By Randena Hulstrand
Some of nature's most complex relationships begin at one of the tiniest scales. Research at the nanometer level — one-billionth of a meter, the width of three to four atoms — is leading to new materials and technology transfer applications that can solve some of the big issues of our day in areas such as bone repair, drug delivery, chip design and solar cells.
At the forefront of this research are University of North Texas scientists whose interdisciplinary approach to nanotechnology combines experimental science and computational research with state-of-the-art facilities for computer simulation and modeling. Devices based on their studies will save time and money — and perhaps lives.
In a world with an aging population and increasing health care expenses, imagine the human body's ability to accept synthetic inorganic materials that can adapt and bond to its living soft tissues. Jincheng Du, assistant professor of materials science and engineering, is working to understand the complex structures of bioactive glasses — a group of biocompatible, surface reactive glass ceramics — that can help restore and repair bones, act as coatings for knee and hip replacements and assist in drug delivery. Through a recent National Science Foundation grant, Du and student researchers are specifically studying the dissolution mechanism of the glasses in aqueous environments.
"We're studying the structure of the glasses at the atomic level, investigating how they dissolve in a body fluid environment and their bioactivity and biocompatibility to soft and hard tissues," he says.
After fabricating the bioactive glasses, Du studies how the atoms are structured through computer simulations using UNT's Talon High-Performance Computing System and instruments at the Center for Advanced Research and Technology, as well as high energy X-ray sources at Argonne National Laboratory.
Through the integrated research of computer simulation and experimental studies, he is uncovering the relationships between the structure and the bioactivity of the material. He specifically looks at how the glasses form a mineralized hydroxyapatite layer on their surface that allows them to grow to the bone.
"Glass structures are one of the frontiers of physical science. Unlike crystal structures, the glass structures lack long-range order," Du says, adding that their complexity is what makes the integrated modeling and experimental approach an ideal methodology.
"With detailed atomic structure from simulations, we can see how they bond to each other, if they form clusters, channels or intermediate-range orders, and how these would influence properties such as diffusion and vibrational behaviors. All of this would help us identify the structural origin of their bioactivity and design new glass compositions for various biomedical applications.
Du also uses computer modeling in other nanotechnology research, in areas such as molecular crystals for flexible electronics, semiconductor nanocrystals, plasma interaction of dielectric materials for micro- and nanoelectronics, and defects, surfaces and interfaces in materials for energy and environmental applications. He is a member of UNT's Center for Advanced Scientific Computing and Modeling and the Materials Modeling research cluster.
"Materials science used to be empirical — trial and error — but now with improved computer modeling and simulation, we can have a deeper understanding of the correlation between different levels of structures and material properties and can predict with deep insights," he says. "We're not replacing experiments, but complementing them, to understand the nature of material behavior."
Keeping up with the demands of technology-savvy consumers has semiconductor companies such as Texas Instruments, Intel Corp. and Apple working to meet needs 10 to 20 years in the future. Saraju Mohanty, associate professor of computer science and engineering, is designing application-specific hardware these companies and customers will want.
Mohanty, director of UNT's NanoSystem Design Laboratory, and student researchers collaborate with major industry players such as Intel using the International Technology Roadmap of Semiconductors. The goal is to invent and design consumer electronic "challenges" (10 years ahead) and "grand challenges" (20 years ahead).
With about $1 million in grants from the National Science Foundation and the Semiconductor Research Corp., Mohanty keeps pushing the boundaries of chip processors' capabilities in the booming technology industry that includes cell phones, laptops and MP3 players. He researches hardware design using computer aided design for low-power, high-performance nanoscale VLSI (very large-scale integration), the process of creating integrated circuits by combining millions of transistor-based circuits into a single chip.
A single transistor in a circuit has hundreds of parameters, and a chip like an Intel i7 has 800 million transistors, Mohanty says, so to simulate an individual test of each parameter is an impossible task unless you reduce the time of the simulation process.
"Modeling uses extremely fast, high-end equipment to run the simulations, so we can see what we need to design better," he says. "Different phones have different circuits, batteries and plastics, so we need different methodologies."
He also is working to create batteries for consumer electronics that have a longer life and don't need frequent charging, an industry roadmap "challenge." The CAD tools at his lab in Discovery Park, UNT's nearly 290-acre research park, include two Intel Quad-Core Xeons, computer and high-end server systems with several terabytes of storage and hardware simulation tools. Through nanoscale device and system modeling with these tools, he's studying how to reduce power leakage while the device is still in the design phase. Eventually, during the manufacturing phase, Mohanty's group will use a new clean room facility at Discovery Park.
"Our goal is batteries that require charging once or twice a week rather than a couple of times a day," he says.
Mohanty has collaborated with Priyadarsan Patra, architect and scientist at Intel Corp., for several years on low-power circuit design and synthesis, leakage and reliability modeling, and network-on-chip research.
"The design challenges of today's advanced semiconductor devices involve such extreme dimensions as the 1.2 nanometer thin oxide, a layer only a couple of atoms thick," Patra says. "That makes Saraju's research collaboration mutually beneficial for UNT and Intel and valuable to tackling some of these issues."
Mohanty also holds two patents for innovative chip technology — digital picture images to securely store biometric personal data such as for electronic passports, and a video processor that can process network and multimedia directly to cell phone or computer, such as direct secure streaming of video without using high-performance computing. And he's published research on a drug delivery innovation that would allow a chip in a patient's body to "electro-chemically deceive the brain" out of symptoms, communicate with doctors or make emergency calls.
With NSF funding, Mohanty organized a UNT-sponsored International Symposium on Electronic System Design in December 2010 in Bhubaneswar, India. The symposium brought together representatives from organizations that develop the main components of cell phones for ideas on new technologies and recruiting the next generation of students.
"I tell my students that design in consumer electronics is a backward process, not forward," Mohanty says. "You have to design with the user in mind and then make what people want."
Who doesn't want a cheap way to heat their home? Harvesting the sun's light to generate electricity is one of the most sought-after energy solutions; however, current technology makes nature's endless source cost prohibitive. Silicon-based solar cells are heavy and expensive to make.
"We're brainstorming new ways to make plastic solar cell manufacturing robust by bridging organic and inorganic materials," he says. "Interactions with light occur in short timescales, and in the nanoscale we can create ways to do something useful very quickly with energy."
Youngblood grows oxide structures hydrothermally in his lab, using zinc oxide nano-rods as a template and creating a porous membrane of zirconium dioxide.
"The structure allows for more electron transfer reactions at the interface of organic and inorganic materials," he says, "which harvests energy."
He's also using organic dye baths to create dye-sensitized solar cells that become energized by absorbing light. They are cheap to produce and could one day inexpensively provide renewable electrical energy for homes, with multitudes of cells manufactured on flexible materials rolled on rooftops.
While other researchers have used single cell and plant-based sources for dyes, Youngblood is the first to use compounds derived from an organic red dye from cochineal insects, the only bio-renewable solar dye source derived from a multi-celled animal.
"The cochineal dye — a source of carminic acid that the insects produce to deter predators — is an age-old source of red dyes used by the Aztecs for their textiles," he says.
After "cooking" his materials in the lab, Youngblood uses CART's Nova NanoSEM, an ultra-high resolution scanning electron microscope, to take magnified 3-D photos at the nanoscale. And he uses a Profilometer, a "record needle-type instrument," to measure the vertical depth of the images' surface. He looks forward to the opening of Discovery Park's new clean room this year to facilitate his processes.
"I see this as 'intellectual prospecting,'" he says. "Sometimes if you revisit ideas, you can strike gold."
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