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July 30th, 2012

Other materials science stories that may be of interest

Published on July 30th, 2012 | Edited by: Peter Wray

An artist’s representation of the proposed on-chip laser design, created via transfer printing of photonic crystal between layers of silicon nanomembrane. Credit: Hongjun Yang.

 

Check ‘em out:

Printed photonic crystal mirrors shrink on-chip lasers down to size

Electrical engineers at the University of Wisconsin-Madison and the University of Texas at Arlington have devised a new laser for on-chip optical connections that could give computers a huge boost in speed and energy efficiency. At just 2 micrometers in height-smaller than the width of a human hair – the surface-emitting laser’s vastly lower profile could make it cheaper and easier for manufacturers to integrate high-speed optical data connections into the microprocessors powering the next generation of computers. But since mirrors are hard to form in such lasers and because the lasers occupy a large chip area, researchers have been challenged to find a practical way to monolithically integrate the mirrors on silicon chips. Surface-emitting lasers necessary for a high-speed optical links between computer cores could be 20 to 30 micrometers tall. Yet the research team’s engineers say that on a 1.5-micrometer wavelength optically connected chip, lasers of that size dwarf their silicon surroundings. As a solution, the researchers propose replacing layers and layers of reflectors necessary in the traditional distributed Bragg reflector laser design with two highly reflective photonic crystal mirrors. Composed of compound semiconductor quantum well materials, each mirror is held in place with silicon nanomembranes, extremely thin layers of a silicon.

NIST measurement advance could speed innovation in solar devices

(NIST Tech Beat) A new versatile measurement system devised by researchers at the National Institute of Standards and Technology (NIST) accurately and quickly measures the electric power output of solar energy devices, capabilities useful to researchers and manufacturers working to develop and make next-generation solar energy cells. As reported in the journal Applied Optics, the NIST team has combined 32 LEDs-each generating light from different segments of the solar spectrum-and other off-the-shelf equipment with their custom-made technologies to build a system that measures the wavelength-dependent quantum efficiency of solar devices over a relatively large area. Anticipated advantages over current approaches,most of which use incandescent lamps or xenon arc and other types of discharge lamps, are greater speed and ease of operation, more uniform illumination, and a service life that is about 10 times longer. The new NIST system for measuring spectral response easily accommodates two unique but complementary methods for determining how much electric current a solar device generates when hit by a standard amount of sunlight. Both methods are straightforward, and they use the same hardware setup. With either method, the automated system produces measurements more rapidly than current instruments used to simulate solar radiation and characterize how efficiently a device converts light energy to electric energy.

Room temperature femtosecond X-ray diffraction of photosystem II microcrystals

(PNAS) Most of the dioxygen on earth is generated by the oxidation of water by photosystem II (PS II) using light from the sun. This light-driven, four-photon reaction is catalyzed by the Mn4CaO5 cluster located at the lumenal side of PS II. Various X-ray studies have been carried out at cryogenic temperatures to understand the intermediate steps involved in the water oxidation mechanism. However, the necessity for collecting data at room temperature, especially for studying the transient steps during the O-O bond formation, requires the development of new methodologies. In this paper we report room temperature X-ray diffraction data of PS II microcrystals obtained using ultrashort (< 50 fs) 9 keV X-ray pulses from a hard X-ray free electron laser, namely the Linac Coherent Light Source. The results presented here demonstrate that the “probe before destroy” approach using an X-ray free electron laser works even for the highly-sensitive Mn4CaO5 cluster in PS II at room temperature. We show that these data are comparable to those obtained in synchrotron radiation studies as seen by the similarities in the overall structure of the helices, the protein subunits and the location of the various cofactors. This work is, therefore, an important step toward future studies for resolving the structure of the Mn4CaO5 cluster without any damage at room temperature, and of the reaction intermediates of PS II during O-O bond formation.

UCLA researchers create highly transparent solar cells for windows that generate electricity

UCLA researchers have developed a new transparent solar cell that is an advance toward giving windows in homes and other buildings the ability to generate electricity while still allowing people to see outside. The team describes a new kind of polymer solar cell that produces energy by absorbing mainly infrared light, not visible light, making the cells nearly 70 percent transparent to the human eye. They made the device from a photoactive plastic that converts infrared light into an electrical current. The solar cells incorporate a near-infrared light-sensitive polymer and use silver nanowire composite films as the top transparent electrode. The near-infrared photoactive polymer absorbs more near-infrared light but is less sensitive to visible light, balancing solar cell performance and transparency in the visible wavelength region. Another breakthrough is the transparent conductor made of a mixture of silver nanowire and titanium dioxide nanoparticles, which was able to replace the opaque metal electrode used in the past. This composite electrode also allows the solar cells to be fabricated economically by solution processing. With this combination, 4% power-conversion efficiency for solution-processed and visibly transparent polymer solar cells has been achieved.

Women soldiers to test female-specific body armor

The Program Executive Office realized through its multiple studies that the typical torso length for women was for the most part shorter than that of men. The female Improved Outer Tactical Vest will be shorter at the bottom. The new design will keep the IOTV from rubbing on the hips, which can cause chafing while walking. Female Soldiers had also advised PEO Soldier that the standard IOTV, with its longer torso, causes the front armor plate to press into their thighs when they are seated. This cuts off blood flow to their legs. The female version of the IOTV, with its shortened torso, will address this issue. Additionally, a new exterior plate pocket will allow the armor plate to be inserted from the side in a more diagonal fashion. Though not part of the female version of the IOTV design, the Army is also looking for ways to develop armor plating that better conforms to the human body. “The challenge right now is that when you bring in those complex curvatures, the plate loses some of its strength,” Lt. Col. Frank J. Lozano, the product manager for Soldier Protective Equipment. “We’re working with some armor manufacturers to invest in a manufacturing capability that finds the right chemistry to develop the soft and hard armor necessary to have a complex curved plate at a light weight that still defeats the threats.”

Archaeologists uncover Palaeolithic ceramic art

Evidence of a community of prehistoric artists and craftspeople who “invented” ceramics during the last Ice Age—thousands of years before pottery became commonplace—has been found in modern-day Croatia. The finds consist of 36 fragments, most of them apparently the broken-off remnants of modelled animals, and come from a site called Vela Spila on the Adriatic coast. Archaeologists believe that they were the products of an artistic culture which sprang up in the region about 17,500 years ago. Their ceramic art flourished for about 2,500 years, but then disappeared. The study, which is published in the journal PLoS ONE, adds to a rapidly-changing set of views about when humans first developed the ability to make ceramics and pottery. Most histories of the technology begin with the more settled cultures of the Neolithic era, which began about 10,000 years ago. Now it is becoming clear that the story was much more complex. Over thousands of years, ceramics were invented, lost, reinvented and lost again. The earliest producers did not make crockery, but seem to have had more artistic inclinations.

Bio-Retina to enter clinical trials in 2013

(GizMag) Nano Retina has now developed the Bio-Retina, a tiny (3 x 4 mm) microchip implant that is inserted into the eye and glued to the retina in a minimally invasive procedure. It does not treat age-related macular degeneration, but rather seeks to relieve the blindness resulting from AMD. A small slit is cut in the eye under local anesthesia, and the implant is inserted and pressed against the damaged macula. The Bio-Retina uses the optical system (lens, iris, and pointing and focusing musculature) of the eye. It consists of an integrated circuit with a grid of photodetectors, microelectrodes and microelectronic circuitry that replace the eye’s natural photoreceptors and feed visual information through the healthy retinal structures to the optic nerve and the visual centers of the brain. The patient does not have to learn to interpret jumbled images, as the photodetectors measure the incoming light in a particular location on the image, and then stimulate the optical neurons immediately below the spot where the light would have hit in any case. In most cases immediate, normal feeling sight will be returned to the patient. The image is only in grayscale at this point, but color implants are not beyond the reach of this basic technology.

Scientists create artificial mother of pearl

Mimicking the way mother of pearl is created in nature, scientists have for the first time synthesised the strong, iridescent coating found on the inside of some molluscs. By recreating the biological steps that form nacre in molluscs, the scientists were able to manufacture a material which has a similar structure, mechanical behaviour, and optical appearance of that found in nature. In order to create the artificial nacre, the scientists followed three steps. First, they had to take preventative measure to ensure the calcium carbonate, which is the primary component of nacre, does not crystallise when precipitating from the solution. This is done by using a mixture of ions and organic components in the solution that mimics how molluscs control this. The precipitate can then be adsorbed to surfaces, forming layers of well-defined thickness. Next, the precipitate layer is covered by an organic layer that has 10-nm wide pores, which is done in a synthetic procedure. Finally, crystallisation is induced, and all steps are repeated to create a stack of alternating crystalline and organic layers.


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