Gyeong S. Hwang's multiscale computational methods help characterize the behavior of tiny structures of silicon/germanium.
Defining how synthesis conditions of tiny crystals and wires of silicon alloys influence their structural and physical properties is the focus of a $400,000 National Science Foundation Early Career Development (CAREER) award received by Gyeong Hwang, a chemical engineer at The University of Texas at Austin. The CAREER awards are prestigious grants for young teacher-scholars expected to be future academic leaders.
The assistant professor will use the grant and allocations of time on the supercomputers at the Texas Advanced Computing Center (TACC) to develop multiscale computational tools for exploring the synthesis, manipulation, and characterization of oxide-embedded nanocrystals and oxide-encapsulated nanowires of silicon and germanium. These silicon-germanium-oxide nanosystems are leading contenders for use in furthering the miniaturization of silicon devices below 100 nanometers. Such devices cannot be fabricated from conventional components and will demand new approaches to permit manufacture under controlled conditions with repeatable characteristics.
"Some of the potential applications for these silicon and germanium nanostructures include memory components, nanowire transistors, and optical interconnects to replace electrical wires," Hwang says. "These applications can be expected to result in much faster semiconductor-based devices that are cheaper to manufacture and have increased functionality."
Interest in combining silicon with germanium stems from discoveries in the late 1990s that the germanium metalloid emits light well and has the potential to operate as a switch at twice the speed of silicon-only transistors. However, researchers know little about controlling a nanomaterial's function, because a material's behavior can change in unusual ways when synthesized to be as little as a billionth of a meter in size.
"Just synthesizing silicon-germanium nanostructures and studying their physical properties after the fact isn't enough," Hwang said. "We need to understand the underlying mechanisms of their synthesis first to determine their structural properties accurately, which will in turn allow a better understanding of the quantitative structure-property relationships."
The unique properties of nanostructured materials and systems markedly depend on their sizes, shapes, and interface structures. Therefore, the ability to control their synthesis with atomic-scale precision, armed with an accurate assessment of the structure-property relationships, offers enormous opportunities for the development of a variety of novel electronic, chemical, and biological devices.
For most nanosystems, however, Hwang notes, many fundamental aspects of the synthesis, manipulation, and structure are still poorly known, which in turn hampers the development of nanotechnology-based novel devices. Experiments may yield many clues to the atomistic properties and behaviors involved in the synthesis and characterization of nanostructured materials, but their interpretation is often controversial due largely to difficulties in direct characterization of the materials experimented upon.
"Using the fundamental understanding gained from ab initio calculations," Hwang says, "we expect to develop predictive, multiscale computational models that can link the conditions of synthesis and the facts of structure to the properties the silicon-germanium-oxide nanosystems acquire after being exposed to various process conditions and environments."
Hwang will integrate various state-of-the-art theoretical techniques, considering atomic and molecular interactions over varying timescales and at sizes ranging from individual atoms and molecules to the larger clusters of atoms at actual device sizes. In addition to first-principles quantum mechanics calculations, Hwang will use molecular dynamics and molecular mechanics simulations. Finally, he will employ Monte Carlo methods to determine the complex structures of nanomaterials on greater length scales, addressing the longer time scale kinetic processes involved in the syntheses he will explore.
"The development of comprehensive computational models capable of predicting the evolution of inorganic nanostructures is an extremely challenging task," Hwang says, "because the final structure is often strongly controlled by synthesis kinetics--namely, process conditions." But progress from this work will contribute greatly to realizing experimental control of the atomic structure and dimensionality of silicon and germanium nanostructures. It will also guide the rational design and fabrication of silicon-germanium-oxide nanosystems to be used in future electronic and optoelectronic devices.
The work is computationally demanding, but Hwang says, "We're blessed with first-class supercomputers at TACC. Without access to such computational resources, our progress in this research would be much slower." His group makes use of both of TACC's largest resources, the 1024-processor Lonestar Dell/Linux cluster, and the 224-processor Longhorn IBM Power 4 system.
Portions of this article appeared as a press release from the College of Engineering on April 5, 2005. Barbra Rodriguez is a science writer in the College of Engineering
Research Feature - April 27, 2005
