HOUSTON - How does graphene affect the environment? Can polymer-based cells be a viable alternative to silicon solar cells? What are the optical qualities of a promising nanomaterial?
These are just a few of the questions five assistant professors at the University of Houston are trying to answer through individual research projects. Their outstanding - and potentially groundbreaking - work as researchers and educators has been recognized by the National Science Foundation (NSF), which recently honored each with a prestigious Faculty Early Career Development (CAREER) Award.
One of the most prestigious grants offered by the NSF, CAREER grants are awarded to promising junior faculty members to help them build their research programs and establish a track record of successful investigations.
NSF CAREER Award recipients "exemplify the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organizations," according to the NSF.
The five-year grants are awarded to tenure-track faculty members and each must integrate research with teaching.
The recent NSF CAREER Award recipients at UH are:
Jiming Bao, assistant professor of electrical and computer engineering. Joined UH in 2008. NSF Career Award valued at up to $400,000.
Bao is studying the optical properties of graphene, one-atom-thick sheets of carbon. He hopes to determine graphene's ability to act as a waveguide for surface plasmon, a collective excitation of the electronic "fluid" in a piece of conducting material.
Electromagnetic wave simulations have shown that graphene has the ability to act as an optical waveguide for surface plasmon, essentially serving as a pathway along which these electromagnetic waves can travel.
This property has not been well established through real-world experimentation. By creating sheets of graphene and then etching nano-scale features into the material, Bao aims to confirm its ability to conduct surface plasmon and characterize how well different types of graphene nanoribbons perform this task.
If Bao is able create and observe graphene with good optical waveguide properties, nano-ribbons of the material could serve as optical interconnects in electronic devices, improving their computing speed.
"If you want to send a message from one transistor to another, right now you have to use copper wire," Bao said. "That's a low-frequency electrical signal. Surface plasmon has a higher frequency. So, the bandwidth will increase a lot, making the information transmission rate much higher than copper."
Additionally, establishing the plasmon-related properties of the material could allow researchers to use it for molecular sensing, Bao said.
But Bao stressed that using graphene is dependent upon him achieving his first goal: confirming the ability of graphene to confine surface plasmon.
"This award represents a kind of recognition from the community of my recent work performed at UH, which includes a Science paper on plasmonics and a Nature Materials paper on graphene," Bao said.
Angela Moeller, assistant professor of chemistry. Joined UH in 2009. NSF Career Award valued at up to $473,071.
Moeller is a fundamental materials research scientist who focuses on finding and developing textbook examples that will allow scientists to understand the inherent properties and mechanisms at work in certain materials.
Moeller and her research group synthesize new materials, using a range of experimental techniques to characterize their properties at the atomic level. The goal is to gain an understanding of the fundamental structure-property relationships so materials can then be synthesized for cutting-edge sensors and microelectronics devices.
"I love my work, and I am naturally curious, taking delight in unexpected results and finding pleasure in unraveling hidden secrets. I also deeply enjoy guiding students so that they develop the skills needed to address challenging and important problems," Moeller said.
"The NSF CAREER grant represents an important validation of the work we are doing, confirming that we are addressing important problems at the forefront of materials research," Moeller said.
Moeller's research will undoubtedly contribute to the general pool of scientific knowledge, which will define the various features of a material that may be tunable or perhaps reveal a predictable property that will facilitate its utilization in an application.
Specifically, Moeller and her research group are dealing with a rare class of ferromagnetic insulators they can tune into "frustrated" anti-ferromagnets. With regard to applications, the phenomenological and theoretical description may allow them to establish new multiferroic systems that are needed for sensors and energy conversion in next-generation devices.
Debora Rodrigues, assistant professor of civil and environmental engineering. Joined UH in 2010. NSF Career Award valued at up to $449,967.
Rodrigues is studying the environmental impact of nano-scale materials that use graphene, single-thick sheets of carbon. Graphene is one of the most promising nanomaterials in existence.
"The nanotechnology industry is growing exponentially. They're finding so many new applications. We need to be careful about what we are producing and releasing to the environment," Rodrigues said.
One of Rodrigues' goals is to determine if and how these nanomaterials impact bacteria that are essential to the treatment of wastewater. She also is developing technologies that use graphene and other nanoparticles.
Rodrigues plans to combine this experimental work with efforts to educate high school science teachers on nanotechnology. She is a co-principal investigator on a NSF Research Experience for Teachers grant that will bring into several laboratories, including hers, during summer breaks to participate in research efforts and learn about this emerging field. Ultimately, they will be able to share what they learn with their middle and high school students.
"As an environmental microbiologist, I am always looking for ways to improve and keep our environment safe. I am always eager to tackle many environmental problems that were previously thought to be intractable," Rodrigues said. "As an educator, I look for ways to teach and motivate others to do the same. This project will allow me to continue to do that.
Gila Stein, assistant professor of chemical and biomolecular engineering. Joined UH in 2009. NSF Career Award valued at up to $500,000.
Stein is working on characterizing and improving polymer-based solar cells, which could be made into a viable alternative to standard silicon-based solar cells. They are lighter and more durable, easier to produce and have a lower raw materials cost.
However, solar cells based on polymers currently aren't considered a viable alternative to silicon because they are less efficient at converting sunlight into electricity.
With polymer-based solar cells, the highest reported efficiency is 8 percent in the lab, but 10 percent in the field is considered the threshold for a viable product. The efficiency of commercial silicon solar cells is around 20 percent.
In polymer-based cells, performance is partly associated with the active layer's structure. It's important to control the interface between the polymer, which generates electrons when exposed to sunlight, and the material that receives those electrons, in Stein's research a spherical carbon molecule known as fullerene.
"It's very disordered and poorly controlled," said Stein. "We're focusing on ways to control the distribution of polymer and fullerene instead of just relying on a spontaneous process that is incredibly sensitive to processing conditions and varies substantially from one polymer to another."
Stein will nanopattern thin films of the polymer material in UH's Nanofabrication Facility, and then coat the polymer nanostructures with fullerene.
She then will determine how efficiently the new solar cells generate electricity, and work to optimize the most promising polymer/fullerene interfaces.
Ognjen Miljanic, assistant professor in chemistry. Joined UH in 2008. NSF CAREER Award valued at up to $600,000.
Miljanic is studying self-sorting chemical systems, which are complex mixtures of many different compounds that are able to spontaneously order themselves and produce complex products in high yields and high purities.
The original self-sorting system is nature, which uses incredibly complex mixtures of simple chemicals found in biological cells to produce sophisticated proteins such as DNA and other molecules of life.
In contrast, traditional organic chemistry is highly reductionist. Typically, a chemist reacts two molecules in isolation to produce a third one, and then purifies this product before reacting it further. This approach is energy- and labor-intensive, but necessary since competing reactivities among the mixture components can completely derail the planned synthetic procedure. Miljanic and his team aim to circumvent this inefficiency of traditional synthesis by using equilibrating mixtures of compounds that can freely transfer material and information among the components, thus bringing this preparative method closer to the operation of natural systems.
"We do not intend to replicate nature. Instead, we plan to use this self-sorting behavior to expediently prepare sophisticated, but unnatural, molecules of interest in materials science, such as sensors for environmental contaminants, nano-sized capsules for gas separations, hierarchical structures for drug delivery, and the like," Miljanic said.
Students in Miljanic's group synthesize and characterize individual compounds using a mixture of spectroscopy and crystallography. The thorough characterization of components is essential to being able to deconvolute the behavior of a complex mixture as a whole.
"My students and I would like to initially demonstrate that different chemical reactions and physical stimuli (light, temperature) can be used to induce self-sorting behaviors," he said. "This survey probably is not the most exciting component of our research program for the general public, but I think it will lay the groundwork for the development of complex self-sorting synthetic sequences that will come in two to five years."