From North Carolina State University, January 25, 2011, by Matt Shipman: "Light-emitting diodes (LEDs) are an increasingly popular technology for use in energy-efficient lighting. Researchers from North Carolina State University have now developed a new technique that reduces defects in the gallium nitride (GaN) films used to create LEDs, making them more efficient.

LED lighting relies on GaN thin films to create the diode structure that produces light. The new technique reduces the number of defects in those films by two to three orders of magnitude. "This improves the quality of the material that emits light," says Dr. Salah Bedair, a professor of electrical and computer engineering at NC State and co-author, with NC State materials science professor Nadia El-Masry, of a paper describing the research. "So, for a given input of electrical power, the output of light can be increased by a factor of two - which is very big." This is particularly true for low electrical power input and for LEDs emitting in the ultraviolet range.

The researchers started with a GaN film that was two microns, or two millionths of a meter, thick and embedded half of that thickness with large voids - empty spaces that were one to two microns long and 0.25 microns in diameter. The researchers found that defects in the film were drawn to the voids and became trapped - leaving the portions of the film above the voids with far fewer defects.

Source: Click on the link to read the entire article:

North Carolina State University Newsroom: http://news.ncsu.edu/releases/wmsbedairganvoids/ 

Nanopatterned Metallic Films Make Wavelength-Tunable Lenses

From SPIE Newsroom, January 7, 2011, by Danhong Huang, et al.: "There is considerable current interest in shaping the spatial dependence of the intensity of light transmitted through a metal film pierced by a 1D array of slits with subwavelength widths. Particular attention has been paid to the use of such structures as metallic nanoscale lenses. In contrast to conventional dielectric refractive lenses, whose focusing ability degrades as their dimensions decrease to the operational wavelength level, nanoscale slit lenses retain their focusing ability in this limit. Because of their planar geometries, they are simpler to fabricate at these dimensions than dielectric lenses, and use of metal rather than a dielectric provides a higher index contrast that leads to a stronger focusing capability. Finally, they focus light in the far rather than the near field, unlike, e.g., perfect (negative-index metamaterial) lenses.

 However, it is not necessary to have slits that completely pierce the metallic film to achieve such focusing. A suitable modulation of the film thickness can produce the same effect. We have demonstrated this by calculating numerically the spatial distribution of the intensity of light transmitted through a metal film with surfaces modeled by two aligned, reversed arrays of nanogrooves of finite depth, sandwiched between vacuum and a dielectric substrate."

Source: Click the link to read the full paper:

SPIE.org: http://spie.org/x43641.xml?ArticleID=x43641  

Image: Danhong Huang and SPIE.org

From SPIE Newsroom, January 7, 2011, by Zetian Mi,
et al.:  "Recently, indium nitride (InN) nanowires have emerged as a promising candidate for a range of nanoscale electronic, photonic, and biochemical devices. Extensive studies have shown that they exhibit a small direct energy bandgap (∼0.6-0.7eV), high electron mobility, and small electron effective mass. However, application devices require precise control of the charge properties of InN nanostructures. The currently reported InN nanowires and films are generally n-type degenerate with a residual doping of ∼1�10¹⁸cm⁻³ or higher. The uncontrollable electron density has made it extremely difficult to achieve p-type doping and to accurately determine many fundamental properties of InN, thereby severely limiting practical device applications. We have succeeded in growing, for the first time, nearly intrinsic (that is, undoped, or extremely pure) InN. In addition, we have experimentally demonstrated InN nanowire solar cells, opening up exciting possibilities for indium gallium nitride (InGaN) nanowire-based, full-solar-spectrum, third-generation solar cells.

Conventional InN nanowires grown on silicon (Si) generally exhibit a tapered morphology, with the presence of large densities of dislocations and stacking faults due to the uncontrolled wire nucleation associated with spontaneous growth, as well as the formation of an amorphous silicon nitride (SiN_x) layer at the InN/Si heterointerface. In our approach, we first deposited a thin (∼0.5nm) In layer on the substrate surface before introducing any nitrogen species, which forms nanoscale In liquid droplets at elevated temperatures and can promote the nucleation and growth of vertically aligned InN nanowires. The wires are remarkably straight, with identical top and bottom sizes, compared to any previously reported InN nanowires. Detailed transmission electron microscopy studies further confirm that the wires are nearly free of dislocations and stacking faults.

Source: Click the link to read the full paper:

SPIE.org: http://spie.org/x43643.xml?highlight=x2400&ArticleID=x43643 

Image: Zetian Mi and SPIE

From Leibniz Institute for New Materials (INM), saarbruken, Germany, January 26, 2011:  "Designing metal structures with a memory is the work of the Leibniz Institute for New Materials  junior research group "Metallic Microstructures".  Researchers, led by Dr. Andreas Schneider, are investigating how to train structured surfaces to switch their special properties on and off.

"This can be achieved with a suitable combination of heat treatment and deformation." Then the material memorizes the shape at a higher and lower temperature. This two-way memory effect allows for making the surface structures switchable via temperature. Thus, for example, friction and adhesion on surfaces can be specifically switched on and off."

"The group's second focus of research is based on microstructures that influence the strength of a metal surface. "We recognize that a metal is the stronger the smaller the structures on the surface are made. Many thin pillars bear a temple roof better than a few thick pillars", explains the junior researcher. The research group studies which influences lead to this effect."

"The scientists produce the microstructures among other things with a scanning ion microscope, removing minutest amounts of metal in layers from the surface. At the end, micropillars with a fixed diameter and a fixed height protrude from the metal. With a stamp, which presses from above onto the pillars, the scientists test the forces which the pillars withstand, before they cave in."

Source: Click on the link to read the entire article:

Leibniz Institute for New Materials (INM): http://www.inm-gmbh.de/2011/01/memory-training-for-metalstructures/ 

Image: Leibniz Institute for New Materials (INM)

From AZO Nanotechnology, March 31, 2011, by Cameron Chai: "A team of researchers at the U.S. Department of Energy's Brookhaven National Laboratory have found that thin molecular films continue to be in a frozen state at a temperature where the bulk material is in the molten state.

These molecules in thin films are deployed in several applications like organic solar cells and biosensors and perceiving the basic features of these molecular films could bring about enhanced devices.

The research was published in Physical Review Letters' April edition and the researchers directly perceived 'surface freezing' phenomenon at the hidden layer between solid surfaces and heavy liquids.

Ben Ocko, Physicist at Brookhaven, worked with researchers from France-based European Synchrotron Radiation Facility (ESRF) and Israel-based Bar-Ilan University. He has stated that the surface of most of the materials will begin to disarray and ultimately melt at a particular temperature where the bulk material remains to be in a solid state. Because outer molecules are less constricted than those molecules that are filled in the inner layers and they can easily travel around. He added that in surface freezing, the interface layers freeze before the bulk material."

Source:  

AZO Nanotechnology: www.azonano.com: http://www.azonano.com/news.asp?newsID=22090 

From EETimes.com:  The EE times has put together the most up-to-date information available about the status of chip fabs and other facilities that have been impacted by damage to structures, equipment and infrastructure stemming from the March 11 earthquake and tsunami in Japan. Listed are chip makers, alphabetically by company, with pages detailing the status of equipment and materials suppliers, consumer electronics companies and automakers, and test and measurement companies. Japan supplies about 60% of the world's electronic grade silicon. Japan is the fifth electronic supplier in the world with 63.3 $B in annual chip revenue according to IHS-ISuppli.

Read the latest updates at:

EETimes.com: http://www.eetimes.com/electronics-news/4214018/Japan-quake--Tracking-the-status-of-fabs-in-wake-of-disaster