Using NCSA supercomputers, scientists calculate the electronic structures of molecules to predict how they will behave under a variety of different conditions.
We normally think of building something as putting parts together to make a whole. Think of a carpenter building a piece of furniture, like a chair. She gathers her plans, tools, wood and other hardware. Legs, seat, nails and all, she uses those parts to make a whole, useable chair that she can then sit on. That's even how Webster's defines building--to make by putting together materials, parts, etc…By contrast, we typically think of taking something apart as demolition, destroying the purpose of the original object. But what if what we could build something in such a way that we actually had to start with the "whole" and take parts away to get a useful object? Think of it like whittling or carving a delicate ice sculpture. That's what some scientists are doing with nanomaterials.
In a lab at the University of Illinois at Urbana-Champaign (UIUC), for example, scientists are building nanomaterials for future lasers, which will be one billionth of a meter long! To do this, the scientists first put a silicon wafer through a process called electrolysis reproduction. They gradually immerse a silicon wafer through an electrolytic process. They gradually immerse the wafer into an etching bath of hydrofluoric acid and hydrogen peroxide. At the same time, the scientists apply an electrical current to the bath. Munir Nayfeh, the lead researcher and member of the Illinois experimental group, explains, "This process erodes the surface layer of the material, leaving behind a delicate network of weakly interconnected nanostructures." They then remove the wafer from the etching bath, immerse it in a liquid solvent bath, and subject it to ultrasound. The ultrasound bath causes the delicate nanostructures to crumble into particles. The particles, silicon nanocrystals, are easily sorted into different sized groups that will emit corresponding colors of light when hit with infrared or ultraviolet light.
Because the nanocrystals emit visible light and are made out of biologically benign silicon, they are useful for a variety of purposes such as sensors, semiconductor lasers, single electron transistors, and even for tagging cancer cells for study. In particular, they could provide a viable alternative to dye markers like the barium drinks used in upper gastrointestinal X-rays and some MRIs that have been used for decades. The nanpocrystals are small enough to fit through the pores in a cell, and according to Nayfeh, they are also photostable--a quality that is quite valuable when researchers need to take repeated measurements under intense radiation.But how do scientists find out which kinds of molecular structures have such special properties and how do they determine what uses can be made of them? The answer is in the electronic structure of molecules. If scientists can perform accurate calculations detailing molecules' electronic structures, they can predict how the molecules will behave under certain conditions. Lubos Mitas, assistant professor of physics at North Carolina State University and former NCSA research scientist; researchers from UIUC's physics department; and teams of scientists from other institutions have been working together to use supercomputers to calculate the molecular electronic structure of silicon nanocrystals and several other materials.
Access Online | Posted 8-26-2003
