential of cryo-electron microscopy, or Cryo-EM, for producing extremely high-resolution images of biological samples in their native environment. The work focused on a structural study of the aquareovirus, a non-envelope virus that causes disease in fish and shellfish, in an effort to better understand how non-envelope viruses infect host cells. The group was able to determine that the aquareovirus employs a priming stage to accomplish cell infection. In its dormant state, the virus has a protective protein covering, which it sheds during priming. Once the outer shell has been shed, the virus is in a primed state and is ready to use a protein called an "insertion finger" to infect a cell. [Cell]

Image in Focus

  

ZnO Nanowire Arrays
SEM image of vertically aligned ZnO nanowire arrays with a standing human-like form. Color was added to the original image. Credit: Surawut Chuangchote, Kyoto University
(One of three First Place winners of the Science as Art competition at the 2010 MRS Spring Meeting)

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