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Houston scientist Dr. Paul Chu upends the physics world

July 24, 2016
Houston scientist Dr. Paul Chu upends the physics world

Thousands of scientists crammed the hallways of the Hilton Hotel in New York, jockeying for a seat inside the ballroom. Televisions were set up for the unlucky who couldn't squeeze inside for the event, which would later be dubbed the "Woodstock of Physics."

For more information, read the original news release.

New Superconducting Coil Improves MRI Performance

July 20, 2016
New Superconducting Coil Improves MRI Performance

A multidisciplinary research team led by University of Houston scientist Jarek Wosik has developed a high-temperature superconducting coil that allows magnetic resonance imaging (MRI) scanners to produce higher resolution images or acquire images in a shorter time than when using conventional coils.

Wosik, a principal investigator at the Texas Center for Superconductivity at UH, said test results show the new technology can reveal brain structures that aren't easily visualized with conventional MRI coils. He also is a research professor in the UH Department of Electrical and Computer Engineering.

The cryo-coil works by boosting the signal-to-noise ratio (SNR) - a measure of the strength of signals carrying useful information - by a factor of two to three, compared with conventional coils. SNR is critical to the successful implementation of high resolution and fast imaging.

Wosik said the cryo-coil reveals more details than a conventional coil because of its enhanced SNR profile. Where a conventional coil does not have enough sensitivity to "see," a superconducting coil can still reveal details. These details will remain hidden to conventional coils even when image acquisition is repeated endlessly.

For the initial tests, the probe was optimized for rat brain imaging, useful for biomedical research involving neurological disorders. But it also has direct implications for human health care, Wosik said.

"Research in animal models yields critical information to improve diagnosis and treatment of human diseases and disorders," he said. "This work also has the potential to clearly benefit clinical MRI, both through high quality imaging and through shortening the time patients are in the scanner."

Results from preliminary testing of the 7 Tesla MRI Cryo-probe were presented at the International Symposium of Magnetic Resonance in Medicine annual meeting in May. The coil can be optimized for experiments on living animals or brain tissue samples, and researchers said they demonstrated an isotropic resolution of 34 micron in rat brain imaging. In addition to its use in MRI coils, superconductivity lies at the heart of MRI scanning systems, as most high-field magnets are based on superconducting wire.

In addition to Wosik, collaborators on the project include Ponnada A. Narayana, director of the Magnetic Resonance Imaging Center and a professor in the Department of Diagnostic and Interventional Imaging at the University of Texas Health Science Center at Houston; Kurt H. Bockhorst, senior research scientist at UT Houston; Kuang Qin, a graduate student working with Wosik; and I-Chih Tan, assistant professor in the Department of Neuroscience at Baylor College of Medicine.

Compared to corresponding standard room temperature MRI coils, the performance of the cooled normal metal and/or the high-temperature superconducting receiver coils lead either to an increase in imaging resolution and its quality, or to a very significant reduction in total scan time," Wosik said.

For more information, read the original news release.

UH Physicist Joins Project to Develop New High Thermal Conducting Material

July 19, 2016
UH Physicist Joins Project to Develop New High Thermal Conducting Material

A University of Houston physicist will participate in a $7.5 million collaboration to develop a new material with thermal conductivity higher than that of diamonds.

The work, funded by the U.S. Navy's Multidisciplinary University Research Initiative, involves researchers from around the country, working to create an effective and affordable thermal conductor of boron arsenide.

Zhifeng Ren, MD Anderson Professor of physics at UH, said previous research predicted that boron arsenide would perform better than diamond as a thermal conductor. A thermal conductor allows energy, in the form of heat, to be transferred within the material; electronic devices require high thermal conductors in order to avoid overheating.

Ren will receive $1.3 million to study the material in single crystals or thin film.

The project is led by Li Shi, professor of mechanical engineering at the University of Texas at Austin. Other participating universities include Boston College, the Massachusetts Institute of Technology, the University of Illinois at Urbana-Champagne, and the University of California at Los Angeles.

Shi noted that Ren's research group has reported the first thermal conductivity measurement of boron arsenide. "They have proposed novel methods to grow this and other potentially ultrahigh thermal conductivity materials," he said. "Their efforts are instrumental for the success of this multidisciplinary project."

Diamond is considered one of the best thermal conductors at room temperature, with thermal conductivity of more than 2,000 watts per meter per Kelvin. That's five times higher than copper.

But it's expensive, and Ren said researchers hope to prove a theory developed by Boston College physicist David Broido that cubic boron arsenide could deliver thermal conductivity on par with the industry standard set by diamond, potentially allowing for improved high tech cooling applications.

Ren's lab began experimenting with the compound last year, making a single crystal of the material. The crystal had defects but reached thermal conductivity of 200 watts/meter/Kelvin, about 10 percent of what Broido predicted, he said.

It indicated they were on the right track, however. "This was very preliminary work, so there is hope that this material can have very high thermal conductivity," he said. "If we are successful, it would be a big improvement for high-powered electronics."

Making the material is difficult, as boron has a high melting point - almost 2,075 degrees Centigrade, or 3,767 degrees Farenheit - while arsenic vaporizes between 400 degrees and 500 degrees C. Beyond those complications, Ren's group will have to produce a crystal between 10 and 100 times larger than that created last year - or about one millimeter - in order to accurately measure the results.

"We have to demonstrate we can make bigger crystals, and that the crystals have thermal conducting properties that are truly high," he said.

For more information, read the original news release.

UH Researchers Discover Key Mechanism for Producing Solar Cells

July 18, 2016
UH Researchers Discover Key Mechanism for Producing Solar Cells

Researchers from the University of Houston have reported the first explanation for how a class of materials changes during production to more efficiently absorb light, a critical step toward the large-scale manufacture of better and less-expensive solar panels.

The work, published this month as the cover story for Nanoscale, offers a mechanism study of how a perovskite thin film changes its microscopic structure upon gentle heating, said Yan Yao, assistant professor of electrical and computer engineering and lead author on the paper. This information is crucial for designing a manufacturing process that can consistently produce high-efficiency solar panels.

Last year Yao and other researchers identified the crystal structure of the non-stoichiometric intermediate phase as the key element for high-efficiency perovskite solar cells. But what happened during the later thermal annealing step remained unclear. The work is fundamental science, Yao said, but critical for processing more efficient solar cells.

“Otherwise, it’s like a black box,” he said. “We know certain processing conditions are important, but we don’t know why.”

Other researchers involved with the project include first author Yaoguang Rong, previously a postdoctoral fellow at UH and now associate professor at Huazhong University of Science and Technology in China; UH postdoctoral fellows Swaminathan Venkatesan and Yanan Wang; Jiming Bao, associate professor of electrical and computer engineering at UH; Rui Guo and Wenzhi Li of Florida International University, and Zhiyong Fan of Hong Kong University of Science and Technology.

Yao is also a principal investigator at the Texas Center for Superconductivity at UH, which provided funding for the work.

The work also yielded a surprise: the materials showed a peak efficiency – the rate at which the material converted light to electricity – before the intermediate phase transformation was complete, suggesting a new way to produce the films to ensure maximum efficiency. Yao said researchers would have expected the highest efficiency to come after the material had been converted to 100 percent perovskite film. Instead, they discovered the best-performing solar devices were those for which conversion was stopped at 18 percent of the intermediate phase, before full conversion.

“We found that the phase composition and morphology of solvent engineered perovskite films are strongly dependent on the processing conditions and can significantly influence photovoltaic performance,” the researchers wrote. “The strong dependence on processing conditions is attributed to the molecular exchange kinetics between organic halide molecules and DMSO (dimethyl sulfoxide) coordinated in the intermediate phase.”

Perovskite compounds commonly are comprised of a hybrid organic-inorganic lead or tin halide-based material and have been pursued as potential materials for solar cells for several years. Yao said their advantages include the fact that the materials can work as very thin films – about 300 nanometers, compared with between 200 and 300 micrometers for silicon wafers, the most commonly used material for solar cells. Perovskite solar cells also can be produced by solution processing at temperatures below 150 degrees Centigrade (about 300 degrees Fahrenheit) making them relatively inexpensive to produce.

At their best, perovskite solar cells have an efficiency rate of about 22 percent, slightly lower than that of silicon (25 percent). But the cost of silicon solar cells is also dropping dramatically, and perovskite cells are unstable in air, quickly losing efficiency. They also usually contain lead, a toxin.

Still, Yao said, the materials hold great promise for the solar industry, even if they are unlikely to replace silicon entirely. Instead, he said, they could be used in conjunction with silicon, boosting efficiency to 30 percent or so.

For more information, read the original news release.

UH Engineers Make Journal Cover With Flexible LED Theoretical Study

April 20, 2016
UH Engineers Make Journal Cover With Flexible LED Theoretical Study

The March 2016 cover of ACS Photonics features a theoretical study authored by Cullen College engineers Jae-Hyun Ryou, assistant professor of mechanical engineering, and Shahab Shervin, a materials science and engineering doctoral student.

The study, titled “Bendable III-N Visible Light-Emitting Diodes Beyond Mechanical Flexibility,” explored the potential for low cost, flexible and color changing light-emitting diodes, or LEDs. Ryou and Shervin’s co-authors included Cullen College doctoral student Mojtaba Asadirad, Seung-Hwan Kim from the Metamaterial Electronic Device Research Center at Hongik University, S. Yu. Karpov of STR Group, and Daria Zimina of STR US, Inc.

LEDs are energy efficient light sources with a wide array of potential applications. LEDs convert electrical current to light approximately 10 times more efficiently than incandescent lamps and approximately two to three times more efficiently than fluorescent lamps. By converting electrical current more efficiently, they offer the potential to reduce green house gas emissions from electricity use.

In recent years, LEDs have become more prevalent in households, automobiles and even large-scale stadium displays. Yet, they are still less commonly used than incandescent and fluorescent light sources.

One of the major barriers to market penetration and widespread household use is the relatively high cost of LED bulbs compared to cheaper traditional light bulbs, said Ryou. LEDs cost more to purchase because they are more expensive to mass-produce. The substrate currently used for LED production is not only higher-priced than its traditional counterparts, but it can only be used in relatively small quantities, further driving up the costs of large-scale manufacturing.

“We need a cheaper option,” said Ryou.

Shervin, who served as first author on the study, researches the potential for flexible LEDs on inorganic material to reduce mass-production costs and increase reliability and efficiency. He said that the theoretical ability to create color-changing LEDs was an unexpected and surprising bonus.

“Through our calculations, we’ve shown that bending or applying strain to an LED structure can improve its efficiency,” he said. “We also demonstrated that bending an LED structure can cause it to emit different colors of light [without changing the composition.]”

Current LED technology uses phosphorous, which is a non-environmentally friendly material, to produce white light emission. Ryou and Shervin achieved white light emission without the use of phosphorous by combining green, red and blue light emissions from a single flexible LED. The researchers said they hope their study promotes the use of eco-friendly alternative materials.

Shervin said he envisions future roll-to-roll LED fabrication using amorphous or polymorphous substrates, enabling cost-efficient mass production.

“We are taking a totally new approach [to LED manufacturing]” said Ryou. With this research, he and Shervin hope to provide the foundation for future LED technology and contribute to its increased everyday use.

“[Being featured on the journal cover] is motivating. We have a lot of work ahead, but it’s exciting to have our efforts recognized with this work on the cover,” Shervin said.

“I’ve always been interested in energy-related research and the University of Houston offers a huge sea of research opportunities,” he added.

ACS Photonics is a monthly journal dedicated to research articles, letters, perspectives, and reviews, encompassing the full scope of published research in the photonics field.

View the article in ACS Photonics online.


For more information, read the original news release.

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